GB1578882A - Solid state detector - Google Patents

Description

PATENT SPECIFICATION ( 11) 1 578 882

> ( 21) Application No 31324/79 ( 22) Filed 4 Jan 1977 O ( 62) Divided out of No 1578881 ( 19) ( 31) Convention Application No 680755 O ( 32) Filed 27 April 1976 in < ( 33) United States of America (US)

b ( 44) Complete Specification published 12 Nov 1980

I ( 51) INT CL 3 GOIT 1/24 HOIL 31/00 ( 52) Index at acceptance H 4 F D 18 K D 27 M D 30 H D 68 D 83 X L HIK 1 l Bl 11 C 4 l IDI l ID l EB 9 A 9 81 9 BIA ECD ( 72) Inventors DON W MILLER and MARK S GERBER ( 54) SOLID STATE DETECTOR ( 71) We, THE OHIO STATE UNIVERSITY of 190 N Oval Drive, Columbus, Ohio, 43210, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:-

This invention relates to a solid state detector for use in a gamma camera 5 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 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 noninvasive 10 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 simultaneously imaging substantially an entire, in vivo, gamma ray source distribution In initially introduced practical 15 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 20 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 25 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 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 30 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 For additional information 35 concerning such camera, see:

I Anger, H O, "A New Instrument For Mapping Gamma Ray Emitters", Biology and Medicine Quarterly Report UCRL-3653, 1957.

A continually sought goal in the performance of gamma cameras is that of achieving a high resolution quality in any resultant image Further, it is desirable to 40 achieve this resolution in combination with concomitant utilization of a highly versatile radionuclide or radiolabel, 99 m-Technetium, having a gamma ray or photon energy in the region of 140 ke V A broadened clinical utility for the cameras also may be realized through the use and image identification of radiopharmaceuticals exhibiting more than one photon energy level With such an arrangement, two or a plurality of diagnostic aspects simultaneously may be availed the operator For example, in carrying out myocardial imaging, the aboveidentified 99 m-Technetium might be utilized in conjunction with I I IIndium, the latter contributing photon energy in the regions of 173 and 247 Ke V Similarly, 81 5 Rubidium, exhibiting photon energy in the range of 350 Ke V might be utilized in conjunction with 81-Krypton, the latter having gamma ray energy at about 120 Ke V The noted dual energy characteristic of Il l -Indium also might be utilized to achieve two aspects of diagnostic data.

The resolution capabilities of gamma cameras incorporating scintillation 10 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 of resolution occurs from scattered photons which are recorded in the image of 15 interest Such photons may derive 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 20 image of the system as photopeak photon representing false spatial information or noise As such scattered photons record photopeak events, the noise increase and consequent resolution quality of the camera diminishes For the noted desirable Ke V photons, the scintillation detector type camera energy resolution is approximately 15 Ke V With this resolution, photons which scatter through an 25 angle from 0 to about 700 will be seen by the system as such photopeak events.

A continuing interest in improving the resolution qualities of gamma cameras 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 30 in statistically limited resolution to provide significant improvements in image quality In this regard, for example, reference may be made to the following publications:

11 R N Beck, L T Zimmer, D B Charleston, P B Hoffer, and N Lembares, "The Theoretical Advantages of Eliminating Scatter in Imaging Systems", 35 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.

111 R N Beck, M W Schuh, T D Cohen, and N Lembares, "Effects of Scattered Radiation on Scintillation Detector Response", Medical 40 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 Scattering in Radioisotope Imaging" 45 IEEE Trans Nuc Sci, Vol NS-20, No 1, pp 266-270, 1973.

Particular interest on the part of investigators has been paid to detectors provided as hybridized diode structures formed basically of germanium To derive discrete regions for spatial resolution of impinging radiation, the opposed parallel surfaces of the detector diodes may be grooved or similarly configured to define 50 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 Dioxide Matrix for Isotope Localization", Phys.

Med Biol, Vol 14, No 2, pp 245-253, 1969 55 VII i 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 60 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 GammaCamera," British Journal of Radiology, Vol 44, 58-62, 1971.

I 1,578,882 X Parker, R P, E M Gunnerson, J S Wankling, R Ellis, "A Semiconductor Gamma Camera with Quantitative Output," Medical Radioisotope Scintigraphy, Vol 1, Vienna IAEA, 1969, p 71.

XI Detko, J F, "A Prototype, Ultra-Pure Germanium, orthogonal-Strip Gamma Camera," Medical Radioisotope Scintigraphy, Vol 1, Vienna, 5 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 10 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-15, June 1968, p 290.

In the more recent past, investigators have shown particular interest in 15 forming orthogonal strip matrix detectors from p-i-n semiconductors fashioned from an ultra pure germanium material In this regard, reference is made to U S.

Patent No 3,761,711 as well as to the following publications:

XIV J F Detko, "A Prototype, Ultra Pure Germanium Orthogonal Strip Gamma Camera," Proceedings of the IAEA Symposium on Radioisotope 20 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 25 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 reducing impurity concentrations are avoided and the detector need only be cooled 30 to requisite low temperatures during its clinical operation Read-out from the orthogonal strip germanium detectors is described as being carried out utilizing a number of techniques, for instance, each strip of the detector may be connected to a preamplifier-amplifier channel and thence directed to an appropriate logic function and visual readout In another arrangement, a delay line readout system is 35 suggested with the intent of reducing the number of preamplifiersamplifier channels, and a technique of particular interest utilizes a charge splitting method.

With this method or technique, position sensitivity is obtained by connecting each contact strip of the detector to a charge dividing resistor network Each end of each network is connected to a virtual earth, charge sensitive preamplifier When a 40 gamma ray interacts with the detector, the charge released enters the string of resistors and divides in relation to the amount of resistance between its entry point in the string and the preamplifiers Utilizing fewer pre-amplifiers, the cost and complexity of such systems is advantageously reduced.

In accordance with this invention we provide, a solid state detector for 45 receiving collimated radiation of given photon energy or energies emitted from a region of interest of an isotopic material, including:

a plurality of solid state detector components, each having a first surface arranged for exposure to impinging radiation and a second surface disposed opposite and substantially parallel to said first surface, each said detector 50 component producing discrete charges at spatially definable locations at which radiation is incident thereon:

each of said first and second surfaces of each said detector component being coupled to first and second charge dividing impedance means respectively which produce position signals relating a location to respective first and second spatial 55 coordinates; said detector components being arranged and connected to the first and second impedance means so that groupings of adjacently disposed ones of said first surfaces produce in said first, impedance means signals relating a location with said first spatial coordinate, and so that groupings of adjacently disposed ones of said second surfaces produce in said second impedance means signals relating a 60 location with said second spatial coordinate.

For a fuller understanding of the nature and the object of the invention, 1,578,882 reference should be had to the following detailed description taken in conjunction with the accompanying drawings In which:

Figure 1 is a schematic representation of a gamma camera arrangement incorporating a detector in accordance with this invention, showing, in block schematic form, general control functions; 5 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 state strip detector and a schematic collimator functionally associated therewith as such system components 10 relate to a radiation source within a region of clinical interest; Figure 4 is an equivalent noise model circuit for solid state detectors; Figure 5 is a circuit model of a detector component and related resistor network, schematically representing a position-sensitive detector arrangement; Figure 6 is a pictorial and schematic representation of an array of detector 15 components showing the interconnections thereof to form a composite detector or region thereof; Figure 7 is a block schematic representation of a control system utilized to receive and treat the outputs of the detector array configuration of Figure 6; Figure 8 is a schematic and pictoral representation of another array of detector 20 components, interconnected in accordance with a "row-column" readout geometry; Figure 9 is a schematic and pictorial representation of another array of detector components, each of which is formed associated with a surface type impedance arrangement, the components being interconnected in the noted "row 25 column" fashion; and Figure 10 is a schematic and pictorial representation of another array of detector components interconnected in accordance with the noted "rowcolumn" geometry; Looking to Fig 1, an exaggerated schematic representation of such a clinical environment is revealed generally at 10 The environment schematically 30 depicts 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 emanating from region 12 as the patient is positioned on some supporting platform 14 Over the region 12 is positioned the head or housing 16 of a gamma camera 35 Extending outwardly from the sides of housing 16 are mounting flanges, as at 18 and 20, which, in turn, may be connected in pivotal fashion with an appropriate supporting assembly (not shown) Housing 16 also supports a vacuum chamber 22 defined by upper and lower vacuum chamber plates shown, respectively, at 24 and 26 conjoined with an angularly shaped side defining flange member 28 Lower 40 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 45 refrigerating unit of a closed-cycle variety, shown generally at 36 An ion pump, as at 38, assures the integrity of the vacuum in chamber 22, such pump, in conjunction with the refrigerating unit 36, being mounted for association with chamber 22 through upper vacuum plate 24, the latter which may be formed, for instance, of stainless steel Vacuum pump-down of the chamber 22 is accomplished by first 50 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 within 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 55 28 Thus connected, the plate 40 evidences a temperature gradient during the operation of the unit which provides a selected ideal temperature environment of operation for the amplification stages The outputs of these stages are directed through subsequent stage electronics, shown within a housing 44, which, in turn, provides electrical communication to externally disposed control electronics 60 through conduit 46 and line 48 To provide for appropriate operation, chamber 22 generally is retained at a temperature of, for instance about 770 K, while the FET's, 40, mounted upon plate 42, are retained at about 130 'K to achieve low noise performance.

I 1,578,882 Mounted outwardly of window portion 30 and in alignment with the detector 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 by attenuating or rejecting off-axis radiation representing false image information That radiation passing collimator 50 impinges upon detector array 32 5 and a significant portion thereof is converted to discrete charges or image signals.

Detector array 32 is so configured as to distribute these signals to resistor chains as well as the noted preamplification stages 40 retained within chamber 22 to provide initial signals representative of image spatial information along conventional coordinate axes as well as representing values for radiation energy levels This data 10 then is introduced, as represented schematically by line 48, to filtering and logic circuitry which operates thereupon to derive an image of optimized resolution and veracity In the latter regard, for instance, it is desired 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, 15 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.

Image spatial and energy level signals from line 48 initially, are introduced into Anti-Symmetric Summation and Energy Level Derivation functions represented at 20 block 52 which 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 output of block 52 is 25 directed to Filtering Amplification and Energy Discrimination functions as are represented at block 54 Controlled from a Logic Control function shown at block 56, function 54 operates upon the signal input thereto to accommodate the system to parallel and series defined noise components through the use of Gaussian amplification or shaping, including trapezoidal pulse shaping of data representing 30 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 level are considered false and are blocked From 35 Amplification and Discrimination stage 54 and Logic Control 56, the analyzed signals are directed into an Information Display and Readout Function, as represented at block 58 Components within function block 58 will include display screens of various configurations, image recording devices, for instance, photographic apparatus of the instant developing variety, radiation readout devices 40 and the like, which are controlled at the option of the system operator.

Looking to figure 2, an exaggerated pictorial representation of a component of a detector array is revealed at 60 Detector component 60 may be fabricated from p-type high purity germanium by depositing an n-type contact on one face and a ptype contact on the opposite face of a rectangular planar crystal Accordingly, a 45 high purity germanium region of the crystal, as at 62, serves as an intrinsic region between p-type semiconductor region contacts 64 and n-type semiconductor region contacts as at 66 The intrinsic region 62 of the p-i-n detector components form a region which is depleted of electrons and holes when a reverse bias is applied to the contacts Grooves as at 68 a-68 c are cut into the continuous p-type 50 contact or region at one face of the component to form strips of isolated p-type semiconductor material On the opposite face of the detector component, orthogonally disposed n-type semiconductor strips similarly are formed through the provision of grooves 70 a-70 c Configured having this geometry, the detector component 60 generally is referred to as an orthogonal strip detector or an 55 orthogonal strip array semiconductor detector component The electrode strips about each of the opposed surfaces of component 60, respectively, are connected to external charge splitting resistor networks revealed generally at 72 and 74.

Resistor network 72 is formed of serially coupled resistors 76 a-76 e which, respectively, are tapped at their regions of mutual interconnection by leads 60 identified, respectively, at 78 a-78 d extending in turn, to the orthogonal strips The opposed ends of network 72 terminate in preamplification 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 1,578,882 provide one detector component orthogonal or coordinate output, for instance, designated as a y-axis signal.

In similar fashion, network 74 is comprised of a string of serially coupled resistors 88 a-88 e, the mutual interconnections of which are coupled with the electrode strips at surface 66, respectively, by leads 90 a-90 e Additionally, 5 preamplification stages as at 92 and 94 provide outputs, respectively, at lines 96 and 98 carrying spatial data or signals representative 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 component 60, any imaging photon absorbed therewithin engenders ionization which, in turn creates 10 electron-hole pairs The charge thus produced is collected on the orthogonally disposed electrode strips by the bias voltage and such charge flows to the corresponding node of the impedance networks 72 and 74 Further, this charge divides in proportion to the admittance of each path to the virtual ground input of the appropriate terminally disposed preamplification stage Such chargesensitive 15 preamplification stage integrates the collected charge to form a voltage pulse proportional to that charge value Assigning charge value designations Q 1 and Q 2, respectively, for the outputs 98 and 96 of network 74, and Q 3 and Q 4, respectively, for the output lines 84 and 86 of network 72, the above-noted Summation and Energy Level Derivation functions for spatial and energy data may be designated 20 In this regard, the x-position of each diode defined by the orthogonal strip geometry is found to be proportional to Q 1, Q 2, and their difference i e (Q,-Q 2), and the y-position is proportional to Q 3, and Q 4, and their difference i e (Q 3-Q 4).

The energy of the incident gamma ray is proportional to Q 1 +Q 2, and (Q 3 +Q 4), and l(Q 1 +Q 2)-(Q 3 +Q 4)l or in the latter expression, l(Q 3 +Q 4)-(Q 1 +Q 2)l As noted 25 above, the operational environment of the detector array 32 and associated amplification stages is one within the cryogenic 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, 30 some value may be gleaned from an examination of more or less typical characteristics of that impinging radiation For instance, looking to Fig 3 a portion of a patient's body under investigation is portrayed schematically at 100 Within this region 100 is shown a radioactively tagged region of interest 102, from which' region the decay of radiotracer releases photons which penetrate and emit from the 35 patient's body These photons are then spatially selected by a portion of collimator and individually detected at component 60 for ultimate participation in the evolution of an image display The exemplary path of seven such photons are diagrammed in the figure, as at a-g, for purposes of illustrating this initial function which the camera system is called upon to carry out In this regard, the function of 40 collimator 50 is to accept those photons which are traveling nearly perpendicular to the detector, inasmuch as such emanating rays provide true spatial image information These photons are revealed at ray traces, a, and b, showing direct entry through the collimator 50 and appropriate interaction coupled with energy exchange within detector component 60 Photon path, c, is a misdirected one 45 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 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 50 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 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 55 collimator, the imaging system still may reject such false information For example, in the event of a Compton scattering of a photon either in the patient or collimator, the energy thereof may have been reduced sufficiently to be rejected by an energy discrimination window of the system Photon path, g, represents a condition wherein component 60 exhibits inefficient absorption 60 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 full energy photons which are absorbed at the detector ultimately are displayed at their corresponding spatial location on an imaging device such as a cathode ray tube to form an image of the source 65 1,578,882 distribution within region 102 of the patient Of course, the clinical value of the gamma camera as a diagnostic implement is directly related to the quality of ultimate image resolution.

As is revealed from the foregoing discourse, the imaging resolution of the camera system is highly dependent upon the quality of collimation exhibited at the 5 entrance of the camera by collimator 50 Generally, collimator 50 is of a multichannel, parallel-hole variety, its performance being dictated by its fundamental geometric dimensions, the material with which it is formed, and thetechnique of its fabrication, all of which are discussed in our copending application No 7931325 (Serial No 1578883) which was divided from application 10 80/77 (Serial No 1578881) as was the present application.

Discounting entrance geometry, the orthogonal strip position-sensitive detector is resolution limited by noise associated with the detector as well as the charge dividing network Consequently, it is necessary to consider the noise characteristics of the system from the stand-point of minimizing the effects thereof 15 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 spatial channel of the system, while the resistor network, coupled with the detector leakage current, represents the dominant noise source in the system's energy channel As will become more 20 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 like are described in conjunction with the singular detector component described heretofore in connection with Fig 2 in the interest of clarity and simplification 25 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, thermal movement of charge carriers in the resistors and the bulk of the detector and imperfections in the crystal structure of the detector Looking to Fig 4, an equivalent noise model circuit for solid state detector components is revealed 30 Note that the model reveals a detector leakage current, i 0, which 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 35 pre-amplifier input as a step function The system input capacitance is the parallel 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 40 of the dividing resistance, RD, is in parallel with the detector capacitance Since RD is less than one hundred kilo-ohms, it represents a significant noise source The thermal noise from resistors in series with the detector capacitance appears as a delta function to the preamplifiers For spectroscopy systems, this resistance is minimized and the noise source is neglected The noise developed by the 45 preamplifier input stage is modeled using a resistor, Req Finally, a noise term which is not shown in Fig 4 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 have a uniform power spectral 50 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 charge due to the electron flow which is integrated by the input circuit capacitance, and series noise representing the charge due to the electron 55 flow which is not integrated by input capacitance These noise sources are considered to be mutually related in terms of filtering to the extent that as efforts are made to diminish one, the other increases The high frequency component noise generally is considered a series type while low frequency noise is considered of the parallel variety The use of Gaussian and the Gaussian-trapezoidal noise 60 filtering circuits has been found to optimize the energy and spatial resolution values of the camera system.

Turning now to Fig 5, a circuit model of the detector component 60 and the resistor networks of Fig 2 is portrayed The discrete nature of the detector system and the method of readout is revealed in the figure with the discrete capacitors 65 1,578,882 forming an nxn array Each row and column is defined by the charge measured at the end of the resistor strings The electron-hole pairs which are formed when a gamma ray interacts with the detector are collected on opposite surfaces A charge enters the resistive network and flows to terminal A or B (C or L) in relation to the resistance between its entry point and the virtual earth terminal of each 5 preamplifier (Fig 2) The intersection of the column and row defines the diode position in which the gamma ray energy was deposited Note in the figure, that individual capacitances are represented which are exemplary of the inherent capacitance of the detector itself When considered in conjunction with the resistor networks, as revealed in the figure, it may be noted that a particular time constant 10 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, T,, 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, 15 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 preamplifier (Fig 2) due to the instantaneous transfer of charge Q O at position xo is:

vo, ( O 3n TX) X ( M Et 00 x O = 2 m Xo -m 2 X 2 t VO.x)S CtL -sin Lt t D ( 8) 20-, X, 3 D2 TT Lx exp + V( Lxt) =O + cos 2 (mit) sin (Li( m 2 t 20 V( L,Cx o L Cf L M 1 mt C L c D ( 9) 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 t O = 2 R O CD), xo defines the position of interaction and m is a summation variable.

Examination of equation ( 8) and ( 9) show that for a time TD t> ( 10) 25 i.e, an output generation time equivalent to one half of the time constant of the detector, the value of V( 0,xo,t) is within 1 % of its final value for all x J/L< 95 and V(L,xo,t) is within 1 , of its final value for all x J/L> 05 Stated otherwise, the error generated from ballistic deficit type characteristics of the system as it relates to the energy of one preamplifier readout diminishes to a value of 1 % within a period of 30 one half the time constant, T 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= 0 position, i e.

V( 0, xo, t) V ( Lx, t) C 1 ( mt X L '1 sin -C L rn-i L m,-1 ( 1 +cos mit) exp ( m 2 2 t (I) 1,578,882 the following important observations may be observed Equation ( 11) shows that as the spatial location of information impingement alters from 0 to L, the resulting voltage readout moves from a positive unit value to a negative unit value Stated otherwise the output signal derived from the above signal treatment subtractive approach ranges from +QJ Cf at x = 0, to -QJC, at x O =L, making the signal twice 5 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 On of its final value for all values x JL< 45 and x/L> 55 after a time:

t> ( 12) 10 Accordingly, it may be observed that through the utilization of a dual preamplifier subtractive or "antisymmetric" method of signal analysis, the necessary time constant related signal treatment within the spatial channel is diminished by a factor of 4.

Turning now to the conditions obtaining within the energy channel of the 15 system, the energy channel is derived by summing the output of each preamplifier to obtain the voltage pulse:

V ( Oxo, t) + V ( L, xo, t)s=i Cnml m ( L) cocs mit) Cf m= 1 mit X -m 2 u T 2 t exp ( it D ( 13) Note again, that the peaking time of the pulse is position dependent At x JL= 5, the maximum peaking time occurs and the pulse is within 1 On of its final 20 value at t TJ 2 Accordingly, it may be observed that ballistic deficit or charge collection type considerations within the energy channel will require a charge collection period, for practical purposes, equivalent to one half of the time constant of the detector.

Now considering noise phenomena, as earlier discussed in combination with 25 ballistic deficit considerations, as derived immediately hereinbefore, dominant spatial noise, which is parallel noise, may be expressed as follows:

e '1/2 Nqsi -5 4 k T Dapz O q R L, ( 14) where N 51 is the equivalent noise charge in number of electrons for one preamplifier spatial measurements, R, is the total resistance of the resistive chain, 30 T O is the temperature of the detector and chain, ap is a weighting factor of the filter, q is the magnitude of the charge on an electron, and k is Boltzmanns 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 35 resistive network For the exaggerated exemplary detector component shown in Fig 2, the term RD represents one-half the sum of the resistance values of networks 72 and 74 Note from equation ( 14) that the noise is proportional to the square root of the temperature as well as the weighting factor and the time constant of the system As disclosed earlier, this time constant is limited by the ballistic deficit 40 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 -9 I 1,578,882 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: 5 1/2 2 4 k T O Nq SAS -q RD ap To O ( 15) From this equation, note that a subtractive arrangement permits the ballistic deficit dictated time constant to reduce by a factor of 4, while the value of noise increases by a factor of 2 for that same time constant, however, since a reduced time constant (factor of 4) is involved in a subtractive arrangement, the noise value, 10 otherwise increased by a factor of 2, remains the same and the signal-tonoise ratio is increased by a factor of 2 Recall the earlier discussion, above, that the unit signal value runs from a positive unit to a negative unit within a subtractive system The value RD is difficult to increase inasmuch as a concomitant reduction in energy resolution generally is witnessed for such alteration Temperature drop can be 15 achieved practically and the weighting factor, ap, can be altered to a more or less ideal value by appropriate selection of filtering systems It has analytically been determined that a 43 4 percent improvement in spatial resolution is realized if antisymmetric summation, i e subtractive summation, is used as opposed to the utilization, for instance, of one preamplifier for spatial measurement 20 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 25 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 pre-filter followed by a gated integrator circuit Such filters generally are referred to as gatedintegrators or trapezoidal filters The filter preferred for the purpose is a Gaussian trapezoidal 30 filter which consists of a time invariant Gaussian filter followed by a gated integrator circuit Such arrangement is revealed in more detail in the disclosure to follow For a detailed discourse concerning the utilization of antisymmetric summation as well as the utilization of trapezoidal filtering within the spatial channel of the system, reference is made to the following unpublished work: 35 XXII Hatch, K F, "Semiconductor Gamma Camera", Ph D Dissertation, Massachusetts Institute of Technology, Cambridge, Massachusetts, February, 1972.

The equivalent noise charge in number of electrons for Gaussian trapezoidal spatial measurements may be represented by the following expression: 40 Nq 5 s T =25 (k Ta 2 ( 1 TL') V ( 16) where ap is the parallel noise weighting function value for Gaussian trapezoidal systems and T, is the integration time Analysis of the foregoing shows that an excellent improvement in spatial resolution is obtained by using antisymmetric Gaussian trapezoidal filtering This improvement is realized because the effects of 45 "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:

1/2 1 q E 51 = q </ 2 q;Da PXO + 4 k TDJRDC( 172 a I Nq E 51= 2 qiapt, + 4 k D 6 t O J ( 17) I 1,578,882 An important aspect of the above energy channel and spatial channel analyses has been observed In this regard, it may be recalled that opposed relationships.

stem from a consideration of 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 5 ( 17) above, represents a straight summation of two preamplifier outputs and the initial parallel noise factor prevented 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, Tr, Te respectively, for spatial resolution and energy resolution may be incorporated within the circuitry treating 10 the output of the system detector For instance, the energy resolution filtering of 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 15 introduced into the longer time constant energy filter individually will be integrated to achieve a peak value above a pre-designated window function of the energy channel (block 54, Fig 1) Accordingly, false information generated from pulse pile-up-phenomena and the like may be rejected without recourse to more involved discrimination circuitry While this description is made in conjunction with the 20 singular detector component embodiment of Fig 2, the theory of its operation will be seen to carry forward into the corresponding operation of a scaled-up control system operative in conjunction with a multicomponent detector array.

Turning to Fig 6, a composite detector, formed as an array of discrete detector components, is revealed generally at 360 This sub-grouping of four 25 detector components, as identified at 362, 364, 366, and 368, may, for instance, be combined with three additional subgroupings to form a full detector array comprising four subgroupings incorporating a total of 16 detector components Of course, a greater or smaller number of detector components may be combined to form an array of desired dimension In the interest of clarity, only one such 30 quadrant designated sub-array, as at 360, is described in conjunction with a control system Detectors 362-366 are dimensioned having mutually equivalent areas designated for the acceptance of impinging gamma radiation Such equivalency serves to achieve accurate ultimate image readout from the camera system The detector components 362-366 are of the earlier-described orthogonal strip array 35 variety, each strip thereof being defined by grooves Note in this regard, that detector component 362 is formed having strips 370 a-370 d located at its upwardly disposed surface and defined by grooves cut intermediate adjoining ones of these said strips The opposite face of the detector component 362, similarly, is formed having strips 372 a-372 d defined by intermediately disposed grooves arranged 40 orthogonally with respect to the grooves at the upper surface Detector components 364 is identically fashioned, having strips 374 a-374 d at its upwardly disposed surface, each being defined by intermediately disposed grooves; the lower surface of the detector being formed having orthogonally disposed strips 376 a376 d defined by intermediately disposed grooves The corresponding strip arrays of 45 detector component 366 are shown to comprise identically disposed strip groupings as at 378 a-378 d and 380 a-380 d Similarly, detector component 368 is shown to be formed of identically structured mutually orthogonally disposed strip arrays 382 a-382 d and 384 a-384 d.

Components 362-368 are illustrated expanded from one another for purposes 50 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, the strip arrays each are mutually associated along common coordinate directions This association is carried out between components 362 and 55 364 by leads 386 a-386 d, coupling respective strips 374 a-374 d of component 364 with strips 370 a-370 d of component 362 In similar, parallel coordinate fashion, leads 388 a-388 d are provided for connecting respective strips 382 a-382 d of component 368 with strips 378 a-378 d of component 366.

The outputs of the thus mutually coupled strip arrays of the upwardly disposed 60 faces of the detector components are coupled with an impedance network, represented generally at 390 Network 390 is configured comprising serially interconnected discrete resistors 392 a-392 i Interconnection between respective strips 370 a-370 d and points intermediate resistors 392 e-392 i is provided by leads 394 a-394 d, while corresponding interconnection between strips 378 a-378 d with 65 1,578,882 1 1 1 1 the intermediate connections of resistors 392 a-392 d is provided by leads 396 a396 d.

In similar fashion, the arrayed strips 372 a-372 d at the lower surface of component 362 are coupled with respect to strips 380 a-380 d of component 366 by leads 398 a-398 d Similarly, strips 376 a-376 d at the lower face of component 364 5 are respectively coupled with corresponding strips 384 a-384 d of component 368 by leads 400 a-400 d The thus associated strip arrays of the lower faces of the detector components are connected with a second impedance network, identified generally at 402, in similar fashion as the orthogonally disposed upward surfaces.

Note, for instance, that strips 380 a-380 d of the lower surface of component 366 10 are connected to intermediate respective discrete resistors 404 a-404 e of network 402 by leads 406 a-406 d Similarly, strips 384 a-384 d of the lower surface of component 368 are connected with respective discrete resistors 404 f-404 i of network 402 through leads 408 a-408 d Thus interconnected, the four discrete detector components provide spatial coordinate parameter outputs; i e x 15 designated coordinate outputs at lines 410 and 412, which are identified thereat as (x 1 A) and (x 1 B) In like manner, the spatial coordinate parameter outputs of the lower surfaces of the detector components are present at lines 414 and 416 and are y-designated, being labeled in the drawing, respectively, as (y 1 A) and (y B).

Fig 7 reveals a first output treating arrangement, present as one set of filtering 20 and control electronics which operates in conjunction with the quadrant detector array of Fig 6 In that figure, spatial coordinate parameter outputs, or xdesignated coordinate outputs (x 1 A), (x 1 B) and (y 1 A), (y 1 B) are represented, respectively, at lines 410-416 These outputs, as at lines 410-416, are shown arranged to address discrete preamplification stages respectively revealed at 430-436 In this regard, 25 note that the output at line 438 of preamplification stage 430 is introduced to an xChannel Antisymmetric Summation Gaussian Filtering and Gated Integrator function, shown at 440, while the corresponding input from preamplification stage 432 is directed along line 442 to that same function.

The inputs from the x-spatial coordinate outputs are subtractively summed 30 and, followed appropriate filtering and pulse shaping as by the noted series of integrations and the like, an output from block 440 is provided as an xdesignated coordinate channel signals at line 446.

The outputs of x-channel amplification stages 430 and 432 also directed, respectively, through lines 450 and 444 to Summing and Gaussian Filtering 35 function 448 which 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 Control and Start Logic function, identified at block 454 Such signal evidencing a predetermined requisite level to provide a preliminary assurance of valid spatial information, the start logic function of block 40 454 responds to provide gate control over Filtering and Summation Function 440, as through line 456.

The corresponding y-coordinate outputs of amplification stages 434 and 436, respectively, are coupled through lines 458 and 460 to a y-Channel Antisymmetric Summation and Gaussian Filtering function 462 Configured in similar fashion as 45 function 440, the signals introduced to function 462 are subtractively summed, appropriately filtered, and pulse-shaped by a series of integrations to provide a ydesignated coordinate channel signal at line 464 Control over the gated integration function, as well as filtering at block 462 is provided from gate control and start logic block 454 as through line 466 The control system further includes an Energy 50 Discriminator, 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 of absence of valid image information Upon interrogation thereof through line 474 from gate control 55 function 454, and response thereto at line 476, the signal treating cycle is permitted to continue However, as described earlier, where the pertinent energy signals fail to meet the window criteria of Energy Discriminator 470, gate control 454 will effect a resetting of the summing functions, as from lines 478, 480, and 482 to carry out the earlier-described short-cycle operation, thereby permitting the system to 60 more rapidly and efficiently process a next incoming spatial signal It may be noted that Energy Discriminator function 470 may operate effectively within the system even though more than one photon energy level of information is asserted Recall that it is desirable to accommodate the system to the utilization of more than one radiopharmaceutical, each such radio-labeled substance having a different gamma 65 1,578 882 l 1) ray energy characteristic Because the germanium detector system enjoys a considerably improved resolution characteristic, 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 Ke V resolution range as opposed to a generally observed range of about 15 ke V 5 achieved with more conventional scintillation type cameras Accordingly, Energy Discriminator 470 readily may be adjusted to pass those energy signals representing the lower acceptable level of the lower photon energy designated radiopharmaceutical.

The filtering and control electronics for a given quadrant also incorporates a 10 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 The 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, 15 462, and the energy additive Summing function at 448 Detector 484 is associated in time control fashion with gate control 454 through line 490 and may be reset therefrom through lines 478 and 480 The peak value output of detector 484 is presented along line 492 to an Energy Channel Driver 494 for ultimate presentment to quadrant processing control circuitry described later herein Note that the 20 energy channel signal present at line 496 a is designated, Qie.

With the occurrence of an appropriate acceptance of the validity of a spatial signal at Energy Discriminator 470, the x-designated coordinate channel or spatial signal at output line 446 is delivered to an x-Channel Driver 498, the output of which is present in line 500 a Note that this channel signal is designated Q 1, 25 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 504 a and identified as, Q 1, The information now delivered from each quadrant of the overall imaged 30 region now, for purposes of convenience, is designated by the noted labels: Q 1, Q 1, and Qie The composite detector array is assumed to be functioning in quadrature and, thereby, developing corresponding signals from four distinct multicomponent quadrants These quadrants are represented by a "Q" with the noted subscripts altered by the values 1-4 Gate control 454 also provides a clocking or data 35 acceptance signal sequencing input to the control system at line 506 a the signal from which is designated, Q 1, and is arranged to receive a reset signal, designated, Q 1 r, as at line 508 a.

In Figs 8-10 as are described hereinafter, another form of composite detector is revealed which provides a "row-column" form of readout of the spatial 40 and energy data within a select grouping, n, of detector components In each of these embodiments shown, a reduced component linear dimension over which resolution is required is achieved to improve the resolution of the entire system.

Two embodiments of this "row-column" arrangement are revealed wherein a larger effective detector area is provided while the earlier described time constant, 45 TD, is minimized to improve the response rate of the system to processing interaction generated image signals.

Referring now to Fig 8, another composite detector formed as an array of discrete detector components is revealed generally at 680 Illustrated in exploded fashion, the detector 680 is comprised of a plurality of detector components, four 50 of which are shown at 682, 684, 686, and 688 Components 682-688 are dimensioned having mutually equivalent areas as are intended for acceptance of impinging radiation This required 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 55information, would result The detector components illustrated are of the earlierdescribed othogonal strip array variety, each strip thereof being defined by grooves Note, in this regard, that detector component 682 is formed having strips 690 a-690 d located at its upward surface and defined by grooves cut intermediate adjoining ones of the said strips The opposite face of detector component 682 60 similarly is formed having strips 692-692 d defined by intermediately disposed grooves arranged orthogonally with respect to the grooves at the upper surface.

Detector component 684 is identically fashioned, having strips 694 a-694 d at its upwardly disposed surface and lower surface, orthogonally disposed strips 96 a96 d each strip being defined, by intermediately formed grooves Similarly, detector 65 I 1,578,882 component 686 is formed having strips 698 a-698 d at its upward surface defined by intermediately disposed grooves, while its lower surface similarly is formed having strips 700 a-700 d defined by intermediately disposed grooves arranged orthogonally with respect to the grooves of the upward surface Detector component 688 may be observed having strips 702 a-702 d at its upward surface 5 defined by intermediately designated grooves, while its lower surface is formed with strips 704 a-704 d 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 10 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 15 which, as 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 694 a-694 d of detector component 684 This network incorporates discrete resistors 706 a-706 e which are tapped at their common junctions by leads 708 a-708 d extending, respectively, to strips 694 a-694 d Thus configured, 20 network 707 closely resembles the impedance 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 716 a-716 e which are tapped at their common 25 interconnections by leads 718 a-718 d Leads 718 a-718 d, in turn, respectively extend to strips 690 a-690 d of detector component 682 Accordingly, the upwardly disposed surfaces of detector components 682 and 684 are identically associated with respective impedance networks 714 and 707, while the latter are interconnected in row fashion and in parallel circuit relationship to extend to 30 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 directional sense i e along a designated row.

Looking now to the functional interrelationship of detector components 686 35 and 688, a similar coordinate parameter direction or row-type informational collection network is revealed In this regard, note that the impedance network, shown generally at 724, is configured comprising discrete resistors 726 a726 e, the points of common interconnection of which are coupled with respective leads 728 a-728 d Leads 728 a-728 d, in turn, respectively, are connected with strips 40 698 a-698 d at the upwardly disposed surface of detector component 686 Likewise, an impedance network, shown generally at 730 incorporating discrete resistors 732 a-732 e, is associated with detector component 688 by leads 734 a-734 d extending, respectively, from strips 702 a-702 d to the points of common interconnection of network discrete resistors 732 a-732 e Additionally, the output 45 lines as at 736 and 738 of network 730 are connected in parallel circuit relationship with the output of network 724 to provide row readout termini, respectively, at 740 and 742 Here again, a row-type directional spatial coordinate parameter is provided at the upwardly disposed surface of the composite detector 680.

Looking now to the lower surfaces of the detector components, it may be 50 observed that the orthogonally disposed strips of detector component 682 are associated with an impedance network identified generally at 744 Network 744 incorporates discrete resistors 746 a-746 e which are coupled from their mutual interconnection by leads 748 a-748 d, respectively, to strips 692 a-692 d of detector 682 Similarly, the orthogonally disposed strips of detector component 686 are 55 associated with an impedance network 750 In this regard, network 750 is formed of discrete resistors 752 a-752 e which, in turn, are coupled, respectively, with strips 700 a-700 d by leads 754 a-754 d 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, 60 which serve to collect all spatial information of the associated paired surfaces of detectors 682 and 686.

Looking to the lower surface of detector component 684, note that a network, designated generally at 764, incorporating discrete resistors 766 a-766 e is functionally associated with strips 696 a-696 d, respectively, by leads 768 a-768 d 65 I 1,578,882 In similar fashion, an impedance network, designated generally at 770, is associated with the orthogonally disposed strips 704 a-704 d at the lower surface of detector component 688 Note that the network, incorporating discrete resistors 772 a-772 e, is functionally associated with the array of strips 704 a704 d, respectively, by leads 774 a-774 d Networks 764 and 770 are electrically coupled in 5 parallel circuit fashion by collector leads 776 and 778 extend to principal collection points of termini 780 and 782 Thus interconnected, the lower surfaces of 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 10 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 15 charge collection time constant of a single detector Connection with the row and column readouts for given spatial coordinate parameters outputs will be seen to be provided by treating circuits which distribute coordinate channel spatial and energy channel signals into analyzing and distributing circuitry Preamplification stages, as described in connection with Fig 2, are coupled with each row readout 20 point as at 720 and 722 or 740 and 742, as well as with each column readout, as at 760 and 762 and 780 and 782 Such preamplification stages generally are located within or near the cryogenic environment of the detector itself The mounting of the contact leads between each of the networks and an associated strip array surface of a detector generally may be carried out by resort to biased contact 25 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 a detector composite is revealed generally in Fig 9 at 800 30 Referring to that figure, the composite detector, or portion thereof, 800, is shown to comprise four discrete detector components 802-808 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 35 character, while, similarly, so lightly doping opposite surface with a ptype 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 802, are shown on the upward surface at 810 and 812 and at the lower surface at 814 and 816 Conductive surfaces 810-816 may be deposited upon the 40 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 character within the surfaces of detector components 802-808, mention may be made of the following publications: 45 XXIV 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.

XXV Berninger, W H, "Pulse Optical and Electron Beam Excitation of Silicon Position Sensitive Detectors", IEEE, Trans Nucl Sci, Vol V S 21, Page 374 50 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 define surfaces and collect at the conductive strips 810-816 For the upwardly disposed surface, these charges then are collected along conduit 818, 55 coupled with conductive strip 812, and conduit 819, coupled with conductive strip 810 The adjacently disposed detector 804 is fashioned in similar manner, the upward surface thereof 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 60 functionally associated with conductive strips 824 and 826 Note that the latter conductive strips are arranged orthogonally with respect to those at 820 and 822.

1 s 1,578,882 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 coupled by lead or conduit 830 to conductive strip 810 of detector 802 Thus interconnected, it will be apparent that any interaction occurring within detector component 804 will be "seen" as a charge division between strips 820 and 822, for one coordinate 5 parameter, along leads 828 and 830, as well as output conduits 818 and 819 As is apparent, a desirable simplification of the structure of the composite detector is available with this form of row readout.

Looking to the adjacently disposed row of detector components 806 and 808, it may be noted that detector component 806 is formed incorporating resistive layers 10 or regions in its opposed surfaces aligned for the acceptance of radiation and, additionally, incorporated conductive strips as at 832 and 834 at the extremities of its upward surface as well as orthogonally oriented conductive strips 836 and 838 about the extremities of its lowermost and oppositely disposed surfaces.

Identically structured detector component 808, similarly, is formed having 15 resistive surfaces or regions arranged normally to the direction of radiation impingement The surfaces also incorporate conductive strips, as at 840 and 842 at the upwardly disposed side and, at 844 and 846, orthogonally disposed at the lowermost surface.

Coupled in similar row-type fashion as detectors 802 and 804, the conductive 20 strips of detectors 806 and 808 are directly electrically associated by leads 848 and 850 Note, in this regard, that lead 848 extends between conductive strips 840 and 832 while lead 850 extends between conductive strips 842 and 834 The output of that particular row at the upward surface of the composite detector is represented by leads 852 and 854 25 A columnar interconnection of the detector components is provided between the 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 detector components are present at conduits 860 and 862 extending, respectively, from 30 conductive strips 836 and 838.

In similar fashion, the columnar association of detector components 804 and 808 is provided by leads 864 and 866 which, respectively, extend between conductive strips 824 and 826 of detector 804 to corresponding conductive strips 844 and 846 of detector component 808 The readouts for the column association of 35 detectors 804 and 808 are provided by conduits 868 and 870 extending, respectively, from conductive strips 844 and 846 of detector component 808.

As in the embodiment of Fig 8, the output conduits 818, 819 and 852, 854 are of a "row" variety having a designated spatial coordinate parameter and are addressed to initial preamplification stages prior to their association with logic 40 circuitry for deriving imaging information for that particular spatial coordinate.

Similarly, the "columnar" outputs at conduits 860, 862 and 868, 870 are directed to preamplification stages, thence to appropriate circuitry for treating that spatial coordinate 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 45 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 8 and 9 reveals certain consistent characteristics between the 50 embodiments 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 evolves 55 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 8 or the interconnection of conductive strips shown in Fig 60 9 Another aspect typifying the structure, 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 65 I 1,578,882 directional sense Because the composite detector embodiments shown in Figs 8 and 9 operate substantially in the same functional manner, their outputs are identified with the same spatial coordinate directional labels For instance, the xdesignated coordinate outputs at lines 722 and 720 of the embodiment of Fig 8 respectively, are identified as (X 1 A) and (X 1 B); while the parallel row y designated 5 coordinate outputs as at lines 742 and 740, respectively, are identified as (X 2 A) and (X 2 B) Similarly, the orthogonally disposed y designated coordinate parameter outputs, as represented for instance, at lines 762 and 760, respectively, are identified as (Y 1 A) and (Y 1 B) Next adjacent to that column of the composite detector, are the detectors whose outputs are represented at 780 and 782 and are lo identified, respectively, as (Y 2 A) and (Y 2 B) This same labeling procedure will be seen to be utilized in the composite detector embodiment of Fig 9.

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 15 improvement is experienced in the resolution of the camera system which may be expressed by the equation:

AEL Ax= ( 20) E Where, Ax, represents spatial resolution in terms of distance; AE, is absolute energy resolution, L, is length of a detector component as measured parallel to the 20 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 equation ( 20) above, the expression, AE E is readily identified as the fraction (or percentage) of energy resolution and is fixed 25 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 example if the detector pictured in Fig 22 were connected as a single detector the measuring distance would be 2 L, effecting a 30 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 35 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 10 40 Referring to that figure, a composite detector formed as an array of discrete detector components is revealed generally at 880 As in the earlierdiscussed embodiments, detector or detector portion 880 is shown in exploded fashion for purposes of clarity and comprises a plurality of detector components, four of which are shown at 882, 884, 888, and 886 Components 882-888 are dimensioned having 45 mutually equivalent areas as are intended for acceptance of impinging radiation and are formed as of an orthogonal strip array variety, each strip thereof being defined by grooves formed within the detector surfaces Of course, other, stripdefining configurations will occur to those skilled in the art Detector 882 is formed having strips 890 a-890 d defined by grooves cut within its upward charge 50 collecting surface The opposite face of detector component 882 similarly is formed having strips 892 a-892 d defined by intermediately positioned grooves arranged orthogonally with respect to the grooves at the upper surface Detector component 884 is identically fashioned, having strips 894 a-894 d formed at its upwardly disposed charge collecting surface; and at its lower surface, orthogonally 55 disposed strips 896 a-896 d, adjacent said strips being defined by intermediately formed grooves Similarly, detector component 886 is formed having strips 898 aI 1,578,882 898 d at its upward surface, adjacent ones of the strips being defined by intermediately disposed grooves, while its lower surface similarly is formed having strips 900 a-900 d 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 902 a-902 d at its upward surface adjacent ones of which 5 are defined by intermediately designated grooves, while its lower surface is formed with adjacently disposed strips 904 a-904 d separated by intermediately disposed grooves arranged orthogonally to the grooves of the upward surface thereof.

In the instant embodiment, strips 894 a-894 d of detector component 884 are directly, electrically associated with corresponding row strips 890 a-890 d of 10 component 882 by electrical leads, respectively identified at 906 a-906 d 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 890 a-890 d opposite the edges thereof coupled with electrical leads 906 a-906 d Network 908 comprises serially 15 associated discrete resistors 910 a-910 e which are tapped at their common junctions by leads 912 a-912 d extending, respectively, to strips 890 a890 d The output, or readout points for the thus defined "row" of the composite detector assembly are represented at 914 and 916 and are provided the same respective spatial or x designated coordinate parameter output labeling, (x B), (x A) as are 20 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 902 a-902 d are electrically coupled with strips 898 a-898 d by respective electrical leads 918 a-918 d The "row" coupling thus provided is associated with an impedance network shown 25 generally at 920 Network 920 is formed comprising serially associated discrete resistors 922 a-922 e which are tapped at their common interconnections by leads 924 a-924 d Leads 924 a-924 d, respectively, extend to strips 898 a-898 d of detector 886 The principal termini of the thus defined "row" are identified at 926 and 928, having outputs respectively labeled (x 2 B), (x 2 A) 30 Looking now to the lower surfaces of the detector components, the orthogonally disposed strips of detector component 882 are electrically coupled as shown with the corresponding strips of detector component 886 by electrical leads 930 a-930 d The thus coupled strip arrays of those detector components are associated in "columnar" fashion with an impedance network identified generally 35 at 932 Network 932 comprises serially associated discrete resistors 934 a934 e, the interconnections between which are connected as shown with strips 900 a900 d of component 886 by leads respectively identified at 936 a-936 d The readout termini for the thus defined "column" association of detectors 886 and 882 are present at 938 and 940 and the corresponding spatial or y designated coordinate parameter 40 outputs are identified respectively as (y A) and (y B).

The lower surfaces of detector components 884 and 888 similarly are associated in "columnar" readout fashion, strips 896 a-896 d of the former being electrically connected through respective leads 940 a-940 d to strips 904 a-904 d of the latter The thus established "columnar" readout is associated with an 45 impedance network identified generally at 942 and comprising serially associated discrete resistors 944 a-944 e Strips 904 a-904 d, respectively, are coupled with the interconnection of the resistors 944 a-944 e of network 942 by leads 946 a-946 d.

As in the earlier embodiments, the principal readouts of the thus defined "columnar" detector component coupling are represented at 948 and 950 and their 50 spatial coordinate parameter outputs are labeled, respectively, (y 2 A) and (y 2 B).

From the foregoing description of the composite detector arrangement 880 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 55

Claims (1)

1. WHAT WE CLAIM IS:-

   1 A solid state detector for receiving collimated radiation of given photon energy or energies emitted from a region of interest of an isotopic material, including:

   a plurality of solid state detector components, each having a first surface 60 arranged for exposure to impinging radiation and a second surface disposed opposite and substantially parallel to said first surface, each said detector component producing discrete charges at spatially definable locations at which radiation is incident thereon:

   1,578,882 each of said first and second surfaces of each said detector component being coupled to first and second charge dividing impedance means respectively which produce position signals relating a location to respective first and second spacial coordinates; said detector components being arranged and connected to the first and second impedance means so that groupings of adjacently disposed ones of said 5 first surfaces produce in said first impedance means signals relating a location with said first spacial coordinate, and so that groupings of adjacently disposed ones of said second surfaces produce in said second impedance means signals relating a location with said second spatial coordinate.

   2 A detector as claimed in Claim 1 wherein said impedance means for each 10 said detector component opposed surface provides said position signals as charges of values defining the location of radiation along the spatial coordinate associated with said surface.

   3 A detector as claimed in Claim 1 or Claim 2, wherein: said second surfaces of a said detector component define arrays of mutually parallel strips, each said 15 strip having a discrete area influenced by the occurrence of a charge thereunder:

   said impedance means for each said surface being present as a resistor network comprising serially coupled resistor components having opposed output terminals and each said strip being coupled intermediate a unique pair of said resistor components to provide said position signals as charges at said opposed output 20 terminals having values defining the location of the strip influenced by a corresponding discrete charge resulting from the incidence of radiation; and wherein the connection of said components associates, in parallel circuit relationship, the output terminals of said resistor networks associated with a given grouping of said surfaces 25 4 A detector as claimed in Claim 3, in which the said array of strips of one said surface of a detector component are orthogonally disposed with respect to the array of strips of said opposed surface oppositely disposed with respect thereto.

   A detector as claimed in Claim 1 or Claim 2, in which: said impedance means are present as a surface-disposed region of predetermined resistance situate 30 at a said detector component second surface and electrically coupled with elongate mutually spaced conductors arranged upon said surface substantially at opposite edges of said component, the elongate dimension of said conductor being oriented in a direction transverse to the spatial coordinate associated with said surface; and wherein the connection of said components associates, in series circuit 35 relationship, the adjoining said conductors situate at the associated surfaces of said adjacently disposed solid state detector components.

   6 A detector as claimed in Claim 1 wherein: said solid state detector components are disposed in substantial mutual adjacency; and interconnecting means are provided directly electrically connecting the said impedance means of 40 said groupings of surfaces.

   7 A detector as claimed in Claim 1, wherein:

   said solid state detector components are disposed in substantial mutual adjacency; and any two adjacent said surfaces of each of any two said adjacent detector 45 components produce signals of relating said location to one of said coordinates.

   8 A detector as claimed in Claim 1, wherein:

   said solid state detector components are disposed in substantial mutual adjacency; said first surfaces of said detector components are disposed in substantially 50 coplanar relationship; and two ad jacent said coplanar surfaces of any two said adjacent detector components are disposed within a said linearly orientated grouping thereof.

   9 A detector as claimed in Claim 8, wherein:

   said impedance means for each said second surfaces provide said position 55 signals as charges of values defining said location along the spatial coordinate associated with said second surface.

   A detector as claimed in Claim 8, in which:

   said impedance means are present as a surface disposed region of predetermined resistance situate at a said detector component second surface and 60 electrically coupled with elongate mutually spaced conductors arranged upon said surface substantially as opposite edges of said component, the elongate dimension of said conductors being oriented in a direction transverse to the spatial coordinate associated with said surface; and wherein the connection of said components associates, in series circuit relationship, the adjoining said conductors situate 65 1.578 882 19 ( 1,578,882 20 _ within the associated surfaces of said adjacently disposed solid state detector components.

   11 A detector as claimed in Claim 8, wherein:

   said solid state detector components are disposed in substantial mutual adjacency; and interconnecting means are provided directly electrically 5 connecting the said impedance means of said groupings of surfaces.

   12 A detector as claimed in any one of the preceding claims, wherein:

   said solid state detector components are formed of germanium.

   TREGEAR, THIEMANN & BLEACH, Chartered Patent Agents, Enterprise House, Isambard Brunel Road, Portsmouth P 01 2 AN and 49/51 Bedford Row, London WC 1 V 6 RU Agents for the Applicants Printed for Her Majesty's Stationery Office, by the Courier Press, Leamingtoln Spa 1980 Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A IAY, from which copies may be obtained.