Gamma camera system with composite solid state detector

A composite solid-state detector for utilization within gamma cameras and the like. The detector's formed of an array of detector crystals, the opposed surfaces of each of which are formed incorporating an impedance-derived configuration for determining one coordinate of the location of discrete impinging photons upon the detector. A combined read-out for all detectors within the composite array thereof is achieved through a row and column interconnection of the impedance configurations. Utilizing the noted read-outs for respective sides of the discrete crystals, a resultant time-constant characteristic for the composite detector crystal array remains essentially that of individual crystal detectors.

BACKGROUND 
The field of nuclear medicine has long been concerned with techniques of 
diagnosis wherein radio pharmaceuticals are introduced into a patient and 
the resultant distribution or concentration thereof as evidenced by gamma 
ray intensities is observed or tracked by an appropriate system of 
detection. An important advantage of the diagnostic procedure is that it 
permits non-invasive investigation of a variety of conditions of medical 
interest. Approaches to this investigative technique have evolved from 
early pioneer procedures wherein a hand-held radiation counter was 
utilized to map body contained areas of radioactivity, to more current 
systems for imaging gamma ray source distributions, in vivo utilizing 
stationary cameras with broadened fields of view. In initially introduced 
practical systems, scanning methods were provided for generating images, 
such techniques generally utilizing a scintillation-type gamma ray 
detector equipped with a focusing collimator which moved continuously in 
selected coordinate directions, as in a series of parallel sweeps, to scan 
regions of interest. A drawback to the scanning technique resides in the 
necessarily longer exposure times required for the derivation of an image. 
For instance, such time elements involved in image development generally 
are overly lengthy to carry out dynamic studies of organ function. 
By comparison to the rectilinear scanner described above, the later 
developed "gamma camera" is a stationary arrangement wherein an entire 
region of interest is imaged at once. As initially introduced, the 
stationary camera systems generally utilized a larger diameter sodium 
Iodide, Na I (TI) crystal as a detector in combination with a matrix of 
photomultiplier tubes. For additional information concerning such a 
camera, see: 
I. anger, H.O., "A New Instrument For Mapping Gamma Ray Emitters", Biology 
and Medicine Quarterly Report UCRL-- 3653, 1957. 
A multiple channel collimator is interposed intermediate the source 
containing subject of investigation and the scintillation detector 
crystal. When a gamma ray emanating from the region of investigative 
interest interacts with the crystal, a scintillation is produced 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 emanation is determined by 
position responsive networks associated with the outputs of the matrix. 
A continually sought goal in the performance of gamma cameras is that of 
achieving a high resolution quality in any resultant image. Particularly, 
it is desirable to achieve this resolution in combination with concomitant 
utilization of a highly versatile radionuclide or radiolabel, such as 
99m-Technetium, having a gamma ray or photon energy in the region of 140 
keV. 
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 radiation witnessed emanating from within 
the in vivo region of investigation. Concerning the latter scattering 
phenomena, a degradation or resolution occurs from scattered photons which 
are recorded in the image of interest. Such photons may derived from 
Compton scattering into trajectories wherein they are caused to pass 
through the camera collimator and interact photoelectrically with the 
crystal detector at positions other than their point of in vivo 
derivation. Should such photon energy loss to the Compton interaction be 
less than the energy resolution of the system, it will effect an off-axis 
recordation in the image of the system as a photopeak photon representing 
false information. As such scattered photons record photopeak events, the 
false information and consequent resoltuion quality of the camera 
diminishes. For the noted desirable 140 keV photons, the scintillation 
detector-type camera energy resolution is approximately 22 keV. With this 
resolution, photons which scatter through an angle from 0.degree. to about 
70.degree., which pass through the collimator, will be seen by the system 
as such photopeak events. 
A continuing interest in improving the resolution qualities of gamma 
cameras has lead to somewhat extensive investigation into imaging systems 
incorporating relatively large area solid-state 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 image quality. In this 
regard, for example, reference may be made to the following publications: 
Ii. r. n. beck, L. T. Zimmer, D. B. Charleston, P. B. Hoffer, and N. 
Lembares, "The Theoretical Advantages of Eliminating Scatter in Imaging 
Systems," Semiconductor Detectors in Nuclear Medicine, (P. B. Hoffer, R. 
N. Beck, and A. Gottschalk, editors), Society of Nuclear Medicine, New 
York, 1971, pp. 92-113. 
Iii. r. n. beck, M. W. Schuh, T. D. Cohen, and N. Lembares, "Effects of 
Scattered Radiation on Scintillation Detector Response", "Medical 
Radioisotope Scintigraphy", IAEA, Vienna, 1969, Vol. 1, pp. 595-616. 
Iv a. b. brill, J. A. Patton, and R. J. Baglan, "An Experimental Comparison 
of Scintillation and Semiconductor Detectors for Isotope Imaging and 
Counting", IEEE Trans. Nuc. Sci., Vol. NS-19, No. 3, pp. 179-190, 1972. 
V. m. m. dresser, G. F. Knoll, "Results of Scatting in Radioisotope 
Imaging", IEEE Trans. Nuc. Sci., Vol. NS-20, No. 1, pp. 266-270, 1973. 
Particular interest on a part of investigators has been paid to detectors 
formed as hybridized diode structures fashioned basically of germanium. To 
provide discrete regions for spatial resolution of impinging radiation, 
the opposed parallel surfaces of the detector diodes may be grooved or 
similarly configured to define transversely disposed rows and columns, 
thereby providing identifiable discrete regions of radiation response. 
Concerning such approaches to treating the detectors, mention may be made 
of the following publications: 
Vi. j. detko, "Semiconductor Diode Matrix for Isotope Localization", Phys. 
Med. Biol., Vol. 14, No. 2, pp. 245-253, 1969. 
Vii. j. f. detko, "A Prototype, Ultra Pure Germanium Orthogonal Strip Gamma 
Camera", Proceedings of the IAEA Symposium on Radioisotope 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. 
Ix. v. r. mcCready, R. P. Parker, E. M. Gunnerson, R. Ellis, E. Moss, W. G. 
Gore, and J. Bell, "Clinical Tests on a Prototype Semiconductor 
Gamma-Camera", British Journal of Radiology, Vol. 44 58-62, 1971. 
X. parker, R. P., E. M. Gunnerson, J. S. Wankling, R. Ellis, "A 
Semiconductor Gamma Camera with Quantitative Output", Medical Radioisotope 
Scintigraphy, Vol. 1, IAEA, 1969, p. 71. 
Xi. detko, J. F., "A Prototype, Ultra-Pure Germanium, orthogonal-Strip 
Gamma Camera", Medical Radioisotope Scintigraphy, Vol. 1, Vienna, IAEA, 
1973, p. 241. 
Xii. schlosser, P. A., D. W. Miller, M. S. Gerber, R. F. Redmond, J. W. 
Harpster, W. J. Collis, W. W. 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. 
Xiii. owen, R. B., M. L. Awock, "One and Two Dimensional Position Sensing 
Semiconductor Dectectors," IEEE Trans. Nucl. Sci., Vol. NS-15, June 1968, 
p. 290. 
In the more recent past, investigators have shown particular interest in 
forming orthogonal strip matrix detectors from p-i-n semiconductors 
fashioned from an ultra pure germanium material. In this regard, reference 
is made to U.S. Pat. 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 Symposium on Radioisotope 
Scintigraphy, IAEA/SM-164/135, Monte Carlo, October, 1972. 
Xv. schlosser, P. A., D. W. Miller, M. S. Gerber, R. F. Redmond, J. W. 
Harpster, W. J. Collis, 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 advantages in gamma camera 
resolution and consequent diagnostic flexibility. For instance, by 
utilizing high purity germanium as a detector, lithium drifting 
arrangements and the like for reducing impurity concentrations are avoided 
and the detector need only be cooled to requisite low temperatures during 
its clinical operation. Readout from the orthogonal strip germanium 
detectors is described as being carried out utilizing a number of 
techniques, for instance, each strip of the detector may be connected to a 
preamplifier-amplifier channel and thence directed to an appropriate logic 
function and visual readout. In another arrangement, a delay line readout 
system is suggested with the intent of reducing the number of 
preamplifier-amplifier channels, and a technique of particular interest 
utilizes a charge splitting method. With this method or technique, 
position sensitivity is obtained by connecting each contact strip of the 
detector to a charge dividing impedance network. Each end of each network 
is connected to a virtual earth, charge sensitive preamplifier. When a 
gamma ray interacts with the detector, the charge release enters the 
string of resistors or area of impedance and divides in relation to the 
amount of resistance between its entry point in the string and the 
preamplifiers at the network output. Utilizing fewer preamplifiers, the 
cost and complexity of such systems is advantageously reduced. A more 
detailed description of this readout arrangement is provided in: 
Xvi. gerber, M. S., Miller, D. N., Gillespie, B., and Chemistruck, R. S., 
"Instrumentation For a High Purity Germanium Position Sensing Gamma Ray 
Detector," IEEE Trans. on Nucl. Sci., Vol. NS-22, No. 1, February, 1975, 
p. 416. 
To achieve requisite performance and camera image resolution, it is 
neceassary that substantially all sources of noise be minimized and that 
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 impracticality. Until the more recent past, 
charge-splitting germanium detector arrangements have not been considered 
to be useful in gamma camera applications in consequence of thermal noise 
anticipated in the above-noted resistor-divider networks, see publication 
VII, supra. However, such noise centered considerations now are 
accommodated for within camera system designs. In this regard, reference 
is made to copending application for U.S. patent, Ser. No. 656,304 by P. 
A. Schlosser et al, filed Feb. 9, 1976, entitled "Gamma Ray Camera for 
Nuclear Medicine": and application Ser. No. 680,754 by O. Miller et al. 
entitled "Control System for Gamma Camera" filed Apr. 7, 1976, both 
applications being assigned in common herewith. 
Another aspect in the optimization of resolution of the images of gamma 
cameras resides in the necessarily inverse relationship between resolution 
and sensitivity. A variety of investigations has 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 spacial resolution Further, it has been pointed out that the decrease 
in sensitivity witnessed in conventional high resolution collimators may 
cancel out any improvements sought to be gained in image resolution. A 
more detailed discourse concerning these aspects of design are provided, 
for instance, in the following publications: 
Xvii. e. l. keller and J. W. Coltman, "Modulation Transfer and 
Scintillation Limitations in Gamma Ray Imaging," J. Nucl. Med. 9, 10, 
537-545 (1968). 
Xviii. b. westerman, R. R. Sharma, and J. F. Fowler, "Relative Importance 
of Resolution and Sensitivity in Tumor Detection," J. Nucl. Med. 9, 12, 
638-640 (1968). 
More recent investigation of gamma camera performance has identified still 
another operational phenomenum tending to derogate from spatial resolution 
quality. This phenomenon is referred to as "aliasing" and represents a 
natural outgrowth of the geometry of the earlier noted orthogonal strip 
germanium detector. A more detailed discussion of the phenomena is 
provided at: 
Xix. j. w. steidley, et al., "The Spatial Frequency Response of Orthogonal 
Strip Detectors, " IEEE Trans. Nuc. Sci., February, 1976. 
To remain practical, it is necessary that the imaging geometry of 
stationary type gamma cameras provide for as large a field of view as is 
practical. More particularly, considerations of clinical practicality 
require a camera field of view large enough to encompass the entire or a 
signifacant extent of the profiles of various organs of interest. Because 
of the considerable limitations encountered in the manufacture of detector 
crystals, for instance, high purity germanium crystals, the size of solid 
state detector components components necessarily is limited. As a 
consequence, composite detector configurations 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 a union of a multitude of detector components must be carried out in 
such a manner that no significant loss of validity and acuity in the final 
image generated by the camera system. For instance, in the latter regard, 
spatial information must have a consistency of meaning across the entire 
extend of an ultimately displayed image of an organ, otherwise, clinical 
evaluation of such images may be encumbered considerally. 
SUMMARY 
The present invention is addressed to an improved gamma camera system and 
detector arrangement related thereto. Advantageously utilizing solid state 
detector components, a composite geometry for a camera detector unit is 
evolved to permit the fabrication of gamma cameras having fields of view 
suited for practical clinical applications. 
While being characterized as a composite assembly of solid state detector 
components fabricable commensurately with the current state of the art, 
the overall detector arrangement advantageously permits informational 
signal readout under conditions wherein the time constant characteristic 
for the detector function remain at advantageously optimum values. 
Another feature and object of the invention is to provide a gamma camera 
system including a composite solid state detector for use in the 
idenfication of the distribution of radiation eminating from a source 
containing region of interest which comprises a plurality of adjacently 
disposed solid-state detector components. Formed, for instance. of 
germanium or the like each of the adjacently disposed detector components 
is configured having a surface arranged for exposure for impinging 
radiation and exhibits discrete interactions therewith at given spatially 
definable locations. That surface of the detector component and the 
surface disposed opposite thereto and parallel therewith are associated 
with an impedance readout arrangement which provides for impedances 
defined output signals relating the location of the noted interaction with 
at least one spatial coordinate parameter of a selected directional sense 
within the array of discrete detector components. Further, the detector 
components are arranged to exhibit rows and columns of the noted 
interaction with at least one spatial coordinate parameter of all of the 
surfaces within such row or column are mutually parallel in alignment. The 
composite detector further incorporates means interconnecting at least two 
of the outputs of such surfaces within a given row or column for 
collecting the impedance defined signals or charges as are derived 
therefrom. Preferably, the collection of this information is made in a 
parallel circuit scheme to provide a minimization of the effective 
capacitance of the entire detector assembly. 
As another object and aspect of the invention, the opposed surfaces of a 
discrete detector component within a composite detector are configured to 
define arrays of mutually parallel strips each of these strips having a 
discrete area of influence over the occurrence of an interaction of the 
detector with impinging radiation. The impedance-type charge treating 
arrangement for each of these surfaces is present as an impedance network, 
for instance a chain of discrete resistor elements associated along the 
extent of the strip array. The output of this chain is coupled in parallel 
circuit relationship with a next adjacent surface impedance network within 
a row or column alignment of the detector, this row or column being 
aligned in the spatial coordinate directional sense predesignated 
therefore. In a preferred embodiment, the opposed surfaces of the discrete 
detector components within a composite detector assembly are arranged to 
record spatial information in a mutually orthogonally disposed coordinate 
sense. 
Another aspect and object of the invention is to provide a composite 
detector assembly incorporating individual detector components, the 
surfaces of which are formed incorporating a readout impedance system 
present as a layer or surface region of predetermined resistance and 
disposed between two contact readout strips. Such region provides an 
impedance structure wherein a proportionality of charge distribution 
between the contact strips is examined by circuit readout arrangements to 
derive coordinate-labeled signals representing spatial information for a 
gamma camera imaging system. To assure appropriate image integrity between 
that subject of clinical interest imaged by the detector structure and the 
ultimate gamma camera system readout, the areas of the discrete detector 
components within a composite detector as they are intended to recieve 
radiation impinging from the subject, are formed having equivalent surface 
areas. As a consequence, no significant distortion in the image ultimately 
perceived by the system operator is generated. 
Another object of the invention is to provide a composite solid state 
detector formed of discrete detector components each of which is formed 
having discrete adjacent parallel and substantially mutually electrically 
isolated strip regions both upon the surface intended to receive impinging 
radiations and the surface opposite thereto. These groupings of parallel 
strip regions are mutually orthogonally disposed with respect to each 
other with each side of a component and the components are arranged in 
mutual adjacency so that the strip regions of a given component surface 
are alligned in parallel with those regions of an adjacent component to 
define groupings described herein as "rows and columns". In one 
embodiment, the adjacent strip regions are correspondingly adjacent 
component surfaces are electrically interconnected in series relationship 
and such serially connected strip regions are provided discrete outputs 
for each grouping. Impedance means and, preferably in the form of a charge 
splitting resistor chain is associated with the outputs of each grouping 
to provide impedance defined signals which relate the location of an 
interaction of impinging radiation with the coordinate direction of the 
appropriately influenced strip region and the relative position of the 
interconnected strip region within a grouping. 
Other objects of the invention will, in part, be obvious and will, in part, 
appear hereinafter. 
The invention, accordingly, comprises the system and apparatus possessing 
the construction, combination of elements and arrangement of parts which 
are exemplified by the following detailed disclosure. 
For a fuller understanding of the nature and objects of the invention, 
reference should be had to the following detailed description taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION 
As indicated in the foregoing discourse, during contemplated clinical 
utilization, a gamma camera arrangement according to the instant invention 
is used to image gamma radiation eminating from a region of 
radiopharmaceutical source distribution within a patient. Looking to FIG. 
1, an exaggerated schematic representation of such a clinical environment 
is revealed generally at 10. The environment 10 schematically shows the 
cranial region 12 of a patient to whom has been administered a 
radiolabeled pharmaceutical, which pharmaceutical will have tended to 
concentrate within a region of investigative interest. Accordingly, 
radiation is depicted as eminating from this region 12 as the patient is 
positioned beneath the head or housing 16 of a gamma camera. Housing 16 is 
pivotally supported at 18 from a beam 20. Beam 20, carrying a 
counter-weight 22, is pivotally supported at 24 in dual axis gimbal 
fashion from an upstanding support 26. Support 26 is fixedly attached to 
and extends from a base member 28. As is represented only in dotted line 
and generalized fashion, the head 16 is configured to retain an ultra-pure 
germanium orthogonal strip type semi-conductor detector 30 as well as 
resistor-divider networks tapping the detector and preamplification stages 
(not shown in FIG. 1) within a vacuum chamber 32. Chamber 32 is retained 
at a predetermined low temperature, for instance 77.degree. K by an 
appropriate cryogenic system during operation of the head 16 to provide 
one aspect of necessary detector and electrode noise diminuation. Adjacent 
to the detector 30 and disposed intermediate the detector and the 
patient-retained source of radiation 12, is a multi-channel collimator 33, 
the design and structure of which is described in detail in the 
above-referenced application for U.S. patent Ser. No. 656,304. 
During the operation of the gamma camera, radiation emunating from source 
12 is spatially coded initially at collimator 33 by attenuating or 
rejecting off-axis radiation representing false image information. That 
radiation passing collimator 33 impinges upon detector 30 and a 
significant portion thereof is converted to discrete charges or image 
signals. Detector 30 is so configured as to distribute these signals to 
resistor chains as well as select preamplification stages retained within 
chamber 32 to provide initial signals representative of image spatial 
infromation along conventional coordinate axes as well as representing 
values for radiation energy levels. This data then is introduced, as 
represented schematically by line 34, to filtering and logic circuitry 
which operates thereupon to derive an image of optimized resolution and 
veracity. In the latter regard, for instance, it is desired that only true 
image information be elicited from the organ being imaged. Ideally, such 
information should approach the theoretical imaging accuracy of the camera 
system as derived, for instance, from the geometry of the detector 
structure 30 and collimator arrangement 33 as well as the limitations of 
the electronic filtering and control of the system. Instrumentation for 
achieving the latter function is described, for instance, in detail and 
the following publication which is incorporated herein by reference: 
Xx. gerber, M. S., Miller, D. W., Gillespie, B., and Chemistruck, R. S., 
"Instrumentation for a High Purity Germanium Position Sensing Gamma Ray 
Detector," IEEE Trans. on Nucl. Sci., Vol. NS-22, No. 1, February 1975, p. 
416. 
Image spatial and energy level signals from line 34 initially, are 
introduced into Anti-Symmetric Summation and Energy Level Derivation 
represented at block 36. As is described in more detail later herein, the 
summation carried out at block 36 operates upon the charges directed into 
the resistive chains or networks associated with the orthogonal logic 
structuring of detector 30 to derive discrete signals or charge values 
corresponding with image element location. Additionally, circuitry of the 
function of block 36 derives a corresponding signal representing the 
energy levels of the spatial information. The output of block 36 is 
directed to Filtering Amplification and Energy Discrimination functions as 
are represented at block 38. Controlled from a Logic Control function 
shown at block 40, function 38 operates upon the signal input thereto to 
accommodate the system to parallel and serially defined noise components 
through the use of Gaussian amplification or shaping, including 
trapezoidal pulse shaping of data representing the spatial location of 
image signals. Other methods, such as delay line filtering, of course, may 
provice this function. Similarly, the energy levels of incoming signals 
are evaluated, for instance, utilizing single channel analyzer components 
controlled by logic 40 to establish an energy level window for data 
received within the system. In this regard, signals evaluated, for 
instance, utilizing single channel analyzer components controlled by logic 
40 to establish an energy level window for data received within the 
system. In this regard, signals falling above and below predetermined 
energy levels are considered false and are blocked. From Amplification and 
Discrimination stage 38 and Logic Control 40, the analyzed signals are 
directed into an Information Display and Readout Function, as is 
represented at block 42. Components within function block 42 will include 
display screens of various configurations, image recording devices, for 
instance, photographic apparatus of the instant developing variety, 
radiation readout devices and the like, which are controlled at the option 
of the system operator. 
Looking to FIG. 2, an exaggerated pictorial representation of a portion of 
a single component detector 30 is revealed. Such gamma ray detectors are, 
in essence, a body of exceedingly high purity material as, for example, 
germanium, wherein a thick depletion region may be established by a high 
reserve bias so as to be sensitive to the impingement of ionizing 
radiation. Basically, such devices include, for example, a body of 
germanium having a relatively thick intrinsic, or near intrinisic, region 
with a donor or n+ surface-adjacent region on one major surface thereof 
and an acceptor or p+ region on the opposite major surface thereof. 
Accordingly, as shown in FIG. 2, a high purity gemanium region of such 
crystal, as at 42, serves as an intrinsic region between p-type 
semiconductor region contacts 44 and n-type semiconductor region contacts 
as at 46. The intrinsic region 42 of the p-i-n detector forms a region 
which is deplected of electrons and holes when a reverse bias is applied 
to the contacts. It should be understood that the detector component 
representation of FIG. 2 is idealized and simplified in the interest of 
facilitating the description thereof. As noted earlier, to achieve 
practical detector structures, a plurality of detector components are 
required which are so associated as to permit the generation of spatial 
image data which is accurate and reliable. In the embodiement shown, 
grooves as at 48a-48c are cut into the continuous p+-type region at one 
face of the detector to form strips of isolated p-type semiconductor 
material. On the opposite face of the detector, orthogonally disposed 
n-type semiconductor strips similarly are formed through the provision of 
grooves 50a - 50c. Configured having this geometry, the detector 30 
generally is referred to as an orthogonal strip detector or an orthogonal 
strip array semiconductor detector. The electrode strips about each of the 
opposed surfaces of detector 30 of FIG. 1, respectively, are connected to 
external charge splitting impedance networks revealed generally at 52 and 
54. Impedance network 52 is formed of serially coupled resistors 56a - 56e 
which, respectively, are tapped at their mutual interconnections by leads 
identified, respectively, at 58a - 58d extending, in turn, to the parallel 
strips. The opposed ends of network 52 terminate in preamplification 
stages 60 and 62, the respective outputs of which, at 64 and 66, provide 
spatial output data for insertion within the above-described Summation and 
Energy Level Derivation function 36 of FIG. 1 to provide one orthogonal or 
coordinate output, for instance, designated as a y-axis signal. 
In similar fashion, impedance network 54 is comprised of a string of 
serially coupled resistors 68a-68e, the mutual interconnections of which 
are coupled with the electrode strips at surface 46, respectively, by 
leads 70a-70d. Additionally, preamplification stages as at 72 and 74 
provide outputs, respectively, at lines 76 and 78 carrying spatial data or 
signals representative of image information along an x-axis or axis 
orthogonally disposed with respect to the output of network 52. 
With the assertion of an appropriate bias over detector component 30, an 
imaging photon absorbed therewithin engenders ionization which, in turn, 
creates electron-hole pairs. The charge thusly produced is collected on 
the orthogonally disposed electrode strips by the bias voltage and such 
charge flows to the corresponding node of the resistor networks 52 and 54. 
Further, this charge divides in relation to the admittance of each path to 
the virtual ground input of the appropriate terminally disposed 
preamplification stage. Note that the distribution of charge across each 
of the impedance networks is one of proportionality, depending upon the 
position of interaction of a given photon with the crossing intersections 
of appropriate detector strips. While this proportion essentially remains 
constant for any given detector-impedance network structure, the value 
thereof may vary in accordance with the capacitance exhibited by the 
detector as well as the parameters of the impedance network associated 
therewith. Spatial informational signal outputs from such detectors also 
may be affected by the earlier noted aliasing phenomena wherein 
informational dysfunctions are evolved by virtue of the geometric 
relationship between the entrance channels of collimator 33 and the 
surface of the detector with which it is associated. Such phenomena, 
particularly, may be witnessed where a grooving technique, as illustrated 
in FIG. 2, is utilized to designate the discrete strips formed within the 
detector. The charge sensitive preamplification stage integrates the 
collected charge (a spatial determined percentage of the total charge 
directed to the network) to form a voltage pulse proportional to that 
charge value. Assigning charge value disignations Q.sub.1 and Q.sub.2, 
respectively, for the output line 64 and 66 of network 52, the above-noted 
Summation and Energy Level Derivation functions for spatial and energy 
data may be designated. In this regard, energy information is derived from 
the sum of the signals Q.sub.1 and Q.sub.2 or signals Q.sub.3 and Q.sub.4. 
This determines the total charge collected on one set of strips which is 
proportional to the energy of the photon detector interaction. 
Antisymmetrical summation is utilized to generate spatial information 
through subtractive logic. For example, the x-channel spatial signal is 
obtained by subtracting Q.sub.1 from Q.sub.2, and x-channel signal of zero 
volts corresponding to an interaction which occurred below the middle 
electrode strips. Similarly, the y-channel spatial signal is obtained by 
subtracting Q.sub.3 from Q.sub.4. The spatial channels of the imaging 
system use Gaussian-trapezoidal pulse shaping amplifiers, while the energy 
chan operating in conjunction with the Logic Control energy discrimination 
function described in connection with block 40, utilizes Gaussian pulse 
shaping and additive summing in carrying out requisite imaging control. As 
noted above, the operational environment of the detector 30 as well as the 
charge splitting resistor networks 52 and 54 is one within the cryogenic 
region of temperature for purposes of reducing Johnson noise phenomena 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 more or less typical 
characteristecs of that impinging radiation. For instance, looking to FIG. 
3, a portion of a patient's body under investigation is portrayed 
schematically at 90. Within this region 90 is shown a radioactively tagged 
region of interest 92, from which region the decay of radiotracer releases 
photons which penetrate and emit from the patient's body. These photons 
then are spatially selected by the collimator 33 and individually detected 
at detector 30 for ultimate participation in the evolution of an image 
display. The exemplary paths of seven such photons are diagrammed in the 
figure, as at a-g, for purposes of illustrating functions which the camera 
system is called upon to carry out. In this regard, the function of 
collimator 35 is to accept those photons which are traveling nearly 
perpendicular to the detector, inasmuch as such eminating rays provide 
true spatial image information. These photons are revealed at ray traces a 
and b, showing direct entry through the collimator 33 and appropriate 
interaction coupled with energy exchange within detector 30. 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 information which should be attenuated, as schematically 
portrayed. Scattering phenomena within collimator 33 itself or the 
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 redirect the path direction such that the 
acceptance geometry of the camera, including collimator 33, permits the 
photon to be accepted as image information. Inasmuch as the detector 30 
and its related electronics measure both the spatial location and energy 
of each photon admitted by the collimator, the imaging system still may 
reject such false information. For example, in the event of a Compton 
scattering of a photon either in the patient or collimator, the energy 
thereof may have been reduced sufficiently to be rejected by the energy 
discrimination window of the system. Photon path, g, represents a 
condition wherein detector 30 exhibits inefficient absorption 
characteristics such that that incident photon path, while representing 
true information, does not achieve a state of interaction with the 
detector. As is apparent from the foregoing, each of the thousands of full 
energy photons which are absorbed at detector 30 ultimately are displayed 
at their corresponding spatial location on an imaging device such as a 
cathode ray tube to form an image of the source distribution within region 
92 of the patient. 
Now considering the practical clinical aspects of such imaging, as noted 
earlier, it is necessary that the detector function of the gamma camera be 
capable of recording the imagewise distribution of a radiopharmaceutical 
as it extends over a region of practical extent, for instance, an active 
organ. Consequently, it is necessary that the detector function of the 
gamma camera be of size sufficient to accept photon information from as 
broad region as is possible. Inasmuch as the size of detector crystals 
inherently is limited by the techniques of its fabrication, it becomes 
necessary to conjoin a plurality of such crystal detectors in some manner 
wherein a broader region of radiation may be witnessed. More particularly, 
it currently is understood that the largest square shape detector that can 
be cut from available high purity germanium crystals or the like is one of 
about 3.7 centimeters per square side. 
Referring now to FIG. 4, a composite detector formed as an array discrete 
detector components is revealed generally at 80. Illustrated in exploded 
fashion, the detector 80 is comprised of a plurality of detectors, four of 
which are shown at 82, 84, 86, and 88. Detectors 82 - 88 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 
of image information, would result. The detector components illustrated 
are of the earlier-described orthogonal strip array variety, each strip 
thereof being defined by grooves. Note, in the regard, that detector 
component 82 is formed having strips 90a - 90d located at its upward 
surface and defined by grooves cut intermediate adjoining ones of said 
strips. The opposite face of detector component 82 similarly is formed 
having strips 92a - 90d defined by intermediately disposed grooves 
arranged orthogonally with respect to the grooves at the upper surface. 
Detector component 84 is identically fashioned having strips 94a-90d at 
its upwardly disposed surface and lower surface, orthogonally disposed 
strips 96a - 96d each strip being defined by intermediately formed 
grooves. Similarly, detector component 86 is formed having strips 98a - 
98d at its upward surface defined by intermediately disposed grooves, 
while its lower surface similarly is formed having strips 100a - 100d 
defined by intermediately disposed grooves arranged orthogonally with 
respect to the grooves of the upward surface. Detector component 88 may be 
observed having strips 102a - 102d at its upward surface defined by 
intermediately designated grooves, while its lower surface is formed with 
strips 104a - 104d separated by intermediately disposed grooves arranged 
orthogonally to the grooves of the upward surface of the component. 
Detector components 82 - 88 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 equivalent to that output which 
would be realized from a large detector of equivalent size, the strip 
arrays are functionally associated under a geometry which may be 
designated "row" and "column" in nature. In this regard, note that an 
impedance network, shown generally at 107, is associated with the strips 
94a - 94d of detector component 84. This network incorporates discrete 
resistors 106a - 106e which are tapped at their common junctions by leads 
108a - 108d extending, respectively, to strips 94a - 94d. Thus configures, 
network 107 closely resembles the impedance networks described herein in 
connection with FIG. 2. Note however, that output lines 110 and 112 of 
network 106 extend to and are coupled in parallel circuit relationship 
with the corresponding output of similar impedance network, identified 
generally at 114. Network 114 incorporates discrete resistors 116a - 116e 
which are tapped at their common interconnections by leads 118a - 118d. 
Leads 118a-118d, in turn respectively extend to strips 90a - 90d of 
detector component 82. Accordingly, the upwardly disposed surfaces of 
detector components 82 and 84 are identically associated with respective 
impedance networks 114 and 107, while the latter are interconnected in row 
fashion and in parallel circuit relationship to extend to principal output 
terminals, as are depicted generally at 120 and 122. It may be noted, that 
the information collected at these principal terminals represents one 
imaging spatial coordinate parameter of a select directional sense i.e. 
along a designated row. 
Looking now to the functional interrelationship of detector components 86 
and 88, a similar coordinate parameter direction or row-type informational 
collection network is revealed. In this regard, note that the impedance 
network, shown generally at 124, is configured comprising discrete 
resistors 126a - 126e, the points of common interconnection of which are 
coupled with respective leads 128a - 128d. Leads 128a - 128d, in turn, 
respectively, are connected with strips 98a - 98d at the upwardly disposed 
surface of detector component 86. Likewise, an impedance network, shown 
generally at 130 incorporating discrete resistors 132a - 132e, is 
associated with detector component 88 by leads 134a - 134d extending, 
respectively, from strips 102a - 102d to the points of common 
interconnection of the network discrete resistors 132a - 132e. 
Additionally, the output lines as at 136 and 138 of network 130 are 
connected in parallel circuit relationship with the output of network 124 
to provide row readout termini, respectively, at 140 and 142. Here again, 
a row-type directional spatial coordinate parameter is provided at the 
upwardly disposed surface of the composite detector 80. 
Looking now to the lower surfaces of the detector components, it may be 
observed that the orthogonally disposed strips of detector component 82 
are associated with an impedance network identified generally at 144. 
Network 144 incorporates discrete resistors 146a - 146e which are coupled 
from their mutual interconnections by leads 148a - 148d, respectively, to 
strips 92a - 92d of detector 82. Similarly, the orthogonally disposed 
strips of detector component 86 are associated with an impedance network 
150. In this regard, network 150 is formed of descrete resistors 152a - 
152e which, in turn, are coupled, respectively, with strips 100a - 100d by 
leads 154a - 154d. The output of impedance network 144 is connected by 
leads 156 and 158 to the corresponding output of impedance network 150 to 
provide column directional coordinate parameter outputs, as at 160 and 
162, which serve to collect all spatial information of the associated 
paired surfaces of detectors 82 and 86. 
Looking to the lower surface of detector component 84, note that a network, 
designated generally at 164, incorporating discrete resistors 166a - 166e 
is functionally associated with strips 96a - 96d, respectively, by leads 
168a - 168d. 
In similar fashion, an impedance network, designated generally at 170, is 
associated with the orthogonally disposed strips 104a - 104d at the lower 
surface of detector component 88. Note that the network, incorporating 
discrete resistors 172a - 172e, is functionally associated with the array 
of strips 104a - 104d, respectively, by leads 174a - 174d. Networks 164 
and 170 are electrically coupled in parallel circuit fashion by collector 
leads 176 and 178 extend to principal collection points or termini 180 and 
182. Thus interconnected, the lower surfaces of detectors 84 and 88, 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 82 and 86. 
With the row and column readout intercoupling of the detector components as 
shown in the figure, it may be observed that the capacitance exhibited by 
all discrete detector components, taken together, remains the same as if 
only a single detector were operating within a camera. Accordingly, the 
signal treating circuitry and logic of the camera, advantageously, may be 
designed to accommodate for the charge collection time constant of a 
single detector. Connection with the row and column readout for given 
spatial coordinate parameters is provided by more or less typical 
multiplexing input networks which then distribute collected spatial and 
energy signals into analyzing and distributing circuitry. Such circuitry 
is described in more detail in connection with FIG. 6. However, it should 
be understood that, in a preferred embodiment, preamplification stages, as 
described in connection with FIG. 2, are coupled with each row readout 
point as at 120 and 122 or 140 and and 144, as well as with each column 
readout, as at 160 and 162 and 180 and 182. Such preamplification stages 
generally are located within or near the cryogenic environment of the 
detector itself. The mounting of the contact leads between each of the 
networks and an associated strip array surface of a detector generally may 
be carried out by resort to biased contact configurations. 
The composite detector arrangement or interrelated detector component 
mosaic also may be formed utilizing detector structures which incorporate 
surface disposed resistive layers to achieve spatially proportioned charge 
readout characteristics. Such as detector composite is revealed generally 
in FIG. 5 at 200. Referring to that figure, the composite detector, or 
portion thereof, 200, is shown to comprise four discrete detector 
components 202-208. The opposed surfaces of the detector components, 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 resistive 
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 collected by conductive strips 
which, for the case of detector component 202, are shown on the upward 
surface at 210 and 212 and at the lower surface at 214 and 216. Conductive 
surfaces 210 - 216 may be deposited upon the detector component 202, 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 
character within the surfaces of detector components 202-208, mention may 
be made of the following publications: 
Xxi owen, R. P., Awcock, M. L.. "One and Two Dimensional Position Sensing 
Semiconductor Detectors," IEEE, Trans. Nucl. Sci., Vol. N.S. - 15, June 
1968, Page 290. 
Xxii berninger, W. H., "Pulse Optical and Electron Beam excitation of 
Silicon Position Sensitive Detectors", IEEE, Trans. Nucl. Sci., Vol. V.S. 
21, Page 374. 
With the impingement of radiation upon detector component 202 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 define surfaces and collect at the conductive strips 210 - 216. 
For the upwardly disposed surface, these charges then are collected along 
conduit 218, coupled with conductive strip 212, and conduit 220, coupled 
with conductive strip 210. The adjacently disposed detector 204 is 
fashioned in similar manner, the upward surface thereof incorporating a 
resistive surface layer or region formed in cooperation with conductive 
strips 220 and 222. The lower surface of detector component 204 is formed 
incorporating a similar resistive layer or region functionally associated 
with conductive strips 224 and 226. Note that the latter conductive strips 
are arranged orthogonally with respect to those at 220 and 222. Conductive 
strip 220 is coupled by a lead or conduit 228 to conductive strip 212 of 
the detector component 202, while conductive strip 222 is coupled by lead 
or conduit 230 to conductive strip 210 of detector 202. Thus 
interconnected, it will be apparent that any interaction occurring within 
detector component 204 will be "seen" as a charge division between strips 
220 and 222, for one coordinate parameter, along leads 228 and 230 as well 
as output conduits 218 and 220. As is apparent, a desirable simplification 
of the structure of the composite detector is available with this form of 
row readout. 
Looking to the adjacently disposed row of detector components 206 and 208, 
it may be noted that detector component 206 is formed incorporating 
resistive layers or regions in its opposed surfaces aligned for the 
acceptance of radiation and, additionally, incorporates conductive strips 
as at 232 and 234 at the extremities of its upward surface as well as 
orthogonally oriented conductive strips 236 and 238 about the extremities 
of its lowermost and oppositely disposed surfaces. 
Identically structured component 208, similarly, is formed having resistive 
surfaces or regions arranged normally to the direction of radiation 
impingement. The surfaces also incorporate conductive strips, as at 240 
and 242, at the upwardly disposed side and, at 244 and 246, orthogonally 
disposed at the lowermost surface. 
Coupled in similar row-type fashion as detectors 202 and 204, the 
conductive strips of detectors 206 and 208 are directly electrically 
associated by leads 248 and 250. Note, in this regard, that lead 248 
extends between conductive strips 240 and 232 while lead 250 extends 
between conductive strips 242 and 234. The output of that particular row 
at the upward surface of the composite detector is represented by leads 
252 and 254. 
A columnar interconnection of the detector components is provided between 
the orthogonally disposed conductive strips 214 and 216 of detector 202, 
respectively, as by leads 256 and 258, to similarly disposed conductive 
strips 236 and 238 of detector 206. The columnar readouts for the paired 
detector components are present at conduits 260 and 262 extending, 
respectively, from conductive strips 236 and 238. 
In similar fashion, the columnar association of detector components 204 and 
208 is provided by leads 264 and 266 which, respectively, extend between 
conductive strips 224 and 226 of detector 204 to corresponding conductive 
strips 244 and 246 of detector component 208. The readouts for the column 
association of detectors 204 and 208 are provided by conduits 268 and 270 
extending, respectively, from conductive strips 244 and 246 of detector 
component 208. 
As in the embodiment of FIG. 4, the output conduits 218, 220 and 252, 254 
are of a "row" variety having a designated spatial coordinate parameter 
and are addressed to initial preamplification stages prior to their 
association with logic circuitry for deriving imaging information for that 
particular spatial coordinate. Similarly, the "columnar" outputs at 
conduits 260, 262 and 268, 270 are directed to preamplification stages, 
thence to appropriate circuitry for treating 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 
practicalities for retaining such components under appropriate cryogenic 
temperature conditions during operation. 
The foregoing examination of the composite detector structures, represented 
in FIGS. 4 and 5, reveals certain consistent characteristics between the 
embodiments. For instance, as alluded to above, the effective areas 
presented to radiation impingment 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 evolves what has been termed as a 
"row-column" orientation. In the latter regard, an observation of this 
geometry shows that the leads interconnecting the impedance networks or 
the impedance structure i.e. at the surface region of the detector 
components, connect them directly, whether in the parallel-series 
connection of the embodiment of FIG. 4 or the interconnection of 
conductive strips shown in FIG. 5. Another aspect typifying the structure 
of the invention, reveals that any two adjacent surfaces of any two 
adjacent detector components exhibit spatial coordinate parameters of a 
common directional sense and, more particularly, two adjacent of the 
coplanar surfaces of any two adjacent detector components are disposed 
within a linearally oriented grouping arranged to exhibit a common spatial 
coordinate parameter directional sense. Because the composite detector 
embodiments shown in FIGS. 4 and 5 operate substantially in the same 
functional manner, their outputs are identified with the same spatial 
coordinate directional labels. For instance, outputs 122 and 120 of the 
embodiment of FIG. 4, respectively, are identified as (X.sub.1 A) and 
(X.sub.1 B); while the parallel row readouts, as at output points 142 and 
140, respectively, are identified as (X.sub.2 A) and (X.sub.2 B). 
Similarly, the orthogonally disposed spatial coordinate parameters, as 
represented for instance, at outputs 162 and 160, respectively, are 
identified as (Y.sub.1 A) and (Y.sub.1 B). Next adjacent to that column of 
the composite detector, are the detectors whose outputs are represented at 
180 and 182 and are identified, respectively, as (Y.sub.2 A) and (Y.sub.2 
B). This same labeling procedure will be seen to be utilized in the 
composite detector embodiment of FIG. 5. 
Turning now to FIG. 6, a schematic block diagram of a control system 
utilized in treating the above-identified output 
Turning now to FIG. 6, a schematic block diagram of a control system 
utilized in treating the above-identified output signals is revealed. Note 
in that figure, that the x coordinate inputs, as above outlined, are shown 
arranged to address discrete preamplification stages 300a - 300d, while 
the corresponding x coordinate outputs are aligned to address 
preamplification stages 302a - 302d. Generally, to accommodate for noise 
considerations, the preamplification stages 300a - 300d and 302a - 302d 
are incorporated within the cryogenic environment of housing 16 of the 
camera (FIG. 1). As is described in more detail in the above-reference 
application for U.S. patent Ser. No. 680,754, the x-channel coordinate 
inputs treated through preamplification stages 300a - 300d are, in turn, 
introduced along respective lines 304a - 304d to an Antisymmetric 
Summation and Gaussian Filtering function, represented at 306. This 
function serves to subtractively sum the inputs from each of the x spatial 
coordinate channels, for instance, the signal at (X.sub.1 A) is subtracted 
from that of (X.sub.1 B). Following appropriate filtering and pulse 
shaping, as by a series of integrations, the output of block 306 is 
submitted along lines 308a and 308b, respectively, to Gated Integrator 
functions 310a and 310b. Within these functions, a trapezoidal filtering 
of the spatial signals is carried under a predesignated idealized 
integration time, generally selected as about one-eighth of the time 
constant characteristic of each of the discrete detector components. 
Control over gated integrators 310a and 310b emanates from a Gate Control, 
Display Control and Multiplexing function 312. In this regard, control 
from function 312 to gated integrator 310a is derived from lines 314 and 
316, while similar control to Gated Integrator 310b is asserted through 
lines 318 and 320. The final integrated spatial x coordinate outputs of 
integrators 310a and 310b, respectively, are directed into a receiving 
network of Gate Control function 312 through lines 322 and 324. When 
accepted by the control circuit, the signals ultimately are asserted from 
function 312 through lines 326 and 328 to Persistent Display Scope 330 and 
Photographic Record 332. 
The input signals at lines 304a and 304b, representing a linerally oriented 
grouping (X.sub.1 A) and (X.sub.1 B), are additionally directed, 
respectively, through lines 334 and 336 to a Summing and Gaussian 
Filtering function identified at block 338. Function 338 operates under a 
relatively extended time constant to additively sum the x-channel spatial 
signals as well as provide the noted filtering function. By carrying out 
an additive summing function, a signal representative of the energy value 
of a quantum of spatial information is derived. The value of this signal 
then may be utilized for purposes of determining whether or not the 
information which it represents is true or false in the sense of its 
ultimate participation in the image of a distribution of a 
radiopharmaceutical. A low level or preliminary evaluation of the signal 
is provided by tapping an initial stage of function 338 wherein the time 
derivative of the summed energy signal is generated. This derivative 
signal, identified as dE.sub.X1 /dt, is provided at line 340 for 
introduction to the control and multiplexing function at block 312. With 
such signal, the system commences an evaluation of the spatial signal, 
which evaluation includes a pulse height analysis of the summed signal 
received from line 342 at function block 344. The acceptance or rejection 
of the spatial signal is determined at block 344 and such determination is 
signalled to the display control networks of function 312, as from along 
line 346. 
The same function is carried out for the (X.sub.2 A) - (X.sub.2 B) input 
signals, derived, respectively, at input lines 304c and 304d. In this 
regard, note that these input lines, respectively, are tapped by lines 348 
and 350 which, in turn, lead to summing and Gaussian Filtering Function 
352. As before, an initial stage of function 352 provides a time 
derivative output signal of the additively summed spatial signal, which is 
represented as dE.sub.X2 /dt, and is provided at line 354. As described in 
connection with the X.sub.1 grouping above, this derivative signal is 
introduced to the display control and multiplexing networks of function 
312 to provide a preliminary or low level analysis of the spatial 
information. Should the derivative signal evidence an appropriate signal 
level, the Gaussian filtered output of block 352 is directed through line 
356 to pulse height analysis function 358. When the signal received 
therein is analyzed and found to fall within the appropriate window 
criteria evidencing appropriately true spatial information, it is passed 
along line 360 to control function 312 to enable a display of the X.sub.2 
coordinate parameter information. 
The orthogonally disposed coordinate channel or y-channel information 
operates in substantially the same manner as the x-channel information 
treatment described above. For instance, the signal data derived at one 
column of the composite detector, as identified at (Y.sub.1 A) - (Y.sub.1 
B), is introduced through respective preamplification stages 302a and 302b 
to lines 370a and 370b which, in turn, lead to a y-channel Antisymmetric 
Summation and Gaussian Filtering function 372. In like manner, the 
corresponding columnar derived spatial signals (Y.sub.2 A) - (Y.sub.2 B), 
respectively, are introduced through preamplification stages 302c and 302d 
to lines 370c and 370d which, in turn, lead to Summation and Filtering 
function 372. The Y.sub.1 channel information initially is tapped, as by 
lines 374 and 376, connected, respectively, with lines 370a and 370b, to 
insert the coordinate signals to a Summing and Gaussian Filtering function 
378. Similarly, lines 380 and 382, respectively tapping lines 380c and 
380d, introduce the spatial Y.sub.2 coordinate signals to a Summing and 
Gaussian Filtering function 386. Functions 378 and 386, operating in 
similar fashion as functions 338 and 352, serve the particular purpose of 
generating a time derivative valuation of the summed energy y-coordinate 
signal. In this regard, note that the output of function 378 at line 388 
is labeled dE.sub.Y1 /dt, while the output of function 386 at line 890 is 
identified as dE.sub.Y2 /dt, both outputs leading to control function 312. 
The derivative signal from these functions is utilized in conjunction with 
coincidence circuits and the like at function 312 to provide an 
identification of that portion of the composite detector from which the 
spatial information signals were derived. In particular, the signal is 
utilized to identify the particular detector component responding by 
interaction with an impinging photon. 
The filtered and subtractively summed signals from function 372 are 
introduced through lines 392 and 394, respectively, to Gated Integrator 
functions 396 and 398. Controlled under the above described time constant 
integrating interval through respective lines 400, 402 and 404, 406, 
integrators 396 and 398 perform a trapezoidal type filtering upon the 
spatial information pulses and deliver such treated information, 
respectively, along 408 and 410 to Multiplexing and Display Control 
function 312. Such information provides the y-coordinate channel inputs to 
readout functions 330 and 332. 
An important aspect of the "row-column" interconnection of the discrete 
detector components resides in the realization of an effective reduction 
in that detector linear dimension over which resolution is evaluated. More 
specifically, an improvement is experienced in the resolution of the 
camera system which may be expressed by the equation: 
EQU .DELTA.x = .DELTA.EL/E, 
where .DELTA.x, represents the spatial resolution in terms of distance; 
.DELTA.E, is absolute energy 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 of an incident photon 
interacting with the detector. Within the right hand side of the equation 
above, the expression, .DELTA.E/E, is readily indentified as the fraction 
(or percentage) of energy resolution. Accordingly, any increase in the 
value of, L, directly and adversely affects that fraction. Where the 
detector components are not interconnected by the "row-column" technique, 
the value, L, in the expression above becomes 2L, effecting a doubling of 
the noted spatial resolution value to the detriment of final imaging. 
Another feature characteristic of a 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 of "row-column" interconnection of detector components 
exhibiting this spatial resolution advantage is revealed in FIG. 7. 
Referring to that figure, a composite detector formed as an array of 
discrete detector components is revealed generally at 420. As in the 
earlier-discussed embodiments detector 420 is shown in exploded fashion 
for purposes of clarity and comprises a plurality of detector components, 
four of which are shown at 422, 424, 426, and 428. Components 422-428 are 
dimentioned having mutually equivalent areas as are intended for 
acceptance of impinging radiation and, for illustrative purposes, are 
formed as of an orthogonal strip array variety, each strip thereof being 
defined by grooves formed within the detector surfaces. In this regard, 
detector 442 is formed having strips 430a - 430d defined by grooves cut 
within its upward surface. The opposite face of detector component 422 
similarly is formed having strips 432a-432d defined by in intermediatly 
positioned grooves arranged orthogonally with respect to the grooves at 
the upper surface. Detector component 424 is identically fashioned, having 
strips 434a-434d formed at its upwardly disposed surface; and, at its 
lower surface, orthogonally disposed strips 436a 14 436d, adjacent said 
strips being defined by intermediatly formed grooves. Similarly, detector 
component 426 is formed having strips 438a-438d at its upward surface, 
adjacent ones of the strips being defined by intermediatly disposed 
grooves, while its lower surface similarly is formed having strips 
440a-440d defined by intermediatly disposed grooves arranged orthogonally 
with respect to the grooves of the upward surface. Detector component 428 
may be observed to have strips 442a-442d at its upward surface adjacent 
one of which are defined by intermediatly designated grooves, while its 
lower surface is formed with adjacently disposed strips 444a-444d 
separated by intermediatly disposed grooves arranged orthogonally to the 
grooves of the upward surface thereof. 
In the instant embodiment, strips 434a-434d of detector component 424 are 
directly, electrically associated with corresponding row strips 430a-430d 
of component 422 by electrical leads respectively identified at 446a-446d. 
Note, that no impedance network is interposed intermediate the strip 
grouping as in the earlier embodiments. However, an impedance network, 
designated generally at 448, is associated with the termini of strips 
430a-430d opposite the edges thereof coupled with electrical leads 446a - 
446d. Network 448 comprises serially associated discrete resistors 
450a-450e which are tapped at their common junctions by leads 452a-452d 
extending, respectively, to strips 430a-430d. The output, or readout 
points for the thus defined "row" of the composite detector assembly are 
represented at 454 and 456 and are provided the same respective output 
signal labeling, (x.sub.1 B), (x.sub.1 A), as are present in the 
corresponding "row" of the embodiments of FIGS. 4 and 5. 
The corresponding upwardly disposed surfaces of components 426 and 428 are 
connected in similar fashion. For instance, strips 442a-442d are 
electrically coupled with strips 438a-438d by respective electrical leads 
458a-458d. The "row" coupling thus provided is associated with an 
impedance network shown generally at 460. Network 460 is formed comprising 
serially associated discrete resistors 462a-462e which are tapped at their 
common interconnections by leads 464a-464d. Leads 464a-464d respectively, 
extennd to strips 438a-438d of detector 426. The principal output termini 
of the thus defined "row" are identified at 466 and 468 and respectively 
labeled (x.sub.1 B), (x.sub.1 A). 
Looking now to the lower surfaces of the detector components, the 
orthogonally disposed strips of detector component 422 are electrically 
coupled as shown with the corresponding strips of detector component 426 
by electrical leads 470a-470d. The thus coupled strip arrays of those 
detector components are associated in "columnar" fashion with an impedance 
network identified generally at 472. Network 472 comprises serially 
associated discrete resistors 474a-474e, the interconnections between 
which are connected as shown with strips 440a-440d of component 426 by 
leads respectively identified at 476a-476d. The readout termini for the 
thus defined "column" association of detectors 426 and 422 are present at 
478 and 480 and identified, respectively, as (y.sub.1 A) and (y.sub.1 B). 
The lower surfaces of detector components 424 and 428 similarly are 
associated in "columnar" readout fashion, strips 436a - 436d of the former 
being electrically connected through respective leads 480a-480d to strips 
444a-444d of the latter. The thus established "columnar" readout is 
associated with an impedance network identified generally at 482 and 
comprising serially associated discrete resistors 484a-484e. Strips 
444a-444d, respectively, are coupled with the interconnection of the 
resistors 484a-484e of network 482 by leads 486a-486d. As in the earlier 
embodiments, the principal readouts of the thus defined "columnar" 
detector component coupling are represented at 488 and 490 and are 
labeled, respectively, (y.sub.2 A) and (y.sub.2 B). From the foregoing 
description of the composite detector arrangement 420 it may be observed 
that the "row-column" association of the components thereof enjoys the 
noted spatial resolution advantages, however, the time constant 
characteristic thereof will reflect a higher capacity evaluation. 
During performance, the composite detector 420 operates in the same manner 
as the control system of FIG. 6, which is described in conjunction with 
composite detector components 80 and 200 of respective FIGS. 4 and 5. For 
this reason, the noted labeling of the output of the "row and column" 
arrangement have remained consistent throughout all of the figures. 
Since certain changes may be made in the above system and apparatus without 
departing from the scope of the invention herein involved, it is intended 
that all matter contained in the above description or shown in the 
accompanying drawings shall be intepreted as illustrative and not in a 
limiting sense.