Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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P~D 80.097 l 18.3.1981
"Compton scatter diagnostic apparatus for determining
structures in a body".
The invention relates to a diagnostic appara-
tus for determining structures in a body, comprising a-t
least one radiation source for generating a primary
radia-tion beam of small cross-section which penetrates
the body and which has at least three different radiat-
ion energies~ at least one slit diaphragm which is
situated outside the primary beam path and which com-
prises a slit~shaped aperture which extends in a direct-
ion approximately transversely of the primary radiation
beam, a detector device which extends transversely of
the longitudinal direction o* the slit and which com-
prises separate detectors for the detection of scatter
radiation which is produced in the body by the primary
beam and which passes -through the slit-shaped aperture,
and also comprising an electronic device for the pro-
cessing and display of detector signals~
An apparatus of this kind is known from German
Offenlegungsschrift 27 13 581. However, such an apparatus
is suitable only for direc-tq~itative reproduction o~,
~0 for example, layer images of a three-dirnensional body if
no additional correction steps are per~ormed For
example, if the attenuation o~ the radiation along the
pa-th ~ollowed by the primary beam or the scatter radiat-
ion is also -to be taken into account, the measurement
values obtained by means of the apparatus must be correct-
ed in accordance with the correction methods which are
also known from German Offenlegungsschrift 27 13 581,
thus necessitating the use of a digital computer.
For the correction of the measurement of a
slice of a body it is assumed, for example, that first aline in the bod~ slice is scanned whose scatter radiation
reaches the ~etector device wi-thout attenuation by inter-
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PHD 80.097 2 18.3.1981
mediate tissue. The scatter radiation emitted by thefirst cell of this line has not yet been attenuated,
so it can be used directly as a measure for the density
in this cell. Primary radiation reaching the second cell
of this line has been attenuated by the energy converted
into sca-tter radiation in the first cell and because
this energy is known from the measurement of the first
cell~ it can be taken into account by way of a corres-
ponding increase of an output signal of the detec-tor
associated with the second cell in comparison with the
output signal of the detector associated with the first
cell. Similarly?for a third cell of this line9 the atten-
uation by the firsttwo cells must be taken into account,
etc. For a first cell of a next line, the primary beam
has not been attenuated either~ but the scatter radiat-
ion from this cell is attenuated by the cells of tha
preceding line which are situated between the slit and
the relevant cell. Because the attenuation of -the radiat-
ion by these cells, however~ has already been determined
during the previous measurement~ the measurement ~alue
associated with the first cell o~ the second line can be
corrected accordingly. For the output signal of the de-
tector which measures the scatter radiation produced in
the second cell of the second line it is necessary to
ta~e into accOunt on the one hand an attenuation of the
primary beam by the first cell of this line and on the
other hand the attenuation of the scatter radiation by
the cells of adjacent lines.
Thus, this correction method enables completely
corrected imaging of internal regions of body slices
only if the outer regions of the body slice to be imaged
are also ir~adiated. Furthermor0, if this correction
methodsw~re used, only be the scatter radiation gen0rated
in the body by the primary beam and extending substant~
ially in the plane of the body slice to be imaged should
be measured, because then the corresponding attenuation
coefficients for -the individual pixels of -the layer
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PHD 80.097 3 18.3.1981
image will not be disturbed by any regions exhibiting
strong absorption (bones, gas inclusions etc.) which are
situated outside the body slice to be imaged.
It is an object of the invention to provide a
Compton scatter diagnostic apparatus for the determinat-
ion of the structure of a body which simply enables the
~ormation of improved layer images without using such
a correction method.
This object is achieved in accordance ~ith
the invention in that each detector supplies detector
output signals which are dependent on the energy o~ the
incident radiation and is connected to an electronic
circuit for the ~ormation of scatter detector signals
from the dif~erent primary radiation energies, the
apparatus furthermore comprising an electronic memory for
the storage of reference scatter signals which have been
recorded ~or a known reference body by means of a similar
diagnostic apparatus and in the same manner, said
electronic memory being connec-ted to the electronic pro-
cessing device which is adapted to perform a comparison
of the scatter signals and the re~erence scatter signals
at different radiation energies and to determine the
internal structure of the body from the scatter signals
and the reference scatter signals thus compared.
As has already been stated) the scatter signals
~S) and re~erence scatter signals (V) (radiation intensi-
tie~) measured in a part of the body irradiated by the
primary beam at a radiation energy are dependent on the
electron density in the body region, on the attenuation
of the primary radiation in the body preceding this
body region, and on the attenuation of the scatter
radiation in the body. These three variables are unknown
~uantities. When the scatter signals are compared with
the reference scatter signals previously recorded for
a known reference body, for example, by forming the quo-
tient of the scatter signal and the reference scatter
signal and therefrom the logarithm (1n(S/V~), the three
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PHD 80.097 ~ 18.3.1981
unknown varia'bles can be determined therefrom if the
procedure is performed each time for a body point with
at least three different radiation energies. The corres-
ponding variables for the reference body are known. The
comparison of a scat-ter signal with a reference scatter
signal, however, should always be performed for -the same
radiation energy. This ena'bles a simple determination of,
for exarnple, the electron density distribution in the
body region irradia-ted by the primary beam and hence the
reproduction of, for example, layer images of' the body
if this procedure is executed for a large number of,
~or e~ample, parallel beam paths situated in the plane
of` the slice.
These layer images need no longer be corrected
as regards the attenuation of the primary radiation or
scatter radiation, Notably the reproduction of high-
quality layer images of parts which are situated inside
a body slice is thus also possible, without the nccessi-
ty, i.e. to measure the total cross-section of the body.
Obviously9 layer images of a body which are not situated
in one plane can also be formed.
It is also advantageous that~ for e~ample,
variables such as the sensitivity of the detectors, the
enargy dependency of the multiple scattering in the
bo~y etc. no longer influence the quality of the re-
constructed body slice or body structure. During the
comparison of the scatter signals and the reference
scatter signals these variables cancel one another if
the body and the reference body have been measured by
means of the same scatter diagnostic apparatus and in
the same manner, i~e. if they have been irradiated with
the same primary radiation. The body and the reference
body should resemble one another as much as possible.
In a pref'erred embodiment in accordance with
the invention, the radiation source consists of an X-ray
source or of at least three substances emitting gamma
rays of different energies.
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PHD 80.097 5 18.3.1981
It is thus achieved that the radiation of` at
least three different radiation energies becomes simply
available.
In a further embodiment in accordance with the
invention, the detector device comprises several de-
tectors each time in a row which extends through a de-
tector and parallel to the principal direction of the
slit-shaped aperture.
The scatter radiation each time measured by a
detector on a line (detector row) is then us0d for the
determination of the internal body structure, for
example, the electron density of the bod~ substance at
the corresponding body region which emits the scatter
radiation. Subsequently, the electron densities thus
obtained are averaged. For example, strongly absorbing
body structures between the activated body region and
the detectors can then be localized and taken into
accourlt in that 9 for example, the electron densities
associated with the corresponding detectors are suitably
weighted for the averaging. The reconstruction accuracy
can be improved by such a detector device. The image
quality is additionally improved because a larger
number of the scatter photons emitted by the scatter
centre are measured. Because the ]ine-shaped detector
described in DE 27 13 581 does not have local resolution
in the line direction, it is not suitable for the re-
construction of highly absorbing body struc-tures (bones,
air inclusions~ etc.) which are situated between the
activated body region and the detector device~ so that
these structures cannot be taken into account~ with
the result that the electron density in the activated
body region is not properly reproduced.
The drawing shows embodiments in accordance
with the invention.
Figure 1 is a sectional view of the diagnostic
apparatus in accordance with the invention,
Figure 2 shows a block diagram for the pro-
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PHD 80.0~7 6 18.3.1981
cessing of' the detector output signals of each time
one detector,
Figure 3 is a perspective view of the diagnos-
tic apparatus, and
Figure L~ shows a radiation source device com-
prising three separate radiation sources of dif~erent
radia-tion energies~
Eigure 1 is a sectional view of a diagnostic
apparatus in accordance with the invention. It comprises~
for example, an X-ray source 1 whose polychromatic
radiation is stopped down by means of a diaphragm 2 in
order to form a primary beam 3 of small cross-section
which irradiates a body 5 positioned on a table 4~ The
primary beam 3 follows a primary beam path def`ined by
lS this beam. The scatter radiation 6, 6~ produced in the
region of the body 5 irradiated by the primary beam 3
reaches a detector device 9, 9~ each time via a sli-t
diaphragm 7~ 7~ which is arranged on the opposite sides
of the primary beam 3 and whose slit-shaped apertures
8, 8~ whose width is preferably adjustable extend per-
pendicularly to the primary beam 3. The detector devices
9, 9~ consist of separate detectors 10, 10~ which are
juxtaposed in a straight line which e~tends parallel to
the primary beam 3. The detectors 10, 10l may be~ for
example, strip-shaped and be arranged so that their
principal dimension extends pa~allel to the slit-shaped
apertures 8, 8'. ~or the scanning o~ diff'erent regions
of the body, the body 5 and the diagnostic apparatus are
arranged to be movable with respect to each other.
Each detector of the de-tector devices 9, 9 t
supplies detector signals I(E) which are dependent on
the energy E of the scatter radiation incident thereon.
The energy E o~ the scatter radiation is determiIled f'or
a given energy E of the primary radia-tion and for a given
scatter angle ~ at which the scatter radia-tion is
scattered with respect to the primary beam 3 in accOr-
dance with the generally known Compton equationO The
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PH~ 80.o97 7 18.3.1981
position of the slit diaphragms 7 t 7~ de~ines the
angles e at which the scatter racliation is measured ~or
any point on the primary beam 3. The energy-dependency
o~ the scatter radlation, there~ore, is determined only
by the energy-dependency of the primary radiation.
Figure 2 shows a block diagram for the pro-
cessing of the de-tector output signals. A detector, for
example~ the detector 10, is each time connected to an
electronic circuit 11 which records scatter photons at
only three different energies, that is to say I(E1),
I(E2) and I(E3), on the basis o~ the scatter photons of
di~ferent energy which arrive at the detector 10 and
which are generated on the basis of the polychromatic
X-rays. Scatter signals S(E1), S(E2), S(E3) are then form-
ed from the de-tector output signals each time associated
with one of the scatter radiation energies E1, E2, E3.
To this end, the electronic circuit 11 may comprise,
for examplé, three circuits 12 which ~orm energy windows
and which produce an output signal only if the input
~0 signal ~detector output signal) is within a given range
which corresponds to a predetermined energy range of
th~ scatter radiation. The output signals of the circuits
12 each time associated with an energy range are then
added in order to produce the scatter signals S(E1),
S(E2), S(E3); this operation can also be per~ormed in
the electronic circuit 11.
A scatter signal recorded ~y means of a de-
tector can be represented as follows:
S(El)~ N(E) ~ Yk [exp -~ /u(E1~ l1)dll~ .
[exp - f/u(E1, 12) dl2] (1)
This formule (1) is applicable to all energies E1, E2~
E3 etc. As has already been stated, S(E1) is the intensi-
ty of the scatter radiation with the energy E1, N(E1)
being the intensity of the primary radiation outside the
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PHD 800097 8 18.3.1981
body 5 with the energy E1, d ~(EI)/d Q being the
differential effective cross-section for the scatt~ring
of the primary radiation, ~k being -the electron density
o~ the body 5 in the body point P considered (see Figure
1), the rourth term being the at-tenuation of the primary
beam 3 between the radiation source 1 and the relevan-t
body point P (path l1), the ~ifth term being the
attenuation of the scatter radiation be-tween the body
point P and the detector measuring the scatter radiation
(path 12).
In the case of biological material, for
energies in excess of 100 KeV mainly the scattering con-
tributes to the attenuation coefficient /u (see formule
1), so that i-t can be expressed as follows: ,
/u (E,l) = ~(E) . y(l) (2)
Therein, ~(E) is the overall Klein-Nishina effective
scatter cross-section and ~(l) is the location-dependent
electron density.
After application of the formule (2) to -the
~ormule (1), the scatter signals S(E1), S(E2), S(E3) are
applied to an electronic computer 13 whereto the electro-
nic circuit 11 is electrically connected and which f'orms
part of the electronic processing device 14. ~lso con-
nected to the electronic computer 13 is an electronic
memory 15 which stores re~erence scatter signals V(E1) 9
V(E2), V(E3) which corr0spond to the scatter signals
S(E1), S(E2), S(E3) and which have bcen recorded under
the same circumstances as the latter signals, that is
to say with the same radiation energies E1, E2, E3, for
a known reference body which corresponds to the body to
be examined and by means o~ the same diagnostic apparatus.
The reference body (not shown) may be, for example, a
water phantom.
The comparison between scatter signals and
reference scatter signals in the computer 13 is executed
so that each time for an energy E1, E2~ E3 the quotient
S(E1)/V(El2) etc. of a scatter signal and a re~erence
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PHD 80.097 9 18.3.1981
scatter signal is formed and the logarithm -thereof is
formed. Thus, a set of three formules with three un-
knowns is obtained. The formule for the scatter radiation
having the energy E1 is as follows:
ln ~ = ln ~ - ~(E1)~fk(11) - ~V(11)~ dl1 - ~(E1)~
[~k(l2) yv(12)~cl12 (3)
Similar formules apply to E2 and E3. The index k denotes
the body 5 to be examined, ~hilst the index ~ denotes
reference bodyG
From the set of formules 3 (formules ~or El~ E2,
E3) the elec-tron clensity ~k can thus be determined each
time for a body point P irradia-ted by the primary beam 3.
'~he electron densities y~ (11) and ~V(12) of the reference
body on the path 11 of the primary beam and the path 12
of the scatter radiation, respectively, are known, so
also the Klein-Nishina effecti~e scatter cross-sections
~(E1), ~(E1) (similar for the energies E29 E3). As has
already been stated, the energy of the scatter radiation
E1 can be calculated from the energy E1 of the primary
radiation via the Compton ~ormule. Obviously, photons
can also be detected at more than three radiation energies.
The electronic circuit 11 would re~uire only more cir-
cuits 12 (or additional channels of a multiple channel)
for this purpose. 'rhe set of` ~ormules thus obtained would
subsequently be suitably minimized.
A detector 10, 101 is thus each time connected
to an electronic circuit 11, only one o~ which is shown
in Figure 2, all said circuits 11 being connected to the
same computer 13. The memory 15 also contains the refer~
en¢e scatter signals f`or all points on the primary beam
3 passing through the reference body. The electron densi-
ties ~k determined by the computer 13, or the ~ariablesderi~ed therefrom, can be displayed on a moni-tor 16 or
be stored in a bulk memory 17 (magnetic tape~ memory disk
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PHD 80.097 10 18.3~1981
or similar).
Figure 3 is a perspec-tive view of the scatter
diagnostic apparatus in accordance with the invention.
The slit diaphragm 7 has an elonga-te slit-shaped aper-
ture 8 9 90 -that a scatter radiation beam 6 having a very
large angle o~ aperture ~ which starts from the body
point P is activated by the primary radiation beam 3.
The scatter radiation beam 6 reaches a detector row which
consists of separte detectors 10a, b etc~ which are
situated in a row which extends parallel to the slit-
shaped aperture 8 which ex-tends perpendicularly to the
primary beam 3. In an extreme case, -the complete detec-
tor device 9 or the slit diaphragm 7 can alternatively
completely enclose the primary beam, for example, in a
lS cylindrical manner, so tha-t the primary beam 3 extends
along the cylinder axis. ~ach ~eparatedetector of the de-
tector device 9 (shaped as a cylinder or a two-dimensional
detector matrix) is then connected to its own electronic
circuit 11 (not shown~ via the connec-tions a-d~ etc. ~
variable, f`or example 9 the electron density k which cha-
racterizes the internal structure of the body 5 can then
each time be derived by means of a detector of the de-
tector device. The electron densities of each detector
row then relate to the same body point P. An improved
electron density at the body point P can be determined
from these densitiesa for e~ample~ ~y weighted
av0raging .
Ob~iously, the detectors 10a, b etc. o~ a de-
tector row can also be replaced by a single, rod-shaped
detector which has a local resolution in the direction
of the row, so that the scatter radiation intensity can
be measured for different row sections (see Figure 2).
For this purpose~ use can be made of, for example~ rod-
shaped scintillators comprising pho-tomul-tipliers which
are arranged at the ends o~ the rod, the outpu-t signals
of said photomultipliers being processed in accordance
with the Anger camera principle. The longitudinal direct-
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PHD 80-097 11 18.3.1981
ion of the rod should be parallel to the slit-shaped
aperture 8 or perpendicular to the primary beam 3c
A ~urther radiation source 1~ for -the emission
o~ primary radiation with at least three dif~erent
radiation energies is shown in ~igure 4. The radiation
source 1~ comprises three radiation sources 18a-c which
emit gamma rays, ~or example, one o~ 137Cs (o.66 Me~),
203Hg (0-28 MeV) and 57~o(0.12 ~e~). The three separate
radiations sources 18a-c are situated, for example,
inside a rotating disk 19 which has a radial duct 20 to
the radiation exit ~or each separate radiation source.
The disk 19 rotates about a sha~t 21 at the correct
angular velocity, so that the separate radiation sources
18a-c are successively positioned in ~ront of an exit
opening 22 o~ a housing 23 which shields the radiation.
The primary radiation beam 24 each time passing through
the exit aperture 22 is collimated by means of a
diaphragm 25. The electronic circuit 11 then comprises
three circuits 12 which ~orm energy windows, ~or example,
pulse amplitude analyzers, which are adapted to the
radiation energies o~ the separate radiation sources
18a-c.
Ob~iously, the separate radiation sources
18a-c can also be arranged or displaced with respect to
the radiation exit aperture in another manner, ~or
example, linearly. For the ~urther radiation source use
can alternatlvely be made o~ a mixture o~ said three
su~stances emitting gamma rays, said mixture being
arranged in the rotating disk 19 at the area o~ one o~
the radiation sources 18a-c.
