Note: Descriptions are shown in the official language in which they were submitted.
;
BACKGROUND
The field of nuclear medicine has long been concenredwith techniques of diagnosis wherein radiopharmaceuticals are in-
troduced into Q patient and the resultant distribution or concen-
tration thereof, as evidenced by gamma ray intensities, is observed
or tracked by an appropriate system of detection. An important
advantage of the diagnostic procedure is that it permits non-
invasive investigation of a variety of conditions of medical in-
terest. Approaches to this investigative technique have evolved
from early pioneer procedures wherein a hand-held radiation counter
was utilized to map body contained areas of radioactivity to more
current systems for simultaneously imaging substantially an entire,
in vivo, gamma ray source distribution. In initially introduced
practical systems, scanning methods were provided for generating
images, such techniques generally utilizing a scintillation-type
gamma ray detector equipped with a focusing collimator which moved
continuously in selected coordinate directions, as in a series
of parallel sweeps, to scan regions of interest. A drawback
to the scanning technique resides in the necessarily longer
exposure times required for the derivation of an image. For
instance, such time elements involved in image development
generally are overly lengthy to carry out dynamic studies
of organ function.
By comparison to the rectilinear scanner described above,
the later developed "gamma camera" is a stationary arrangement
wherein an entire region of interest is imaged at once. As ini-
tially introduced the stationary camera systems generally utilized
a larger diameter sodium Iodide, NaI (TI) crystal as a detector
in combination with a matrix of photomultiplier tubes. A multiple
channel collimator is interposed intermediate the source containing
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subject of investigation and this scintillation detector crystal.
When a gamma ray emanating from the region of investigative inter-
est interacts with the crystal, a scintillation is produced at the
point of gamma ray absorption and appropriate ones of the photo-
multiplier tubes of the matrix respond to the thus generated light
to develop output signals. The original position of gamma ray
emanation is determined by position responsive networks associated
with the outputs of the matrix. For additional information con-
cerning such camera, see:
I. Anger, H.O., "A New Instrument For
Mapping Gamma Ray Emitters", Biology
and Medicine Quarterly Report UCRL-
3653, 1957.
A continually sought goal in the performance of gamma
cameras is that of achieving a high resolution quality in any
resultant image. Further, it is desirable to achieve this resolu-
tion in combination with concomitant utilization of a highly
versatile radionuclide or radiolabel, 99m-Technetium, having a
gamma ray or photon energy in the region of 140 KeV. A broadened
clinical utility for the cameras also may be realized through the
use and image identification of radiopharmaceuticals exhibiting
more than one photon energy level. WIth such an arrangement, two
or a plurality of diagnostic aspects simultaneously may be availed
the operator. For example, in carrying out myocardial imaging, the
above-identified 99m Technetium might be utilized in conjunction
with lll-Indium, the latter contributing photon energy in the re-
gions of 173 and 247 KeV. Similarly, 81-Rubidium, exhibiting
~, . .
photon energy in the range of 350 KeV might be utilized in conjunc-
tion with 81-Krypton, the latter having gamma ray energy at about
- 30 120 KeV. The noted dual energy characteristic of Ill-Indium
also might be utilized to achieve two aspects of diagnostic data.
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The resolution capabilities of gamma cameras incorporat-
ing scintillation detector crystals, inter alia, is limited both by
the light coupling intermediate the detector and phototube matrix
or array as well as by scatter phenomena of the garnna radiation
witnessed emanating from within the in vivo region of investiga-
tion. Concerning the latter scattering phenomena, a degradation
of resolution occurs from scattered photons which are recorded in
the image of interest. Such photons may derive frorr\ Compton
scattering into trajectories wherein they are caused to pass
through the camera collimator and interact photoelectrically with
the cyrstal detector at positions other than their point of in
vivo derivation. Should such photon energy loss to the Compton
interaction be less than the energy resolution of the system, it
will effect an off-axis recordation in the image of the system as
a photopeak photon representing false spatial information or noise.
As such scattered photons record photopeak events, the noise in-
crease and consequent resolution quality of the camera diminishes.
For the noted desirable 140 KeV photons, the scintillation detector
type camera energy resolution is approximately 15 KeV. With this
20 resolution, photons which scatter through an angle from 0 to
about 70 will be seen by the system as such photopeak events.
A continuing interest in improving the resolution quali-
ties of gamma cameras has led to somewhat extensive investigation
into imaging systems incorporating relatively large area semi-
conductor detectors. Such interest has been generated principally
in view of theoretical indications of an order of magnitude im-
provement in statistically lirnited resolution to provide signifi-
cant improvements in image quality. In this regard, for example,
reference may be made to the following publications:
-3-
s
Il. R.N. Beck, L.T. Zimmer, D.B. Charleston,P.B. Hoffer, N. Lembares, "The
Theoretical Advantages of Eliminating
Scatter in Imaging Systems", Semi-
ductor Detectors in Nuclear Medicine,
(P.B. Hoffer, R.N. Beck, and A.
Gottschalk, editors), Society of
~ Nuclear Medicine, New York, 1971,
-~ pp. 92-113.
III. R.N. Beck, M.W. Sehuh, T.D. Cohen, and
N. Lembares, "Effects of Scattered
Radiation on Scintillation Detector
Response", Medical Radioisotope Scin-
ti~raphy, IAEA, Vienna, 1969, Vol. 1,
pp. 595-616.
IV. A.B. Brill, J.A. Patton, and R.J.
Baglan, "An Experimental Comparison
Scintillation and Semiconductor
Detectors for Isotope Imagîng and
Counting", IEEE Trans. Nuc. Sci., Vol.
NS-l9, No. 3, pp 197-190, 1972.
V. M.M. Dresser, G.F. Knoll, "Results of
Scattering in ~adioisotope Imaging"
IEEE Trans. Nuc. Sci., Vol. NS-20, No.
; 1, pp. 266-270, 1973.
Particular interest on the part of investigators has
been paid to detectors provided as hybridized diode structures
; formed basically of germanium. To derive discrete regions for
~- spatial resolution of impinging radiation, the opposed parallel
; 30 surfaces of the detector diodes may be grooved or similarly con-
figured to define transversely disposed rows and columns, thereby
;~ providing identifiable discrete regions of radiation response.
Concerning such approaches to treating the detectors, mention
may be made of the following publications:
VI. J. Detko, 'ISemiconductor Dioxide Matrix
; for Isotope Localization", Phys. Med.
Biol., Vol. 14, No. 2, pp. 245-253, 1969.
VII. J.F. Detko, "A Prototype, Ultra Pure
Germanium Orthogonal Strip Gamma
Camera," Proceedings of the IAEA
DoSium on RadioisotoDe Scintieraphy,
IAEA/SM-164/135, Monte Carlo, October
1972.
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VIII. R.P. Parker, E.M. Gunnerson. J.L.
Wankling, and R. Ellis, "A Semiconductor
Gamma Camera with Quantitative Output,"
Medical Radioisotope Scinti~raphy.
IX. V.R. McCready, R.P. Parker, E.M.
Gunnerson, R. Ellis, E. Moss, W.G. Gore,
and J. Bell, "Clinical Tests on a Proto-
type Semiconductor Gamma-Camera,"
British Journal of Radiolo~y, Vol. 4~,
58-g2, 1971.
X. Parker, R.P., E.M. Gunnerson, J.S.
Wankling, R. Ellis, "A Semiconductor
Gamma Camera with Quantitative Out-
put," Medical RadioisotoDe Scinti-
graphy, Vol. ï, Vienna, IAEA, 1969,
p. 71.
XI. Detko, J.F., "A Prototype, Ultra-Pure
: Germanium, orthogonal-Strip Gamma
Camera," Medical Radioisoto~Scin-
tigraphy~ Vol. 1, Vienna, IAEA, 1973,
P. 241.
XII. Schlosser, P.A., D.W. Miller, M.S.
Gerber, R.F. Redmond, J.W. Harpster,
W.J. Collis, W.W. ~Iunter, Jr., "A
Practical Gamma Ray Camera System
Using High Purity Germanium," presented
at the 1973 IEEE Nuclear Science Sym-
posium, San Francisco, November 1973;
also published in IEEE Trans. Nucl. Sci.,
Vol. NS-21, No. 1 February 1974, p. 658.
XIII. Owen, R.~., M.L. Awcock, "One and Two
Dimensional Position Sensing Semicon-
ductor Detectors," IEEE Trans._Nucl 7 Sci .
Vol. NS-51, June 1968, p. 290.
In the more recent past, investigators have shown par-
ticular interest in forming orthogonal strip matrix detectors
from p-i-n semiconductors fashioned from an ultra pure germanium
material. In this regard reference is made to U.S. Patent No.
3,761,711 as well as to the following publications:
XIV. J.F. Detko, "A Prototype3 Ultra Pure
Germanium, Orthogonal Strip Gamma
Camera," Proceedin~s of the IAEA
S~mposium on Radioisotope Scinti~raphy,
IAEA/SM-164/135, Monte Carlo, October,
1972.
-,, .
~ ~ .
XV. Schlosser, P.A.~ D.W. Miller, M.S.
- Gerber, R.F. Redmond, J.W. Harpster,
.J. Collins, W.W. Hunter, Jr., "A
Practical Gamma ~ay Camera System
- Using High Purity Germanium," presented
at the 1973 IEEE Nuclear Science Sympo-
sium, San Francisco, November 1973; also
published in IEEE Trans. Nucl~ Sci., Vol.
NS-21, No. 1, February 1974, p. 658.
; 10 High purity germanium detectors promise numerous advan-
tages both in gamma camera resolution as wel] as practicality.
For instance, by utilizing high purity germanium as a detector,
lithium drifting arrangements and the like for reducing impurity
concentrations are avoided and the detector need only be cooled
to requisite low temperatures during its clinical operation. Read-
out from the orthogonal strip germanium detectors is described as
being carried out utilizing a number of techniques, for instance,
; each strip of the detector may be connected to the preamplifier-
amplifier channel and thence directed to an appropriate logic
function and visual readout. In another arrangement, a delay line
- readout system is suggested with the intent of reducing the number
'` of preamplifiers-amplifier channels, and a technique of particular
interest utilizes a charge splitting method. With this method or
~`~ technique, position sensitivity is obtained by connecting each
contact strip of the detector to a charge dividing resistor net-
work. Each end of each network is connected to a virtual earth,
. charge sensitive preamplifier. When a gamma ray interacts with the
detector, the charge released enters the string of resistors and
divides in relation to the amount of resistance between its entry
, 30 point in the string and the preamplifiers. Utilizing fewer pre-
amplifiers, the cost and complexity of such systems is advan-
'! tageously reduced. A more detailed description of this readout
arrangement is provided in:
~'
,~
~YI. Gerber, M.S., Miller, D.W., Gillespie,B., and Chemistruck, R.S., "Instrumeta-
tion For a High Purity Germanium
Position Sensing Gamma Ray Detector,"
IEEE Trans. on Nucl. Sci., Vol. NS-22
No. 1, February, 1975, p. ~16
To achieve requisite performance and camera image resolu-
tion, it is necessary that substantially all sources of noise or
false information within the system be accounted for. In the ab-
sence of adequate noise resolution, the performance of the imagingsystems may be compromised to the point of impracticality. Until
the more recent past, charge splitting germanium detector arrange-
ments have not been considered to be useful in gamma camera appli-
catlons in consequence of thermal noise anticipated in the above-
noted resistor divider networks, see publication VII~ supra. How-
ever, as will be evidenced in the description to follow, such
considerations now are moot.
Another aspect in the optimization of resolution of the
images of gamma cameras resides in the necessarily inverse relation-
ship between resolution and sensitivity. A variety of investiga-
tions havé been conducted concerning this aspect of camera design,
it being opined that photon noise limitations, i.e. statistical
fluctuations in the image, set a lower limit to spatial resolution.
Further, it has been pointed out that the decrease in sensitivity
witnessed in conventional high resolution collimators may cancel
out any improvements sought to be gained in image resolution. A
more detailed discourse concerning these aspects of design are
provided, for instance, in the following publications:
XVII. E.L. Keller and J.W. Coltman, "Modu-
lation Transfer and Scintillation
Limitations in Gamma Ray Imaging"
J. Nucl. Med. 9, 10, 537-545 (1968)
~VIII. B. Westerman, R.R. Sharma, and J.F.
Fowler, "Relative Importance of
Resolution and Sensitivity in Tumor
Detection", J. Nucl. Med. 9, 12
63~-640 (1968)
I~ S
Generally, the treatment of the signals derived at the
entrance detection portion of gamma cameras involves a form of
spatial or coordinate identification of photons reaching the de-
tector and additionally, a form of analysis of the energy of ra-
diation reaching the detector. Spatial analysis may be carried
out by difference summing circuits, while energy determination
is carried out by additive summing circuits. Further pulse height
analyzers may be utilized as one discriminating component of a sys-
tem for determining the presence of true or false imaging informa-
tion. In any of the systems both treating noise phenomena and
~` seeking a high integrity of spatial information, a control is re-
quired which carries out appropriate noise filtering while segre-
gating true from false information. In addition to the foregoing,
it ls necessary that the "through-put rate" of the system be maxi-
mized in order that it may accommodate a highest number of bits
,,
or pulses representing spatial and energy data.
~nother operational phenomenon tending to derogate from
.. the spatial resolution quality performance of the cameras is re-
,:~
ferred to as "aliasing". This phenomenon represents a natural
... .
outgrowth of the geometry of the earlier-noted orthogonal strip
germanium detector. A more detiled discussion of this aspect of
the gamma cameras is provided at:
XIX. J.W. Steidley, et al., "The Spatial
Frequency Response of Orthogonal
Strip Detectors: IEEE Trans. Nucl.
Sci., February, 1976.
To remain practical, it is necessary that the imaging
; geometry of stationary type gamma cameras provide for as large a
field of view as practical. More particularly, such considerations
require a camera field of view large enough to encompass the entire
or a significant extent of the profiles of various organs of
interest. Because of limitations encountered in the manufacture of
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detector crystals, for instance, high purity germanium crystals,
the size of solid state detector components necessarily is limited.
As a consequence, composite detector configurations are required
which conjoin a plurality of smaller detector components to pro-
vide an imaging field of view or radiation acceptance geometry of
effectively larger size. However, such union of a multitude of
:
- detector components must be carried out without the concurrent
generation of noise phenomena and without a significant loss of im-
. ,.,~
age information validity and acuity. For instance, in the latter
regard, spatial information must have a consistency of meaning
across the entire extent of an ultimately displayed image of an
organ, otherwise, clinical evaluation of such images may be encum-
bered. Preferred arrangements for inter-coupling the discrete de-
tector components within an overall array thereof is described in
United States Patent by M.S. Gerber and D.W. Miller, entitled
:
~; "Gamma Camera System", Patent No. 4,061,919.
The control systems utilized with gamma cameas having
multi-component detectors further are called upon to collect image
~ data therefrom at an optimum rate while evaluation the validity
; 20 thereof and assigning it an appropriate address function. Such
address assignment may vary in nature depending upon the selected
mode of circuit interrelationship of the discrete detector com-
ponents with the array. An additional function of the control
:;
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system is to identify the spatial position of the detector-photon
interaction for select but different energy levels. This requires a
technique for normalizing the spatial labels of such signals while
properly evaluating the energy level states thereof as representing
valid image information. The rapidity with which this data is
treated, as by assigning spatial regional factors to it, as well
as evaluating it for validity becomes a particularly important as-
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pect of the control systems where they are contemplated for use
.
in clinical dynamic function studies. With such studies, dynamic
alterations in an image component occurring within any segment of
the image area should be followed closely in correspondence with
the actual movement of the image source. Accordingly, efficient
image signal treatment by the camera system is required.
: .
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The present invention is addressed to an improved system
~; for imaging the distribution within a region of interest of iso-
~i
s~ 10 topic materials emitting radiation. Characterized as a gamma cam-
era, the system operates in conjunction with a solid state detec-
. .
: tor, for instance of the ultra-pure germanium variety, which is
formed having a plurality of discrete components. These detector
components are arranged in mutual adjacency to form a composite
; detector and, accordingly, are operationally associated with im-
pedance deriving arrangements to provide spatial coordinate para-
meter outputs representing the spatial disposition of correspond-
ing interactions of the radiation impinging upon the detector.
The association of the detector components may take on
a variety of configurations. For example, the components are
formed and arranged in the composite detector such that each has
; :~ .
one of two oppositely disposed charge collecting surfaces po-
sitioned within a common plane for exposure to radiation. These
components then are arranged to establish linearly oriented group-
ings of the respective surfaces, each of the groupings of surfaces
being electrically intercoupled and associated with the noted
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impedance arrangement for providing coordinate ouputs which may
be designated as x- and y- designated coordinate parameter outputs.
These outputs are derived from respective mutually orthogonally
aligned and oppositely disposed ones of the groupings associated
with a com~on detector component at which an interaction with radi-
ation corresponding with the output occurs. Such an operational
grouping of the components is generally referred to as being "row-
column" in nature. The outputs of any predetermined grouping of
the detector components are, in accordance with the invention,
selectively filtered and summed to derive corresponding coordinate
channel signals as well as an energy channel signal which have
values related to the noted spatial disposition and given photon
energy exhibited at an interaction with a given detector component.
A control arrangement associated with the grouping regulates the
noted summation and filtering and derives a data acceptance signal
as well as carries out resetting functions to permit a next pro-
cessing procedure to be carried out.
The system further includes spatial coordinate multiplex-
ers and energy channel multiplexers which are arranged so as to be
addressed by the noted coordinate channel and energy channel sig-
nals. Each of the multiplexers is connected for response to a
coded actuating signal to provide proper transference of the
channel signals to further processing treatment. In this regard,
a process control arrangement including a memory circuit, receives
the data aeceptance signals and is arranged to selectively retain
them in a serialized fashion. The memory circuit is actuable to
derive the noted coded actuating signal in correspondence with the
--11--
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serialized data acceptance signals to effect the noted transfer-
ence of the channel and energy signals. A sequential control means
is provided for selectively controlling or actuating the proccess
control and for regulating an overall operational cycle of the
system. Further treating arrangements within the system respond
to the transferred channel signals for deriving readout information
representative thereof which may be used for clinical analysis
purposes and the like.
....
As another object and feature, the invention further con-
templates the provision of a storage arrangement within the con-
,~;,
trol system which may be in the form of a series of sample and
hold components serving, when in a receive mode, to receive the co-
ordinate and channel signals derived from the noted multiplexers.
Upon actuation to a hold mode, the signals are retained over a
given interval while being asserted within additional signal
treatment functions of the system. The noted sequential control
function of the system is further utili~ed during this interval
to effect the carrying out of the noted reset function associated
with the control components immediately processing the outputs of
the detector component groupings. In consequence, an improved
throughput rate for the system is achieved to enhance the imaging
capability of the camera.
Another object and feature of the invention is to pro-
vide a control system of the type described above wherein isotopic
material sources of radiation, i.e. radiopharmaceuticals or the
like, exhibiting more than one photon energy level may be provided
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for purposes of broadened clinical practicality. For such an ar-
rangement, the imaging system incorporates components treating the
noted spatial coordinate channel as well as energy channel signals
transferred from the multiplexer function of the system and carries
out normalization operation over the spatial channel signals
such that they are characterized as representing only accurate
spatial information for imaging purposes. This operation is pro-
vided utilizing divider networks which are configured and arranged
to, in effect, divide the spatial channel signals by their cor-
~0 responding energy signal. The thus normalized signals then aretransmitted to appropriate readout components of the system.
Another aspect and object of the invention provides
, ~
evaluating features within the imaging system. For instance, an
evaluating arrangement in the form of multi-channel analyzer is
incorporated to evaluate and respond to the peak values of each
energy channel signal submitted thereto as transferred from the
~ noted multiplexing functions and/or the sample and hold components.
; ~ The analysis performed is one wherein each energy signal peak value
: .
is evaluated with respect to predetermined upper and lower level
` ~ 20 window criteria which are pre-established in accordance with the
~-; known photon energy levels of the isotopic material distribution
. ~
~; being imaged. In the event of a failure of a given energy channel
signal to meet this window criteria, the control features of the
: invention carries out a noted reset function to effect a short
cycle performance of the sytem, thereby permitting a more rapid
;; processing of a new quantum of image information. In one embodi-
: . `
ment, two evaluating stages are utilized, one associated with that
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~ circuitry immediately treating the outputs of a Predetermined
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is carried out following a first evaluation and subseauent
~: to the transference of the signal into later treatment stages.
A further object of the invention is to provide an
improved system for imaging the distribution of isotopic
,~
~; materials which utilizes a composite solid state detector
arrangement of the "row-column" variety described hereinabove.
In such embodiment, the spatial coordinate signals, which may
- 10 be designated x- and y- coordinate signals which are derived
from select groupings of detector components, for instance,
four are initially summed and filtered as described above
and in the course of such summation, a time derivative of the
,
..
energy signal is provided from each x- coordinate output and
y- coordinate output processing arrangement to generate
corresponding data signals. These data slgnals are then
transmitted to a coincidence network which, in turn, generates
a pair of code signal which, in turn, is submitted to the
earlier described memory arrangement. Accordingly, the
spatial coordinate aspects of the x- and y- channel signals
are established within processing system to properly locate
the resultant spatial information signals within a readout
component.
The present invention is broadly defined as an
,
improvement in a system for imaging the distribution of a
;~ radiation emitting isotope within a region of interest, the
system including solid state detector means having regions
which are operatively associated with charge splitting
impedance means 9 the impedance means being arranged to
receive radiation-induced charges in spatial disposition
corresponding with the interaction location of the radiation
upon the regions~ the charge receipt being time variant in
,;. 5
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correspondence wi.th the position of interaction to exhibit
a collection time constant, ~D~ the improvement comprising:
amplifier means coupled with the impedance means and having
OUtpllt signals corresponding with the charge receipt; first
summing means responsive to the amplifier means output
signals for deriving a spatial signal corresponding to the
spatial orientation of the interaction location; second
summing means responsive to the amplifier means output signals
for deriving an energy signal of value corresponding with
the spatial signal; evaluating means responsive to the
second summing means energy signal for evaluating the peak
value of the energy signal over a time, te, and having a
select output when the energy signal peak value li.es within
predetermined limits; means actuable to treat the spatial
signals to improve the signal-to-noise aspects of the system;
readout means responsive, when actuated, to receive the
treated spatial signal and derive perceptible information
corresponding thereto; and control means for regulating an
operational cycle of the system including the actuation of
the readout means only upon the occurrence of the evaluating
means select output.
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For a fuller understanding of the nature and the object
. of the invention, reference should be had to the following de-
tailed description taken in conjunction with the accompanying
drawings.
,
-BRIEF DESCRIPTION OF THE DRAWINGS
.~Figure 1 is a schematic representation of a gamma camera
arrangement as may utilize the improvement of the invention, show-
` ~ing, in block schematic form, general control functions;
.~Figure 2 is a pictorial representation of a solid state
.
..10 orthogonal strip high purity germanium detector component in-
~ .
.. corporating a charge splitting resistor network in combination with
preamplification electronics;
. Figure 3 is a schemati-c representation of a solid stage
strip detector and a schematic collimator functionally associated
therewith as such system components relate to the radiation source
within a region of clinical interest;
:Figures 4(a)-4(c) are a schematic and graphical representa-
``~ tion of the fundamental geometry associated with the interrela-
,:,
: tionship of a multi-channel collimator and a solid state detector;
:, .
.:- 20 Figure 5 is a pictorial representation of a collimator
....
. array which may be utilized with the system of the invention;
Figure 6 is a pictorial view of two internested members
: of the collimator of Figure 5;
~ Figures 7(a)-7(c) respectively and schematically depict
..
~ representations of a source distribution as related with the geo-
; metry of an orthogonal strip detector and image readouts for il-
~ lustrating aliasing phenomena;
'';
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.
--15--
Figures 8(a)-8(d) portray vertically aligned graphs re-
- lating modulation transfer function with respect to resolution
as such data relates to aliasing phenomena, Figure 8(a) showing
collimator modulation transfer function (MTFC) with F~HM resolu-
tion of 1.33~ , Figure 8(b) showing a consequent alias frequency
spectrum which is processed by the electronics of the camera sys-
tem, Figure 8(c~ showing electronic MTF for given resolutions,
and Figure 8(d~ showing camera system MTF's revealing aliasing in-
troduced by the orthogonal strip solid state detector;
10Figures 9(a)-9(d) provide curves showing the results of
aliasing correction as compared with the curves of figures 8(a)-
: 8(d), Figure 9(a) looking to collimator design as an anti-aliasing
filter, Figure 9(b) showing a consequent aliasing frequency spec-
trum which is processed by the electronics of the system, Figure
9(c) showing the consequence of electronics used for anti-aliasing
post-filtering, and Figure 9(d) showing total system MTF revealing
the elimination of aliasing phenomena;
.~ Figure 10 is an equivalent noise model circuit for solid
stage detectors as utilized in accordance with the instant in-
vention;
Figure 11 is a circuit model of a detector compnent and
: related resistor network, schematically representing a position-
sensitive detector arrangement;
Figure 12 is a block schematic diagram of a gam~a camera
control system configured as it is related to a single detector
component output;
:
. .
;
-16-
;
~ Figure 13 is a schematic block diagram of a gated in-
tegrator configuration which may be utilized with the instant
invention;
, .
Figure 14 is a schematic circuit representation of the
configuration described in connection with Figure 13;
`~ Figure 15 is a schematic representation of the logic
components of a control arrangement which may be utilized with the
system of the invention;
Figure 16 is a circuit timing diagram corresponding with
; 10 the schematic representation shown in Figure 15;
Figure 17 is a pictorial and schematic representation
of an array of detector components showing the interconnections
thereof to form a composite detector or region thereof as may be
utilized with the system of the invention;
Figure 18 is a block schematic representation of the con-
.~ trol system utilized to receive and treat the outputs of the
detector array configuration of Figure 17;
Figure 19 is a block schematic diagram of an embodiment
.
of the control system of the invention as it is utilized for
.~ 20 treating the signals developed by the control arran~ement of
~ Figure 18,
.,:,
,; Figure 20 is a schematic and pictorial representation of
another array of detector components, interconnected in accordance
with a "row-column" readout geometry;
Figure 21 is a schematic and pictorial representation of
another array of detector components, each of which is formed
associated with a surface type impedance arrangement, the
:~ components being interconnected in the noted "row-column" fashion;
-17-
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Figure 22 is a schematic and pictorial representation of
another array of detector components interconnected in accordance
with the noted "row-column" geometry;
Figure 23 is a block schematic diagram of a control
system utilized in treating one spatial channel output of the
noted "row-column" detector component interconnection geometry;
Figure 24 is a schematic block diagram of a control
circuit operating in conjunction and cooperation with the control
system of Figure 23; and
Figure 25 is a block diagram of a control arrangement
for utili~ation with the noted "row-column" interconnection of
detector components, the figure representing an alternate
. control arrangement within the diagram of Figure l9.
:
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DETAILED DESCRIPTION
In the discourse to follow, the control system of the
invention initially is described in conjunction with the arrange-
ments utiliæed for physically accepting gamma radiation from a
clinically determined region of interest. In particular, initial
acceptance techniques for collimating such radiation as well as
pararneters required for such collimation are set forth. Following
that discussion, the discourse sets forth techniques for achieving
optimized system performance with respect to noise characteristics
which otherwise would be encountered with the solid state detector
arrangement of the invention. Looking additionally to techniques
for improving through-put rate characteristics for the system, the
discussion initially is concerned with a control over a detector
arrangement incorporating only a one detector component. Following
this basic description, however, preferred techniques are set forth
;; for associating a plurality of solid state detector components
~ within a predetermined array or mosaic configuration. Such con-
. .
.
figurations and operatoinal criteria therefore being established,
the discussion then looks to a control system which may operate
with radiopharmaceutical sources of more than one detectible energy
level and which serves to treat resulting signals as well as label
and address them to achieve practical overall imaging fields of
view which maintain efficient signal treatment.
As indicated in the foregoing, during contemplated clin-
ical utilization, a gamma camera arrangement according to the in-
stant invention is used to image gamma radiation within patients.
Looking to Fig. 1, an exaggerated schematic representation of such
a clinical environment is revealed generally at 10. The environ-
,~,.. . .
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ment schematically depicts the cranial region 12 of a patient towhom has been administered a radio-labeled pharmaceutical, which
~- pharmaceutical will have tended to concentrate within a region of
investigative interest. Accordingly, radiation is depicted as
emanating from region 12 as the patient is positioned on some sup-
porting platform 14. Over the region 12 is positioned the head or
housing 16 of a gamma camera. Extending outwardly from the sides
of housing 16 are mounting flanges, as at 18 and 20, which, in turn,
may be connected in pivotal fashion with an appropriate supporting
assembly (not shown). Housing 16 also supports a vacuum chamber
22 defined by upper and lower vacuum chamber plates shown, respec-
tively, at 24 and 26 conjoined with an angularly shaped side defin-
ing flange member 28. Lower vacuum chamber plate 26, preferably,
is formed of aluminum and is configured having a thin entrance win-
dow portion 30, directly above which is provided an array of dis-
crete solid state detector components, as shown generally at 32.
Array 32, in turn, is operationally associated with the "cold
. finger" component 34 of an environmentai control system, which
; preferably includes a cryogenic region refrigerating unit of a
closed-cycle variety, shown generally at 36. An ion pump, as at
38, assures the integrity of the vacuum in chamber 22, such pump,
in conjunction with the refrigerating unit 36, being mounted for
association with chamber 22 through upper vacuum plate 24, the lat-
ter which may be formed, for instance, of stainless steel. Vac-
uum pump-down of the chamber 22 is accomplished by first using a
sorption-type roughing pump, then using the ion pump shown to
reduce and maintain the chamber pressure at 10 6 Torr or less.
- -20-
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Electronics incorporated within chamber 22 include pre-
liminary stages of amplification, for instance field effect tran-
sistors (FET's) as at 40 which are mounted upon a plate 42 coupled,
in turn, between cold-finger 34 and side channel 28. Thus connected,
the plate 40 evidences a temperature gradient during the opera-
tion of the unit which provides a selected ideal temperature
environment of operation for the amplification stages. The outputs
:
of these stages are directed through subsequent stage electronics,
;~ shown within a housing 44, which, in turn, provides electrical
communication to externally disposed control electronics through
::
conduit 46 and line ~8. To provide for appropriate operation,
chamber 22 generally is retained at a temperature of, for in-
.;.
stance, about 77K, while the FET's, 40, mounted upon plage 42,
are retained at about 130K to achieve low noise performance.
Mounted outwardly of window portion 30 an in alignment
with the detector array 32 is u collimator, shown generally at 50.
During the operation of the gam~a camera, radiation emanating from
source 12 is spatially coded initially at collimator 50 by attenu-
ating or rejecting off-axis radiation representing false image in-
formation. That radiation passing collimator 50 impinges upon de-
tector array 32 and a significant portion thereofis converted to dis-
crete charges or image signals. Detector array 32 is so configured as
to distribute these signals to resistor chains as well as the noted
preamplification stages 40 retained within chamber 22 to provide
initial signals representative of image spatial information along
conventionalcoordinateaxesaswellasrepresenting values forradia-
tion energy levels. This data then is introduced, as represented
schematically by line 48, to filtering and logic circuitry which
operates thereupon to derive an image of optimized resolution
and veracity. In the latter regard, for instance, it is desired
21
that only true image information be elicited from the organ being
- imaged. Ideally, such information should approach the theoretical
imaging accuracy of the camera system as derived, for instance,
from the geometry of the detector structure 32 and collimator
arrangement 33 as well as the limitations of the electronic filter-
ing and control of the system.
Image spatial and energy level signals from line 48 in-
itially, are introduced into Anti-Symmetric Summation and Energy
Level Derivation functions represented at block 52. As is described
in more detail later herein, the summation carried out at block
:
52 operates upon the charges directed into the resistive chains
or networks associated with the orthogonal logic structuring of de-
tector array 32 to derive discrete signals or charge values corre-
sponding with image element location. Additionally, circuitry of
the function of block 52 derives a corresponding signal represent-
ing the energy levels of the spatial information. The output of
block 52 is directed to Filtering Amplification and Energy Dis-
criminationfunctions as arerepresented at block54. Controlledfrom
a Logic Control function shown at block 56, function 54 operates
upon the signal input thereto to accommodate the system to paral-
lel and series defined noise components through the use of
Gaussian amplification or shaping, including trapezoidal pulse
shaping of data representing the spatial location of image bits or
signals. Similarly, the energy levels of incoming signals are
evaluated, for instance, utilizing for instance multiple channel
analyzer components controlled by logic circuitry at 56 to establish
energy level windows for data received within the system. In this
regard, signals falling above and below predetermined energy levels
are considered false and are blocked. From Amplification and Dis-
crimination stage 54 and Logic Control 56, the analyzed signalsare directed into an Information Display and Readout Function, as
~;,, .
-22-
represented at bloek 58. Components within function block 58 will
. .
include display screens of various configurations, image recording
devices, for instance, photographic apparatus of the instant de-
veloping variety, radiation readout devices and the like, which
are controlled at the option of the system operator.
As outlined above, the instant description now looks in
more detail to the configuration of the collimator structure 50.
To facilitate such description, however, the structure of a
single compnent within the detector array 32 is described in con-
.:- 10 junction with Fig. 2. Later discussion and figures will reveal
the interrelationships of such impedance networks and their equiva-
lents as they are operatively associated with a multi-component
detector array. Looking to that figure, an exaggerated pictorial
representation of such a component of the detector array is
revealed at 60. Detector component 60 may be fabricated from p-type
high purity germanium by depositing an n-type contact on one face
and a p-type contact on the opposite face of a rectangular planar
crystal. Accordingly, a high purity germanium region of the crystal,
as at 62, serves as an intrinsic region between p-type semiconduc-
tor region contacts 64 and n-type semiconductor region contacts as
at 66. The intrinsic region 62 of the p-i-n detector compnents forms
a region which is depleted of electrons and holes when a reverse bias
is applied to the contacts. Grooves as at 68a-68c are cut into the
continuous p-type contact or region at one face of the component
to form strips of isolated p-type semiconductor material. On the
opposite face of the detector component, orthogonally disposed n-
type semiconductor strips similarly are formed through the provi-
sion of grooves 70a-70c. Configured having this geometry, the de-
ector component 60 generally is referred to as an orthogonal strip
detector or an orthogonal strip array semiconductor detector com-
ponent. The electrode strips about each of the opposed surfaces
of compnent 60, respectively, are connected to external charge
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splitting resistor networks revealed generally at 72 and 74. Re-
sistor network 72 is formed of serially coupled resistors 76a-76e
which, respectively, are tapped at their reglons of mutual inter-
- connection by leads identified, respectively, at 78a-78d extending,
: ,.
in turn, to the orthogonal strips. The opposed ends of network 72
terminate in peramplification stages 80 and 82, the respective out-
puts of which, at 84 and 86, provide spatial output data for in-
.; .
sertion within the above-described summation and energy level de-
rivation function 52 to provide one detector component orthogonal
or coordinate output, for instance, designated as a y-axis signal.
In similar fashion, network 74 is comprised of a string
of serially coupled resistors 88a-88e, the mutual interconnections
of which are coupled with the electrode strips at surface 66, re-
spectively, by leads 90a-9Oe. Additionally, preamplification stages
as at 92 and 94 provide outputs, respectively, at lirles 96 and 98
carrying spatial data or signals representative of image informa-
tion along an x axis or axis orthogonally disposed with respect to
the output of network 72.
With the assertion of an appropriate bias over detector
~- 20 component 60, as described in U.S. Patent No. 3,761,711 granted
to Robert N. Hall on September 25, 1973 any imaging photon ab-
sorbed therewithin engenders ionization which, in turn, creates
electron-hole pairs. The charge thusly produced is collected on
the orthogonally disposed electrode strips by the bias voltage
and such charge flows to the corresponding node of the impedance
networks 72 and 74. Further, this charge divides in proportion
to the admittance of each path to the virtual ground input of the
appropriate terminally disposed preamplification stage. Such
charge-sensitive preamplification stage integrates the collected
charge to form a voltage pulse proportional to that charge value.
,
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Assigning charge value designations Q1 and Q2' respectivelyJ for
the outputs 98 and 96 of the netowrk 74, and Q3 and Q4, respective-
` ly, for the output lines 84 and 86 of network 72, the above-noted
Summation and Energy Level Derivation functions for spatial and
. . .~.
energy data may be designated. In this regard, the x-position of
each diode defined by the orthogonal strip geometry is found to be
proportional to Q1 and Q2' and their difference i.e. (Q1-Q2)' and
the y-position is proportional to Q3, Q4, and their difference i.e.
(Q3-Q4). The energy of the incident gamma ray is proportional to
2 3 4 ' [(Ql Q2) (Q3+Q4)~ or in the latter ex-
pression, [(Q3+Q4) ~ (Q1+Q2)]- As noted above, the operational
environment of the detector array 32 and associated amplification
stages is one within the cryogenic region of temperature for pur-
poses of avoiding Johnson noise characteristics and the like.
As a prelude to a more detailed consideration of the
spatial resolution of gamma radiation impinging upon the entrance
components of the gamma camera, some value may be gleaned from an
examination of more or less typical characteristics of that im-
pinging radiation. For instance, looking to Fig. 3 a portion of
a patient's body under investigation is portrayed schematically
at 100. Within this region 100 is shown a radioactively tagged
region of interest 102, from which region the decay of radiotracer
releases photons which penetrate and emit from the patient's body.
These photons are then spatially selected by a portion of collima-
tor 50 and individually detected at component 60 for ultimate par-
ticipation in the evolution of an image display. The exemplary path
of seven such photons are diagrammed in the figure, as at a-g, for
purposes of illustrating this initial function which the camera
system is called upon to carry out. In this regard, the function
of collimator 50 is to accept those photons which are traveling
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:
nearly perpendicular to the detector, inasmuch as such emanating
rays provide true spatial image information. These photons are
revealed at ray traces, a, and, b, showing direct entry through
the collimator 50 and appropriate interaction coupled with energy
: exchange within detector component 60. Photon path, c, is a mis-
directed one inasmuch as it does not travel perpendicularly to the
detector. Consequently, for appropriate image resolution such path
represents false information which should be attenuated, as sche-
~ matically portrayed. Scattering phenomena within collimator 50
-~ 10 itself or the penetration of the walls thereof allows "non-colli-
mated" photons, i.e. ray traces, d, and e, to reach the detector.
Photon path trace, f, represents Compton scattering in the patient's
;~ body. Such scattering reduces the photon energy but may so re-
direct the path direction such that the acceptance geometry of the
camera, including collimator 50, permits the photon to be accepted
; as image information. Inasmuch as the detector component 60 and
its related electronics measure both the spatial location and en-
ergy of each photon admitted by the collimator, the imaging system
still may reject such false information. For example, in the
event of a Compton scattering of a photon either in the patient or
collimator, the energy thereof may have been reduced sufficiently
to be rejected by an energy discrimination window of the system.
. : :
Photon path, g, represents a condition wherein component 60 ex-
- hibits inefficient absorption characteristics such that the inci-
dent photon path, while representing true information, does not
interact with th~ detector. As is apparent from foregoing, each
of the thousands of full energy photons which are absorbed at the
detector ultimately are displayed at their corresponding spatial
~ .
location on an imaging device such as a cathode ray tube to form
an image of the source distribution within region 102 of the pa-
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tient. Of course, the clinical value of the gamma camera as a
diagnostic implement is directly related to the quality of ultimate
image resolution
As is revealed from the foregoing discourse, the imaging
resolution of the camera system is highly dependent upon the qual-
ity of collimation exhibited at the entrance of the camera by
collimator 50. Generally, collimator 50 is of a multichannel,
parallel-hole variety, its performance being dictated by its fun-
damental geometric dimensions, the material with which it is formed,
and the technique of its fabrication. Referring to Figs. 4(a)-
4(c), a designation of the geometric aspects of collimator 50, as
such aspects relate to photon path travel, and spatial intensity
distribution over the corresponding spatial axis of detector com-
ponent 60 are shown schematically. Fig. 4(b) shows the photon in-
tensity distribution at the mid-plane 60' of the detector due to a
line source of radiation at distance B from the collimator 50 out-
wardly disposed plane defining side. Note that the source position
is designated "L". Source point, L, is located, for purposes of the
instant analysis, within a plane 104 lying parallel to the out-
wardly disposed plane definng side of collimator 50 as well QS itSinwardly disposed plane defining side and the plane defined by the
midpoint 60' of detector 60. The intensity distribution pattern of
photons, revealed in Fig. 4(b), is pro~ided under the assumption
that the collimator 50 is fixed in position. Fig. 4(a), on the other
hand, assumes that the collimator 50 moves during an exposure and
produces, in consequence, a triangular intensity distribution pat-
tern of photons. A location of value "R" designates a full width at
half maximum (FWHM) spatial resolution. Such spatial or position
resolution capability of the camera system may be defined utilizing
several approaches. However, for the latter designation, FWHM is
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:
derived from a consideration that if a very small spot of radiation
exits at the object plane, the image generally will be a blurred
spot with radially decreasing intensity. The position resolution
then is defined as twice the radial distance at which the intensity
is half of the center intensity.
Looking in particular to Fig. 4(c), considering the sim-
ilar triangles EFG and LMN, the resolution of collimator 50 gen-
; erally may be expressed as:
Rc = A (A + B + C) (1)
where
A = the collimator thickness,
AE= the effective collimator thickness due
to septal penetration,
~. B = the source to collimator distance,
;. C = the collimator to detector midplane
distance and
D = the effective diameter of each
channel within the multi-channel
collimator
Effective diameter, D, is considered to be the square
root of the cross-sectional area of a given collimator channel
multiplied by 1.13.
: The effective collimator thickness is given approxi-
mately by:
AE = A - ~r~ (2)
where ~ (E) is the attenuation coefficient of the collimator
:. material at a photon energy, E.
For a given collimator material, sufficiently thick septal
~0 walls are required to reduce the number of photons or gamma
rays that enter within a given collimator channel, penetrate the
septal wall thereof and exit through an adjacent or other channel
'
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'
.
opening. Looking to Fig. 4(c), one such gamma ray or photon path
is traced as UV . Note, that for this condition, the photon or ray
passes through a collimator vane or channel side of thickness, T,
along with minimum septal distance, W, thereby allowing the ray or
photon to exit from a channel adjacent the channel of initial en-
trance. The fraction of photons or rays traveling UV that actually
penetrate the septal wall is given by the penetration fraction:
P = exp (- ~ (E) W). (3)
It is considered the practice of the art to design the
collimator structure such that the penetration fraction, P, is
given a value less than about 5%. In this regard, mention may be
made of the following publication:
XX H.O. Anger, "~adioisotope Cameras,"
` Instrumentation in Nuclear Medicine,
G.J. Hine, ed. ~ol. 1, Academic Press,
New York, 485-552 (1967).
The minimum septal distance, W, is found from the simi-
lar triangles IJK and UVY approximately as:
AT
W = 2D + T (4)
by assuming A is greater that 2D + T where T, as noted above, isthe septal wall thickness. Solving equations (3) and (4) for the
septal wall thickness, T, gives:
T = -2D ln P (5)
~(E) A + ln P
The value, T, as set forth in equation (5) serves to define that
minimal septal thickness for collimator 50 which is required for
a given penetration fraction, P.
The geometric efficiency of the collimator is defined
as the ratio of the number of gamma rays or photons which pass
through the collimator to the number of photons or gamma rays
emitted by the source. Described in terms of the collimator para-
meters, such efficiency may be given by:
:,
. i
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_ 2 2
0S = AE (D + T)] (6)
; where K = 0.238 for hexagonally packed circular holes and 0.282
for square holes or chambers in a square array.
As described above, the clinical value of the gamma cam-
era imaging system stems importantly from the system's capability
for achieving quality image resolution. Given the optmwm image
resolution which is practically available, it then is desirable
to provide a design which achieves a highest efficiency for that
resolution. For a collimator design, it is desirable to provide
a low septal penetration fraction as well as a practical fabrica-
tion cost. Further, an inspection of equations (1) and (6), given
above for collimator resolution and geometric efficiency, respect-
ively, reveals that as resolution is enhanced, the efficiency of
the collimator is diminished. It has been determined that a multi-
channel, parallel-hole collimator, the channels of which are con-
figured having square cross sections represents a preferred geo-
metric design feature. In this regard, where the latter are com-
pared with collimator channels formed as round holes, hexagonallypacked arrays or hexagonally packed bundles of tubes all of given
identical dimensions, resolution remains equivalent, but the ef-
ficiency of the preferred square cross sectional channel array
; will be a factor of 1.4 times greater than the round hole design,
. ~ .
while the efficiency of the hexagonally packed bundle of tubes will
be intermediate the efficiency value of the above two designs. Con-
sequently, as noted above, on the basis of maximum efficiency at a
':
desired resolution, the square hole cross sectional chamber design
is preferred.
~:'
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.
Concerning the materials which may be selected for con-
structing the collimator, those evidencing a high density, high
atomic number characteristic are appropriate for consideration.
In particular, mention may be made of tungsten, tantalum and lead
for the purpose at hand. The primary criterion for thé material
is that of providing a short mean free path at the photon energy
level of interest. For the desirable energy level of 140 KeV, the
mean free path for photon attenuation is 0.012 inch in tungsten,
0.015 inch in tantalum and 0.016 inch in lead. Accordingly, for
a selection based upon a mean free path for attenuation, tungsten
represents the optimum collimator material. Heretofore, however,
pragmatic considerations of machinability or workability have
required a dismissal of the selection of tungsten and/or tantalum
for collimator fabrication. For instance, for multi-channel col-
limators having round channel cross sections, tungsten and tanta-
. I
lum are too difficult and, consequently, too expensive for drill-
.~
~~ ing procedures and, in general, hexagonally packed arrays providing
i ~; such cross sections are restricted to fabrication in lead. Simi-
; larly, other designs formed out of the desired material do not
lend themselves to conventional machining and forming techniques,
the cost for such fabrication being prohibitive even for the so-
phisticated camera equipment within which the collimator units are
intended for utilization.
In the instant preferred arrangement, a square hole col-
limator design, fabricable utilizing the optimum material tungsten,
is provided. Revealed in perspective fashion in ~ig. 5, the col-
limator is shown to comprise an array of mutually parallel adjacent-
ly disposed channels having sides defining a square cross sec-
tion. These channels extend to define inwardly and outwardly
~ 30 disposed sides which are mutually parallel and the channels
;~- are formed axifllly normally to each of these side planes.
The highly desirable square structure shown in Fig. 5 is
achieved utilizing the earlier described preferred tungsten ma-
terial or tantalum, such materials normally being difficult or im-
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practical to subject to more conventional manufacturing procedures.
However, practical assembly of the collimator array 50 is achieved
through the use of a plurality of discrete rectangularly shaped
sheet members, as are revealed in the partial assembly of the col-
limator 114 shown in Fig. 6. Referring to that figure, note that
member 110 is formed as a flat rectangular sheet of height, h,
corresponding with desired collimator thickness, A. Formed in-
wardly from one edge of member 110 are a plurality of slots spaced
in regularly recurring parallel fashion and identified generally
at 112. Slots 112 are formed having a height equivalent to h/2
and are mutually spaced to define a pitch or center-to-center
,,
spacing D + T. The slots are formed having a width of T + e,
where e will be seen to be a tolerance. When the plurality of sheet
members, for instance, as shown at 110 and 114 are vertically
reversed in mutual orientation and the corresponding slots, respec-
tively, as at 112 and 116 are mutually internested as shown, the
~i`
collimator may be built-up to desired dimensions without recourse
; to elaborate forming procedures. Note that the width of slots 112
and 116 closely approximates the width of each of the sheet mem-
bers within the array with a controlled allowance for tolerances.
In determining the value for the above described pitch of the re-
gularly recurring slots within the sheet members, assuming resolu-
tion criteria are met, a spacing may be selected to match the center-
to-center electrode strip spacing of a detector component 60
or a multiple thereof so that the septal walls for the collimator
50 can be aligned with less accurate grooves formed within the de-
tector. Practical fabrication techniques are available for forming
., .
; the slots as exemplified at 112 and 116. In particular, chemical
~.
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milling or chemical machining techniques are available for this
purpose. With such techniques, a wax type mask is deposited over
- the sheets to be milled, those material portions designated for
removal being unmasked. The sheets then are subjected to selected
~` etchants whereupon the slots are formed. Pollowing appropriate
cleaning, the sheet members then are ready for therelatively sim-
ple assembly build-up of a completed collimator. Through the use
of such chemical milling techniques, desired tolerances in forming
the slots are realizable. By utiizing the collimator structure
shown in combination with optimal tungsten sheet material, a com-
putable 35 to 40 percent improvement in collimator efficiency may
be gained over round hole, hexagonally packed lead collimators of
identical dimension, as well as a 50 to 80 percent improvement in
septal penetration characteristics and an average 5% improvement
in geometric resolution. The collimator fabrication technique
and structure are seen to offer several advantages over more con-
ventional collimator structures. As evidenced from the foregoing
such advantages include the availability to the design of the su-
perior shielding capabilities of tungsten; a simplicity of compo-
- 20 nent design and conseguent ease of assembly and the use of optimal
square hold chamber geometry for maximum geometrical efficiency.
However, to achieve optimal performance, the assembly technique
necessarily introduces small gaps at the intersections of the septal
walls of a completed collimator structure. These gaps exist
by virtue of the tolerances required for interlocking fit
of the septal wall and the effect of gamma ray streaming through
such gaps should be considered.
In earlier commentary herein, it has been noted that
septal penetration of five percent or less of impinging gamma ra-
diation is preferred for collimator design. It follows, therefore,that the streaming factor for the particular collimator structure
. !
--33--
~4~5
at hand should be assigned the same configurational parameter in
the interest of desired unity of system design. Through utiiza-
tion of a geometric analysis of a worst case condition, requisite
lowest tolerance required for the interlocking fit of the septal
walls and for a desired source to collimator distance can be de-
rived. Such analysis will reveal that the slot tolerance should
preferably be no more than 0.001 inch, and more preferably, should
be less than that to the extent of practical milling application.
.....
In the discourse given heretofore concerning the func-
: 10 tional inter-relationships of collimator 50 and detector array 32,
' .
~ no commentary was provided concerning the effect of the discrete
,~ electrode strips of the detector upon ultimate image resolution.
It has been determined that, by virtue of their geometric confi-
guration, orthogonal strip detectors, without appropriate correc-
tion, will introduce "alias" frequency components into the output
of the system. For instance, in a purely linear system, the output
of the camera would consist of the same spatial frequency com-
ponents as the input except with the possibility of reduced contrast.
Looking to Figs. 7(a)-(c), the aliasing phenomenon is demonstrated
in connection with an exemplary and schematic representation of a
strip electrode detector 130. In this worst case representation,
no collimator is present and the electronic resolution is less than
. one strip width. Looking to Fig. 7(a), a source distribution is
shown as may be obtained, for instance, utilizing three discrete
collimated point sources spaced at equal distances of 1.5 times
the strip spacing. The reciprocal of the periodic spacing of the
components depicted may be represented as, v. The source distri-
bution shown is one with primary frequency components of vl = 0
and v2 - 2vs/3. Such source input is provided in the instant re-
-
34-
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presentation inQsmuch as it combines the three qualities which
accentuate an aliasing phenomenon, namely, a periodic input, 100%
contrast, and a high signal-to-noise ratio.
Fig. 7(b) reveals a portion of strip electrode detector
130 having the earlier described detector region grooves aligned
with respect to the input signals depicted at Fig. 7(a). The one-
dimensional spatial image which may be derived, for instance, from
a multi-channel analyzer is shown in Fig. 7(c) as curve 132. By
comparison, the corresponding spatial image which would be re-
ceived within a system incorporating a collimator capable of re-
solving the input signals, a detector with strip spacing satisfying
the anti-aliasing criterion and an anti-aliasing electronic chan-
nel, is revealed at 134. This image shows no aliased components.
Looking more particularly to the aliasing phenomenon
represented at curve 132, the four lowest spatial frequency com-
ponents revealed are:
(1) a component at v = 0, a zero frequency
component which represents the average
value of the four peaks;
20 (2) a component at v = 2v /3, which is the
frequency equal to the reciprocal of the
spacing betwen one of the two outer
peaks and the average position of the
two inner peaks;
(3) a component at v = v , which is the
frequency equal to the reciprocal of
the spacing between each of the four
peaks; and
(4) a component at v = v /3, which is the
frequency equal to t~e reciprocal of
the spacing between the two outer peaks.
The first two components above are the fundamental source
components, while the second two components are aliased components
of the fundamental source components centered at the first har-
monic of the strip sampling frequency.
s
As a prelude to considering a typical representation of
the spatial frequency response of a one-dimensional gamma camera
as revealed in Pigs. 8(a) - (d) the modulation transfer functions
(MTF) merit comment. As described in detail in publication (III)
hereinabove, the MTF is a measure of spatial resolution that can
be defined for lineflr systems and which takes into account the
shape of an entire line spread function. The rationale for such
description of spatial response arises from the fact that any ob-
ject and its image can be described in terms of the amplitudes and
phases of their respective spatial frequency components. The MTF
is a measure of the efficiency with which modulation or contrast
at each frequency is transferred by the imaging system from
the object to the image. This is analogous to the temporal frequency
response of an electronic amplifier or filter. Looking now to
Pig. 8(a) - 8(d) MTF is plotted against spatial frequeney, v, for
a series of stages within a gamma camera not accommodating for
aliasing phenomena. In Fig. 8(R) a collimator modulation transfer
function (MTFC) with FWHM resolution of 1.33 ~ is revealed, i.e.,
",; -
the curve distribution, incorporating some high frequency compon-
ents, is representative of the signal passed to the semiconductor
detector of the camera. Fig. 8(b) reveals the output frequency
spectrum of the detector which is seen by the spatial channel elee-
tronics of the camera system. An aliased frequency spectrum is
revealed, the input signal frequency spectrum being present in the
output, centered at zero frequency and additional side bands of
theprimaryinputcomponentarepresent,centered atintegermultiples
of the strip spacing or sampling frequency, VS = 1/ ~ . Fig. 8(c)
'`,
-36-
.'.
represents the MTF of the electronics of the system, i.e., the trans-
fer function of the spatial channel electronics, while Fig. 8(d)
shows the product of the MTF values of the curves of Figs. ~(b) and
8(c). Accordingly, the curve of Fig. 8(d) shows the spatial fre-
quency response of the entire system, including the introduction of
spurious spatial frequency content in the system MT~, represented
in the figure as the bump in the frequency range slightly below vs.
Looking by comparison to Figs~ 9~a) - (d) the effect
of inserted correction on the part of the collimator design and
structure of the instant invention is revealed. The collimator
50 design is selected to provide an MTF prefilter to limit the
spatial frequency content seen by the detector 32 to frequencies
less than vs/2. Accordingly, Fig. 9(a) reveals that the collima-
tor MTF is forced to a zero value at spectrum position vs/2. Such
design insures that the fundamental input frequency components
and the first harmonic frequency components centered at VS do not
overlap and this condition obtains in Fig. 9(b), that figure
revealing the alias frequency spectrum which is processed by the
electronic pickoff arrangement of the camera from the detector.
The spatial channel electronics complete the anti-aliasing filter
system by insuring that no spatial frequencies greater than vs/2
are passed to the imaging system of the camera. Such post-filtering
of the electronics is illustrated in Fig. 9(c). The product
of MTF conditions represented by Figs. 9(b) and 9(c) again are rep-
resented in Fig. 9(d) which, particularly when compared with the
corresponding Fig. 8(d), reveals the elimination of aliasing
phenomena.
Turning now to the prefiltering or corrective functions
carried out by the collimator in contrGlling aliasing phenomena,
it may be observed from the foregoing that the system resolution
- -37-
~ )7~5
`.`.`.`":
of an orthogonal strip germanium detector type gamma camera is de-
-~ termined by the collimator resolution, the strip width spacing,
and the resolution of the spatial channel readout electronics.
The collimator is assumed to have a Gaussian point spread function
(PSF) and FWHM spatial resolution Rc. The value of Rc should be
equal to or greater than about 1.7 ( ~ ), where ~ is the center-
to-center strip spacing in one dimension of the detector. A more
~ detailed discussion of the derivation of this valus is provided
: in the following publication:
XXI. J.W. Steidley, et al., "The Spatial
Frequency Response of Orthogonal
Strip Detectors," IEEE Trans. Nuc.
; Sci., February, 1976.
Looking now to the specific design parameters of the col-
limator of the invention, it may be recalled that collimator re-
` solution, ~c' has been derived geometrically at equation (1) given
hereinabove. By now substituting the ideal valuation, 1.7 ( ~ )
determined for anti-aliasing prefiltering on the part of the col-
limaator, the inventive collimator geometry or structure may be
defined. Accordingly, the collimator is defined under the follow-
ing expression:
.i , ~
: ' Q ' - AE (A + B + C) ( )
The collimator further ean be defined utilizing equation
- (5) above for septal wall thickness once the values of the para-
meter of equation (7) are determined. Further, given the value,
Rc, for collimator resolution and the geometric parameters deter-
mined thereby as described above, the collimator geometric effi-
`:
: ' ~
-38-
liQ74US
ciency, 0s' as given in equation (6) above, can be applied to fur-
ther maximize the performance of the collimator. Additionally, it
may be noted that the suppressing frequencies above vs/2 input sig-
nal contributions to aliasing phenomena are accommodated for.
As has been alluded to earlier herein, discounting en-
trance geometry, the orthogonal strip position-sensitive detector
is resolution limited by noise associated with the detector as
well as the charge dividing network. Consequently, it is necessary
to consider the noise characteristics of the sytem from the stand-
point of minimizing the effects thereof upon resolution as well astreating such phenomena to derive desired imaging effects. Gen-
erally, it may be concluded that the resistor network is the domi-
nant source of noise within the electronic spatial channel of the
system, while the resistor network, coupled with the detector leak-
age current, represents the dominant noise source in the system's
energy channel. As will become more apparent as the instant de-
scription unfolds, spatial noise dominantly is electrically parallel
in nature, whereas energy channel noise may be considered to be
electrically series in nature. In the discourse to follow, noise
treatment and the like are described in conjunction with the singu-
lar detector component described heretofore in connection with Fig.
2, in the interest of clarity and simplification. In the later
portions of the instant discussion, however, the control system of
the camera will be seen to be described in conjunction with detec-
tor component array embodiments.
Noise is the random fluctuation of the preamplifier out-
put voltage when there is no stimulus. It is generated by imper-
fections in the preamplifier input device, thermal movement of
charge carriers in the resistors and the bulk of the detector and
:
~ -39-
a ~4~S
~ i.~ .,
; .
imperfections in the crystal structure of the detector. Looking to
Fig. 10, an equivalent noise model circuit for solid state detec-
tor components is revealed. Note that the model reveals a detec-
tor leakage current, iD~ which is assumed to be formed of indi-
~; vidual electrons and holes crossing the depletion layer of the
detector. Such electron hole pairs are thermally generated in
.the depletion layer. Resistive elements which are in parallel
with the system input capacitance, CIN, generate thermal noise
which is integrated by this capacitance and appears at the pre-
10 amplifier input as a step function. The system input capacitance
is the parallel combination of stray capacitance at the pream-
plifier input and the feedback capacitor of the preamplifier.
Those resistive components which contribute to this noise term are
the high voltage bias resistor, the preamplifier feedback resistor
and the detector bulk resistance. For a charge dividing resis-
tive strip network, a portion of the dividing resistance, ~ ,
` is in parallel with the detector capacitance. Since ~ is less
;than one hundred kilo-ohms, it respresents a significant noise
source. The thermal noise from resistors in series with the de-
- 20 tector capacitance appears as a delta function to the preampli-
fiers. For spectroscopy systems, this resistance is minimized
` and the noise source is neglected. The noise developed by the
- preamplifier input stage is modeled using a resistor, Req. Fin-
~`ally, a noise term which is not shown in Fig. 10 is "flicker"
noise caused by structural changes and surface effects in the
conduction material of the noted preamplifier input stage. This
noise aspect generally is considered to be insignificant.
.; .
-40-
Since the noise sources discussed above have a uniform
power spectral density, bandwidth limiting filtering or pulse
shaping generally is considered appropriate for maximizing the
signal-to-noise ratio of the system. As suggested earlier, the
fundamental noise sources are classifiable as two types, parallel
noise representing the change due to the electron flow which
is integrated by the input circuit capacitance, and series noise
representing the charge due to the electron flow which is not
integrated by input capacitance. These noise sources are con-
sidered to be mutually related in terms of filtering to the ex-
tent that as efforts are made to diminish one, the other increases.
The high frequency component noise generally is considered a
series type while low frequency noise is considered of the parallel
variety. As has been detailed in the publications given above,
the use of Gaussian and the Gaussian-trapezoidal noise filtering
circuits has been found to optimize the energy and spatial resolu-
tion values of the camera system.
Turning now to Fig. ll, a circuit model of the detector
component 60 and the resistor networks of Fig. 2 is portrayed.
The discrete nature of the detector system and the method of read-
out is revealed in the figure with the discrete capacitors form-
ing an n x n array. Each row and column is defined by the
-, ,
charge measured at the end of the resistor strings. The elec-
tron-hole pairs which are formed when a gamma ray interacts with
the detector are collected on opposite surfaces. ~ charge enters
the resistive network and flows to the terminal A or B (C or D)
in relation to the resistance between its entry point and the
virtual earth terminal of each preamplifier (Fig. 2). The in-
tersection of the column and row defines the diode position in
-41-
t7
.~`.
which the gamma ray energy was deposited. Note in the figure,
; that individual capacitances are represented which are exemplary
of the inherent capacitance of the detector itself. When con-
sidered in conjunction with the resistor networks, as revealed
in the figure, it may be noted that a particular time constant
or interval is required for any impinging charge to be represented
by a charge flow to the output taps of the resistor chains.
Accordingly, the system must provide an adequate time interval or
time constant, r D' for this charge flow to avoid error in informa-
tion collection. In effect, it may be assumed that the detector
and each of the resistor strings of the noted impedance networks
respond as a diffusive line, and the peaking time of the pream-
plifier output pulses will vary as a function of the position of
interaction, xO, of an incident gamma ray. The voltage output of
each preamplifier (Fig. 2) due to the instantaneous transfer of
.. ..
charge QO at position xO is:
'.,' 00
V(O,x ,t) C- [1 - o ~ ~ _7~ sin ( L )exp [ ~ ]] (8)
QO [xO + ~ ~ cos(m ~)sin ( L )exp [ ~ 1-
where Cf is the feedback capacitance of a preamplifier in farads,
L is a given linear dimension of the detector, ~D is the time
constant of the detector (i.e. D 2RDCD), xO defines the po-
sition of inter~cti~n and m is a summation variable.
-42-
~V7~
Examination of equation (8) and (9) show that for a time
t ~ D , (10)
i.e., an output generation time equivalent to one-half of the time
constant of the detector, the value of V(O,xo,t) is within 1% of
its final value for all xo/L ~.95 and V(L,xo,t) is within 1% of
its final value for all xo/L-~.05. Stated otherwise, the error
generated form ballistic deficit type characteristics of the
system, as it relates to the energy of one preamplifier readout
diminishes to a value of 1% within a period of one-half the time
constant, / D of the detector.
By subtracting the output of the one preamplifier of a
network, i.e. at the x - L position from the corresponding ampli-
fier output at the x = 0 position, i.e.
~o
V(O,Xot) ~ V(L~Xo~t) = Cf L l ~ L ~ ~7rsin L~ )
(1 + cos m ~) exp ~ )1
D ~ , (11)
the following important observations may he observed. Equation
(11) shows that as the spatial location of information impingement
alters from 0 to L, the resulting voltage readout moves from a
positive unit value to a negative unit value. ~tated otherwise
the output signal derived from the above signal treatment sub-
tractive approach ranges from + Qo/Cf at xO=0, to -Qo/Cf at
xO = L, making the signal twice that of earlier suggested one
-43~
~1~74(~S
preRmplifier collection technique. Further, it may be observed
that the odd numbered series terms vanish, thereby reducing the
position signal peaking time. The value of equation (11) is
within 1% of its final value for all values xo/L ~.45 and x/L~
.55 after a time: t~ ~D (12)
Accordingly, it may be observed that through the utilization of a
dual preamplifier subtractive or "antisymmetric" method of signal
analysis, the necessary time constant related signal treatment
~; within the spatial channel is diminished by a factor of 4.
;~ Turning now to the conditinos obtaining within the energy
channel of the system, the energy channel is derived by summing
the output of each preamplifier to obtain the voltage pulse:
' 00
V(O,xo,t~ ~ V(L,xo,t) Cf ~ ~ m~ sin ( L )
m=
(1 - cos m~ exp ( ~ ~ (13)
D
:
Note again, that the peaking time of the pulse is posi-
tion dependent. At xo/L = .5, the maximum peaking time occurs and
the pulse is within 1% of its final value at t~D/2. According-
ly, it may be observed that ballistic deficit or charge collection
type considerations within the energy channel will require a charge
collection period, for practical purposes, equivalent to one-half
of the time constant of the detector.
''`~'
` :
:,
,
-44-
4~
Now considering noise phenomena, as earlier discussed in
combination with ballistic deficit considerations, as derived
immediately hereinabove, dominant spatial noise, which is parallel
: noise, may be expressed as follows:
N~51 = I ( ~ ) I/a (14)
where NqSl is the equivalent noise charge in number of electrons
for one preamplifier spatial measurements, RD is the total re-
sistance of the resistive chain, TD is the temperature of the
~` detector and chain, ap is a weighting factor of the filter, q is
the magnitude of the charge on an electron, and K is Boltzmans
constant.
In the expressions given above, i.e. equations 8 through14, the term ~ is intended as the value representing the aver-
age of the total resistance of each resistive network. For the
exaggerated exemplary detector component shown in Fig. 2, the term
represents one-half the sum of the resistance value of net-
works 72 and 74. Note from equation (14) that the noise is pro-
portional to the square root of the temperature as well as theweighting factor and the time constant of the system. As disclosed
earlier, this time constant is limited by the ballistic deficit
- conditions of the system. Note further that the noise is inversely
proportional to total resistance of one chain or resistor network.
Therefore, it is desirable for system efficiency to minimize the
temperature under which it operates as well as the weighting fac-
tor and time constant and to elevate the resistance value to the
-45-
s
`i extent practical. Equation (14) is for one preamplifier readout.
Reconfiguring the equation to represent a subtractive or anti-
symmetric arrangement, the following expression obtains:
N = 2 (4kTD a ~O) l/2 (lS)
From this equation, note that a subtractive arrangement
permits the ballistic deficit dictated time constant to reduce
by a factor of 4, while the value of noise increases by a factor
~: .
of 2 for that same time constant. However, since a reduced time
; constant (factor of 4) is involved in a subtractive arrangement,
. . .
the noise value, otherwise increased by a factor of 2, remains
:;
' ~ the same and the signal-to-noise ratio is increased by a factor of
:~ 2. Recall the earlier discussion, above, that the unit signal value
runs from a positive unit to a negative unit within a subtractive
system. The value ~ is difficult to increase inasmuch as a
concomitant reduction in energy resolution generally is witnessed
,~,,
~; for such alteration. Temperature drop can be achieved practically,
and the weighting factor, ap, can be altered to a more or less ideal
value by appropriate selection of filtering systems. It has analyti-
cally been determined that a 43.4 percent improvement in spatial
resolution is realized if antisymmetric summation, i.e. subtractive
summation, is used as opposed to the utilization, for instance,
of one preamplifier for spatial measurement.
.::
Looking additionally to the "ballistic deficit" phenome-
: non, for thin detectors, i.e. about five mn in thickness, the de-
tector charge collection time is small and does not affect cir-
cuitry treating a detected signal. For thick detectors, however,
. .:
; i.e. having a thickness in the range of about 2 cm, the bulk charge
30 collection time varies rom approximately 100 to 200 nanoseconds.
,
~ -4~-
Since this collection time is approximately the same as the col-
lection time of the charge dividing network, its contribution
to ballistic deficit problems must be considered. For such sys-
tems the optimum filtering arrangement consists of a time invari-
ant pre-filter followed by a gated integrator circuit. Such fil-
ters generally are referred to as gated-integrators or trapezoidal
filters. The filter preferred for the purpose is a Gaussian
trapezoidal filter which consists of a time invariant Gaussian
filter followed by a gated integrator circuit. Such arrangement
is revealed in more detail in the disclosure to follow. For a
detailed discourse concerning the utilization of antisymmetric
summation as well as the utilization of trapezoidal filtering
within the spatial channel of the system, reference is made to
the following unpublished work:
XXII. Hatch, K.F., "Semiconductor Gamma Camera",
Ph. D. Dissertation, Massachusetts Institute
of Technology, Cambridge, Massachusetts,
February, 1972.
The equivalent noise charge in number of electrons for
Gaussian trapezoidal spatial measurements may be represented by
the following expression:
qSGT 2 (4kTD~pT1 1 79) (16)
where ap is the parallel noise weighting function value for Gaus-
sian trapezoidal systems and TI is the integration time. Analy-
sis of the foregoing shows that an excellent improvement in spa-
tial resolution is obtained by using antisy~etric Gaussian trape-
zoidal filtering. This improvement is realized because the effects
of "ballistic deficit" are greatly reduced.
-47-
~ ,- .
~ '""
` ~
7~(~5
'; '
, .. .
The corresponding equivalent noise charge in number of
electrons for the energy channel of the system may be expressed
by the following formulation:
; NqESI q {2qiD~pro 4kTD 6 ~ 9 } (17)
. .
~; An important aspect of the above energy channel and
spatial channel analyses has been observed. In this regard, it
may be recalled that opposed relationships stem from a considera-
tion of parallel vs. series noise phenomena. Por instance, it has
been describedthat energy noiseis consideredserial innaturewhere-
as spatial noise is considered to be parallel in nature. The energy
~, noise equation, as shown at (17) above, represents a straight summa-
tion of two preamplifier outputs andthe initial parallel noise factor
.,
presented within the brackets thereof is of dismissable magnitude.
When compared with the spatial noise equation (16) above, it may be
observedthat twoseparatetime constant values,~O, ~ respectively,
for spatial resolution and energy resolution may be incorporated
within the circuitry treating the output of the system detector.
~:,
~ For instance, the energy resolution filtering of the system
.;. . .
requires a relatively extended time constant, whereas corre-
sponding spatial filtering requires a relatively short one for
highest signal to noise ratio considerations. Inasmuch as the
outputs of the filtering media reach the output displays of the
camera or imaging system simultaneously, any multiple pulse errors
introduced into the longer tîme constant energy filter indivi-
dually will be integrated to achieve a peak value above a pre-
designated window function of the energy channel (block 45, Fig. 1)
. .
-48-
'
"
~74~S
' , .
Accordingly, false information genmerated from pulse pile-up pheno-
mena and the like may be rejected without recourse to more in-
volved discrimination circuitry. Such a desired system circuit
arrangement will be revealed in the description of the control
system to follow. While this description is made in conjunction
with the singular detector component embodiment of Fig. 2, the
theory of its operation will be seen to carry forward into the
corresponding operation of the scaled-up control system operative
in conjunction with a multicomponent detector array.
Referring now to Pig. 12, a block schematic representation
of a control system is presented for receiving spatial coordinate
outputs of the detector. In the figure, preamplification stages
96,98 and 80, 82 are reproduced and the outputs thereof, respec-
tively, are revealed at lines 110-116. Arbitrarily designating, for
instance, preamplifiers 96 and 98 as deriving energy information
along an x-axis, the outputs thereof at 110 and 112 are coupled,
respectively, through lines 118 and 120 to the input of a Summing
and Gaussian Filtering function 122. As discussed in detail above,
function 122 operates under a relatively extended time constant,
identified within the block as ~e. One output from function 122
is directed to a pulse height analysis function 124 from along
line 126. The other output of function 122 is directed to a Gate
Control and Display Control function 128 from along line 130.
This is an energy derivative pulse, as identified at line 130, and
provides a start pulse input to function 128. Output lines 110
and 112 also provide the spatial channel input to Antisymmetric
Summation and Gaussian Filtering function 132. From function 132,
a subtractive filtered signal is directed along line 134, to a
.
-49-
.~ .
Gated integrator 136 operating under an integrating period cor-
; responding with time constant ~ o Control into the gated in-
-` tegrator, for instance, establishing the time constant value, ~ o~
~: emanates from gate control function 128 through line 138. Addi
tionally, a reset control is provided to the integrator from line
140.
Similar to the x-axis spatial chanel inputs, the y-axis
.~
~ spatial channel inputs deriving through lines 114 and 116 are
.~ introduced into an Antisymmetric Summation and Gaussian Filtering
. i
function shown at block 142. The output from block 142, as is
present at line 144, is introduced to a Gated Integrator function
;~ 146, structured identically to Gated Integrator function 136.
. ~
Time constant ¦ O control over integrator 146 is asserted from
gate control function 128 through line 148, while reset control
is asserted from line 150. The outputs from the x-axis Gated
~ Integrator Function 136 is presented along line 152 to a Photo-
~ graphic Record readout 154 and through lines 152 and 156 to a
: Persistant Display Scope 158 may be utilized for purposes of
patient positioning and other information desired by the opera-
tor. Similarly, the y-axis spatial channel information derived
from Gated Integrator function 146 is presented along line 160 to
Photographic Record output 154 and through lines 16~ and 162 to
: Persistent Display Scope readout 158. Readowt control to Photo-
: graphic Record 154 and Persistent Display Scope function 158 is
; derived from Gate Control and Display Control function 128 through
lines 164 and 166. The control asserted thereby is one wherein
.
.,.
-50-
'
outputs 154 and 158 are not actuated or are blanked until control
function 128 receives an input display signal from Pulse Height
Analysis function 124 through line 168. Interrogation of function
128 is provided from control 128 through line 170. Inasmuch as
a re~atively extended time constant, re, is utilized at Summing
` function 122, any pulse pile-up phenomena will be integrated to
derive a peak pulse level beyond the upper window limitations
of the channel analyzer operating within function 124. Accordingly,
error otherwise introduced into the system from the spatial channels
is blanked upon the assertion of an interrogation request from
line 17Q and a responding blanking type signal or no response
signal from function 124 through line 168.
Looking now to Fig. 13, a block schematic diagram is
provided showing the basic components of the Gated Integrator
and associated functions depicted generally at blocks 136 and 146
in Fig. 12. Note that the circuit includes an input amplifier
172 which feeds, in turn, into a delay line 174. Delay line 174
is utilized to insure that the integrator gates are open before
any spatial informational pulse arrives thereat. The circuit
further includes a base line restorer, as at 176, which opeates
in cooperation with gated integrator 178. The output of integra-
tor 178 is directed to an output amplifier 180, the output from
which is directed along lines 152 or 160, as shown in Fig. 12,
dependingupontheparticularorthogonalsenseoftheincomingsignal.
A corresponding and more detailed schematic representa-
tion fo the circuit is revealed in Fig. 14. Referring to that
figure, either of the coordinate spatial inputs as developed at
-51-
, ~
~74(}5
;r
lines 144 or 134 (Fig. 12) is asserted through an input resistor
;~ 182 to an amplification stage 184. Stage 184, corresponding to
amplifier blo~k 172 in ~ig. 13, includes a feedback line incor~
porating feedback resistor 186, as well as a ground reference in-
put at line 188. Delay line 174 is shown represented at 190 re-
.,~, . .
,'; ceiving an input from output 192 of amplifier 184. A resistor
194 is coupled between delay line 190 and ground, while the out-
put thereof is AC coupled through capacitor 196 to the input of
a base line restorer function. The base line restorer is of a
. 10 Robinson type as is generally described, for instance, in the
following publication:
,:.:';
XXIII. Robinson, L.B., "Relations of Baseline
Shift in Pulse Amplitude Measurements",
` Rev. Sci. Inst., 32, 1961, p. 1057.
Essentially, the restorer function is provided for the
purpose of assuring a net zero charge value at the gated inte-
,.~.
grator input prior to the reception of any input signal. Further,the restorer defines the maximum charge that can be placed on the
coupling capacitor 196. In the absence of the restoring function,
the ~ated integrator would integrate areas below the baseline as
well as under the Gaussian shaped spatial signal. For carrying
out its assigned functions, the restorer includes an emitter-
follower stage at NPN transistor 198, the base of which is coupled
through resistor 200 and line 202 to one side of capacitor 196.
:
The emitter of transistor 198 is coupled through a resistor 204
to -Vcc potential, while its collector is coupled through a re-
sistor 206 to +Vcc. The restorer function additionally includes
., .
:;' .
.
-52-
., ,~ ~,j;
:
~'
4~5
a cur~ent supply network oepra$ing such that, upon the occurrence
of spurious elevations of current, accommodation is made to con-
trol the quiescent point at the emitter-follower stage 198. Note
. .
: that this current supply includes a PNP transistor 208, the emitter
and base of which, respectively, are coupled through resistors 210
and 212 to +Vcc. This base, additionally, is coupled to ground
.~ through a resistor 214. The collector of transistor 208 is
~: coupled through diode 216 to line 202 and through diodes 218 and
220 to a variable resistor 222, the termini of which are con-
nected between the positive and negative sides of the supply
voltage.
~ The output of the base line restorer function is coupled
through resistor 224 to one terminal, for instance the source,
of a field effect transistor (FET) 226 representing the intput of
the gated integrator function, while the opposite electrode of
the transistor is coupled to line 228. Line 228, in turn, is
directed to one side of an integrating amplifier 230. The gate
input to FET 226 is present at line 232 and is shown as selective-
ly receiving a signal designated y from the control function 128
; 20 (Fig. 12). Also influencing line 228 is a network including line
234 and variable capacitor 236 which is coupled to receive an
.. ~ input designated ~ . The opposite input to amplification stage
230 is coupled to ground through line 238. Amplification stage
230 performs an integrating function by virtue of its feedback
connection with an integrating capacitor 240 coupled between
lines 242 and 244. A shunting resistor 246 is coupled between
lines 242 and 244 in parallel with capacitor 240 and is selec-
~53-
i~7~(~S
tively activated by a reset gate present as field effect transis-
- tor (FET) 248, the source and drain terminals of whieh are con-
nected in switch defining fashion within line 244 and the gate input
to which at line 250 is configured to selectively receive a reset
signal identified as,~, from Gate Control Function 128 (Fig. 12).
A varfliable resistor 252 is connected between the positive supply
voltage and the interconnection of resistor 246 with FET 248.
The output of amplification stage 230 is present at line 254 and
is coupled through a variable capacitor 25~ and line input 258 for
` 10 seleetively receiving a signal input identified as, ~.
; The output at line 254 of the gated integrator is direct-
ed through resistor 260 to the input of a unity gQin inverting
amplifier 262 which includes a feedback line incorporting re-
sistor 264 and is connected with ground reference at line 266.
~; The output of the amplifier, at line 268, is that represented in
Fig. 12 either at line 152 or line 160 and is directed to the
readout components of the camera system. As will be apparent in
; the discussion to follow, gate control over integrator 178 is
derived by the noted signal inputs into lines 232, 234 and 250
.'''~
and 258.
Looking to Figs. 15 and 16, the control circuit repre-
sented in Fig. 12 at 128 is disclosed in more detail in combina-
tion with a timing sequence diagram. At time, t = 0, as shown
:
in the timing diagram of Fig. 16, the sytem is prepared to pro-
cess an incoming set of signals or pulses. The time derivative
of the energy pulse or signal dE/dt is directed along line 130
to a comparator 292. When its value exceeds a reference voltage
representing the lower level of the window level established by
~x~ -54-
.
~.,.
."'
~o~
`~
evaluation or Pulse Height Analysis functin 124 (Fig. 12) it
serves as a start or to actuate the control system. The voltage
reference against which the derivative of the energy pulse or sig-
nal is compared is inserted from line 290 to the comparator.
These predetermined, preliminary signal level conditions being met5
comparator 292 provides a positive going output pulse atline 294
which is introduced to a dual, D-type flip-flot FF-l. Convention-
ally, the D form of flip-flop incorporates an actuating (clock)
input signal terminal, Ck, along with a signal input terminal, D.
The flip-flop output signal Q becomes 1 at the time of a 0-to-1
change at the clock terminal4 In conventional manner, the Q out-
put of the flip-flop represents the inverse of the Q output.
The D flip-flop also is characterized in incorporating a clear
feature designated at "Cl" in the diagram. To further fac-
ilitate the description of the circuit, Boolean designation is
utilized to represent input or output values. For instance, a
"low" signal is considered to be one having a potential essentially
at ground and is typically represented by a logical "zero".
Conversely, a "high" signal is considered positive and may be
depicted b~ a logical "one".
Returning to Figs. 15 and 16, with the presence of a
positive going pulse at line 294~ flip-flop FF-l is clocked such
that its Q output at line 298 assumes a high value and its Q
output at line 296 assumes a low value. Note that the Q output
of flip-flop FF-I is identified as ~ and is introduced to the
reset gate of each integrator, as shown in Fig. 12-14. With the
opening, for instance, of reset gate transistor FET 250, the
shunt about timing capacitor 240 is removed to enable the inte-
grating amplifier. Similarly, the Q output of flip-flop FF-l
assumes a low status and, by connection through line 296, couples
the ~ signal input to the gated integrator as at line 258 in
Fig. 14. This ~ signal output of the flip-flop FF-l is used to
compensate for charge injection into the feedback capacitor caused
by the capacitance coupling between the gate and drain electrodes
of FET 248.
The Q output of flip-flop FF-l additionally is presented
through line 298 to the B input terminal of a monostable multi-
vibrator M-4, and, through line 300, to the B input terminal of
:
monostable multivibrator M-l. Accordingly, these multivibrators
` 10 are trggered, the Q output of multibivrator M-4 being programmed
?, ~
for closing each integrator input gate for a time slightly greater
than the base width of the Gaussian shaped spatial pulses. In
; this regard, note that the Q output, as is represented at line
, 232 of the multivibrator M-4, carries a y signal which is intro-
duced into the input gate of FET 226 (Fig. 14). Simultaneously,
an inverted q input is provided along line 234 to variable
capacitor 236 to provide compensation for off charge injection.
The gated integrator then com~nences an integrating mode of per-
formance, the time over which operation is controlled by multi-
vibrator M-4. It may be observed that multivibrator M-4 retains
this output state in correspondence with a spatial time constant
determined interval, ts, as is more clearly portrayed in Fig. 16.
; Note in that figure, the representation of a Gaussian spatial
pulse, S, corresponding with the activation of the integrator
function.
As noted above, the Q output of flip-flop FF-l also is
introduced to the B input terminal of monostable multivibrator M-l.
.
, ,
-56-
,.~. ,
,s..
'
With the presence of the forward edge of this signal at line 300,
the Q output of the latter alters from a low to a high value and
retains such value over an interval, te, selected for delaying
the start of the display sequence until the energy pulse has been
analyzed at pulse height analysis function 124 as shown in Pig.
12. Note that this interval, te, always will be greater than the
integrating interval, ts. The Q output of multivibrator M-l is
coupled through line 302 to the A input of monostable multivibrator
M-2. On the occurrence of the negative edge of the pulse of the
Q output of multivibrator M-l, multivibrator M-2 is triggered and
the resultant Q output transition thereof is directed along lines
304 and 306 to driver circuit Dl. The output at line 170 of
driver Dl serves as the earlier described interrogation pulse
directed to the pulse height analysis function 124 described in
connection with Fig. 12. Note additionally, that line 306 extends
to one input of a NAND gate Nl. Accordingly, the signal from line
306 is inverted and introduced through line 308 to the A input
terminal of monostable multivibrator M-5. This input serves to
enable the latter to permit the carrying out of a full control
cycle. During typical display operation of the camera system,
the "interrupted" and "on/off" inputs to NAND gate Nl are high
at the option of the operator. By converting either or both to
a low value, multivibrator M-5 is inhibited to, in turn, inhibit
the displays as referred to earlier in Fig. 12 at 154 and 158.
The remaining components of the circuit function on the
basis of whether an interrogating signal issued from line 170 to
-57-
;..
. ~
.~,. .
Pulse Height Analysis Function 124 (Fig. 12~ has been responded
to, al~ng line 168, to indicate a pass or no pass condition of
signal energy level. If function 124 does not respond to the
interrogating pulse from line 170, thus indicating that the peak
- value of the energy pulse did not fall within the window setting
of the evaluation function, multivibrator M-S receives no signal
input at terminal B thereof. Additionally, upon the occurrence
of the negative edge of the Q output signal of multivibrator M-2,
multivibrator M-3 is triggered from line 304 such that its Q
output at line 310 asserts a clearing signal through AND gate ANl
to the clear input terminal, Cl, of flip-flop FF-l. The output
thereof, as reflected at the multivibrator M-4, causes the inte-
grator to be reset. With this operation, the sytem is short
cycled, andthe through-put ratethereof advantageouslyis increased.
Note, that the opposite input at line 314 of AND gate ANl is nor-
mally high by virtue of its connection through line 316 and re-
sistor 312 to a positive voltage source.
Assuming that multivibrator M-5 has been enabled from the
line 308, A, input thereto and that a positive response has been
received from Pulse Height Analysis function 124 and line 168 at
; the B terminal input thereto, the multivibrator will react by de-
veloping a positive output pulse at its Q terminal and line 320,
while a pulse of opposite sense is developed at its Q output along
line 332. The Q output signal at line 320 is directed to line 324
whereupon it addresses the clock input, Ck, of D flip-flop FF-2.
In consequence, the Q output of flip flot FF-2, at line 322, con-
.,
-58-
~ 5
. ~
verts to a low value which is asserted at the B input of multi-
vibrator M-3 to inhibit the output thereof. The short cycle fea-
ture thereby is inhibited. This signal at line 324 may also be
utilized for clocking a scaler or count recording apparatus
through a driver circuit D2.
The outputs of multivibrator M-5 also are utilized to
switch a Z-axis driving circuit from a negative to positive volt-
age, thereby turning on the display functions represented in Fig.
12 at 154 and 158. In this regard, note that line 324, carrying
the Q output signal of multivibrator M-5, is connected to the
; gate electrode of a field effect transistor (FET) 328. By cor-
responding connection, the Q output of multivibrator M-5 is as-
serted along lines 332 and 334 to the gate input field effect
transistor (FET) 330. Note that the drain-to-source chflnnel of
FET 328 is connected through resistors 336 and 338 to a positive
; voltage source, while the corresponding source-to-drain channels
of FET 330 are coupled through resistors 340 and 342 to a negative
voltage supply. The respective opposite sides of FET's 328 and
330 are connected through line 344 and line 346 to one input of
the Z-Axis amplifier 348 and are biased such that, under conditions
wherein monostable multivibrator M-5, is not clocked, the output of
amplifier 348 is retained at a negative value. Upon the clocking
of multivibrator M-5, however, FET 330, in effect, closes while
FET 328 opens, to cause the output of amplifier 348 to change
from a negative to positive value, thereby permitting the activa-
tion of display and record functions 154 and 158 (Fig. 12).
'
-59-
,.., ~ ~,
, ..
74~S
. .
.
Zener diodes as at Zl and Z2 are present in the input
. network to Z-axis amplifier 348 for the conventional purpose of
, ... - -
voltage regulation, the diodes being commonly coupled to ground at
their respective anodes. Additionally, the respective cathodes of
s the diodes Zl and Z2 are coupled at the common connections of
resistors 336 and 338, 340 and 342.
Looking further to the outputs of multivibrator M-5 as
they respond to an energy evaluation input at line 168, the posi-
tive edges of the output signal at Q thereof also activates a
10 multivibrator M-6 in consequence of the connection of line 332
- with the B terminal thereof. Multivibrator M-6 serves to provide
a delay function assuring an adequate interval for turning off the
electron means of display scopes and the like. The Q output of
multivibrator M-6 is coupled through line 352 to the B terminal
input of another monostable multivibrator M-7. The positive going
edge of the Q output signal of the multivibrator M-6 triggers multi-
;.'.
vibrator M-7 to provide a corresponding pulse signal at its Q
~; output at line 354. Line 354 is coupled through AND gate AN2, the
output of which is coupled through line 356 to the clear terminal,
Cl, of flip-flop FF-2. The opposite input to AND gate AN-2 is
operator preselected and ls asserted from line 314. With the
`` presence of a clearing input to flip-flop FF-2, the Q output there-
of at line 322 returns to a high status which, in turn, is im-
posed at the B input of multivibrator M-3 which, in turn, functions
to clear flip-flop FF-l by virtue of the connection therewith of
its Q output at line 310 through AND gate AN-l. With the clearing
~` of flip-flop FF-l, the gated integrator is discharged or reset
-60-
~,
f'4QS
through the ~ input signal at line 250, described earlier in con-
nection with Fig. 14.
With the noted return of monostable multivibrator M-3 to
its standby state, the control system is fully reset and ready to
process another set of information signals. If the output of
comparator 292 is high at this time, the system will not process
such incoming information. This lock-out feature prevents the
- partial integration of spatial pulses too narrowly spaced in
insertion time. Note that comparator 292 is coupled to receive
the ~ signal output from the Q terminal of flip-flop FF-l through
lines 296 and 297. This input signal is utilized by the compara-
tor as a bl~ck to any enabling of the system to respond to in-
coming signals until such time as a full cycle of evaluation has
terminated. Fig. 16 reveals the time-based correspondence be-
tween the output of comparator 292 and the Q output or ~ signal
of flip-flop FF-l~ In the absence of such 6 signal input from
line 297, error would be introduced into the system, for instance,
by virtue of the generation of start signals at line 294, inte-
grator timing is disrupted to invalidate an ongoing signal pro-
cessing procedure. As may be evidenced from Fig. 16, the ~signal input from line 297 (flip-flop FF-l, Q terminal) serves to
. inhibit comparator 292 until the reset point of a given signal
processing cycle.
As noted earlier, any display of spatial pulses which
overlap is prevented because, for the optimized filtering system,
the base width of the spatial Gaussian pulse is less than the
peaking time of the energy Gaussian pulse or interval of energy
-61-
.,
7~ OS
-`
analysis. Because of this, should two or more gamma rays photo-
.~ electrically interact with the detector and their total energy be
absorbed in a time less than the rise-time of the filtered energy
P,., ,~,
pulse, the resulting energy pulse peak value would not fall within
the window defined at pulse height analysis function 124. As a
consequence, the control system would carry out a short cycle
function as revealed in the timing diagram of Fig. 16 by a dashed
line alteration of the curves.
Examination of the dashed curves of Fig. 16 reveals that
- 10 upon interrogation of Pulse Height Analysis 124, should no re-
: -
sponse signal be received therefrom within the interrogation in-
terval defined by multivibrator M-2, the negative going edge of
the output thereof causes multivibrator M-3 to carry out a reset
function, thereby inhibiting the carrying out of the remainder of
the signal processing cycle.
~; ,.,
As noted earlier, it is important that the detector func-
., .
tion of the gamma camera be capable of accepting photon information
. .
~ from as broad a spatial region as possible. Inasmuch as the size
;- of detector crystals inherently is limited by the techniques of
their fabrication, it becomes necessary to conjoin a plurality of
such detector components in some manner wherein a broader region
of radiation may be witnessed and imaged.
One preferred technique for associating the discrete
.i .
detector components provides for their mutual operational inter-
connection in subgroupings of predetermined numbers, for instance,
4, which subgroupings then are coupled with the control system
~of the camera. An array of detector components having a requisite
; camera entrance area acceptance geometry then is formed preferably
.
-62-
,. ..
.
of a symmetric compilation of component subgroupings. One prac-
tical size for the detector array comprises four subgroupings
each of which is formed of four detector components. With such
an array, the control system advantageously may operate by ob-
serving the performance of the subgroupings as they are represented
in quadrature. Another aspect to be considered in "scaling-up"
the camera system for clinical utility resides in the earlier-dis-
cussed feature permitting their accepting and properly imaging in-
.:..
formation derived from two discrete photon energy levels. Accord-
ingly, the scaled-up gamma camera would incorporate a control
` system accommodating both of these desired features. In the dis-
course to follow, the general signal treatment described herein-
above in connection with Figs. 12-16 remains substantially the
same with an appropriate multiplication of functions where neces-
sary to accommodate for the greater number of generated signal inputs
. from the detector groupings.
Turning to Fig. 17, a composite detector, formed as an
array of discrete detector components, is revealed generally at
360. This sub-grouping of four detector components, as identified
at 362, 364, 366, and 368, may, for instance, be combined with
three additional subgroupings to form a full detector array
` comprising four subgroupings incorporating a total of 16 detector
components. Of course, a greater or smaller number of detector
components may be combined to form an array of desired dimension.
In the interest of clarity, only one such quadrant designated sub-
array, as at 360, is described in conjunction with a control sys-
tem. Detectors 362-366 are dimensioned having mutually equivalent
areas designated for the acceptance of impinging gamma radiation.
Such equivalency serves to achieve accurate ultimate image read-
out from the camera system. The detector components 362-366
are of the earlier-described orthogonal strip array variety, each
:
-63-
.
strip thereof being defined by grooves. Note in this regard, that
~ detector component 362 is formed having strips 370a-370d located
- at its upwardly disposed surface and defined by grooves cut
intermediate adjoining ones of these said strips. The opposite
face of the detector component 362, similarly, is formed having
strips 372a-372d defined by intermediately disposed grooves arranged
~: .
orthogonally with respect to the grooves at the upper surface.
Detector component 364 is identically fashioned, having strips
374a-374d at its upwardly disposed surface, each being defined by
intermediately disposed grooves; the lower surface of the detector
being formed having orthogonally disposed strips 376a-376d defined
by intermediately disposed grooves. The corresponding strip arrays
of detector component 366 are shown to comprise identically disposed
strip groupings as at 378a-378d and 380a-380d. Similarly, detec-
tor component 368 is shown to be formed of identically structured
mutually orthogonally disposedstrip arrays 382a-382dand384a-384d.
Components 362-3B8 are illustrated expanded from one
another for purposes of illustration only, it being understood
that in an operational embodiment these components are internested
together in as practical a manner as possible. To achieve an
in~ormational spatial and energy output from the discrete detec-
tor components, the strip arrays each are mutually associted along
- common coordinate directions. This association is carried out
between components 362 and 364 by leads 386a-386d, coupling re-
spective strips 374a-374d of component 364 with strips 370a-370d
of component 362. In similar, parallel coordinate fashion, leads
388a-388d are provided for connecting respective strips 382a-382d
of component 368 with strips 378a-378d of component 366.
-64-
....
. ,~,,~.
:
The outputs of the thus mutually coupled strip arrays
of the upwardly disposed faces of the detector components are
coupled with an impedance network, represented generally at 390.
~ Network 390 is configured comprising serially interconnected dis-
- crete resistors 392a-392i. Interconnection between respective
....
strips 370a-370d and points intermediate resistors 392e-392i is
provided by leads 394a-394d, while corresponding interconnection
between strips 378a-378d with the intermediate connections of
resistors 392a-392d is provided by leads 396a-396d.
` 10 In similar fashion, the arrayed strips 372a-372d at the
lower surface of component 362 are coupled with respect to strips
380a-380d of component 366 by leads 398a-398d. Similarly, strips
376a-376d at the lower face of component 364 are respectively
coupled with corresponding strips 384a-384d of component 368 by
- leads 400a-400d. The thus associated strip arrays of the lower
faces of the detector components are connected with the second
impedance network, identified generally at 402, in similar fashion
~; as the orthogonally disposed upward surfaces. Note, for instance,
that strips 380a-380d of the lower surface of component 366 are
connectedto intermediate respective discrete resistors 404a-404e of
, .
network 402 by leads 406a-406d. Similarly, strips 384a-384d of
the lower surface of component 368 are connected with respective
; discrete resistors 404f-404i of network 402 through leads 408a-
:
408d. Thus interconnected, the four discrete detector components
provide spatial coordinate parameter outputs; i.e. x-designated
coordinate outputs at lines 410 and 412, which are identified
thereat as ~xlA) and (xlB). In like manner, the spatial coordinate
.~'
;
:
-65-
, i,
parameter outputs of the lower surfaces of the detector components
are present atlines 414 and 416 and are y-designated, being
labeled in the drawing, respectively, as (ylA) and (ylB).
- Fig. 18 reveals a first output treating arrangement,
present as one set of filtering and control electronics which
operates in conjunction with the quadrant detector array of Fig.
17. In that figure, spatial coordinate parameter outputs, or
x-designated coordinate outputs (xlA), (xlB) and (ylA), (ylB) are
represented, respectively, at lines 410-416. These outputs,
as at lines 410-416, are shown arranged to address discrete pre-
amplification stages respectively revealed at 430-436. In this re-
gard, note that the output at line 438 of preamplification stage
430 is introduced to an x-Channel Antisymmetric Sumnation Gaussian
Filtering and Gated Integrator function, shown at 440, while the
corresponding input from preamplification stage 432 is directed
along line 442 to that same function. The summing and filter-
ing functions at 440 operate on the x-coordinate outputs intro-
duced thereto in the same fashion as described above in connection
with Figs. 12-16. For instance, the inputs from the x-spatial
coordinate outputs are subtractively summed and, following ap-
propriate filtering and pulse shaping as by noted series of
integrations and the like, an output from block 440 is provided
as an ~-designated coordinate channel signals at line 446.
The outputs of x-channel amplification stages 430 and
; 432 also are directed, respectively, through lines 450 and 444 to
Summing and Gaussian Filtering function 448. As described in
conjunction with Figs. 12-16, function 448 includes an initial
stage deriving the time deriva$ive of the summed energy signal
provided from lines 444 and 450 and submits such derivative signal,
from along line 452, to a Gate Control and Start Logic function,
-66-
s
~ identified at block 454. Such signal evidencing a predetermined
: requisite level to provide a preliminary assurance of valid spa-
:`: tial information, the start logic function of block 454 responds
to provide gate control over Filtering and Summation Function 440,
as through line 456.
:~ The corresponding y-coordinate outputs of amplification
stages 434 and 436, respectively, are coupled through lines 458
^ and 460 to a y-Channel Antisymmetric Summation and Gaussian Fil-
tering function 462. ~onfigured in similar fashion as function 440,
~ 10 the signals introduced to function 462 ar subtractively summed,
:. appropriately filtered, and pulse-shaped by a series of integra-
. tions to provide a y-designated coordinate channel signal at
line 464. Control over the gated integration function, as well
~^ as filtering at block 462 is provided from gate control and start
.. logic block 454 as through line 466. In fashion similar to that
:;~ described in connection with Figs. 12-16, the control system
further includes an Energy discriminator, revealed at block 470,
i :`
~ ~ which receives the sum~ed energy signal output at line 472 from
,. .
Summing and Gaussian Filtering function 448. As before, Energy
. : 20 Discriminator 470 provides a pulse height analysis of the energy
signal to evolve an accurate evaluation thereof as to the presence
or absence of valid image information. Upon interrogation thereof
through line 474 from gate control function 454, and response
thereto at line 476, the signal treating cycle is permitted to
continue. However, as described earlier, where the pertinent energy
. .
signals fail to meet the window criteria of Energy Discriminator
470, gate control 454 will effect a resetting of the summing func-
: tions, as from lines 478, 480, and 482 to carry out the earlier-
.~ descrlbed short-cycle operation, thereby permitting the system
; 30 to more rapidly and efficiently process a next incoming spatial
~,"
,
.
-67-
,' '
.,
, .~. .
.
.~. .. .
signal. It may be noted that ~nergy Discriminator function 470
may operate effectively within the system even though more than
one photon energy level of information is asserted. Recall that
it is desirable to accommodate the system to the utilization of
more than one radiopharmaceutical, each such radio-labeled sub-
stance having a different gamma ray energy characteristic. Beeause
the gemanium detector system of the invention enjoys a consider-
ably improved resolution characteristc, the discriminator 470 is
capable of performing its assigned function in a practical fashion
at this stage of the control system. In this regard, the ger-
manium detector exhibits a capability of from 3 to 4 keV resolu-
tion range as opposed to a generally observed range of about 15
keV achieved with more conventional scintillation type cameras.
Accordingly, Energy Discriminator 470 readily may be adjusted to
pass those energy signals representing the lower acceptable level
of the lower photon energy designated radiopharmaceutical.
; In accordance with the invention, the filtering and
control electronics for a given quadrant also incorporates a
Peak Detector function represented at 484. Detector 484 is
- 20 coupled through lines 472 and 486 to receive the energy signal
; generated from summing function 448. The detector 484 serves to
hold the peak value of this signal, thereby providing an analogue
storage function to accom~nodate for variations in signal treatment
times as are represented for instance, between antisymmetric
Summation functions 440, 462 and the energy additive Swmming
function at 448. Detector 484 is associated in time control
fashion with gate control 454 through line 490 and may be reset
therefrom through lines 478 and 480. The peak value output of
detector 484 is presented along line 492 to an Energy Channel
-68-
.
7~
Driver 494 for ultimate presentment to quadrant processing control
~- circuitry described later herein. Note that the energy channel
. .
signal present at line 496a is designated, Qle.
With the occurrence of an appropriate acceptance of the
validity of a spatial signal at Energy Discriminator 470, the
x designated coordinate channel or spatial signal at output line
446 is delivered to an x-Channel Driver 498, the output of which
is present in line 500a. Note that this channel signal is desig-
nated Qlx Similarly, the y-designated channel signal, having
been treated at function 462 and admitted to the system by the
Energy Discriminator 470 and gate control functions, is presented
along line 464 to a y-Channel Driver 502, the output of which is
present at line 504a and identified as, Qly.
The information now delivered from each quadrant of the
overall imaged region now, for purposes of convenience, is desig-
nated by the noted labels: Qlx' Qly and Qle. In the immediate
discussion to follow, the composite detector array is assumed to
be functioning in quadrature and, thereby, developing correspond-
ing signals from ~our distinct multi-component quadrants. These
quadrants are represented by a "Q" with the noted subscripts
altered by the values 1-4. Gate control 454 also provides a
clocking or data acceptance signal sequencing input to the control
system at line 506a the signal from which is designated, Ql, and
is arranged to receive a reset signal, designated, Qlr~ as at
line 508a. The latter signal is selectively derive~ from the
quadrant processing control system to be described in conjunction
with Fig. 19.
,''"
'
-69-
'
.
~ s
` Turning to that figure, the noted processing arrangement
is revealed in block schematic fashion and is shown to include
three multiplexing input networks, an x-Position Multiplexer 510,
a y-Position Multiplexer 512, and an Energy Multiplexer 514. The
inputs to multiplexers 510-514 derive from each of the four
quadrant circuits and, as an example of the designations utilized
in the instant figure, for the quadrant circuit described in
connection with Fig. 18, such inputs are represented and labeled
at lines 500a, 504a, 496a, 506a, and 508a. Correspondingly, the
inputs from the three remaining circuits to each of the multi-
plexers are represented and labeled, respectivley, at 500 b-d,
504 b-d, 496 b-d. Additionally, the outputs from Gate Control
- and Start logic functions, as described, for example, at 454 in
Fig. 18 are represented, respectively at 506a-506d as leading to
F.l.F.O. Memory 516, while the input to functions as at 454 in
Fig. 18 are represented as output lines 50~a-508d extending from
Reset Drive function 520. Note, additionally, that the quadrant
signals leading to the quadrant processing control arrangement
of Fig. 19 are identified by an ascending numeration suffix for
each input function, i.e. the inputs for x-Position Multiplexer
510 are identified as Qlx-Q4x' the inputs to y-Position Multiplexer
512 are identified as Qly~Q4y the inputs to Energy Multiplexer
514 are identified as Qle~Q4e the data acceptance signal inputs
to F.I.F.O. Memory are identified as Ql-Q4 and the outputs of
Reset Drive function 520 are identified as QlR-Q4R.
In conventional fashion, multiplexers 510-514 perform
a switching type function wherein the channel signals addressed
:
;i :
-70-
. ,
Q~
thereto are selected and forwarded into the system upon appropriate
control logic commands present as coded actuating signals. These
multiplexers are regulated from a quadrant interface control func-
tion, represented within a dashed line boundary 522. Function 5229
in addition to incorporating the F.I.F.O. Memory and input clocking
516 and Reset drive function 520, includes a 4-to-3 Line Decoder 524
and aSequentialControlfunction526. F.I.F.O.(first-in,first-out)
Memory and Input Clocking 516 is conventionally formed incorporating
somewhat independent input and output stages or networks. It serves
; 10 within the system as a de-randomizer which receives and collects
or records the randomly generated data acceptance signals, which
i::
are presented at lines 506a-506d. These quadrant labeled signals
are received and serialized at the input clocking stage of F.I.F.O.
Memory and Input Clocking 516 following which, an appropriate sig-
naling or clocking pulse is sent to the Sequential Control 526,
through line 572 which tells the sequential control that quadrant
information is available. In consort, the quadrant identification
signal is passed through output 534 and 570 to the 4-to-3 line de-
coder 524 and the reset drive 520. The resultant coded actuating
signals are presented to the multiplexers along grouped liens 536,
537, and 539 which, in turn, signal the appropriate gates within
respectivemultiple~ers510,512, and514 topass theretainedspatial
;.
and energy signals to a Sample and Hold Amplified function (S/H).
, In this regard, note that the output of x-Position Multiplexer 510
is provided along line 542 to a Sample and Hold Amplifier 544,
while the corresponding y-Position Multiplexer 512 output is pre-
sented along line 546 to Sample and Hold Amplifier 548. Similarly,
` the output of Energy Multiplexer 514 is provided along line 550 to
Sample and Hold Amplifier 552. Sample and Hold Amplifiers 544, 548
and 552 are utilized within the circuit as an analog storage medium
so that the aforementioned quadrant circuits can be reset for pro-
,. . . .
` ~ -71-
.~ :
cessing incoming signals. Line 530 extends through line 556 to
Sample and Hold Amplifier 552; through line 558 to Sample and Hold
Amplifier 548; and directly to Sample and Hold Amplifier 544.
A command from Sequential Control 526 emanating from line 530
- provides an initial sample command whereupon the multiplexers out-
put signals are sampled by the Sample and Hold Amplfiiers. Pollow-
ing a select interval, a hold signal is passed to amplifiers 544-
; 552, following which a next succeeding interval is provded. In
consort with the issuance of the hold signal to amplifiers 544-
552, a reset col~mand signal is passed by the Sequential Control
through line 566 to the Reset Drive circuit, 520. Since the spatial
and energy information contained in the quadrant circuit being
addressed is now stored in the processing circuit, the appropriate
quadrant circuits can be reset through the appropriate reset line
QlR-Q4R (lines 508a-508d). In carrying out the latter functions,
it may be noted that reset drive function 520 derives the quadrant
selective information through lines 570 from the P.I.~.O. Memory
516, at the end of the reset command a clock-out pulse is sent to the
F.I.F.O. Memory 516 along line 532 from the Sequential Control
unit 526. By doing this the information at the output of F.I.F.O.
Memory 516 is clocked out so that the next usable information
appears at F.I.F.O. Memory 516 output. The fact that valid informa-
tion appears at F.I.F.O. Memory 516 output is sent along line
572 to the Sequential Control circuit 526 for current or future
use. At the time valid ouput appears at ~.I.F.O. Memory 516
output the 4/3 Line Decoder 524 decodes it for processing by the
multiplexer circuits. During the latter interval, the energy sig-
nal, now passed to the hold functoin of amplifier 552, is present
; at the output thereof at line 560, during which period it further
is introduced at line 561 and analyzed by a Two-Channel Analyzer
562. Analyzer 562 provides pulse-height analysis requisite to
1 _~" .....
-72-
:"\
~1~7~0~i
evaluating the energy levels of the earlier noted two radiopharma-
ceuticals, for example, which may be utilized within the system.
Note that the analysis performed at function 562 is the second
within the system, the initial evaluation being carried out in the
earlier-described circuitry associated with each quadrant of the
detector. Should the energy signal passed to the Two Channel Ana-
lyzer 562 fail to meet the window criteria for either select pho-
ton energy level, an appropriate representation or signal is pro-
vided at output line 564 to Sequential Control function 526~ If a
valid, information present pulse was received from F.I.F.O. Memory
and Input Clocking 516 along line 572, then the sample and hold am-
plifier 544, 548, and 552 are placed in the sample mode and the pro-
cess described above repeats itself. If a valid information present
pulse was not received, the Sequential Control 526 waits until one
is received before the process described above repeats itself.
Where more than two photon energy levels are selected for the system,
.,
- anappropriatemulti-channelanalyzerissubstitutedatcomponent562.
: An advantageous aspect of the invention resides in the
controlled interrelationship between multiplexers 510-514 and
; 20 corresponding Sample and Hold Amplifiers 544-552. As controlled
by sequential control 526, an initial clocking input to multi-
plexers 510-514 causes a quadrant signal received thereby, in given
arrival order, to be clocked to the appropriate ones of Sample and
Hold ~nplifiers 544, 548, and 552. ~ollowing the initial interval
described hereinabove, com~encing with the noted hold function,
the initial treating system may be cleared in anticipation of a next
- quadrant signal to be processed as described above. This feature
advantageously improves the through-put rate of the overall system
permitting correspondingly improved imaging performance. With the
clearing of the intial treatment or input networks as well as
:,
s: -73-
74(~S
clocking of F.I.F.O. Memory 516, the entrance portion of the quad-
rant processing circuitry is preapred to accept the next succeeding
quantum of information form the quadrant circuits. ~pon appropri-
ate command from sequential control 526 following an interval suited
to permit the noted two-channel analysis to be carried out at
block 562, the x- and y- spatial output signals of Sample and Hold
Amplifiers 544 and 548 respectively which are passed along lines
580 and 582 to Divider networks 584 and 586 are stable and propor-
- tioned respectively to the x- and y- positions. The latter networks
serve the function of normalizing the spatial signals received
from lines 580 and 582 with respect to the particular photon energy
of the detector interaction which they represent. The correspond-
ing energy signal introduced at this point to the system and ana-
lyzed at 562 may be representd as, Qe~ while the spatial signal may
be represented as,GCQe. Erom the earlier discussion presented here-
in, the spatial information~oc~ which the system, notwithstanding
quadrature data, provides as spatial visual information may be re-
presented by the expression:
~ OC 2xo ) (18)
where, L, is equivalent detector length and, xO, is the position of
interaction of a gamma ray. The spatial information quantity,O~,
also may be derived and expressed by the relationship:
~ E ) (l9)
Equation (l9) reveals the function of Dividers 584 and 586, i.e.
by dividing by QE~ the measured energy channel signal, as it re-
'
-74-
: ~5
presents one or more photon energy levels, the desired spatial
signal,dC, is derived. In carrying out this function, the divisor
of the last expression (19) is derived as a signal from Sample
and Hold Amplifier 552 through lines 560 and 588. Line 588 is
coupled with a Bias Amplifier 590 which provides an appropriate
d.c. offset to prevent the presentment of a non-zero denominator
to the divider circuits. The outputs of Bias Amplifier 590 are
shown directed along line 592 to Divider 586 and along line 594
to Divider 584. Because of the advantageous high quality resolu-
tion of germanium type solid state detectors, the dividing function
provided herein is required only for systems intended to utilize
radioisotope imaging sources to present more than one photon energy
level but can be used with a monoenergetic source.
. .,
'; The thus normalized x- and y- spatial channel signals
are directed, respectively, from Dividers 584 and 586 along line
596 and 598 to an x-,y- Display Bias and Orientation Control func-
'':i'
; tion, identified at control block 600. At function 600, the sig-
nals introduced thereto are weighted in correspondence with the
~;~ quadrant or coordinate from which they weere derived by virtue of a
weighting signal input from control 526 as directed thereto through
, .,
: line 602. Control 600 also may include appropriate circuitry
..
providing for an operator selection of the alignment of the x- and
y-axes wherein they may be inter-changed for desired clinical analy-
sis purposes. Control 600 is coupled in information exchange rela-
tionship for x-channel information with a Camera Display Control 604
through lines 606 and, for y-channel communication purposes through
-~ line 608 with the same control. Display activations information
''. '
'
. ,
-75-
~ s
to the Camera Display Control 604 is derived from the output of
Sequential Control 526 through lines 666, 610 and 612. In conven-
tional fashion, the spatial data and the display on/off control is
coupled to a CRT Display 614 through the three channel input lines
extending thereto and identified at 616, 618 and 620.
- In similar fashion, a Patient and Positioning Display
function is provided by Positioning Display Control circuit 622
operating in conjunction with a positioning display readout, i.e.
CRT tube or the like, as represented at block 624. Spatial chan-
nel information is directed to Positioning Display Control 622
from lines 626 and 628 which, in turn, are connected with respec-
tive lines 606 and 608. A display activating signal is sent to
control 622 from Sequential Control 526 through lines 666, 610, 612
and 630. The spatial and energy channel intercoupling between con-
trol function 622 and its corresponding display readout at 624 are
shown represented by lines 632, 634, and 636.
The control system also incorporates a readout identified
in Fig. 19 as a Spectrum and Energy Window Display represented at
block 638. This readout serves to permit the operator of the
system to adjust the window settings of the two-channel analyzer
562 to achieve accurate evaluation of the energy level of the
particular isotopes utilized for imaging. The informational in-
put of function 638 is derived from the energy related output
level of Sarnple and ~old Amplifier 552, as is present at line
560. To convert this level to a corresponding transitional
signal, a Linear Gate 640 is arranged to receive the energy signal
at line 560 and transmit a corresponding transitional type signal
-76-
~.. ;
" ,, .~.
s
along lines 642 and 644 to a Multi-channel Analyzer 646. The chan-
nel outputs of analyzer 646 are presented along lines 648-654 to
a spectrum display control 656 which, in turn, provides display
control over Spectrum and Energy Window Display 638 by virtue of
its connections therewith represented at lines 658-662.
-The system also provides a count rate meter 664 which is
coupled with the display control signal from Sequential Control 526
through lines 666 and 670. Such a device apprises the operator of
the presence of imaging photons at the region of analysis and their
'10 reaction rate with the system. Note, additionally, that the output
; .
display control of Sequential Control 526 also is directed through
line 666 and 670 to Linear Gate 640. The output of Linear Gate 640,
`at line 642, also is directed to a Total Count function 6~2, the
i
latter serving to apprise the operator of the quantity of imaging
information received at the camera. Other components which might be
incorporated within the system, which are not shown in the figure,
may include, for instance a total time recorder apprising the
operator of the span or interval of operation of the camera for
given clinical analysis as well as an isotope gain control for regu-
lating the Summation and Filtering function described hereinbefore
in connection with Fig. 18.
With the final imaging of a given energy signal, at CRT
Display 614, sequential control 526 directs a signal along line
530 to the Sample and Hold Amplifiers 544-548 and 552 placing them
in the sampling mode. Since, as described above, the information
,, .
from the next quadrant is presented as each Sample and Hold Ampli-
fier input through lines 542, 546 and 550 an improvement in system
throughput rate is realized.
74~5
.
In Figs. 20-22 as are described hereinafter, another
form of composite detector is revealed which provides a "row-colunn"
. form of readout of the spatial and energy data within a select
grouping, n, of detector components. In each of these embodiments
shown, a reduced component linear dimension over which resolution
is required is achieved to improve the resolution of the entire
system. Two embodiments of this "row-column" arrangement are re-
vealed wherein a larger effective detector area is provided while
the earlier described time constant, ~ D' is minimized to improve
the response rate of the system to processing interaction genera-
ted image signals.
. .
Referring now toPig. 20, another composite detector formed
as an array of discrete detector components is revealed generally
at 680. Illustrated in exploded fashion, the detector 680 is com-
prised of a plurality of detector components, four of which are
shown at 682, 684, 686, and 688. Components 682-688 are dimensioned
having mutually equivalent areas as are intended for acceptance of
impinging radiation. This required eguivalency serves to achieve
; an accurate ultimate image readout from the camera system. In the
absence of such equivalency, distortion at such readout, exhibiting
a discontinuity of image information, would result. The detector
components illustrated are of the earlier-described orthogonal
strip array variety, each strip thereof being defined by grooves.
Note, in this regard, that detector component 682 is formed having
strips 690a-690d located at its upward surface and defined by
grooves cut intermediate adjoining ones of the said strips. The
opposite face of detector component 682 similarly is formed having
strips 692a-692d defined by intermediately disposed grooves ar-
'''
-78-
.~ ' '~,
~1~7~0S
ranged orthogonally with respect to the grooves at the upper
surface. Detector component 684 is identically fashioned, having
strips 694a-694d at its upwardly disposed surface and lower sur-
face, orthogonally disposed strips 96a-96d each strip being
defined by intermediately formed grooves. Similarly, detector com-
,
ponent 686 is formed having strips 698a-698d at its upward surface
defined by intermediately disposed grooves, while its lower surface
~ similarly is formed having strips 700a-700d defined by inter-
; mediately disposed grooves arranged orthogonally with respect to
the grooves of the upward surface. Detector component 688 may be
observed having strips 702a-702d at its upward surface defined by
intermediately designated grooves, while its lower surface is formed
; with strips 704a-704d separated by intermediately disposed
grooves arranged orthogonally to the grooves of the upward surface
of the component.
Detector components 682-688 as well as similar components
in later figures are illustrated expanded from one another for pur-
poses of illustration only, it being understood that in an opera-
tional embodiment these components are internested together in as
practical a manner as possible. To achieve an informational
spatial and energy output from the discrete detector components,
which essentially is equivalent to that output which would be real-
ized from a large detector of equivalent size, the strip arrays
are functionally associated under a geometry which, as noted above,
may be designated 'Irow" and "column" in nature. In this regard,
note that an impedance network, shown generally at 707, is as-
sociated with the strips 694a-694d of detector component 684. This
':"
-79-
~. '
,:
4~S
network incorporates discrete resistors 706a-706e which are tapped
at their common junctions by leads 708a-708d extending, respective-
ly, to strips 694a-694d. Thus configured, network 707 closely
resembles the impedance networks described herein in connection
with Fig. 2. Note however, that output lines 710 and 712 of net-
work 707 extend to and are coupled in parallel circuit relationship
with the corresponding oùtput of a similar impedance network, identi-
fied generally at 714. Network 714 incorporates discrete resis-
tors 716a-716e which are tapped at their common interconnections
by leads 718a-718d. Leads 718a-718d, in turn, respectively extend
to strips 690a-690d of detector component 682. Accordingly, the
upwardly disposed surfaces of detector components 682 and 684 are
identically associated with respective impedance networks 71~ and
707, while the latter are interconnected in row fashion and in
parallel circuit relationship to extend to principal output
terminals, as are depicted generally at 720 and 722. It may be
noted that the information collected at these principal terminals
represents one imaging spatial coordinate parameter of a select
directoinal sense i.e. along a designated row.
Looking now to the fundamental interrelationship of de-
tector components 686 and 688, a similar coordinate parameter
direction or row-type informational collection network is revealed.
In this regard, note that the impedance network, shown generally
at 724, is configured comprising discrete resistors 726a-726e, the
; points of common interconnection of which are coupled with respec-
tive leads 728a-728d. Leads 728a-728d, in turn, respectively,
are connected with strips 698a-698d at the upwardly disposed surface
of detector component 686. Likewise, an impedance network, shown
generally at 730 incorporting discrete resistors 732a-732e,
:'
:,
-80-
'
. ~
; is associated with detector component 688 by leads 734a-734d e~-
ri ,' ~,
tending, respectively, from strips 702a-702d to the points of com-
mon interconnection of network discrete resistors 732a-732e. Ad-
ditionally, the output lines as at 736 and 738 of network 730 are
connected in parallel circuit relationship with the output of net-
work 724 to provide row readout termini, respectively, at 740 and
742. Here again, a row-type directional spatial coordinate para-
;; meter is provided at the upwardly disposed surface of the com-
, posite detector 680.
.'
Looking now to the lower surfaces of the detector com-
; ponents, it may be observed that the orthogonally disposed strips
of detector component 682 are associated with an impedance net-
work identified generally at 744. Network 744 incorporates dis-
crete resistors 746a-746e which are coupled from their mutual
interconnections by leads 748a-748d, respectively, to strips 692a-
~" ~
692d of detector 682. Similarly, the orthogonally disposed strips
of detector component 686 are associated with an impedance network
750. In this regard, network 750 is formed of discrete resistors
752a-752e which, in turn, are coupled, respectively, with strips
700a-700d by leads 754a-754d. The output of impedanae network 744
is connected by leads 756 and 758 to the corresponding output of
impedance network 750 to provide column directional coordinate para-
meter outputs, as at 760 and 762, which serve to collect all spatial
, ~:
information of the associated paired surfaces of detectors 682
and 686.
Looking to the lower surface of detector component 684,
note that a network, designated generally at 764, incorporating
,:
` discrete resistors 766a-766e is functionally associated with strips
` 696a-696d, respectively, by leads 768a-768d.
:
,
-81-
~'
:: ~os
In similar fashion, an impedance netowrk, designated
generally at 770, is associated with the orthogonally disposed
strips 704a-704d at the lower surface of detector component 688.
Note that the network, incorporating discrete resistors 772a-772e,
is functionally associated with the array of strips 70~a-704d,
respectively, by leads 774a-774d. Networks 764 and 770 are elec-
trically coupled in parallel circuit fashion by collector leads
776 and 778 and extend to principal colleetion points of termini 780
and 782. Thus interconnected, the lower surfaces of detectors
~84 and 688 are coupled in column readout fashion to provide another
spatial coordinate parameter of direction parallel with the cor-
responding lower surface strip array readout arrangement of
detector components 682 and 686.
With the row and column readout intercoupling of the
detector components as shown in the figure. it may be observed
that the capacitance exhibited by all discrete detector components,
taken together, remains the same as if only a single detector
were operating within a camera. Accordingly, the signal treating
circuitry and logic of the camera, advantageously, amy be designed
to accommodate for the charge collection time constant of a single
detector. Connection with the row and column readouts for given
spatial coordinate parameters outputs will be seen to be provided
by treating circuits which distribute coordinate channel spatial
and energy channel signals into analyzing and distributing cir-
cuitry. Such circuitry is described in more detail in connection
with Figs. 19 and 23-25. Preamplification stages, as described in
.
-82-
; .
: -"
s
~ connection with Fig. 2, are coupled with each row readout point as
''`',U.!.,~
at 720 and 722 or 740 and 744, as well as with each column readout,
as at 760 and 762 and 780 and 782. Such preamplification stages
generally are located within or near the cryogenic environment of
the detector itself. The mounting of the contact leads between
each of the networks and an associated strip array surface of a
detector generally may be carried out by resort to biased contact
configurations.
. ;
The composite detector arrangement or interrelated de-
tector component mosaic also may be formed utilizing detector
structures which incorporate surface disposed resistive layers to
achieve spatially proportioned charge readout characteristics.
Such a detector composite is revealed generally in Fig. 21 at 800.
Referring to that figure, the composite detector, or portion there-
of, 800, is shown to comprise four discrete detector components
802-808. The opposed surfacers of the detector components, which
are situated generally normally to impinging radiation, are formed
having a resistive character. This resistance is provided, for in-
stance, by so lightly doping the n-type surface as to achieve a
i
region of resistive character, while, similarly, so lightly doping
; the opposite surface with a p-type acceptor as to achieve a sur-
face resistive character thereat. The readout from these resis-
;~ tive surfaces is collected by conductive strips which, for the case
- of detector component 802, are shown on the upward surface at 81D
:
and 812 and at the lower surface at 814 and 816. Conductive sur-
faces 810 and 816 may be deposited upon the detector component 802,
for instance, by conventional evaporation techniques utilizing a
highly conductive metal such as a noble metal, i.e. gold.
'-''
' '
-83-
,...
~ ~7~S
Concerning the techniques for developing the noted re-
sistive regional character within the surfaces of detector com-
ponents 802-808, mention may be made of the following publications:
~XIV. Owen, R.P., Awcock, M.L., "One and Two
Dimensional Position Sensing Semiconduc-
tor Detectors,'l IEEE, Trans. Nucl. Sci.,
Vol. N.S. - 15, June 1968, Page 290.
XXV. Berninger, W.H., "Pulse Optical and
Electron Beam Excitation of Silicon Po-
sition Sensitive Detectors", IEEE, Trans.
Nucl. Sci., Vol. V.S. 21, Page 374.
With the impingement of radiation upon detector compo-
nent 802 and resultant development of an interaction therewithin,
charge will be collected on the opposed surfaces, as discussed
above, and will split proportionally at the impedance defined sur-
faces and collect at the conductive strips 810-816. For the up-
wardly disposed surface, these charges then are collected alon~
conduit 818, coupled with conductive strip 812, and conduit 8199
coupled with conductive strip 810. The adjacently disposed de-
tector 804 is fashioned in similar manner, the upward surface there-
of incorporating a resistive surface layer or region formed in
cooperation with conductive strips 820 and 822. The lower surface
of detector component 804 is formed incorporating a similar resis-
tive layer or region functionally associated with conductive
strips 824 and 826. Note that the latter conductive strips are
arran~ed orthogonally with respect to those at 820 and 822. Con-
ductive strip 820 is coupled by a lead or conduit 828 to conductive
strip 812 of the detector component 802, while conductive
strip 822 is coupled by lead or conduit 830 to conductive strip
810 of detector 802. Thus interconnected, it will be apparent that
any interaction occurring within detector component 804 will be
-84-
~ 7~0S
,-
"seen" as a charge division between strips 820 and 822, for onecoordinate parameter, along leads 828 and 830, as well as output
conduits 818 and 819. As is apparent, a desirable simplification
of the structure of the composite detector is available with this
form of row readout.
Looking to the adjacently disposed row of detector com-
ponents 806 and 808, it may be noted that detector component 806
is formed incorporating resistive layers or regions in its opposed
surfaces aligned for the acceptance of radiation and, additionally,
incorporated conductive strips as at 832 and 834 at the extremities
of its upward surface as well as orthogonally oriented conductive
strips 836 and 838 about the extremities of its lowermost and
oppositely disposed surfaces.
Identically structured detector component 808, similarly,
is formed having resistive surfaces or regions arranged normally
to the direction of radiation impingement. The surfaces also
incorporate conductive strips, as at 840 and 842 at the upwardly
disposed side and, at 844 and 846, orthogonally disposed at the
lowermost surface.
Coupled in similar row-type fashion as detectors 802 and
804, the conductive strips of detectors 806 and 808 are directly
electrically associated by leads 848 and 850. Note, in this regard,
that lead 848 extends between conductive strips 840 and 832
while lead 850 extends between conductive strips 842 and 834.
The output of that particular row at the upward surface of the
composite detector is represented by leads 852 and 854.
A columnar interconnection of the detector components is
, .
` provided between the orthogonally disposed conductive strips 814
~ ,.
-85-
''
; ;.~'
:
.'' ' '
and 816 of detector 802, respectively, as by leads 856 and 858,
to similarly disposed conductive strips 836 and 838 of detector 806.
The columnar readouts for the paired detector components are pre-
sent at conduits 860 and 862 extending, respectively, from conduc-
tive strips 836 and 838.
In similar fashion, the columnar association of detector
components 804 and 808 is provided by leads 864 and 866 which,
respectively, extend between conductive strips 824 and 826 of
detector 804 to corresponding conductive strips 844 and 846 of
detector component 808. The readouts for the column association
of detectors 80~ and 808 are provided by conduits 868 and 870 ex-
tending, respectively, from conductive strips 844 and 846 of de-
tector component 808.
As in the embodiment of Fig. 20, the output conduits 818,
819 and 852, 854 are of a "row" variety having a designated spa-
tial coordinate parameter and are addressed to initial preamplifi-
cation stages prior to their association with logic circuitry
for deriving imaging information for that particular spatial co-
ordinate. Similarly, the "columnar" outputs at conduits 860, 862
and 868, 870 are directed to preamplification stages, thence to
appropriate circuitry for treating that spatial coordinate para-
meter. It will be understood, of course, that the number of
detector components formed within a matrix or array thereof de-
pends upon the field of view desired for a particular camera ap-
plication as well as the practicalities for retaining such com-
~- ponents under appropriate cryogenic temperature conditions during
operation
;'
:"
-86-
-~'
,,~ .
S
The foregoing examination of the composite detector
structures, represented in Figs. 20 and 21 reveals certain con-
sistent characteristics between the embodiments. For instance, as
alluded to above, the effective areas presented to radiation im-
pingement of the discrete detector components must be substantially
equivalent, in order to avoid distortion in an ult;mately developed
image. Additionally, these components should be as closely nested
as possible and aligned such that the spatial coordinate which may
be designated for each surface evoles what has been termed as a
- 10 "row-column" orientation. In the latter regard, an observation of
this geometry shows that the leads interconnecting the impedance
networks or the impedance stucture i.e. at the surface region of
the detector components, connect them directly, whether in the
parallel-series connection of the embodiment of Fig. 20 or the
interconnection of conductive strips shown in Fig. 21. Another
aspect typifying the structure of the invention, reveals that any
two adjacent surfaces of any two adjacent detector components ex-
hibit spatial coordiante parameters of a common directional sense
and, more particularly, two adjacent of the coplanar surfaces of
any two adjacent detector components are disposed within a linear-
ly oriented grouping arranged to exhibit a common spatial co-
ordinate parameter directional sense. Because the composite detec-
tor embodiments shown in Figs. 20 and 21 operate substantially in
..:
;; the same functional manner, their outputs are identified with
`-~ the same spatial coordinate directional labels. For instance, the
x- designated coordinate outputs at lines 722 and 720 of the em-
bodiment of Fig. 20, respectively, are identified as (XlA) and
'
-87-
.
"
~10740S
~'
(XlB~; while the parallel row y- designated coordinate outputs
as at lines 742 and 740, respectively, are identified as (X2A) and
(X2B). Similarly, the orthogonally disposed y- designated coordi-
nate parameter outputs, as represented for instance, at lines 762
and 760, respectively, are identified as (YlA) and (YlB). Next
adjacent to that column of the composite detector, are the detec-
tors whose outputs are represented at 780 and 782 and are identi-
fied, respectively, as (Y2A) an (Y2B). This same labeling pro-
;cedure will be seen to be utilized in the composite detector em-
bodiment of Fig. 21.
;~An important aspect of the "row-column" interconnection
of the discrete detector components resides in the realization of
an effective reduction in that detector linear dimension over which
reoslution is evaluated. More specifically, an improvement is
experienced in teh resolution of the camera system which may be
expressed by the equation:
~x = ~E L
E (20)
Where,~ x, represents spatial resolution in terms of distance; ~E,
is absolute energy resolution; L, is length of a detector component
as measured parallel to the directional sense of an associated im-
pedance network; and E, represents the energy of an incident pho-
ton interacting with the detector. Within the right hand side of
equation (20) above, the expression, ~EE, is readily identified as
the fraction (or percentage) of energy resolution and is fixed
for a given input energy. Accordingly any increase in the
value of, L, directly and adversely affects the spatial resolu-
tion. Where the de$ector components are not interconnected by
'
-88-
,~ .
,,,5'
' ~
~()~ 5
the "row-column" technique, the value, L, in the expression above
becomes larger. For ex~nple if the detectors pictured in F;g. 22
were connected as a single detector, the measuring distance would
be 2L, effecting a doubling o~ the noted spatial resolution
value to the detriment of final imaging. ~nother feature charac-
teristic of the detector "row-column" interconnection resides in
the presence of a common detector component for each combination of
an associated row and column. Stated otherwise, a row or column
configuration also may be designated as an orthogonally disposed
linearly oriented grouping of charge collecting surfaces. Any
interaction within any given common component will provide x- and
y- designated coordinate output signals from the thus associated
linear surface groupings.
A third embodiment for "row-column" interconnection of
detector components exhibiting this spatial resolution advantage
is revealed in Fig. 22. Referring to that figure, a composite
detector formed as an array of discrete detector components is
revealed generally at 880. As in the earlier-discussed embodiments,
detector or detector portion 880 is shown in exploded fashion for
purposes of clarity and comprises a plurality of detector components
"~
~ four of which are shown at 882, 884, 888, and 886. Components 882-
~....
!:~;' 888 are dimensioned having mutually equivalent areas as are in-
tended for acceptance of impinging radiatoin and are formed as of
an orthogonal strip array variety, each strip thereo being defined
by grooves formed within the detector surfaces. Of course, other,
- strip-defining configurations will occur to those skilled in the
; art. Detector 882 is formed having strips 890a-890d defined by
;~ grooves cut within its upward charge collecting surface. The op-
posite face of detector component 882 similarly is formed having
:
-89-
"'
~\
~ 05
; strips 892a-892d defined by intermediately positioned grooves
arranged orthogonally with respect to the grooves at the upper
surface. ~etector component 884 is identically fashioned, having
strips 894a-894d formed at its upwardly disposed charge collecting
surface; and at its lower surface, orthogonally disposed strips
896a-896d, adjacent said strips being defined by intermediately
formed grooves. Similarly, detector component 886 is formed having
strips 898a-898d at its upward surface, adjacent ones of the
strips being defined by intermediately disposed grooves, while its
lower surface similarly is formed having strips 900a-9OOd defined
by intermediately disposed grooves arranged orthogonally with
respect to the grooves of the upward surface. Detector component
888 may be observed to have strips 902a-902d at its upward surface
adjacent ones of which are defined by intermediately designated
grooves, while its lower surface is formed with adjacently disposed
strips 904a-904d separated by intermediately disposed grooves
arranged orthogonally to the grooves of the upward surface thereof.
In the instant embodiment, strips 894a-894d of detector
component 884 are directly, electrically associated with corre-
sponding row strips 890a-890d of component 882 by electrical leads,
respectively identified at 906a-906d. Notej that no impedance
network is interposed intermediate the strip groupings as in the
earlier embodiments. However, an impedance network, designated
generally at 908, is associated with the termini of strips 890a-890d
opposite the edges thereof coupled with electrical leads 906a-906d.
Network 908 comprises serially associated discrete resistors 910a-
910e which are tapped at their common junctions by leads 912a-912d
--90--
: .
, ~;''
.
. . .
4~5
.
extending, respectively, to strips 890a-890d. The output, or read-
out points for the thus defined "row" of the composite detector
assembly are represented at 914 and 916 and are provided the same
respective spatial or x- designated coordinate parameter output
labeling, (xlB), (xlA) as are present in the corresponding "row"
of the embodiments of Figs. 2~ and 21.
The corresponding upwardlydisposedsurfaces of components
886 and 888 are connected in similar fashion. For instance, strips
902a-902d are electrically coupled with strips 898a-898d by re-
spective electrical leads 918a-918d. The "row" coupling thus pro-
vided is associated with an impedance network shown generally at 920.
Network 920 is formed comprising serially associated discrete re-
sistors 922a-922e which are tapped at their common interconnections
by leads 924a-924d. Leads 924a-924d, respectively, extend to
strips 898a-898d of detector 886. The principal termini of the
thus defined "row" are identified at 926 and 928, having outputs
respectively labeled (x2B), (x2A).
Looking now to the lower surfaces of the detector com-
ponents, the orthogonally disposed strips of detector component
882 are electrically coupled as shown with the corresponding strips
of detector component 886 by electrical leads 930a-930d. The thus
coupled strip arrays of those detector components are associated
in ~'columnar" fashion with an impedance network identified gener-
ally at 932. Network 932 comprises serially associated discrete
resistors 934a-934e, the interconnections between which are con-
nected as shown with strips 900a-9OOd of component 886 by leads
respectively identified at 936a-936d. The readout termini for the
thus defined "colwmn" association of detectors 886 and 882 are
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present at 938 and 940 and the corresponding spatial or y- designa-
ted coordinate parameter outputs are identified respectively as
(ylA) and (ylB).
The lower surfaces of detector components 884 and 888
similarly are associated in "columnar" readout fashion, strips
896a-896d of the former being electrically connected through respec-
tive leads 940a-940d to strips 904a-904d of the latter. The thus
established "columnar" readout is associated with an impedance net-
work identified generally at 942 and comprising serially associated
discrete resistors 944a-944e. Strips 904a-904d, respectively, are
coupled with the interconnection of the resistors 944a-944e of
network 942 by leads 946a-946d. As in the earlier embodiments, the
principal readouts of the thus defined "columnar" detector com-
ponent coupling are represented at 948 and 950 and their spatial
coordinate parameter outputs are labeled, respectively, (y2A)
and (y2B). From the foregoing description of the composite detec-
tor arrangement 880 it may be observed that the row-column asso-
ciation of the components thereof enjoys the noted spatial resolu-
tion advantages, however, the time constant characteristic thereof
will reflect a higher capacity evaluation.
Figs. 23 and 24 reveal filtering and control electronics
which operate in conjunction with the quadrant of composite de-
tectors arrayed in the "row-column" manner described hereinabove
in connection with Figs. 20-22. Note that the spatial coordinate
parameter outputs from the arrays shown in those figures aredesig-
nated (xlA), (xlB) and (x2A), (x2B) for the row readouts and
(ylA), (ylB) and (y2A), (y2B) for the corresponding columnar read-
outs. Looking to Fig. 23, the x-channel spatial coordinate para-
meter outputs as are derived from one such x-channel row type read-
3~ out, to wit (xlA), (~lB) are again reproduced at intput lines 1000and 1002, representing the input addressing respective discrete
preamplification stages 1004 and 1006. It should be understood
., ~
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that each row within each quadrant would incorporate the initial
or first signal treating functions, including the control electron-
ics revealed in Fig. 23 and that the components to be described
in connection therewith are substantially identical in function
as those described heretofore under substantially the same label-
ing, the description now being reduced to single channel analysis
in the interest of clarity and simplicity. The output at line 1008
of preamplification stage 1004 is introduced to an x-Channel Anti-
symmetric Summation and Trapezoidal Filtering function 1010, while
the corresponding input from preamplification stage 1006 is directed
through lines 1012 and 1014 to that same function. The Summing
.":
and Trapezoidal function at 1010 operates on the xl-Channel Spatial
signals introduced thereto in the same fashion as described above
in connection with Figs. 12-16. For instance, the inputs from
the xl-Channel are subtractively summed and, following appropriate
Trapezoidal Filtering and Gaussian Shaping, for instance, by the
noted series of integrations or the like, an output from function
block 1010 is provided at line 1016.
The outputs of amplificat;on stages 1004 and 1006 also
~0 are directed,respectively, through lines 1008, 1018 and 1012, and
1014, to the Summing and Gaussian Filtering function 1020. As de-
, scribed earlier in detail in conjunction with Figs. 12-16, function
1020 includes an initial stage deriving the time derivative of
the summed energy signal provided through lines 1014 and 1018 and
submits such derivative signal, from along line 1022, to a Control
function depicted generally at 1024. When this signal evidences
a predetermined requisite level to provide a preliminary assurance
of valid spatial information, a start logic function within block
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1024 responds to provide gate control over the Filtering and Sum-
; mation function at block 1010. Controls over gates and the like
of function 1010 are asserted, for instance, from lines as at 1026,
while appropriate information feedback is derived from the Filter-
ing and Summation function 1010 from communication line 1028. Con-
trol 1024 also comnunicates with sn Energy Discriminator function
1030 which receives the summed energy signal output of block 1020
from along lines 1032 and 1034. As in the earlier embodiments,
Energy Discriminator 1030 provides a pulse-height analysis of the
energy signal deriving from Summing function 1020 for purposes of
evolving an initial evaluation thereof as to the presence or ab-
sence of valid image information. For instance, discriminator 1030
evaluates the energy signals in correspondence with the lowest
photon energy level to be accepted from those radioisotopes extant
within the noted region of clinical interest. Appropriate accep-
tance or rejection of the energy level is signalled along line 1036
to Control function 1024 and, in the absence of an appropriate
such level, the latter function serves to reset the system by carry-
ing out the earlier-described short-cycle operation. As in the
earlier embodiments, the circuit of Fig. 23 further includes a
Peak Detector function 1038. Associated with Control 1024 through
line 1040 and receiving the summed or energy signal from block 1020
through line 1032, Peak Detector 1038 serves to hold the peak value
of the signal passed thereto to provide an analogue storage function
for accommodating variations in signal treatment at times as are
represented, for instance, between Antisymmetric Summation and
Trapezoidal Filtering function 1010 and Swmming and Gaussian Fil-
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.
tering function 1020. The peak value output of detector 1038 is
presented along line 1042 to an energy channel driver 1044 for
ultimate presentment to quadrant processing control circuitry from
along line 1046. Note that the energy channel signal at that line
is identified as, Qle.
The output at line 1016 of Antisymemtric Summation and
Trapezoidal Filtering function 1010 is presented to an xl-Channel
driver 1048 for delivery to quadrant processing control circuitry
::,:.
~' through line 1050. Note, as in the earlier embodiments, this
coordinate channel signal is identified by the label Qlx Similar-
ly, the output of control block 1024 is provided at line 1052 and
the coordinate channel signal thereat is identified by the label
'x-Channel Ql.ll Additionally, for purposes of effecting a full
cycle or short cycle termination, an input provided at line 1054
for carrying such appropriate signal is labeled l'x-Channel Q1R~-
Looking to Fig. 24, the corresponding initial input
treating or columnar or y-Channel processing circuit is revealed,
it again being understood that this circuit represents that as-
sociated wlth only one col~nn within a "row-column" detector compo-
nent array, similarly such circuits being required for each suchcolumn. Of course, the term "row" or "column" is for descriptive
purposes only and designates one given coordinate parameter of
directional readout from a detector matrix or mosaic. Looking to
the figure, column readouts (ylA), lylB) are asserted, respectively
; at input lines 1060 and 1062 of input preamplification stages 1064
and 1066. The output of amplification stage 1064 is directed
through line 1068 to a yl-Channel Antisymmetric Summation and Trape-
zoidal Filtering function 1070 performing the operations described
,,
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.
hereinabove. Similarly, the output of preamplification stage 1066
is introduced through lines 1072 and 1074 to signal treatment
at function 1070, the yl-Channel signals being subtractively summed,
appropriately filtered and pulse-shaped as by a series of
integrations to provide a y-Channel signal at line 1076. This
signal is introduced through a yl-Channel driver 1078 from which
it exits at line 1080 for introduction as a signal designated
"Q1Y" to second or further treatment at a processing control func-
tion.
The yl-Channel signals also are introduced from lines
1082 and 1072 to a Summing and Gaussian Filtering function 1084
which additively sums and filters the signals to generate an energy
signal which is submitted, as through line 1086, to an Energy Dis-
criminator function 1088. As before, Energy Discriminator 1088
carries out a pulse height analysis of the energy signal to pro-
vide an accurate evaluation thereof as to the presence or absence
of valid image information. The lower value selected for this
analysis corresponds with the acceptable lower value for the lowest
photon energy selected for receipt and treatment by the system.
The output of discriminator function 1088 is directed through line
1090 to Control function 1092. In addition to providing appro-
priate gate control over Summation and Filtering function 1070
through line 1094, Control function 1092 also receives the time
derivative of the yl-Channel energy signal from along line 1096.
As in the earlier embodiments, this signal generally is obtained
from an initial stage within Summing and Gaussian Filtering opera-
tions performed at block 1084. This derivative signal serves both
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to provide an appropriate start signal logic for the Control 1092,
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as described earlier herein and, additionally, will be seen to
provide a coincidence signal for later control over the entire
~ multi-component detector arrangement of the invention. The output
i~ of control function 1092 is present at line 1098 and is identified,
. :
for illustrative purposes, as "y-Channel Ql" This signal is in-
~;, troduced to the noted second or further treatment at a processing
:i'
~ control function, that same circuitry providing a reset input to
"
control 1092 identified as "y-Channel Q1R" and submitted from along
~ 10 line lloo.
.' . .
Turning now to Figs. 19 and 25, the second treating or
quadrant processing control arrangement for use with the "row-
, .. ..
~ column"readoutarrangementsfordetectorarraysremainssubstantially
. , - . . .
similar to the system described above in connection with Fig. 19.
` However, in consequence of the isolated readout geometry neces-
sarily present in a "row-column" interconnection, a further arrange-
ment is required to properly identify and treat a data pair input
deriving from the given x- and y- Channel outputs of any given
detector component within the array. Accordingly, the quadrant
interface control function represented in Fig. 19 within dashed
boundary 522 lS replsced by the slightly revised arrangement at
522' in Fig. 25. For purposes of clarity, the latter drawing in-
corporates broadened arrows to represent a multi-line input as
would be derived from the multiple channels of networks of Pigs.
23 and 24 as well as the multiple line couplings already depicted
in Fig. 19. Further in this regard, to represent the several in-
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puts from each row of the detector array, typical ones of which are
represented in Fig. 23 as "x-Channel Ql"' and in Fig. 24 as "y-
Channel Ql"' the corresponding multiple channel input for such
readouts is identified as "x-Channel Qn" and Y-Channel Qn". Ad-
ditionally, the reset signals from the processing circuitry at
Fig. 25 are generally denoted by the labels "x-Channel QnR" and
"y-Channel QnR". These labels represent typical reset signals, two
of which are identified above in connection with the description
associated with Figs. 23 and 24 at respective lines 1052 and 1100.
Looking now in detail to Fig. 25, x-Channel Qn signals, as well
` as y-Channel Qn are submitted from each respective row and column
readout through input conduits, represented generally at 1110 and
1112, to a Coincidence Network and x, y Pair Code Generator func-
tion 1114. Network 1114 provides a read-in function which checks
the inputs at 1110 and 1112 corresponding to a given gamma ray
interaction within a given detector component for the coincidence
of their time derivative signals. When the coincidence of such
a data pair is received, the spatial position represented by such
signals is assured and a corresponding x, y Pair Code is generated
and presented through appropriate conduits represented generally
by the transfer conduit at 1116. This pair code output is inserted
into F.I.F.O. Asynchronous Memory and Line Decoder function 1118
by virtue of a clocked signal or pulse provied through line 1120.
F.I.F.O. Asynchronous Memory 1118 corresponds with the same func-
tion provided at 516 in Fig. 19. As before, the F.I.F.O. (first-
in, first-out) memory is conventionally formed incorporating gen-
erally independent input and output stages or networks. It serves
within the system as a de-randomizer which receives and collects
or records the x, y Pair Codes from circuit 1114 and, following
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a four-to-three line decoding thereof, submits signals to multi-
plexers 510-514 (Fig. 19) providing for the selective acceptance of
the signals addressed ther~to. Note in the latter regard, that the
; signal labeling for the instant embodiment remains the same as
that shown in Fig. 19. These coded instructions to the noted
:
multiplexers are represented in Fig. 25 by the broad conduit arrows
appropriately labeled and respectively identified at 1122-1126.
Returning to the Coincidence Network and Pair Code Gen-
erator function 1114, in the absence of a noted signal coincidence
identifying a proper spati~l pair code, appropriate signal return
channel alignment will be provided through a multi-channel conduit
represented generally at 1128 to a Reset Control function 1130.
Operating in similar fashion at reset drive function 520 in Fig.
19, control 1130 responds to a non-coincidence condition to pro-
vide for the resetting of appropriate ones of the row or colunn
readout networks as described in connection with Figs. 23 and 24.
In this regard, note that multiple row reset outputs are represent-
- ed generally by arrow 1132, while the corresponding column or
y-Channel output signals are directed through a conduit arrangement
represented generally at 1134. As noted above, the signals
labeled at the latter two outputs are representative of
multi-row and multi-colurnn interconnections. Reset signal trans-
mitting control over Reset Control 1130 is derived from Sequential
Control block 1140 as through the conduit represented generally at
1142. Control 1140 additionally provides the functions described
_99 _
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in connection with block 526 in Fig. 19, i.e. clocking the informa-
tion codes from F.I.P.O. Asynchronous Memory and Line Decoder
1118 by outputs submitted thereto through line 1144; controlling
the Sample and Hold Amplifiers 544, 548 and 552 to receive informa-
tion from Multiplexers 510 and 514 and assert appropriate delays
suited for the proper operation of Two Channel Analyzer 562, so
as to assure that a signal of proper energy level criteria is
processed. Further, function 1140 activates Reset Control 1130
to generated end-of-cycle resetting as well as short cycle resetting
performance occasioned with the failure of a given signal to pass
the window criteria of analyzer 562. The outputs of Control 1140
to the noted Sample and Hold ~mplifiers are represented generally
by the broad arrow at 1146, while the corresponding input thereto
from the processing system providing for the noted resetting or
recycling features is represented by the broad arrow designated
1148.
With the noted replacement of processing control 522'
for that earlier represented at 522 in Fig. 19, the sytem operates
. essentially in the same manner, i.e., multiple channel analysis
being carried out over the several energy levels which may be pro-
:
vided by components of the general type described at 562; sample
and hold functions are carried out, as described at 544-552; and
a dividing function is provided to normalize the signals with re-
spect to their corresponding energy levels by divider functions
as at 584 and 586 in Fig. 19.
Since certain changes may be made in the system and ap-
paratus without parting from the scope of the invention herein
- 1 0 0 -
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involved, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be inter-
preted es illustrrtive and not in a limiting sense.
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