Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND
The field of nuclear medicine has long been concerned with techniques of
diagnosis wherein radiopharmaceuticals are introduced into a patient and the
resultant distribution or concentration thereof, as evidenced b~ gamma ray in-
tensities, is observed or tracked by an appropriate system of detection. An
important advantage of the diagnostic procedure is that it permits noninvasive
investigation of a variety of conditions of medical interest. Approaches to thisinvestigati~le technique have evolved from early pioneer procedures wherein a hand-
held radiation coun~er was utili~ed to map body contained areas of radioactivity to
10 more current systems for simultaneously imaging substantially an entire, in vivo,
gamma ray souree 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 parallelsweeps, to scan regions of inter~st. A drawback to the scaMing 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 d~escribed above, the later developed
~0 "gamma camera" is a stationary arrangement wherein an entire region of interest is
imaged at once. As initiaLly introduced the stRtionary 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 subject of investigation and this
scintillation detector crystal. When a gamma ray emanating from the region of
investigative interest interacts with the crystal, a scintillation is produeed at the
point of gamma ray absorption and appropriate ones of the photomultiplier tubes of
the matrix respond to the thus generated light to develop output signals. The
original position of gamma ray emanatiorl is determined by position responsive
3~ networks assoeiated with the outputs of the matrix. For additional information
concerning such camera, see:
I. Anger, H.O., "A New Instrument For Mapping Gamma Ray Emit--
ters", 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 resolution in cornbination with concomitant utilization of a highlyversatile 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 realizes~ through the use and image identification of radiopharmaceuticals
exhibiting more than one photon energy level. Wlth such an arrangement, two or aplurality of diagnostic aspects simultaneously may be availed the operator. For
example, in carrying out myocardial imaging, the above-identified 99m-Technetiummight be lltilized in conjunction with lll-lndium, the latter contributing photon
energy in the regions of 173 and 247 KeV. Similarly, 81-Rubidium, exhibiting photon
10 energy in the range of 350 Ke~ might be utilized in conjunction with 81-Krypton, the
latter having gamma ray energy at about 120 KeV. The noted dual energy
characteristic of Ul-Indium also might be utilized to achieve tlNo aspects of
diagnostic data.
The resolution capabilities of gamma cameras incorporating 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
gamma radiati~n 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
20 photons may derive from Compton scattering into trajectories wherein they arecaused to pass through the camera collimator and interact photoelectrically withthe 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 wiU effect an off-axis recordation in the image of the
system as a photopeak photon representing false spatial information or noise. Assuch scattered photons record photopeak events, the noise increase 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 resolution, photons which scatter through an angle from 0 to about
30 70 will be seen by the system as such photopeak events.
A continuing interest in improving the resolution qualities of gamma calneras
has led to somewhat extensive investigation into imaging systems incorporating
relatively large area semiconductor detectors. Such interest has been generated
principally in view of theoretical indications of an order of magnitude improvement
in statistically limited resolution to provide significant improvements in imagequality. In this regard, for example, reference may be made to the following
publications:
~L3~
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. Beckl and A. C:ot~schalk, editors), Society of
Nuclear Medicine, New York, 1971, pp. 92-113.
III. R.N. Beck~ M.W. Schuh, T.D. Cohen, and N. Lembares, "Effects of
Seattered Radiation on Scintillation Detector Response", Medical
Radioisotope Scintigraphy, IAEA, Vienna, 1969, Vol. 19 pp. 595-6i6.
IV. A.B. Brill, J.A. Patton, and R.J. Baglan, "An Experimental Com-
parison Scintillation and Semiconductor Detectors for Isotope
Imaging and Countingl', IEEE Trans. Nuc. 5ci., Vol. NS-l9, No. 3, pp
197-190, 1972.
V. M.M. Dresser, G.F. Knoll, "Results of Scattering in Radioisotope
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 derivediscrete regions for spatial resolution of impinging radiatis)n, the opposed parallel
sur~aces of the detector diodes may be grooved or similarly configured to define20 transversely disposed rows and columns, thereby providing identifiable discrete
regions of radiation response. Concerning such approaches to treating the de-
tectors, mention may be made of the following publications:
VI. JO Detko, "Semiconductor Dioxide Matrix for Isotope Localization",
Phys. Mecl. Biol., Vol. 14, No. 2, pp. 245-253,1969.
VII. J.F. Detko, "A Prototype, Ultra Pure Germanium Orthogonal Strip
Gamma Camera," Proceedin~s of the IAEA Symposium on Ra-
dioisotope Scintigraphy, IAEA/SM-164/135, Monte Carlo, October
1972.
VIII. R.P. Parker, E.M. Gunnerson. J.L. Wankling, and R. Ellis, "A
Semiconductor Gamma Camera with Quantitative Output," Medical
Radioisotope Scintigraphy
.
I~. V.R. McCready, R.P. Parker, E.M. Gunnerson, R. Ellis, E. Moss,
W.G. Gore, and J. Bell, "Clinical Tests on a Prototype Semi-
conductor Gamma-Camera," British Journal of Radiolo~y, Vol. 44,
58-62, 1971.
X. Parker, R.P., E.M. Gumlerson, J.S. Wankling7 R. Ellis, "A Semi-
conductor Gamma Camera with Quantitative Output," Medical
Radioisot~ee Scintigraphy, Vol. 1, Vienna, IAEA, 1969, p. 71.
XI. Detko, J.E., "A Prototype, Ultra-Pure Germanium, orthogonal-
Strip Gamma Camera," Medical Radioisotope Scinti~a~y9 Vol. 1,
Vienna, IAEA, 1973, P. 241.
~3~36~
XII. Schlosser, P.A., D.W. Miller, Nl.S. Gerber9 R.F. Redmond, J.W.
Harpster~ W.J. Collis, ~V.W. Hunter, Jr., IIA Practical Gamma Ray
Camera System Using High Purity Germanium,'l presented at the
1973 I~EE Nuclear Science Symposium, San Franeisco, November
1973; also published in IEEE Trans. Nucl. Sci., Vol. NS-21, No. 1
February 1974, p. 658.
XIII. Owen, R.B., M.L. Awcock, "One and Two Dimensional Position
Sensing Semiconductor Detectors," IEEE Trans. Nucl, Sci., Vol. NS-
51, June 1~68, p. 290.
In the more recent past, im~estigators have shown particular interest in Eormingorthogonal 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 Prototype, Ultra Pure Germanium, Orthogonal Strip
Gamma Camera," Proceedings of the IAEA S~mposium on Ra-
dioisotope Scinti~raphy, IAEA/SM-164tl35, Monte Carlo, October,
1972.
XV. Schlosser, P.A., D.W. Miller, M.S. Gerber, R.F. lRedmond, J.W.
Harpster, W.J. Collins, W.W. Hunter, Jr., "A Practical Gamma Ray
Camera System Using High Purity Germanium," presented at the
1973 IEEE Nuclear Science Symposium, San Francisco, November
1973; also published in IEEE Trans. Nucl. Sci., Vol. NS-21, No. 1,
February 1974, p. 658.
High purity germanium detectors promise numerous advantages both in gamma
camera resolution as well as practicality. For instance, by utilizing high purity
germanium as a detector, lithium drifting arrangements and the like for reducingimpurity concentrations are avoided and the detec~or need only be cooled to
requisite low temperatures during its clinical operation. Read-out from the orth~
30 gonal strip germanium detectors is described as being carried out utilizing a number
of teehniques, 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 redueing the number of preamplifiers-amplifier
channels, and a technique of particular interest utilizes a charge splitting method.
With this method ~r technique, position sensitivity is obtained by connecting each
contact ship of the detector to a charge dividing resistor network. Each end of
each network is connected tc a virtual earth, charge sensitive preamplifier~ When a
gamma ray interacts with the detector, the charge released enters the string of
40 resistors and divides in relation to the amount of resistance between its entry point
--4--
~39L~
in the string and the preamplifiers. Utilizing fewer preamp~ifiers, the cost andcomplexity of such systems is advantageously reduced. A more detailed description
of this readout arran~ement is provided in:
XVI. Gerber, M~S., Miller, D.W., Gillespie, B., and Chemistruck, R.S., "Instrumetation For a High Purity Germanium Position Sensing
Gamma Ray Detector," I~EE Trans. on Nucl. Sci., Vol. NS-22 No. 1,
February, 1975, p. 416
To achieve requisite performance and camera image resolution, it is necessary
10 that substantially all sources of noise or false information within the system be
accounted for. In the absence of adequate noise resolution, the performance of the
imaging systems may be compromised to the point of impractieality. Until the more
recent past, charge splitting germanium detec tor arrangements have not been
considered to be useful in gamma camera app]ications in consequence of thermal
noise anticipated in the above-noted resistor divider networks, see publication VII,
~ However, as will be evidenced in the description to follow, such considera-
tions now are moot.
Another aspect in the optimization of resolution of the images of gamma
cameras resides in the necessarily inverse relationship between resolution and
20 sensitivity. A variety of investigations have 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 highresolution collimators may cancel out any improvements sought to be gained in
image resolution. A more detailed discourse concerning these aspec~s of design are
provided, for instance, in the following publications:
XVII. E.L. Keller and J.W. Coltman, "Modulation Transfer and Scintilla-
tion Limitations in Gamma Ray Imaging" J. Nucl. Med. 9,10, 537-
545 (1968)
XVIII. B. Westerman, R.R. Sharma, and J.F. Fowler, "Relative Im-
portance of Resolution and Sensitivity in Tumor Detection", J.
Nucl. Med. 9,12 638-640 (1968)
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 detector and additionally, a form of analysis of the energy of
radiation reaching the detector. Spatial analysis may be carried out by difference
summing circuits, while energy determination is carried out by additive summing
~5--
3~
circuits. Further pulse height analyzers may be u~ ed as one discriminating
component of a system for de~ermining the presence of true or false imaging
information. In any of the systems both treating noise phenomena and seeking a
higil integrity of spatial information, a control is required which carries out
appropriate noise ~iltering while segregating true from false information. In
addition to the foregoing, it is necessary that the "throughput rate" of the system be
maximized in order that it may accommodate a highest number of bits or pulses
representing spatial and energy data~
Another operational phenomenon tending to derogate from the spatial resolu-
10 tion quality performance of the cameras is referred to as "aliasing". Thisphenomenon represents a natural outgrowth of the geometry of the earlier-noted
orthogonal strip germanium detector. ~ more detiled discussion of this aspect ofthe gamma cameras is provided at:
XIX. J.W. Steidley, et al., "The Spatial Frequency Response of Ortho-
gonal Strip Detectors: IEEE Trans. Nucl. Sci., February, 1976.
To remain practical, it is necessary that the imaging geometry OI stationary
type gamma camer~s provide for as large a field of view as practical. More
particularly, such considerations require a camera field of view large enough to20 encompass the entire or a significant extent of the profiles of various organs of
interest. Because of limitations encountered in the manufacture of detector
crystals, for instance, high purity germanium crystals, the si`ze of solid statedetector components necessarily is limited. As a consequence, composite detectorconfigurations are required which conjoin a plurality of smaller detector components
to provide 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 loæ of image informa~ion validi~y and acuity. For instance, in the latter
regard, spatial information must hRve a consistency of meaning across the entire30 extent of an ultimately displayed image of an organ, otherwise, clinical evaluation
of such images may be encumbered. Preferred arrangements for intercoupling the
discrete detector 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 utili~ed with gamma camelas having multi-component
detectors further are called upon to collect image data therefrom at an optimum
rate while evaluating the validity thereof and assigning it an appropriate address
~3~
function. ~uch address assignment may Yary in nature depending upon the selectedmode of circuit interrelationship of the discre~e detector components with the
array. An additional function of the control system is to identify the spatial
position of the deteetor-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 aspect of the control systems where they are contemplated for use in
10 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.
SU MMARY
The invention provides a composite solid state detector for use in deriving a
display, by spatial coordinate information, of the distribution or radiation emanating
from a source thereof situate within a region of interest, comprising:
a plurality of solid state deteetor componentsJ each having a given
surface arranged for exposure to impinging radiation and exhibiting discrete0 interactions therewith at given spatially definable locations;
said given surface of each said detector component and the surface
disposed opposite and substantially parallel thereto, respectively, being associated
with impedance means configured to provide, for each of said opposed surfaces,
outputs for impedance defined signals relating the said given location of said
interactions with one spatial coordinate parameter of one select directional sense;
said detector components being arranged to provide groupings of ad-
jacently disposed ones of said given surfaces mutually linearly oriented to exhibit a
common said directional sense of said spatial coordinate parameter; and
meuns interconnecting at least two of said outputs associated with each
30 of said surfaces within a given said grouping thereof for col1ecting said impedance
defined signals deriving therefrom.
The invention also provides a camera system for imaging the distribution of a
source of gamma radiation situate within a region of interest, comprising:
a housing positionable a select distance from said region of interest at a
location for receiving said radiation;
means collimating said recived radiation;
a composite, solid state detector mounted within said housing in an
orientation for receiving said collimated radiation, said detector including;
an array of solid state detector components, having given surfaces
arranged in mutual, close adjacency to define a composite detector radiation
acceptance plane exposable to incoming collimated radiation, said detector com-
ponents exhibiting discrete interactions, at given spatial locations, with radiation
impinging thereupon at said acceptance plane,
said given surface of each said detector component and the surface
10 thereof disposed opposite thereto, respectively, being operationally associated with
impedance means;
said impedance means being configured in correspondence with th0
e2~tent of an associated said detector component surface and having ~utputs situate
at two opposed peripheries of said associated surface for providing signals relating
the location of a said interaction within said component to the respective locations
of said outputs;
said detector components being arranged within said array to define
spatially aligned discrete rows and orthogonally disposed columns of said surfaces
and the said impedance means outputs associated therewith;
20means interconnecting said impedance means outputs within each said
discrete row in parallel circuit relationship to provide a signal collection output,
means interconnecting said impedance means outputs within each said
discrete column in parallel cirucit relationship to provide a column signal collection
output; and
means responsive to signals received from said row signal collection
outputs and said column signal collection outputs for deriving ~n image correspond-
ing with said interactions.
For a fuller understanding of the nature and the object of the invention,
reference should be had to the following detailed description taken in conjunction
30 with the accompanying drawings.
BRIEF :[)E~CRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of a gamma camera arrangement as
may utilize the improvement of the invention, showing, in block schematic form,
general control functions;
~3~
Figure 2 is a pictorial representation of a solid state orthogonal strip high
purity germanium detector component incorporating a charge splitting resistor
network in combination with preamplification electronics;
Figure 3 is a schematic representation of a solid stage strip detec$or and a
schematic collimator functionally associated therewith as such system componentsrelate to the radiation source within a region of clinical interest;
Figures 4(a)-4(c) are a schematic and graphical representation of the funda-
mental geometry associatad with tha interrelationship of a multi-channel collimator
and a solid state detector;
Figure 5 is a pictorial representation of a collimator array which may be
utilized with the system of the invention;
Figure 6 is a pietorial 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 geometry of an orthogonal strip detector and
image readouts for illustrating aliasing phenomena;
Figures 8(a)-8(d) portray vertically aligned graphs relating modulation transferfunction with respect to resolution as such data relates to aliasing phenomena,
Figure 8(a) showing collimator modulation transfer function (MTFC) with FWHM
20 resolution of 1.331, Figure 8(b) showing a consequent alias frequency spectrum which
is processed by the electronics of the camera system, Figure 8(c) showing electronic
MTF for given resolutions, and Figure 8(d) showing camera system MTF's revealingalîasing introduced by the orthogonal strip solid state detector;
Figures 9(a)-9(d) provide curves showing tlhe results of aliasing correction as
compared with the curves of figures 8(&~8(d), Figure 9(a) looking to collimator
design as an antialiasing filter, Figure 9(b) showing a consequent aliasing frequency
spectrum which is processed by the electronics OI the system, Figure 9(c) showing
the consequence of electronics used for antialiasing post-filtering, and Figure 9(d)
showirg total system MTF revealing the elimination of aliasing phenomena;
3û Figure 10 is an equivalent noise model circuit for solid stage detectors as
utilized in accordance with the instant invention;
Figure 1:1 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 gamma camera control system
configured as it is related to a single detector component output;
Figure 13 is a schematic block diagram of a gated integrator configuration
which may be utilized with the instant invention;
L34~D5j
Figure 14 is a schematie circuit representation of the configuration described
in colmection 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 the schematic
representation shown in Figure 15;
Pigure 17 is a pictorial and schematic representation of an array of detector
cornponents showing the interconnections thereof to form a composite detector orregion thereof as may be utilized with the system of the invention;
Figure 18 is a block schematic reprssentation of the control 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 treating the signals developed by the
control arrangement of Figure 18;
Figure 20 is a sehematic 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
20 impedance arrangement, the components being :interconnected in the noted "row-
column" fashion;
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 inter-
connection geometry;
Figure 24 is a schematic block diagram of a eontrol 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 utilization with the
no$ed "row-column" interconnection of detector components, the figure representing
an alternate control arrangement within the diagram of Figure 19.
DETAILED DESCRIPTION
.
In the discourse to follow, the control system of the invention initially is
described in conjunction with the arrangements utilized for physieally accepting
--~0-
gamma radiation from a clinically determined region of interest. In particular,
initial acceptance techniques for collimating such radiation as well as parameters
required for such collimation are set forth. Following that discussion, the discourse
sets forth techniques for achieving optimi~ed system performance with respect tonoise characteristics which otherwise would be encountered with the solid state
detector arrangement of the invention. Looking additionally to techni~ues for
improving through-pu~ rate characteristics for the systemt the discussion initially is
concerned with a control over a detector arrangement incorporating only a one
detector comp-onent. Following this basic description, however, preferred techniques
10 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 establishedJ 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
tham to achieve practical overall imaging fields of view which maintain efficient
signal treatment.
As indicated in the foregoing, during contemplated clinical utilization, a
gamma camera arrangement according to the instant invention is used to image
gamma radiation within patients. Looking to Fig. 1, an exaggerated schematic
20 representation of such a clinical environment is revealed generally at 10. The
environment schematically depicts the cranial region 12 of a patient to whom hasbeen administered a radio-labeled pharmaceutical, which pharmaceutical will havetended to concentrate within a region of investigative interest. ~ccordingly,
radiation is depicted as emanating from region 12 as the patient is positioned on
some supporting platform 1~. Over the region 12 is positioned the head or housing 16
of a gamma camera. Extending outwardly from the sides of housing 16 are mountingflanges, 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 2~ defined by upper and lower vacuum chamber plates shown, respectively,30 at 24 and 26 conjoined with an angularly shaped side defining flange member 28.
Lower vacuum chamber plate 26, preferably, is formed of aluminum and is
configured having a thin entrance window portion 30, directly above which is
provided an array of discrete solid state detector components, as shown generally at
32. Array 32, in turn, is operationally associated with the "cold finger" component
34 of an environmental control system, which preferably includes a cryogenic region
refrigerating unit of a closed-cycle variety, shown generally at 36. An ion pump, as
~3~
at 38, assures the integrity of the vacuum in chamber 22, such pump, in conjunction
with the refrigerating unit 36l being mounted for associa$ion with chamber 22
through upper vacuum plate 24, the latter whieh may be formed, for instance, of
stainless steel. Vacuum 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.
Electronics incorporated w;thin chamber 22 include preliminary stages of
amplification~ for instance field effect transistors ~FET's) as at 40 which are
mounted upon a plate 42 coupled, in turn, between cold-finger 34 and side channel
l0 28. Thus connected, the plate 40 evidences a temperature gradient during the
operation of the unit which provides a selected ideal temperature environment ofoperation for the amplification stages. The outputs of these stages are directedthrough subsequent stage electronics, shown within a housing 44, which, in turn,provides electrical communication to externally disposed control electronics through
eonduit 46 and line 48. To provide for appropriate operation, chamber 22 generally
is retained at a temperature of, for instance, about 77K, while the FET's, 40,
mounted upon plage 42, are retained at about 130K to achieve low noise perform-ance.
Mounted outwardly of window portion 30 an in alignment with the detector
20 array 32 is a collimator, shown generally at 50. During the operation of the gamma
camera, radiation emanating from source 12 is spatially coded initially at collimator
50 by attenuating or rejecting off-axis radiation representing false image informa-
tion. That radiation passing collirnator 50 impinges upon detector array 32 and a
significant portion thereof is converted to discrete charges or image signals.
Detector array 32 is so config~red 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 inf ormation along conventional
coordinate axes a~ well as representing values for radiation energy levels. This data
then is introduced, as represented schematically by line 48, to filtering and logic
30 circuitry which operates thereupon to derive an image of optimized resolution and
veracity. In the latter regard, for instance9 it is desired that only true imageinformation 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 filtering and control of
the system.
-12-
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Image spatial and energy level signals from line 48 initially, 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 detector array 32 to derive
discrete signals or charge values corresponding with image element location.
Additionally, circuitry of the function of block 52 derives a corresponding signal
representing the energy levels of the spatial information. The ou~put of block 52 is
directed to Filtering Amplification and Energy Discrimination functions as are
10 represented at block 54. Controlled from a Logic Control function shown at block
56, function 54 opera1es upon the signal input thereto to accommodate the systemto parallel 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. FromAmplification and Discrimination stage 54 and Logic Control 56, the analyzed
20 signals are directed into an Information Display and Readout Eiunction, as repre-
sen~ed at block 58. Components within function block 58 will include display
screens of various configurations, image recording devices, for instance, photo-graphic apparatus of the instant developing 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 component within the detector array 32 is
described in conjunction with Fig. 2. Later discussion and figures will reveal the
interrelationships of such impedance networks and their equivalents as they are
30 operatively associated with a multi-component detector array. Looking to thatfigure, an exaggerated pictorial representation of such a component of the detector
array is revealed at 60. Deteetor 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 puritygermanium region of the crystal, as at 62, serves as an intrinsie region between p-
type semiconductor region contacts 64 and n-type semiconductor region contacts as
--13--
at fi6. The intrinsic region 62 of the ~i-n detector components 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 ~type semiconductor
material. On the opposite face of the detector component, orthogonally disposed n-
type semiconductor strips similarly are formed through the provision of grooves 70a-
70c. Configured having this geometry, the detector component 60 generally is
referred to as an orthogonal strip detector or an orthogonal strip array semi-
conductor detector component. The electrode strips about each of the opposed
10 surfaces of compnent 60, respectively, are connected to external charge splitting
resistor networks revealed ~enerally at 72 and 74. Resistor network 72 is formed of
serially coupled resistors 76a-76e which, respectively, are tapped at their regions of
mutual interconnection 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 outputs of which, at 84 and 86,
provide spatial output data for insertion within the above-described summation and
energy level derivation 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
20 resistors 88a-88e, the mutual interconnec tions of which are coupled with theelectrode strips at surface 66~ respectively, by leads 90a-9Oe. Additionally,
preamplification stages as at 92 and 94 provide outputs, respectively, at lines 96 and
98 carrying spatial data or signals representativ2 of image information 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 cor~ponent 60, as
described in U.S. Patent No. 3,761,711 granted to Robert N. Hall on September 25,
1973 any imaging photon absorbed therewithin engenders ionization which, in turn,
creates elactron-hole pairs. The charge thusly produced is collected on the ortho-
gonally disposed electrode strips by the bias voltage and such charge flows to the
30 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. Assigning charge v~lue designations Q1 and Q2'
respectively, for the outputs 98 and 96 of the netowrk 74, and Q3 and Q4,
respectively, for the output lines 84 and 8~ of network 72, the above-noted
~ummation 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 Ql and Q2' und 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 Q1+Q2' and lQ3~Q4),and [(Q1+Q2) ~ (Q3-~Qd~)] or in the latter expression, [(Q3~Q4) ~ (Q1+Q~)]- As
noted above, the operational environment of the detector array 32 and associatedamplification stages is one within the eryogenic region of temperature for purposes
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 character-istics of that impinging radiation. For instance~ looking to Fig. 3 a portion of a
patient's bocy under in~restigation is portrayed schematically at 100. Within this
region 100 is shown a radioactively tagged region of interest 1029 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 collimator
50 and individually detected at component 60 for ultimate participation in the
evolution of an image display. The exemplary path of seven such photons are
20 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 nearly perpendicular to
the cletector, inasmuch as such emanating rays provide true spatial image informa-
tion 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 misdirected one inasmuch as it
does not travel perpendicularly to the detector. Consequently, for appropriate
image resolution such path represents false inform~tion which should be attenuated,
as schematically portrayed. Scattering phenomena within collimats:r 5n itself or the
30 penetration of the walls thereof allows "non-collimated" 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 ca~nera,
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 energy of each photon admitted by the collimator, the imaging
-15-
3~i
system still may reject such false informat;on. For exa~nple, in the event of a
(:~ompton scatterirlg of a photon either in the patient or collimator, the energy
thereof may have been reduced sufficiently to be rejected by an energy discrimina-
tion window of the system. Photon path, g, represents a condition wherein
component 60 exhibits inefficient absorption characteristics such that the incident
photon path, while representing true information, does not interact with the
detector. As is apparent from foregoing, each of the thousands of fuU energy
photons which are absorbed at the detector ultimately are displayed at their
corresponding spatial location on an imaging device sueh as a cathode ray tube to
10 form an image of the source distribution within region 102 of the patient. Of course,
the clinical value of the gamma eamera 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 quality 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 funda-
mental 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 thegeometric aspects of collimator 50, as such aspects relate to photon path travel, and
20 spatial intensity distribution over the corresponding spatial axis of detector com-
ponent 60 are shown schematically. Fig. g(b) shows the photon intensity distribution
at the mid-plane ~0' of the detector due to a line source of radiation at distance B
from the collimator 50 outwardly 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 outwardly disposed plane defining
side of collimator 50 as well as its inwardly disposed plane defining side and the
plane defined by the midpoint 60' of detector 60. The intensity distribu~ion pattern
o~ photons, revealed in Fig. 4(b), is provided under the assumption that the
collimator 50 is fixed in position. Fig. 4(a), on the other hand, assumes that the
30 collimator 50 moves during an exposure and produces, in consequence, a triangular
intensity distribution pattern 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
approaehes. However, fcr the latter designation, FWHM is derived from a
consideration that if a very sma~l spot of radiation exits at the object plane, the
image generally will be a blurred spot with radially decreasing intensity. The
-16-
9L~
position resolution then is defined as twice the radial distance at which the intensity
is hal~ o the center intensity.
Looking in particular to Fig. 4(c), considering the similar ~riangles ~FG and
LMN, the resolution of collimator 50 generally may be expressed as:
c AE (1
where
A = the collimator thickness,
AE = the effective collimator thickness
due to the 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 OI a given collimator channel multiplied by 1.13.
The effective collimator thiclcness is given approximately by:
AE = A - ~@~ (2)
20 where u(E) is the attenuation coefficient of tlle coll;mator material at a photon
energy, E.
For a given collimator material, sufficiently thick septal walls are required toreduce the mlmber of photons or gamma rays that enter within a given collimator
channel, penetrate the septal wall thereof and exit through an adjacent or otherchannel 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 fractiorl of photons or rays traveling UV that actually
30 penetrate the septal wall is given by the penetration fraction:
P = exp (- 11 (E) W). (3)
It is considered the practice of the art to design the collimator structure suchthat the penetration fraction, P, is given a value less than about 596. In this regard,
mention may t~e made of the following publication:
XX. H.O. Anger, "Radioisotope Cameras," Instrumentation in Muclear
Medicine, G.J. Hine7 ed. Vol. 1, Academic Press~ New York, 485-
~52 (1967).
The minimum septal distanee, W, is found from the simi-lar triangles IJK and
10 UVY approximately as: AT
W = ~D+T (4)
by assuming A is greater that 2D ~ T where T, as noted above, is the septal wallthickness. Solving equations (3) and (4) for the septal wall thickness, T, gives:
T = -2D ln P
ll(E) A + in P ~5)
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
20 collimator para-meters, such efficienc ~ may be given b~k:
KD2 ~ (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 camera imaging system
stems importantly from the system's capability for achieving quality image resolu-
tion Given the optimum 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 fabrication cost. Further, an inspection of equations (1) and
30 ~6), given above for collimator resolution and geometric efficiency, respectively,
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 configured having square cross sections represents a preferred
--18--
~13~
geometric design feature. In this regard, where the latter are compared with
collimator channels formed as round holes, hexagonally packed arrays or hexagonally
packed bundles of tubes all of given identical dimensions, resolution remains
equivalent, but the efficiency 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. Consequently, as noted above, on the basis OI maximum
efficiency at a desired resolution~ the square hole cross sectional chamber design is
preferred.
Concerning the materials which may be selected for constructing the col-
limator, 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 the 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 theoptimum collimator material. EIeretofore, however, pragmatic considerations of
machinability or workability have required a dismissal of the selection of tungsten
2û and/or tantalum for collimator fabrication. For instance, for multi-channel
collimators having round channel cross sections, tungsten and tantalum are too
difficult and, consequently, too expensive for drilling procedures and, in general,
hexagonally packed arrays providing such cross sections are restricted to fabrication
in lead. Similarly, other designs formed out Oe the desired material do not lendthemselves to conventional machining and forming techniques, the cost for such
fabrication being prohibitive even ~or the sophisticated camera equipment wîthinwhich the collimator units are intended for utilization.
In the instant preferred arrangement, a square hole collimator design, fabric-
able utilizing the optimum material tungsten, is provided. Revealed in perspec~ive
30 fashion in Fig. 5, the collimator is shown to comprise an array of mutually parallel
adjacently disposed channels having sides defining a square cross sectionO Thesechannels extend to define inwardly and outwardly disposed sides whieh are mutually
parallel and the channels are for~ned axially normally to each of ~hese side planes.
The highly desirable square structure shown in Fig. 5 is achieved utili~ing the earlier
described preferred tungsten material or tantalum, such materials normally beingdifficult or impractical to subjeet to more conventional manufacturing procedures.
--19--
~3~
However, practical assembly of the collimator array 50 is achieved through the use
of R plurality of discrete rectangularly shflped sheet members, as are revealed in the
partial assembly of the collimator 11~ shown in Fig. 6. Referring to that figure,
note that member 110 is formed as a flat rectangular sheet of height, h, correspond-
ing with desired collimator thickness, A. Formed inwardly 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~ Theslots are formed having a width of T + e~ where e will be seen to be a tolerance.
10 When the plurality of sheet rnembers, for instance, as shown at 110 and 114 are
vertically reversed in mutual orientation and the corresponding slots, respectively,
as at 112 and 116 are mutually internested as shown, the 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
members within the array with a con~rolled allowance for tolerances. In determin-
ing the value for the above described pitch of the regularly recurring slots within
the sheet members, assuming resolution criteria are met, a spacing may be selected
to match the center-to-center electrode strip spacing of a detector corDponent 6û or
a multiple thereof so that the septal walls for the collimator 50 can be aligned with
20 less accurate grooves formed within the detector. Practical fabrication techniques
are available for forming the slots as exemplified at 112 and 116. In particular,
chemical 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 unmasl~ed. The sheets then are
subjected to selected etchants whereupon the slots are formed. Following a~
propriate eleaning, the sheet members then are ready for the relatively simple
assembly build-up of a completed collimator. Through the use of such chemical
milling techniques, desired tolerances in forming the slots are reali~able~ By
utiizing the collimator structure shown in combination with optim~l tungsten sheet
30 material, a computable 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 conventional collimator structures~ As evidenced from the foregoing
such advantages include the availability to the design of the superior shielding
--20--
~34~
capabilities of tungsten; a simplicity of component design and consequent 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 e~ist 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 radiation is preferred for collimator design. It
10 follows, therefore, that the streaming factor for the particular eollimator structure
at hand should be assigned the same configurational parameter in the interest ofdesired unity of system design. Through utiliæation of a geometric analysis of aworst case condition, requisite lowest tolerance required for the interlockin~ fit of
the septal walls and for a desired source to collimator distance can be derived. 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 mi~ling
application.
In the discourse given heretofore concerning the functional inter-relationships
of collimator 5û and detector array 32, no commentary was provided concerning the
20 effect of the discrete electrode strips of thle detector upon ultimate image
resolution. It has been determined that, by virtue of their geometric configuration,
orthogonal strip detectors, without appropriate correction, 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
components as the input except with the possibility of reduced contrast. Looking to
Figs. ~(a)-(c), the ali asing 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
30 be obtained, for instanee, 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 distribution shown
is one with primary frequency components of vl = O and v2 = 2vs/3. Such source
input is provided in the instant representation inasmuch as it combines the three
qualities which accentuate an aliasing phenomenon, namely, a periodic input, 100%
contrast, and a high signal-to-noise ratio.
--21 -
~3~
Fig. 7~b) reveals a portion of strip electrode detector 130 having the earlier
described cletector 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 received within a system incorporating
fl collimator capable of resolving the input signals, a detector with strip spacing
satisfying the anti-aliasing criterion and all anti-aliasing electronic channel, is
revealed at 13~. This image shows no aliased components.
I.ooking more particularly to the aliasing phenomenon represented at curve
10 132, the four lowest spatial frequency components revealed are:
(1) a component at v = 0, a zero frequency componen-t which
represents the average value of the four peaks;
(2) a component at v = 2v /3, which is the frequency equal to the
reciprocal of the spaciSng between 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
reeiprocal of the spacing between each of the four peaks; and
(4) a component at v = vs/3, which is the frequency equal to the
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 harmonic of the strip samp]ing frequency.
As a prelude to considering a typical representation of the spatial frequency
response of a one-dimensional gamma camera as revealed in Figs. 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 linear systems and which takes into account the shape of an entire line
spread function. The reationale for such description of spatial response arises from
the fact that any object and its image can be described in terms of the ampl;tudes
30 and phases of their respective spatial frequency components. The MTF is a measure
of the effieiency 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 toFig. 8 (a) - 8 (d) MTF is plotted against spatial frequency, v, for a series of stages
within a gamma camera not accommodating for aliasing phenomena. In Fig. 8 (a) a
collimator modulation transfer function (MTF~) with FWHM resolution of 1.331 is
revealed, i.e., the curve distribution, incorporating some high frequency com-
--22--
ponents, 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 isseen by the spatial channel electronics 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 the primary input
component are present, centered at integer multiples of the strip spacing or
samp]ing frequency, VS = 1/1. Fig. 8(c) represents the MTF of the electronics of the
system, i.e., the transfer function of the spat;al channel electronies, while Fig. 8(d)
shows the product of the MTF values of the curves of Figs. 8(b) and 8(c).
10 Accordingly, the curve of Fig. 8(d) shows the spatial frequency response of the
entire system, including the introduction of spurious spatial frequency content in the
system MTF, represented ;n 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. According-
ly, Fig. 9(a) reveals that the collimator MTF is forced to a zero value at spectrum
position vs/2. Such design insures that the fundamental input frequency components
20 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 freguency 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 imagin~
system of the camera. Such post-filtering of the electronics is illustrated in Fig.
9(e). The product of MTF conditions represented by Figs. 9(b) and 9~c) again arerepresented 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
30 collimator in controlling aliasing phenomena, it may be observed from the foregoing
that the system resolution of an orthogonal strip germanium detector type gamma
camera is determined 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 ~1), where 1 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:
--23--
XXI. J.W. Steidley, et al., "The Spatial Frequency Response of Orthogonal
Strip Detectors," IEEE Trans. Nuc. 5cL, February, 1976.
Looking now to the speci~ic design parameters of the collimator of the
invention, it may be recalled that collimator resolution, Rc, has been derived
geometrically at equation (1) given hereinabove. By now substituting the ideal
valuation, 1.7 ( I ) determined for antialiasing prefiltering on the part of thecollimaator, the inventive collimator geome-try or structure may be defined.
Accordingly, the collimator is defined under the following expression:
AR (A + B ~ C)
The collimator further can be defined utilizing equation (5) above for septal
wall thickness once the values of the parameter of equation (7~ are determined.
Further, given the value, Rc, for collimator resolution and the geometric para-
meters determined thereby as described above9 the eollimator geometric efficiency,
~s, as given in equation (6) above, can be applied to further maximize the
performance of the collimator. Additionally, it may be noted that the suppressing
freguencies above vs/2 input signal contributions to aliasing phenomen~ are ac-
commodated for.
As has been alluded to earlier herein, discounting entrance geometry, the
orthogonal strip position-sensitive detector is resolution limited by noise associated
20 with the detector as well as the charge dividing network. Consequently, it isnecessary to consider the noise characteristics of the sytem from the standpoint of
minimizing the effects thereof upon resolution as well as treating such phenomena
to derive desired imaging effects. Generally, it may be concluded that the resistor
network is the dominant source of noise within the electronic sp~tial channel of the
system9 while the resistor network, coupled with the detector leakage current,
represents the dominant noise source in the system's energy channel. As will
beeome more apparent as the instant description 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
30 llke are described in conjunction with the single detector component described
heretofore in connection with Fig. 2, in the interest of clarity and simplification.
In the later pations of the instant discussion, however, the control system of the
camera will be seen to be described in conjunction with d~tector component arrayembodiments.
Noise is the random fluctuation of the preamplifier output voltage when there
is no stimulus. It is generated by imperfections in the preamplifier input device,
--24--
thermal movement of chalge carriers in the resistors and the bulk of the detector
and imperfections in the crystal structure of the detector. Looking to Fig. 10, an
equivalent no1se model circuit for solid state detector components is revealed. Note
that the model reveals a detector leakage current, iDJ whieh is assumed to be
formed of individual 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-
amplifier input as a step function. The system input capacitance is the parallel10 combination of stray capacitance at the preamplifier 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 resistive strip network, a portion
of the dividing resistance, RD, is in parallel with the detector capacitance. Since
RD is less tharl one hundred kiloohms, it respresents a significant noise source. The
thermal noise from resistors in series with the detec$or capacitance appears as a
delta function to the preamp]ifiers. 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~ Finally, a noise term20 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.
Since the noise sources discussed above havle 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 considered to be30 mutually related in terms of filtering to the extent that as efIorts 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 OI the parallelvariety. As has been detailed in the publications given above, the use of Gaussian
and the Gaussian trapezoidal noise ~iltering circuits has been found to optimize the
energy and spatial resolution values of the camera system.
Turning now to Fig. Il, a circuit model of the detector component ~0 and the
-25-
~f3 9 ` ~
resistor networlcs of Fig. 2 is portrayed. The discrete nature of the detector systern
and the method of readout is revealed in the figure with the discrete capacitorsforming an n x n array. Each row and column is defined by the charge measured atthe end of the resistor strings. The electron-hole pairs which are formed when agamma ray interacts with the detector are collected on opposite surfaces. A 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 intersection of the eolumn and row defines the diode
position in which the gamma ray energy was deposited. Note in the figure, that
10 individual capacitances are represented which are exemplary of the inherent
capacitance of the detector itself. When considered 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, TD, for this charge flow to avoid error in
information 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 preamplifier output pulses will vary as a function of the
position of interaction, xO, of an incident gamma ray. The voltage output of each
20 preamplifier (Fig. 2) due to the instantaneous transfer of charge Q0 at position xO is:
cO _
V(O,x,t) = Qo [~ - o - ~ 2 sin ( lrL ) exp [ ~n T i ~ (8)
m=l
Q [xO + ~ 2 cos(m7r) sin ~ L ) P T D~
m=l
where Cf is the feedback capacitance of a preamplifier in farads, L is a given linear
dimension of the detector, TD is the time constant of the detector (i.e. TD =
2RDCD)9 xO defines the position of interaction and m is a summation variable.
Examination of equation (8) and (9) show that for a time
t ~ TD ao)
--26--
~3~
i.e., un output generation time equivalent to one-half of the time constant of the
cletector, the value of V(O,xo,t) is within 1~ of its final value for all x~/L ~ .95 and
V(L,xo,t) is within 1% of its final value for all xotL ~ .05. Stated otherwise, the
error generated form ballistic deficit type characteristics of the system, as itrelates 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 amplifier output at the x = O position, i.e.
(11)
~o
tO V(~Xot~ ~ V(L~Xo't) = Cf [I~ L ~~ m--7rSin( ~L~ o)(l ~ cos mT~) exp~D)~
the following important observations may be made. 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. Stated otherwise
the output signal derived from the above signal treatment subtractive approach
ranges from + Qo/Cf at xO=0~ to -Qo/Cf at xO = L, making the signal twice that of
earlier suggested one preamplifier 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 xJL ~ .45 and x/L ~ .55 after a time:
t ~ TD (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 treatm ent within the spatial channel is diminished by afactor of 4.
Turning now to the conditions 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:
c~o
V(O,xo,t) + VtL,xO~t) = C ~ m~rsin ( Llr ) (1- cos mrr) exp ( m ~ (13)
Note again, that the peaking time of the pulse is position dependent. At xo/L
30 = O5~ the maximum peaking time occurs and the pulse is within 1% of its final value
--27--
:~3~
at t >,D/2. Accordingly, it may be observed that ballistic deficit or charge
collection type considerations within the encrgy channel will require a charge
collection period, for practical purposes, equivalent to one-half of the time constant
of the detector.
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:
Nqsl = 1 ~} (14)
where N~sl is the equivalent noise charge in number of electrons for one pre-
10 amplifier spatial measurements, RD is the total resistance of the resistive chain, TD
is the temperature of $he detector and chain, ap is a weighting factor of the filter, q
is the magnitude of the charge on an electron, and K is Boltzman's constant.
In the expressions given above, i.e. equations 8 through 14, the term RD is
intended as the value representing the average of the total resistance of each
resistive networlc. For the exaggerated exemplary detector component shown in
Fig. 2, the term RD represents one-half the sum of the resistance value o networks
72 and 74~
Note from equation (14) that the noise is prs)portional to the square root of the
temperature as well as the weighting factor and the time constant of the system.20 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 factor and time constant and to elevate the resistance value to the extent
practical. Equation (14) is for one preamplifier readout. Reconfiguring the equation
to represent a subtractive or antisymmetric arrangement, the following expression
obtains:
NqSAS = 2 { D ap ~, (15
--28--
~3~
E~rom this equation, note that a subtractive arrangement permits the ballistic
deficit àictated time constant to reduce by a factor of ~, while the value of noise
increases by a factor of 2 for that same time constant. However, since a reducedtime constant (factor of 4) is involved in a subtractive arrangement, the noise value,
otherwise increased by a ïactor of 2, remains the same and the signal-to-noise ratio
is increased by a fa~tor 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 RD is difficult to increase inasmuch as a concomitant reduction in energy
resolution generally is witnessed for such alteration. Temperature drop ean be
10 achieved practically, and the weighting factor, ap, can be al~ered to a more or less
ideal value by appropriate selection of filtering systems. It has analytically been
determined that a ~3.4 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" phenomenon, for thin detectors,
i.e. about five mm in thickness, the detector charge collection time is small and
does not affect circuitry treating a detected signal. For thick detectors, however,
i.e. having a thickness in the range of about 2 cm, the bulk charge collection time
varies from approximately 100 to 200 nanoseconds. Since this collection time is
20 approximately the same as the collection time of the charge dividing network, its
contribution to ballistic deficit problems must be considered. For such systems the
optimum filtering arrangement consists of a time invariant prefilter followed by a
gated integrator circuit. Such filters 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. ~or a detailed dis~ourse con~erning the utilization of antisymmetric
summation as well as the utilization of h~apezoidal fil~ering within the spatialchannel of the system, reference is made to the following unpublished work:
XXII. Hatch, K.F., "Semiconductor Gamma Camera", Ph. D. I issertation,
Massachusetts Institute of Technology, Cambridge, Massachusetts,
February, 1972.
The egui~ralent noise charge in number of electrons for Gaussian trapezoidal
spatial measurements may be represented by the following expression:
\1/2
NqsGT = 2 ~4kTDapTI L79 1 (16)
--29--
~ ~3~ $
where ap is the parallel noise weighting func tion value for Gaussian trapezoidal
systems and Tl is the integration time. Analysis of the foregoing shows that an
excellent improvement in spatial resolution is obtained by using antisymmetric
Gaussian trspezoiclal filtering. This improvement is realized because the effects of
"ballistic deficit" are greatly reduced.
The corresponding equivalent noise charge in number of electrons for the
energy channel of the system may be expressed by the following formulation:
N ESl = 1 ~qiDa = 4kTD RDCD~1/2 (17)
An important aspect of the above energy channel and spatial channel analyses
10 has been observed. In this regard, it may be recalled that opposed relationships
stem from a consideration OI parallel vs. series noise phenomena. For instance, it
has been described that energy noise is considered serial in nature whereas spatial
noise is considered to be parallel in nature. The energy noise equation, as shown at
(17) above, represents a straight summation of two preamplifier outputs and the
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
observed that two separate time constant values, To~ Te~ respectively, for spatial
resolution and energy resolution may be incorporated within the circuitry treating
the output of the system de$ector. For instance, the energy resolution filtering of
20 the system requires a relatively extended time constant, whereas corresponding
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 time constant energy f'ilter individually will be integrated
to achieve a peak value above a predesignated window function of the energy
channel (blo~k 45, Fig. 1). Accordingly, false information generated from pulse pile-
up phenomena and the like may be rejected without recourse to more involved
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
30 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 detectorarray.
--30--
~ 3~
Referring now to Fig. 12, a block schematic representation of a control system
is presented for receiving spatial coordinate outputs of the detector. In the figure,
preamplificatisn stages 96, 98 and 8~, 82 are reproduced and the outputs thereof,
respectively, 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 flnd 112 are eoupled, respec~ively, through lines 118 and 120 to the input
of a Summing and Gaussian Filtering function 122. As discussed in detail above,
function 122 OpeiRteS under a relatively extended time constant, identified livithin
the block as Te. 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 Gated integrator 136 operating under
an integrating period corresponding with time constant To. Control into the gated
integrator, for instance, establishing the time constant value, ~O, emanates from
gate control function 128 through line 138. Additionally, 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 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 To control over
integrator 146 is asserted from gate control function 128 through line 148, whil~ reset
control is asserted from line 150. The outputs from the x-axis Gated Integrator
Function 136 is presented along line 152 to a Photographlc 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 operator.
30 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 160 and 162 to Persistent Display Scope readout 158. Readout control
to Photographic 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 outputs 154 and 158 are not actuated or are
blanked until control function 128 receives an input display signal from Pulse Height
--31 -
~34~ 65
~nalysis func~ion 124 through line 168. Interrogation of function 128 is provided from
control 128 through line 170. Inasmuch as a relatively extended ~ime constant, le~ 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 interroga-
tion request from line 170 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
10 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 pulsearrives thereat. The circuit further includes a base line restorer, as at 176, which
opeates in cooperation with gated integrator 178. The output of integrator 178 is
directed to an output amplifier 180, the output from which is directed along lines 152
cr 160, as shown in Fig. 12, depending upon the particular orthogonal sense of the
incoming signal.
A corresponding and more detailed schematic representation fo the circuit is
20 revealed in ~ig. 14. Referring to that figure, eitller of the coordinate spatial inputs
as developed at lines 144 or 134 (Fig. 12) is asserted through an input resistor 182 to
an amplification stage 184. Stage 184, corresponding to amplifier bloclc 172 in Fig.
13, includes a feedback line incorporating feedback resistor 186, as well as a ground
reference input at line 188. Delay line 174 is shown represented at 190 receiving an
input from output 192 of amplifier 18~. A resistor 194 is coupled between delay line
190 and ground, while the output thereof is AC coupled through capacitor 196 to the
input of a base line restorer function. The base line restorer is of a 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., 32,19~1, p. 1057.
EssentiaUy, the restorer function is provided for the purpose of assuring a net
zero charge value at the gated integrator 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 gated
integrator would integrate areas below the baseline as well as under the Gaussian
-32~
~3~6~
shaped spatial signal. For carrying out its assigned functions, the restorer includes
an ernitter-follower sta?e at NPN transistor 198, the base of which is eoupled
through resistor 200 and line 202 to one side of capacitor 196. The emitter of
transistor 198 is coupled through a resistor 204 to -Vc~ potential, while its collector
is coupled through a resistor 206 to ~Vcc. The restorer function additionally
includes a cul rent supply network oeprating such that, upon the occurrence of
spurious elevations of current, accommodation is made to control 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
10 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
connected between the positive and negative sides of the supply voltage.
The output of the base line restorer function is coupled through resistor 224 toone 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 ~ET 226 is present at
line 232 and is shown as selectively receiving a signal designated y from the
20 control function 128 (Fig. 12). Also influencing line 228 is a network including line
234 and variable capacitor 236 which is coupled to receive an input designated y.
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 eapacitor
240 and is selectively activated by a reset gate present as field effect transis-tor
(FET) 248, the source and drain terminals of which are connected in switch defining
fashion within line 244 and the gate input to which at line 250 is configured toselectively receive a reset signal identified as, ~, from Gate Control ~unction 128
30 (Fig. 12). A variable resistor 252 is connected between the positive supply voltage
and the interconnection of resistor 246 with FET 248. The output of ampli:fication
stage 230 is present at line 254 and is coupled through a variable capacitor 256 and
line input 258 for selectively receiving a signal input identified as, B.
The output at line 254 of the gated integrator is directed through resistor 260
to the input of a unity gain inverting amplifier 262 which includes a feedback line
incorporting resistor 264 and is connected with ground reference at line 266. The
~L~3~ 4~
O~ltpUt of the amplifier, at line 268, is that represented in Fig. 12 either at line 152
or line 180 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 represented in Fig. 12 at 128 isdisclosed in more detail in combination with a timing sequence diagram. At time, t
- 0, as shown in the timing diagram of Fig. 16, the sytem is prepared to process 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 i$s value exceeds a
10 reference voltage representing the lower level of the window level established by
evaluation or Pulse Height Analysis function 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 signal is compared is inserted from line 290 to the comparator.
These predetermined, preliminary signal level conditions being met, eomparator 292
provides a positive going output pulse at line 294 which is introduced to a dual, D-
type flip-flop FF-l. Conventionally, the D form of flip-flop incorporates an
actuating (clock) input signal terminal, Ck7 along with a signal input terminal, D.
The flip-aop output signal Q becomes 1 at the time of a 0-to-1 change at the clock
terminal. In conventional manner, the Q output of the flip-flop represents the
20 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 facilitate 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 by 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 fli~flop
FF-l is identified as ~ and is introduced to the reset gate of each integrator, as
30 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 integrating amplifier.
Similarly, the Q output of flip-flop FF-l assumes a low status and, by connection
through line 296, couples the B signal input to the gated integrator as at line 258 in
Fig. 14. This B signal output of the flip-flop FF-l is used to compensate for charge
injection into the feedback eapacitor caused by the capacitance coupling betweenthe gate and drain electrodes of FET 248.
-34--
~3~
The Q output o~ ~lip-flop FF-l additionally is presented through line 298 to theB input terminal of u monostable multivibrator M-4, and, through line 300, to the B
input terminal of monostable multivibrator M-l. Accordingly, these multivibrators
are triggered, the Q output of multivibrator 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 miltivibrator M-4, carries a y signal which is introduced into the
input gate of FET 226 (Fig. 14). Simultaneously, an inverted y input is providedalong line 234 to variable capacitor 236 to provide compensation for off charge
lû injection. The gated integrator- then commences an integrating mode of perform-
ance, the time over which operation is controlled by multivibrator 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 protrayed 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 inputterminal of monostable multivibrator M-l. With the presence of the forward edge of
this signal at line 300, the Q output of the latter alters from a low to R high value
and retains such value over an interval, te, selected for delaying the start of the
20 display sequence until the energy pulse has been analyzed at pulse height analysis
function 124 as shown in Fig. 12. Note that this lnterval, 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 D1 serves as the
earlier described interrogation pulse directed to the pulse height an~lysis function
124 deseribed 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
30 introduced through line 308 to the A input terminal of monostable multivibrator M-
5. l`his 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.
--35--
The remaining components of the circuit function on the basis of lNhether an
interrogating signal issued from line 170 to Pulse Height Analysis Function 124 (Fig.
12) has been responded to, alon~f line 168, to indicate a pass ~r no pas.s condition of
signal energy level. If function 1~4 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-5 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 sueh that its ~ output at line 310 asserts a clearing signal through AND gate ANl
10 to the clear input terminal, Cl, of flip-flop FF-l. The output thereof, as reflected at
the multivibrator M-4, causes the integrator to be reset. With this operation, the
sytem is short cycled, and the through-put rate thereof advantageously is increased.
Note, that the opposite input at line 314 of AND gate ANl is normally high by virtue
of its connection through line 316 and resistor 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 developing a positive output pulse at its ~ terminal and line 320, while a pulse of
opposite sense is developed at its Q output along line 332. The ~ output signal at
20 line 320 is directed to line 324 whereupon it addresses the clock input, Ck, oï D flip-
flop FF-2. In consequence, the Q output of flip-flop FF-2, at line 322, converts to a
low value which is asserted at the B input of multivibrator M-3 to inhibit the output
thereof. The short cycle feature thereby is inhibited. This signal at line 324 may
also be utilized for cloeking 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 voltage, 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 com~ected to the gate elect~ode of a field
30 effect transistor (FET) 328. By corresponding connection, the Q output of
multivibrator M-5 is asserted along lines 332 and 334 to the gate input field effect
transistor (FET~ 330. Note that the drain-to-source channel 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
-36-
~L:L3~
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 l?ET 328
opens, to cause the output of amplifier 348 to change from a negative to positive
value, thereby permitting the activation of display and record functions 154 and 158
(Fig. 12).
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 re
10 spective cathodes of the diodes Zl and Z2 are coupled at the common connections OI
resistors 336 and 338, 340 and 342. Looking further to the outputs of multi-
vibrator M-5 as they respond to an energy evaluation input at line 168, the positive
edges of the output signal at Q thereof also activates a multivibrator M-6 in
consequence of the connection of line 332 with the B terminal thereof. Multi-
vibrator 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 i9 coupled through line 352 to the B terminal input of anothermonostable multivibrator M-7. The positive going edge of the Q output signal of the
multivibrator M-6 triggers multivibrator M-7 to provide a corresponding pulse signal
20 at its Q output at line 354. Lnie 354 is coupled through AND gate AN2, the output
of which is coupled through line 358 to the clear terminal, Cl, of fli~flop FF-2. The
opposite input to AND gate AN-2 is operator preselected andis asserted from line314. With the presence of a clearing input to fli~flop FF-2, the Q output thereof at
line 322 returns to a high status which, in turn, is imposed 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 theclearing of flip-flop FF-l~ the gated integrator is discharged or reset through the B
input signal at line 250, described earlier in connection with Fig. I4.
With the noted return of monostable multivibrator M-3 to its standby state,
30 the control system is fully reset and ready to process another set of informat;on
signals. If the output of comparator 292 is high at this time, the system will not
proce~s such incoming information. This lockout 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 $he Q terminal of
flip-flop FF-l through lines 296 and 297. This input signal is utilized by the
comparator as a block to any enabling of the system to respond to incoming signals
~3~3~i
until such time as a full cycle of evaluation has terminated. ~ig. 16 reveals the
tirne-based correspondence between the output of comparator 292 and the Q outputor ~ signal of ~lip-flop YF-l. In the absence of such ~ signal input from line 297,
error would be introduced into the system, for instance, by virtue of the generation
of start signals at line 2~, integrator timing is disrupted to invalidate an ongoing
signal processing procedure. As may be evidenced from Fig. 16, the B signal input
from line ~97 (fli~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
10 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
analysis. Because of this, should two or more gamma rays photoelectrically interact
with the detector and their total energy be absorbed in a time less than the rise-
time of the filtered energy 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 systern 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 upon interrogation of
Pulse Height Analysis 124, should no response signal be received therefrom within
20 the interrogation interval 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.
~ s noted earlier, it is important that the detector function 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 thetechniques of their fabrication, i~ becomes necessary to conjoin a plurality of such
detector components in some manner wherein a broader region of radiation may be
witnessad and imaged.
One preferred technique for associating the discrete detector components
30 provides for their mutual operational interconnection in subgroupings of pre~determined numbers, for instance, 4, which sub~roupings then are coupled with the
control system of the camera. An array of detector components having a requisitecamera entrance area aeceptance geometry then is formed preferably of a sym-
metric compilation of component subgroupings. One practical size for the detectGr
array comprises four subgroupings each of which is formed of four detector
--38--
~ 3~
co~ponents. With such an array, the control system advantageously may operate byobserving the pel formance of the subgroupings as they are represented in quad-
rature. Another aspect to be considered in "scaling-up" the camera system for
clinical utility resides in the earlier-discussed feature permitting their accepting
and properly imaging information derived from two discrete photon energy levels.Accordingly, the scaled-up gamma camera would incorporate a control system
accommodating both of these desired features. In the discourse to follow, the
gener~l signal treatm ent described hereinabove in comlection with ~igs. 12-16
remains substantially the same with an appropriate multiplication of functions
10 where necessary 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 subgrouping 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 compris-
ing 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 dim ension. In the interest of clarity, only one such quadrant
designated subarray, as at 360, is described in conjunction with a control system.
20 Detectors 362-366 are dimensioned having mutually equivalent areas designated for
the acceptance of impinging gamma radiation. 5uch equivalency serves to achieYe
accurate ultimate image read-out from the camera system. The detector com-
ponents 362-366 are of the earlier-described orthogonal strip array variety, each
strip thereof being defined by grooYes. Note in this regard, that detector
component 362 is formed having strips 370a 370d located at its upwardly disposedsurface 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
3~2a-372d defined by intermediately disposed grooves arranged orthogonally with
respect to the grooves at the upper surIace. Detector component 364 is identically
30 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, detector component 368 is shown to be formed of identically
structured mutually orthogonally disposed strip arrays 382a-382d and 38-~'a-384d.
-39-
~L~3~6~
Cornponents 362-368 are illustrated expanded from one another for purposes of
illustration only, it heing understood that in an operational 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, the strip arrays each are mutually associted along common coordinatedirections. This association is carried out between components 362 and 364 by leads
386a-386d, coupling respective strips 37~a-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 strips10 378a-378d of component 366.
The outputs of the thus mutually coupled strip arrays of the upwardly disposed
faces of the detector components are coupled with an impedance network, repre-
sented generally at 3sO. Network 390 is configured comprising serially inter-
connected discrete resistors 392a-392i. Interconnection between respective strips
370a-370d and points intermediate resistors 392e-392i is provided by leads 394a-394d, while corresponding intereonnection between strips 378a-3~8d with the
intermediate connections of resistors 392a-392d is provided by leads 3~6a-396d.
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
20 leads 398a-398d. Similarly, strips 376a-376d at the lower face o~ component 364 are
respectively coupled with corresponding strips 384a-384d of component 368 by leads
400a-400d The thus associated strip arrays o~F the lower faces of the detector
components are connected with the second impeclance 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 connected
to intermediate respective discrete resistors 404a-404e of network 402 by leads
406a-406d. Similarly, strips 384a-384d of the lower surface of component 368 areconnected with respective discrete resistors 404f-404i of network 402 through leads
408a-408d. Thus interconnected, the four discrete detector components provide
30 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 parameter outputs of the lower surfaces of the detector com-
ponents 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
--40--
~ ~3~16~
detector array of Fig. 17. In thflt 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 preamplification stages respeetively revealed at d~30-436. In this
regard, note that the output at line 438 of preamplification stage 430 is introduced
to an x-Channel Antisymmetric Summation Gaussian Filtering and Gated Integrator
function, shown at 440, while the corresponding input from preamplification stage
~32 is directed along line 442 to that same function. The summing and filtering
functions at 441) operate on the x-coordinate outputs introduced thereto in the same
10 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
appropriate filtering and pulse shaping as by noted series of integrations and the
like, an output from block 440 is provided as an x-designated coordinate channelsignals at line 446.
The outputs of x-channel amplification stages 430 and 432 also are directed,
respectively, through lines 4~0 and 444 to Summing and Gaussian Filtering function
448. As described in conjunction with Figs. 12-16, i~nction 448 includes an initial
stage deriving the time derivative of the summed energy signal provided from lines
444 and 450 and submits such derivative signal, from along line 452, to a Gate
20 Control and Start Logic function, identified at bloclc 454. Such signal evidencing a
predetermined requisite level to provide a preliminary assurance of valid spatial
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 AntisymmetricSummation and Gaussian Filtering function 462. Configured in similar fashion as
function 440, the signals introduced to function 4~2 ar subtractively summed,
appropriately filtered, and pulseihaped by a series of integrations to provide a y-
designated coordinate channel signal at line 464. Control over the gated integration
30 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 dis-
criminator, revealed at block 470, which receives the summed energy signal output
at line 472 from Summing and Gaussian Filtering function 448. As before, Energy
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 informa-
-41-
tiom Vpon interrogation thereo~ 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
wirldow criteria of Energy Discriminator 470, gate control 454 will effect a
resetting of the summing functions, as from lines 478, 480, and 482 to carry out the
earlier-described short-cycle cperation, thereby permitting the system to more
rapidly and efficiently process a next incoming spatial signal. It may be noted that
Energy Discriminat~ function 470 may operate effectively within the system even
though more tharl one photon energy level of information is asserted. Recall that it
10 is desirable to accommodate the system to the utilization of more than one
radiopharmaceutical, each such radio-labeled substance haYing a different gamma
ray energy characteristic. Because the gemanium detector system of the inventionenjoys a considerably 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 germanium detector exhibits a capability of from
3 to 4 keV resolution 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 radiopharma-
20 ceutical.
In accordance with the invention, the filtering and control electronics for agiven quadrant also incorporates a Peak Detector function represented at 484.
Detector 484 is coupled through lines 472 and 486 to receive the energy signal
generated from summing function 448. rhe detector 484 serves to hold the peak
value of this signal, thereby providing an analogue storage function to accommodate
for variations in signal treatment times as are represented for instance, between
Antisymmetric Summation functions 440, 462 and the energy additive ~umming
function at ~48. Detector 484 is associated in time control fashiorl with gate
control 454 through line 490 and may be reset therefrom through lines 478 and 480.
30 The peak value output of detector 484 is presented along line 492 to an Energy
Channel Driver 494 for ultimate presentment to quadrant proeessing 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 i~s delivered to an x-Channel Driver 498, the output of
-42-
which is present in line 5û0a. Note that this channel signal is designated 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 5û4a and identified as, Qly.
The information now delivered from each quadrant of the overall imaged
region now, for purposes of convenience, is desi~nated by the noted labels: Qlx' Qly
and Qle. In the immediate discussion to follow, the composite detector array is
assumed to be eunctioning in quadrature and, therehy, developing corresponding
10 signals from follr distinct multi-component quadrants. These quadrants are repre-
sented 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 sig^nal is
selectively derived from the quadrant processing control system to be described in
conjunetion with Fig. 19.
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 Ener~y Multiplexer
20 514. The inputs to multiplexers 510~514 derive from each of the four quadrantcircuits 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
und labeled at lines 500U1 504a, 496a, 506a, and 508a. Correspondingly~ the inputs
from the three remaining circuits to each oP the multiplexers 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 Fi~. 18
are represented, respectively at 506a~506d as leading to F.I.F.O. Memory 516, while
the input to functions as at 454 in Fig. 18 are represented as output lines 508a-508d
extending from Reset l:lrive function 520. Note, additionally, that the quadrant30 signals leading to the quadrant processing control arrangement of Fig. 19 areidentified 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.C). Memory are
identified as Q1-Q4 and the outputs of Reset Drive function 520 are identified as
Q1R Q4R-
--43-
In conventional fashion, multiplexers 510-514 perform a switching type function
wherein the channel signals addressed 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 function,
represented within a dashed line boundary 522. Function 522, in addition to
incorporating the F.l.F.O. Memory and input clocking 516 and Reset drive function
520, includes a 4-to-3 Line Decoder 524 and a Sequential Control function 526.
F.I.F.O. (first in, first-out) Memory and Input Cloelcing 51f; is conventionally formed
incorporating somewhat independent input snd output stages or networks. It serves
10 within the system as a derandomizer which receives and collects or records the
randomly generated data acceptance signals, which flre presented at lines 506a-
506d. These quadrant labeled signals are received and serialized at the input
clocking stage of F.I.F.C). Memory and Input Clocking 516 following which, an
appropriate signaling 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 S34 and 570 to
the 4-to-3 line decoder 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 respective multiplexers 510, 512,
20 and 514 to pass the retained spatial 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 presented 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
Ampli~iers 544, 54~ and 552 are utilized within the circuit as an analog storagemedium so that th~ aforementioned quadrant circuits can be reset for processing
incoming signals. I.ine 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
30 Hold Amplifier 544. A command from Sequential Control 526 emanating from line530 provides an initial sample command whereupon the multiplexers output signalsare sampled by the Sample and Hold Amplifiers. Following a select interval, a hold
signal is passed to amplifiers 544552, following which a next sueceeding interval is
provded. In consort with the issuance of the hold signal to amplifiers 544-552, a
reset command signal is passed by the Sequential Control through line 566 to theReset Drive circuit, 520. Since the spatial and energy information contained in the
quadrant Cil'CUit being addre~ssed is now stored in the processing circuit, the
appropriate quadrant circuits can be reset through the appropriate reset line Q1R-
~ R (lines SU8a-508d). ln carrying Ollt the latter functions, it may be noted that
reset drive function 520 derives the quadrant selective information through lines 570
from the F.l.F.O. Memory 516, at the end of the reset command a clockout pulse is
sent to the F.l.F.O. Memory 516 along line 532 from the Sequential Control unit 526.
By doing this the information at the output of F.I.P.O. Memory 516 is clocked out so
that the next usable information appears at F.I.F.O. Memory 516 output. The faetthat valid information appears at F.I.F.O. Memory 516 output is sent along line 5~2
lo to the Sequential Control circuit 526 for current or future use. At the time valid
ouput appears at F.l.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
signal, 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 evaluating the energy levels of the earlier noted two radio-
pharmaceuticals, for example, which may be utilized within the system. Note thatthe 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
20 quadrant of the detector. Should the energy signal passed to the Two Channel
Analyzer 5~2 fail to meet the window criteria for either select photon energy level,
an appropriate representation or signal is provided 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 teh sample and hold
amplifier 544, 548, and 552 are placed in the sample mode and the process described
above repeats itself. I~ a valid information present pulse was not received, theSequential Control 526 waits until one is received before the process described
above repeats itself. Where more than two photon energy levels are sele~ted for the
system, an appropriate multichannel arlalyzer is substituted at component 562.
An advantageous aspect of the invention resides in the controlled inter-
relationship between multiplexers 510-514 and corresponding Sample and Hold
Amplifiers 544-552. As controlled by sequential control 526, an initial clockinginput to multiplexers 510-514 causes a quadrant signal received thereby, in given
arrival order, to be clocked to the appropriate ones of Sample and Hold Amplifiers
544, 548, and 552. Following the initial interval described hereinabove, commencing
with the noted hold function, the initial treating system may be cleared in
-45-
3~09~
anticipat;on of a next quadrant signal to be processed as described above. This
feature advantageously improves the throughput rate of the overall system permit-
ting correspondingly improved imaging performance. With the clearing of the intial
treatment or input networks as well as clocking of F.I.F.O. Memory 516, the
entrance portion of the guadrant processing circuitry is preapred to accept the next
succeeding quantum of information form the quadrant circuits. Upon appropriate
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- spatialoutpul signals of Sample and Hold ~mplifiers 544 and 548 respectively which are
10 passed along lines 580 and 582 to Divider networks 58~1 and 586 are s$able arld
proportioned respectively to the ~- and y- positions. The latter networks serve the
function of normalizing the spatial signals received from lines 580 and 582 withrespect to the particular photon energy of the detector interaction whieh they
represent. The corresponding energy signal introdueed at this point to the system
and analyzed at 562 may be representd as, Qe~ while the spatial signal may be
represented as, ~Qe From the earlier discussion presented herein, the spatisal
information, ~, which the system, notwithstanding quadrature data, provides as
spatial visual information may be represented by the expression:
( 1 L ), (18)
20 where, L, is equivalent detector length and, xO, is the position of interaction of a
gamma ray. The spatial information quantity, c~, also may be derived and expressed
by the relationship:
~ ~QE
QE ~ (1
Equation (19) reveals the function o Dividers 584 and 586, i.e. by dividing by QE~
the measured energy channel signal, as it represents one or more photon energy
levels, the desired spatial signal, ~9 is derived. In carrying out this function, the
divisor of the last expression in Equation (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
30 of a nonzero denominator to the divider circuits. The outputs of Bias Amplifier 590
--~6--
L3~L~
are shown directed along line 592 to Divider 586 and along line 594 to Divider 5~.
Because of the advantageous high quality resolution of germanium type sol;d state
detectors, the dividing function provided herein is required only for systems
intended to utilize radioiso~ope imaging sources to present more than one photonenergy level but can be used with a monoenergetic source.
The thus normalized x- and y- spatial channel signals are directed, respec-
tively9 from Dividers 584 and 586 ~long line 596 and 598 to an x-,y- Display Bias and
Orientation Control function, identified at eontrol block 600. At function 600, the
si~nals introduced thereto are weighted in correspondence with the quadrant or
lû 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 interchanged for desired clinical analysis purposes.
Control 600 is coupled in information exchange relationship for x-channel informa-
tion with a Camera Display Control 604 through lines 606 and, for y-ehannel
communication purposes through line 608 with the same control. Display activations
information to the Camera Display Control 604 is derived from the output of
Sequential Control 526 through lines 666, 610 and 612. In conventional fashion, the
spatial data and the display on/off control is coupled to a CRT Display 614 through
20 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. Spatialchannel information is directed to Positioning I)isplay Control 622 from lines 626
and 628 which, in turn, are connected with respective 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 control
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 servesto 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 input of function 638 is
derived from the energy related output level of Sample and Hold Amplifier 552, as is
present at line 560. To convert this level to a corresponding transitional signal, a
--4~--
Linear ~ate 64n is arranged to receive the energy signal at line 560 and transmit a
corresponding transitional type signal along linPs 642 and 644 to a Multi-channel
Analyzer 646. The channel outputs of analyzer 646 are presented along linss 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 of10 analysis and their 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 672, the latter serving to apprise the operator of the guantity
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 ofoperation of the camera for given clinical analysis as well as an isotope gain control
for regulating 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 Amplifier
input through lines 542, 546 and 550 an improvement in system throughput rate isrealized.
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
30 resolution is required is achieved to improve the resolution of the entire system.
Two embodiments of this "row-column" arrangement are revealed 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 interaetion
generated image signals.
Referring now to Fig. 20, another composite detector formed as ~n array of
discrete detector components is revealed generally at 680. Illustrated in exploded
--48--
~L~ 3~
fashion, the detector 680 is comprised of a plurality of detector components, four of
which are shown at 68~, 684, 686, and 688. Components 682-688 are dimensioned
having mutually equivalent areas as are intended for acceptance of impinging
radiation. This required equivalency 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 OI image information, would result. Thedetector components illustrated are of the earlier-described orthogonal strip array
variety, each strip thereof being defined by grooves. Note, in this regard, thatdetector component 682 is formed having strips 690a-690d located at its upward
10 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 arranged orthogonally with respect
to the grooves at the upper surface. Detector component 684 is identically
fashioned9 having strips 694a-694d at its upwardly disposed surface and lower
surface, orthogonally disposed strips 96a-~6d each strip being defined by inter-mediately formed grooves. Similarly, detector component 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 7û0a-700d defined by
intermediately disposed grooves arranged orthogonally with respect to the grooves
20 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 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 informational spatial
and energy output from the discrete detector components, which essentially is
30 eguivalent to that output which would be realized from a large detector of
equivalent size, the strip arrays are functionally associated under a geometry which,
QS noted above, may be designated "row" and "column" in nature. In this regard,
note that an impedance network, shown generally at 707, is associated with the
strips 694a-694d o~ detector component 684. This network incorporates discrete
resistors 706a-706e which are tapped at their common junctions by leads 708a-708d
extending, respectively, to strips 694a-694d. Thus configured, network 707 closely
-4~-
resembles the impedarlce networks described herein in connection with Fig. 2. Note
however, that output lines 710 and 712 of network 707 extend to and are coupled in
parallel circuit relationship with the corresponding output of a similar impedance
network, identified generally at 714. Network 714 incorporates discrete resistors
716a-716e which are tapped at their common interconnections by leads 718a-718d.
Leads 718a-718d9 in turn, respectively extend to strips 690a-690d of detector
component 682. Accordingly, the upwardly disposed surfaces of detector com-
ponents 6B2 and 684 are identically associated with respective impedance networks
714 and 707, while the latter are interconnected in row fashion and in parallel circuit
10 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 detector components 686
and 688, a similar coordinate parameter direction or row-type informational
co~lection 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 eoupled with respective leads 728a-
728d. Leads 728a-728d, in turn, respectively, are connected with strips 698a-698d
20 at the upwardly disposed sureace of detector component 686. Likewise, an
impedance network, shown generally at 730 incorporting discrete resistors 732a-
732e, is assoeiated with detector component 68g by leads 734a-734d extending,
respectively, from strips 702a-702d to the points of common interconnection of
network discrete resistors 732a-732e. Additionally, the output lines as at 736 and
738 of network 730 are connected in parallel cir<-uit relationship with the output of
network 724 to provide row readout termini, respectively, at 740 and 742. ~Iere
again, a row-type directional spatial coordinate parameter is pro~lided at the
upwardly disposed surface of the composite detector 680.
Looking now to the lower surfaces of the detector components, it may be
30 observed that the orthogonally disposed strips of detector comp~nent 682 are
associated with an impedance network identified generally at 744. Network 744
incorporates discrete resistors 746a-746e which are coupled from their mutual
interconnections by leads 7~8a-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
--50--
~ ~3~
700a-700d by leads 754a-754d. The output of impedance network 744 is connected
by leads 756 and 758 to the corresponding output of impedance network 750 to
provide column directional coordinate parameter outputs~ as at 760 and 762, which
serve to collect all spatial information of the associated paired surfaces of
detectors 682 and 6g6.
Looking to the lower surface of detector component 684, note that a network,
designated generally at 764, incorporating discrete resistors 766a-766e is function-
ally associated with strips 696a-696d, respectively, by leads 768a-768d
In similar fashion, an impedance netowrk, designated generally at 770, is
10 associated with the orthogonaUy 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 704a-704d3 respective-
ly, by leads 774a-774d. Networks 764 and 770 are electrically coupled in parallel
circuit fashion by collector leads 776 and 778 and extend to principal colleetion
points of termini 780 and 782. Thus interconnecte~, the lower surfaces OI detectors
684 and 688 are coupled in column readout fashion to provide another spatial
coordinate parameter of direction parallel with the corresponding lower surface
strip array readout arrangement of detector components 682 and 686.
With the row and column readout intercoupling of the detector components as
20 shown in the figure, it may be observed that the capacitance exhibited by alldiscrete detector components, taken together, remains the same as if only a single
detectcr were operating within a camera. Accordingly, the signal treating circuitry
and logic of the camera, advantageously, may 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 distribut~ coordinate channel spatial and energy
channel signals into analyzing and distributing circuitry. Sueh circuitry is described
in more detail in conrlection with Figs. l9 and 23-25. Preamplification stages, as
described in connection with Fig. 2, are coupled with each row readout point as at
30 720 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 detectorgenerally may be carried out by resort to biased contact configurations.
The composite detector arrangement or interrelated detector component
mosaic also may be formed ut;lizing detector structures which incorporate surface
--51--
disposed resistive layers to achieve spatially proportioned charge readout character-
istics. Such a detector composite is revealed generally in Fig. 21 at 800. Referring
to that figure, the eomposite detector, or portion thereof, 800, is shown to comprise
four discrete detector components 802-808. The opposed surfaeers of the detectorcomponentsa which are situated generally normally to impinging radiation, are
formed having a resistive character. This resistance is provided, for instance, by so
lightly doping the n-type surface as to achieve a region of re~istive character, while,
similarly, so lightly doping the opposite surface with a p-type acceptor as to achieve
a surface resistive character thereat. The readout from these resistive surfaces is
10 collected by conductive strips which, for the case of detector component 802, are
shown on the upward surface at 810 and 812 and at the lower surface at 814 and 816.
Conductive surfaces 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.
Concerning the techniques for developing the noted resistive regional char-
acter within the surfaces of detector components 802-808, mention may be made ofthe following publications:
XXlV.Owen, R.P., Awcock, M.L., "One and Two D;mensional Position
Sensing Semiconductor Detectors," IEEE, Trans. Nucl. Sci., Vol.
N.S. -15, June 1968, Page 290.
XXV.Berninger, W.H., "Pulse Optical and Electron Beam Excitation of
Silicon Position Sensitive Detectors", IE~E, Trans. Nucl. Sci., Vol.
V.S. 21, Page 374.
With the impingement of radiation upon detector component 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
surfaces and collect at the conductive strips 810-816. For the upwardly disposedsurface, these charges then are collected along eonduit 818, coupled with conductive
strip 812, and conduit 819, coupled with eonduc$ive strip 810. The adjacently
30 disposed detector 804 is fashioned in similar manner, the upward surface thereoI
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 resistive layer or region functionally ~ssociated with
conductive strips 824 and 826. Note that the latter conductive strips are arranged
orthogonally with respect to those at 820 and 822. Conductive strip 820 is coupled
by a lead or conduit 828 to conductive strip 812 of the detector component 802,
while conductive strip 822 is coupl~d by lead or conduit 830 to conductive strip 810
-52-
~l~3~
of detector 802. Thus interconnected, it will be apparent that any interaction
occurring within detector component 804 will be "seen" as a charge division between
strips 820 and 822, for one coordinate parameter, along leads 828 and a30, as ~vell as
output eonduits 818 and 819. As is apparent, a desirable simplification of the
strueture of the composite detector is available with this form o row readout.
Looking to the adjacently disposed row of deteetor components 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 aeceptance of radiation and3
additionally, incorporated conductive strips as at 832 and 834 at the extremities of
10 its uplNard 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 up~Nardly disposed side andg at 844 and 846, orthogonally disposed at the
lowermost surface.
Coupled in similar rowtype fashion as detectors 802 and 804, the conductive
strips of detectors 806 and 808 are directly electrically associatecl by leads 848 and
850. Note, in this regard, that lead 848 extends between conductive strips 84û and
20 832 while lead 850 extends between conductive strips 842 and 834. The output of
that particular row at the upward surfaee of the composite detector is represented
by leads 852 and 854.
~ columnar interCOIlneCtiOn of ~he detector components is provided betweenthe orthogonally disposed conductive strips 814 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 detec-tor co~nponents are
present at conduits 860 and 862 extending, respeetively, from conductive strips 836
and 838.
In similar fashion, the columnar association of detector components 804 and
30 808 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 804and 808 are provided by conduits 868 and 870 extending, respectively, from
eonduetive strips 844 and 846 of detector component 808.
As in the embodiment of Fig. 20, the output conduits 818, 819 and 8S2, 854 are
of a "row" variety having a designated spatial coordinate parameter and are
--53-
~,3~
addressed to initial preamplification stages prior to their association with logic
cireuitry for deriving imaging in~ormation for that particular spatial coordinate.
Similarly, the "columnar" outputs at eonduits 860, 862 and 868, 870 are directed to
preamplification stages, thence to appropriate circuitry for treatirlg that spatial
coordinate parameter. It will be understood, of course, that the number of detector
components formed within a matrix or array thereof depends upon the field of view
desired for a particular camera application as well as the pracffcal ities for
retaining such components under appropriate cryogenic temperature conditions
during operation.
The foregoing examination of the composite detector structures, represented
in Figs. 20 and 21 reveals certain consistent characteristics between the embodi-
ments. For instance, as alluded to above, the effective areas presented to radiation
impingement of the discrete detector components must be substantially equivalent,
in order to avoid distortion in an ultimately 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 "row-columnl' 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
20 directly, whether in the parallel-series connection of the embodiment of ~ig. 2û 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 exhibit spatial coordiante parameters OI a common
directional sense and, more particularly, two adjacent of the coplanar surfaces of
any two adjacent detector components are disposed within a linearly oriented
grouping arranged to exhibit a common spatial coordinate parameter directional
sense. Because the composite detector 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
30 coordinate outputs at 3ines 722 and 720 of the embodiment of Fig. 20, respectively,
are identified as (XlA) and (XlB); while the parallel row y- designated coordinate
ou~puts as at lines 742 and 740, respectively, are identified as (X2A~ and (X2B).
Similarly, the orthogonally disposed y- designated coordinate 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
detectors whose outputs are represented at 780 and 782 and are identified,
~54-
~L~L3~
respectively, as (Y2A) an (Y2B). This same labeling procedure will be seen to beutilized in the composite detec~or cmbodiment 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 thatdetector linear dimension over which resolution is evaluated. More specifically, an
improvement is experienced in the 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
10 resolution; L, is length of a detector component as measured parallel to the
directional sense of an associated impedance network; and E, represents the energy
OI an islcident photon interacting with the detector. Within the right hand side of
equation (20) above, the ~xpression, ~E~ is readily identified as the fraction (or
percentage) of ener~y resolution and is fixed for a given input energy. Accordingly
any increase in the value of, L, directly and adversely affects the spatial resolution.
Where the detector components are not interconnected by the "row-column"
technique, the value, L, in the expression above becomes larger. For exflmple if the
detectors pictured in Fig. 22 were connected as a single detector, the measuringdistance would be 2L, effecting a doubling of the noted spatial resolution value to
20 the detriment of final imaging. Another feature characteristic 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
30 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 eomponents four of which are shown at 882, 884,
8889 and 886. Components 882-888 are dimensioned having mutually equivalent
areas as are intended for acceptance of impinging radiatoin and are formed as of an
-55-
orthogonal strip flrray 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 Cllt within its upward charge collecting surface. The opposite
face of detector component 882 similarly is formed having strips 892a-892d defined
by intermediately positioned grooves arranged orthogonally with respect to the
grooves at the upper surface. Detector component 884 is identically fashioned,
having strips 894a-894d formed at its upwardly disposed charge collecting surfar.e;
and at its lower surf~ce, orthogonally disposed strips 896a-896d~ adjacent said strips
10 being defined by intermediately ~ormed grooves. Similarly, deteetor component S86
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-900d 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 di~sposed 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 corresponding row strips 890a-890d of com-
ponent 882 by electrical leads, respectively identified at 906a-906d. Note, 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-9OBd. Network 908 comprises serially associated discrete
resistors 910a-9lûe which are tapped at their common junctions by leads 912a-912d
extending, respectively, to strips 890a-890d. The output, or readout points for the
thus definPd "row" of the c~mposite detector assembly are represented at 914 and30 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. 20 and 21.
The corresponding upwardly disposed surfaces of components 886 and 888 are
connected in similar fashion. For instance, strips 902a-902d are electrically coupled
with strips 898a-898d by respective electrical leads 918a-918d. The "row" coupling
thus provided is associated with an impedance network shown generally at 920.
~L~3{~
Networlc 920 is formed comprising serially associated discrete resistors 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'l are identified at g26 and 928, having outputsespectively labeled (x2B), (x2A).
Looking now to the lower surfaces of the detector components, the ortho-
gonally disposed strips of detector component 882 are electrically coupled as shown
with the corresponding strips OI detector component 886 by electrical leads 930a-
930d. The thus coupled strip arrays of those detector components are assoeiated in
10 'Icolumnarll fashion with an impedance ne$work identified generally at 932. Network
932 comprises serially associated discrete resistors 934a-934e, the interconnections
between which are connected as shown with strips 900a-900d of component 886 by
leads respectively identified at 936a-936d. The readout termini for the thus defined
"column" association of detectors 886 and 882 are present at 938 and 940 and thecorresponding spatial or y- designated coordinate parameter outputs are identified
respectively as (ylA) and (ylB).
The lower surfaces of detector components 88d~ and 888 similarly are asso-
ciated in "columnflr" readout fashion, strips 896a-896d of the former being electric-
ally connected through respective leads 940a-940d to strips 904a-904d of the latter.
20 The thus established "columnar" readout is associated with an impedance network
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
component coupling are represented at 948 and 950 and their spatial coordinate
parameter outputs are labeled, respectively, (y2A) and (y2B). From the foregoingdescription of the composite detector arrangement 880 it may be observed that the
row-column association of the components thereof enjoys the noted spatial resolu-
tion advantages~ however, the time constant characteristic thereof will reflect a
30 higher capacity evaluation.
Figs. 23 and 24 reveal filtering and control electronics which operate in
conjunction with the quadrant of composite detectors arrayed in the "row-column"manner described hereinabove in connection with Figs. 20-22~ Note that the spa~ial
coordinate parameter outputs from the arrays shown in those figures aredesignated
(xlA), (xlB~ and (x2A), (x2B) for the row readouts and (ylA), (ylB) and (y2A), (y2B) for
the corresponding columnar readouts. Looking to Fig. 23, the x-channel spatial
-57-
~3~
coorclinate parameter outputs as are derived from one such x-channel row type
readout, to wit (xlA), (XlB) are again reproduced at intput lines 101)0 and 1002,
representing the input addressing respective discrete preamplification stages 1004
and 1006. It should be understood that each row within each quadrant would
incorporate the initial or first signal treating functions, including the control
electronics 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 labeling, the description now being reduced
to single channel analysis in the interest of clarity and simplicity. The output at
10 line 1008 of preamplification stage 1004 is introduced to an x-Channel Anti-
symmetric Summation and Trapezoidal Filtering function 1010, while the correspond-
ing 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 thexl-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 aresubtractiYely 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 amplification stages 1004 and 1006 also are directed, respect-
20 ively, through lines 1008, 1018 and 1012, and 1014, to the Summing and Gaussian
Filtering function 1020. ~s described 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 ~nd 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 1024 responds to
provide gate control over the Filtering and Summation 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
30 Filtering and Summation function 1010 from communication line 1028. Control 1024
also communicates with an Energy Discriminator function 1030 which receives the
summed energy signal output OI block 1020 from along lines 1032 and 1034. ~s 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 absenee of valid image information.
For instance, discriminator 1030 evaluates the energy signals in correspondence with
--58--
the lowest photon energy level to be accepted from those radioisotopes extant
within the noted region of clinical interest. Appropriate acceptance or rejection of
the energy level is signalled along line 1036 to Control function 11)24 and3 in the
absence of an appropriate such level, the latter function serves to reset the system
by carrying out the earlier-described short-cycle operation. As in the earlier
embodiments1 the circuit OI Fig. 23 further includes Q 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
10 accommodating variations in signal treatment at times as are represented, forinstance, between Antisymmetric Summation and Trapezoidal Filtering function 1010
and Summing and Gaussian Filtering function 1020. The peak value ou~put 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 ]ine 1016 of Antisymemtric Summation and Trapezoidal Filtering
function 1010 is presented to an xl-Channel driver 1048 for del;very to quadrantprocessing control circuitry through line 1050. Note, as in the earlier embodiments,
this coordinate channel signal is identified by the label Q1X. Similar-ly, the output
20 of control block 1024 is provided at line 1052 and the coordinate channel signal
thereat is identified by the label "x-Channel Ql-'~ 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 "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 associated with only one column within a "row-column" detector
component array, similar such circuits being required for each such column. 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
30 mosaic. Looking to the figure, column readouts (ylA)9 (ylB) are asserted, re-spectively at input lines 1060 and 1062 of input preamplifieation stages 1064 and 1066.
The output of amplification stage 1064 is directed through line 1068 to a yl-Channel
Antisymmetric Summation and Trapezoidal Filtering function 1070 performing the
operations described hereinabove. Similarly, the output of preamp]ification stage
1066 is introduced through lines 1072 and 1074 to signal treatment at function lû70,
the yl-Channel signals being subtractively summed, appropriately filtered and pulse
--59--
shaped by a series of integrations to provide a y-Channel signal at line 1076. This
signal is introduced through a yl-Channel driver l07~ from which it ez~its at line 1080
for introduction as a signal designated "Q1Y" to second or further treatment at a
processing control function.
The yl-Channel signals also are introduced from lines 1082 and 10~2 to a
Summing ~nd 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 Discriminator function 11)8~. As before; Energy Discriminator lOB8 carries
out a pulse height analysis of the energy signal to provide an accurate evaluation
10 thereof as to the presence or absence of valid image information. The lower value
selected for this analysis corre~sponds with the acceptable lower value for the lowest
photon energy selected Eor 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~riate gate control over ~ummation and Filtering
function 1070 through line 109~, 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 operations performed at block 1084. This derivative signal
serves both to provide an appropriate start signal logic for the Control 1092, as
20 described earlier herein and, additionally, will be seen to provide a coincidence
signal for later control over the entire multi-component detector arrangement ofthe invention. The output of control function 1092 is present at line 1098 and is
identified, for illustrative purposes, as "y-Channel Ql". This signal is introduced to
the noted second or further treatment at a processing control function, that same
circuitry providing a reset input to control 1092 identified as "y-Channel Q1R" and
submitted from along line 1100.
Turning now to Figs. 19 and 25, the second treating or quadrant processing
control arrangement foe use with the "row-column" readout arrangements for
detector arrays remains substantially similar to the system ~scribed above in
30 connection with Fig. 19. However, in consequence of the isolated Peadout geometry
necessarily present in a "row-column" interconnection, a further arrangement 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 is replaced by the slightly revised arrangement at 522' in Fig.
25. For purposes of clarity~ the latter drawing incorporates broadened arrows to
-60-
6~
represen~ a mult~-line inpul as would be deri~ed ftom the multiple channels of
networks of Figs. 23 and 24 as well as the multiple line couplings already depicted
in Fig. 19. Further in this regard, to represent the several inputs 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 ~n" and y-Channel Qn". Additionally, 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 resetsignals, two of which are identified above in connection with the description
10 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 ~n 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
function 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 presentedthrough appropriate conduits represented generally by the transfer conduit at 1116.
20 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 function provided at51~ in Fig. 19. As before, the F.I.F.O. (first-in, first-out~ memory is conventionally
formed incorporating generally 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 I114 and, following a four-to-three line decoding
thereof, submits signals to multiplexers 51~514 (Fig. 19) providing for the selective
acceptance o~ ~he signals addressed thereto. ~ote in the latter regard, th~t thesignal labeling for the instant embodiment remains the same as that shown in Fig.
30 19. These coded instructions to the noted multiplexers are represented in Fig. 25 by
the broad conduit arrows appropriately labeled and respeetively identified at 1122-
1126.
Returning to the Coincidence Network and Pair Code Generator function 1114,
in the absence of a noted signal coincidence identifying a proper spatial pair code,
appropriate signal return channel alignment will be provided through a multi-channel
conduit represented generally at 1128 to a ~eset Control funetion 1130. Operating in
--61--
similar fashion at reset drive function 520 in Fig. 19, control 1130 responds to a non-
coincidence condition to provide for the resetting of appropriate ones of the row or
colunn readout networks as described in connection with Figs. 23 and 24. In thisregard, note that multiple row reset outputs are representec~ generally by arrow 1132,
while the corresponding column or y-Channel output signals are directed through a
eonduit arrangement represented generally at 1134. As noted above, the signals
labeled at the latter two outputs are representative of multi-row and multi-column
interconneetions. Reset signal transmitting control over Reset Control 1130 is
derived from Sequential Control block 1140 as through the conduit represented
10 generally at 1142. Control 1140 additionaLly provides the functions described in
connection with block 52~ in Fig. 19, i.e. clocking the information codes from
F.I.F.O. Asynehronous Memory and Line Decoder 1118 by outputs submitted thereto
through line 1144; controlling the Sample and Hold Amplifiers 544, 548 and 552 to
receive information 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 Sample20 and Hold Amplifiers 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 lhe broad arrow designated 1148.
With the noted replacement of processing control 522' for that earlier
represented at 522 in Fig. 19, the sytem operatles essentially in the same manner,
i.e., multiple channel analysis being carried out over the several energy levels which
may be provided 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 normali~e the signals with respect to their corresponding energy levels
by divider functions as at 5~4 and 586 in Fig. 19.
Sinee certain changes may be made in the system and apparatus without
parting from the scope of the invention herein involved, it is intended that allmatter contained in the above description or shown in the aCCOmpRnying drawings
shall be interpreted as illustrative and not in a limiting sense.
--~2--
