Abstract:
A radiation detection camera head having a focal-plane array of pixelated detectors having constant pitch between pixels over the whole of the camera head, while using detector modules having normal production tolerances, and which can nevertheless be readily removed and replaced in the detector array by means of predetermined gaps between adjacent detector modules. The pixels on the side walls of the detector modules have reduced size to maintain constant pitch over the array in spite of production variation between modules. The reduction in sensitivity due to this reduced size is compensated for by the addition of insulated conductive bands on the side walls. The head collimator is such that the septa fall between pixels and between modules, such that head sensitivity is maintained at its optimum value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application 60/588,191, filed Jul. 14, 2004, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to the field of radiation detection, and in particular to the field of X-ray and Gamma ray detection and imaging cameras.  
       BACKGROUND OF THE INVENTION  
       [0003]     Solid-state cameras are capable of acquiring high quality images due to their good energy resolution and their high spatial resolution. The energy resolution is mainly dependent on the intrinsic physical properties of the materials from which the detectors of the camera head are made. Such materials are generally various types of semiconductors, such as, CdTe, CdZnTe, Si, GaAs, Ge, InGaAs, and AlGaAs. On the other hand, the spatial resolution of solid-state cameras is mainly dependent on the geometrical design and the dimensions of the pixels that form the focal-plane arrays of the detectors in the camera heads. In the field of X-ray and Gamma ray imaging, the spatial resolution is dictated by the convolution between the resolution of the pixels in the detector focal plane and the resolution of the collimator that is generally placed in front of this focal plane.  
         [0004]     In order to produce a high quality image, the detector must be capable of achieving high energy resolution, high spatial resolution, and high sensitivity, which provides good contrast. In addition the spatial transformation from the object plane to the focal plane array should be done accurately. In order to produce this transformation accurately and without image deformation, the pitch between the pixels in the focal-plane of the detectors of the camera head should be maintained constant over the whole of this plane.  
         [0005]     A technology known as Z-technology, whose development started in the early 1970&#39;s, enables the production of a focal plane array of any desired size by butting individual pixelated detector modules from all their sides. Z-technology is described in a recent review article entitled “Applications of Advanced Z-Technology Focal Plane Architectures” by J. C. Carson, published in SPIE Vol. 930, Infrared Detectors and Arrays, pp. 164-182 (1988), and variously in U.S. Pat. Nos. 4,490,626, 4,525,921, 4,551,629 and 4,555,623, all of which are hereby incorporated by reference, each in its entirety. This butting capability is achieved by integrating all the read-out electronics coupled to each of the detector pixels, on the back side of the detector and in a form of stacks of layers in the Z-direction, the detector plane being oriented in the X-Y plane. This configuration, with the electronic read-outs in the Z-direction, leaves the module sides free to be butted with their neighbors and with surrounding modules.  
         [0006]     In this technique, each module includes an integral number of pixels, set apart from each other by the pixel pitch. To maintain this pitch over the whole of the focal plane, which is required for obtaining an accurate image, individual modules must be butted with no dead spaces between them, and at a fixed pitch between module and module. Butting of the modules with no spaces between them also assures that there will be no dead areas in the camera head, which do not contribute to image acquisition.  
         [0007]     However, normal production techniques are such that the module dimensional tolerances, and those of the assembly components by means of which they are mounted onto the electronic base board in the camera head, may result in either unacceptable gaps between neighboring modules, or conversely, interference between the adjacent edges of the modules, such that they cannot even be fitted into the base board side-by-side. Even if all the modules could be fitted into the array, the periodicity of the pixel pitch would be degraded because of these tolerances. Production of the modules with such tight tolerances that they would all fit together “perfectly” would make the cost of such a camera head prohibitive.  
         [0008]     There therefore exists a need for a method of constructing and arranging detector modules, which can be tiled to produce focal-plane arrays of pixelated detectors having constant pitch, such that, in spite of generally used production tolerances for these modules, they can be mounted in a continuous and regular tiled pattern on a Detector Carrier Board (DCB). Furthermore, the need exists that in such a focal-plane arrays of detector modules, the modules can be freely removed from and inserted into the DCB, while still maintaining constant pitch of the pixels over the whole focal-plane of the cameras.  
         [0009]     The disclosures of each of the publications mentioned in this section and in other sections of the specification are hereby incorporated by reference, each in its entirety.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention seeks to provide a new radiation camera head having a focal-plane array of pixelated detectors having constant pitch between pixels over the whole of the camera head, while using detector modules having normal production tolerances, and which can nevertheless be readily removed and replaced in the detector array. Furthermore, the head collimator is such that the head sensitivity is maintained at its optimum value.  
         [0011]     There is thus provided in accordance with a preferred embodiment of the present invention, a radiation camera head incorporating an array of pixelated detector modules, each module having essentially the same pixel pitch. The pitch between modules is made to be slightly larger than the module size, by an amount exceeding the largest production tolerance expected between module and module, or between any of the modules&#39; associated mounting hardware, such that a gap is generated between modules which enables the simple removal and insertion of modules in the array, without interference from the varying production sizes of the modules.  
         [0012]     Furthermore, in accordance with another preferred embodiment of the present invention, in order to maintain constant pixel pitch over the whole of the array, in spite of the gaps between neighboring modules, the pixels adjacent to the side walls of each pixels are preferably of reduced size, the reduction in dimension of these pixels being “donated” to provide the space required for the inter-module gaps. However, since reduced size pixels have reduced sensitivity, and constant overall pixel sensitivity is important to avoid contrast changes over the image, insulated conductive bands are preferably applied to the module side-walls, in order to improve the performance of these side wall pixels.  
         [0013]     In accordance with yet another preferred embodiment of the present invention, the collimator is arranged such that its septa fall on the gaps between detector pixels, and hence also on the gaps between modules. In this manner, the collimator is registered to the pixels, and does not contribute any loss of sensitivity in the array because of shadowing of active pixel areas of the detector. As a result of this novel construction, there is provided a radiation camera head with the advantages that it: 
    (i) maintains constant pitch between pixels, thus avoiding deformation of the acquired image;     (ii) utilizes a collimator that is properly registered relative to the pixels, thus increasing the detection sensitivity;     (iii) minimizes detection loss due to dead areas produced by the inter-module gaps; and     (iv) allows the insertion and removal of the modules respectively into and out of the camera head, while still maintaining advantages (i) to (iii) mentioned above.    
 
         [0018]     There is also provided in accordance with another preferred embodiment of the present invention, a radiation detector camera head comprising an array of at least two pixelated detector modules mounted in the head, wherein each of the at least two modules has module lateral dimensions, the modules being mounted at a pitch at least equal to the largest module lateral dimension of any of the at least two modules, such that a gap generally exists between an adjacent pair of the at least two modules, and wherein the pixelated detector modules have side walls, the pixels on the modules not located adjacent to a side wall having first lateral dimensions, and those disposed along a side wall having second lateral dimensions generally smaller than the first lateral dimensions.  
         [0019]     In the above-described radiation detector camera head, any one of the adjacent pair of modules may be removable from or insertable into the head, without interference from the other of the adjacent pair. Furthermore, the gap between the modules is designed to compensate dimensionally for the fact that the second lateral dimensions are generally smaller than the first lateral dimensions, such that an essentially constant pixel pitch is maintained across the array. The constant pitch between pixels is operative to reduce deformation of images acquired by the camera.  
         [0020]     Additionally, in accordance with yet another preferred embodiment of the present invention, in the above-described radiation detector camera head the module lateral dimension may vary according to the production tolerance of the module and has a maximum permitted value, and the gap is preferably at least twice as large as the maximum permitted value. Furthermore, if the at least two modules are mounted in the camera head by means of mounting hardware, the mounting hardware too may vary in lateral dimension according to the mounting hardware production tolerance and may have a maximum permitted value, and the gap may be at least twice as large as the sum of the maximum expected production tolerances of the modules and the mounting hardware.  
         [0021]     There is further provided in accordance with yet another preferred embodiment of the present invention, a radiation detector camera head comprising an array of at least two pixelated detector modules mounted in the head, wherein each of the at least two modules has module lateral dimensions, the modules being mounted at a pitch at least equal to the largest module lateral dimension of any of the at least two modules, such that a gap generally exists between an adjacent pair of the at least two modules, and wherein the pixelated detector modules have side walls, the pixels on the modules not located adjacent to a side wall having first lateral dimensions, and those disposed along a side wall having second lateral dimensions generally smaller than the first lateral dimensions, and wherein the camera head also comprises a collimator having multiple holes, the holes being arranged in a pitch generally equal to the pitch of the pixels of the modules and the holes being spaced by septa, and wherein the collimator is arranged such that the septa fall generally in the region between the detector pixels.  
         [0022]     In the above-described camera head, the collimator and the modules are preferably arranged such that the septa also fall on the gaps between the modules. Consequently, the camera head preferably reduces detection loss due to dead areas in the array. Furthermore, any one of the adjacent pair of modules may be either removable from or insertable into the head without interference from the other of the adjacent pair. The gap between the modules preferably compensates dimensionally for the second lateral dimensions being generally smaller than the first lateral dimensions, such that an essentially constant pixel pitch is maintained across the array. In the above-described radiation detector camera head the constant pitch between pixels is preferably operative to reduce deformation of images acquired by the camera.  
         [0023]     In accordance with still another preferred embodiment of the present invention, in the above-described radiation detector camera head, the module lateral dimensions generally vary according to the production tolerance of the module and have a maximum permitted value, and the gap is preferably at least twice as large as the maximum permitted value. The at least two modules may be mounted in the camera head by means of mounting hardware, and the mounting hardware may also vary in lateral dimension according to the mounting hardware production tolerance and may have a maximum permitted value, and the gap is preferably at least twice as large as the sum of the maximum expected production tolerances of the modules and the mounting hardware.  
         [0024]     There is further provided in accordance with still another preferred embodiment of the present invention, a radiation detector camera head comprising an array of at least two pixelated detector modules mounted in the head, and wherein each of the at least two modules has module lateral dimensions, the modules being mounted at a pitch at least equal to the largest module lateral dimension of any of the at least two modules, such that a gap generally exists between an adjacent pair of the at least two modules, and wherein the pixelated detector modules have side walls, the pixels on the modules not located adjacent to a side wall having first lateral dimensions, and those disposed along a side wall having second lateral dimensions generally smaller than the first lateral dimensions, and wherein the camera head also comprises an insulated conductive band applied to at least one of the side walls of at least one of the modules, such as to compensate for reduced sensitivity arising from the smaller lateral dimensions of the pixels disposed along the at least one side wall.  
         [0025]     In the above-described radiation detector camera head, the gap is preferably sufficiently large also to accommodate the insulated conductive band. Any one of the adjacent pair of modules may be either removable from or insertable into the head, without interference from the other of the adjacent pair. Furthermore, the gap between the modules compensates dimensionally for the second lateral dimensions being generally smaller than the first lateral dimensions, such that an essentially constant pixel pitch is maintained across the array. This constant pitch between pixels is preferably operative to reduce deformation of images acquired by the camera.  
         [0026]     In accordance with a further preferred embodiment of the present invention, in the above-described radiation detector camera head, the module lateral dimensions may vary according to the production tolerance of the module and have a maximum permitted value, and the gap is preferably at least twice as large as the maximum permitted value. Additionally, the at least two modules are preferably mounted in the camera head by means of mounting hardware, the mounting hardware also varying in lateral dimension according to the mounting hardware production tolerance and having a maximum permitted value, and wherein the gap is at least twice as large as the sum of the maximum expected production tolerances of the modules and the mounting hardware.  
         [0027]     There is also provided in accordance with yet a further preferred embodiment of the present invention, a radiation detector camera head as described above, and also comprising a collimator having multiple holes, the holes being arranged in a pitch generally equal to the pitch of the pixels of the modules and being spaced by septa, and the collimator being arranged such that the septa fall generally in the region between the detector pixels. In this camera head, the collimator and the modules are preferably arranged such that the septa also fall on the gaps between the modules. Such a camera head preferably reduces detection loss due to dead areas in the array. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0029]      FIG. 1  is a schematic cross-sectional view from the side of a prior-art detector array, constructed according to conventional Z-technology;  
         [0030]      FIG. 2  is a schematic cross-sectional view from the side of a camera head incorporating a detector array, constructed and operative according to a preferred embodiment of the present invention, in which the module pitch is made slightly larger than the module size, and the collimator is arranged such that its septa fall on gaps between detector pixels;  
         [0031]      FIG. 3  is a composite schematic illustration from a side view and a top view, of the camera head shown in  FIG. 2 , but incorporating a further preferred embodiment for improving according to the present invention, wherein the side-wall and corner pixels of the detector are reduced in size to enable the maintenance of a constant pixel pitch in spite of the inter-module gaps, and also including a conductive band around each module to maintain the sensitivity of the reduced size pixels; and  
         [0032]      FIG. 4  is a schematic drawing in enlargement of two modules taken from the plan view of the camera head of  FIG. 3 , with the collimator in place. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Reference is now made to  FIG. 1  which is a schematic cross-sectional illustration from the side of a prior-art detector array constructed according to conventional Z-technology. According to this technology, individual detector modules  100  are tiled by a butting process, to form a focal plane array  102  of cathodes  104 . The tiling of modules  100  is preferably achieved by mounting the modules on a Detector Carrier Board (DCB)  106 . The DCB  106  is generally made of Printed Circuit Board (PCB) and may include mounting holes  108  either for direct mounting of the modules  100 , or alternatively for receiving the pins  112  of mounting sockets  110 . Modules  100  are preferably mounted on sockets  110  by inserting their Pin Grid Array (PGA)  114  into mounting holes  116  of sockets  110 . PGA  114  is arranged along a further PGA frame  118 . PGA frame  118  is attached to carrying plate  120 , to which a detector or detectors  122  are bonded by conductive glue  124 . The conductive glue  124  electrically and mechanically couples pixels  125  of detectors  122  with contact pads  127  of plate  120 . Carrying plate  120  also carries an Application Specific Integrated Circuit (ASIC)  129  whose inputs are electrically connected to each of pixels  125  for processing the signal produced by these pixels. The outputs of ASIC  129  are electrically connected to PGA  114  to transmit the signals, processed by the ASIC to the read-out system through the Detector Carrier Board  106 . The size of each detector plane  126  is generally larger than or equal in size to the carrying plate  120  and carrying plate  120  is generally larger than or equal in size to the PGA frame  118 . PGA  114  is used for mounting modules  100  on the DCB by inserting the pins of the PGA  114  directly into holes  108  in the DCB  106  or into holes  116  of sockets  110  attached to the DCB  106 .  
         [0034]     The holes  108  in the DCB  106  are arranged in a form of groups of holes under sockets  110 . Groups of holes  108  have the same spatial arrangement as the pins  112  of sockets  110  and thus have the same pitch as the pitch of pins  112 . The pitch space between the groups of holes  108  is equal to the lateral length  126  of modules  100 . The cathode plane of detectors  122 , carrying plate  120 , PGA frame with its pins  114 , socket  110  with its pins  112 , and the groups of holes of PGA  118 , should all be centered around the symmetry axis of modules  100 . Such a symmetry axis  128  is shown for clarity, only on the second module  100  from the left of the drawing. To produce buttability with no dead area between modules  100 , the production accuracy of these modules would thus need to be extremely high.  
         [0035]     On the right hand side of  FIG. 1  are shown two more modules  101  and  103 , having the same components as modules  100 , but showing the effects of production tolerances on the modules. Module  101  illustrates an extreme situation when all the production tolerances in the group of detectors  122 , carrying plate  120 , PGA frame with its pins  114 , socket  110  with its pins  112 , and PGA holes  118  are such as to be accumulative in one direction, shown as the direction to the right in  FIG. 1 . On the other hand module  103  illustrates another extreme situation when all the above tolerances are accumulated in the opposite direction, to the left. It can be seen that in this situation, it is impossible to insert module  101  in DCB  106 , or even into its socket without interfering with its neighboring module  103 . It is thus clear that butting of modules with no dead space between them, according to the prior art construction methods, requires very tight production tolerances that are economically unrealistic to achieve.  
         [0036]     Reference is now made to  FIG. 2 , which is a schematic cross-sectional view from the side, of a camera head  190  incorporating a detector array, constructed and operative according to a preferred embodiment of the present invention. According to this construction, the assembly of modules  100  are mounted into sockets  110  on the DCB  106  in a manner that enables correct insertion even when the modules, or any of their associated mounting components, are produced with normal production tolerances. According to this preferred configuration, pitch  200  between the groups of holes  108  should be greater than module size  126 . For the tightest tolerances that can be economically achieved today, pitch  200  should be larger than module dimension  126  by at least 250-300 microns. Such an enlarged pitch  200  is also essentially to allow for simple replacement of any module  100 , when such replacement is needed. The implication of this 250-300 micron reserve is that for two neighboring modules  100  which have dimensions exactly as designed and hence zero tolerances, the gap  202  between those modules is 250-300 microns. For another group of modules with the maximum allowed tolerances, a situation may arise in which one of the modules will almost touch its neighbor on one side and will produce a gap of 500-600 microns on the other side.  
         [0037]     Each of modules  100  contains integral number of pixels  125 . In this configuration, when modules  100  are tiled with spaces  202  between them, the constant pitch of pixels  125  is not maintained over the focal plane array  102  over the whole camera head.  
         [0038]     A collimator  204  having septa  210  and holes  206  is preferably disposed in front of the focal plane array  102 . The holes and septa are arranged to have a pitch  208  equal to the pitch between the pixels  125  within each module  100 . The holes are arranged to transmit the incident radiation to the surface of detectors  122  in modules  100 . The ideal alignment of collimator  204  is achieved when the projections of its septa coincide with a grid of lines passing between pixels  125 . When the collimator  204  has a pitch  206  having an ideal alignment with respect to the pixels  125  of all of the modules  100 , the collimator is known as a registered collimator. The ability to align collimator  204  in a registered position is very important for two reasons: 
    (i) Events produced by absorbing photons in the vicinity of the symmetry lines between pixels  125  suffer from the charge sharing effect, as described in the article by A. E. Bolotnikov et al., entitled “Charge loss between contacts of CdZnTe pixel detectors”, published in Nuclear Instruments and Methods in Physics Research A, Vol. 432, pp. 326-331 (1999). The sphere of the charge carriers produced by the absorbed photon is split into two groups of charge carriers. Each of these groups drifts toward different adjacent pixels  125  under the influence of the symmetric electrical field in the mid-region between the pixels. Events occurring in the mid region between pixels are not therefore suitable for measuring the photon energy, since the energy of the absorbed photon is divided and measured by two different pixels  125 .     (ii) Furthermore, if there exists surface conductivity between adjacent pixels  125 , the mid-region between these pixels suffers most from surface recombination and charge loss, as described by Bolotnikov,  op. cit . This charge loss is also a contributing factor to the inability to measure the energy of photons absorbed in the between-pixel regions. For both of the above reasons, this region is essentially useless for imaging by single photon counting.    
 
         [0041]     The septa  210  of collimator  204  screen the radiation impinging on the camera head and prevent the incidence of photons on the regions of the detectors that are under these septa, which cannot therefore be used for image processing. In order to reduce loss of true events, and in order to increase the camera sensitivity, there should be essential spatial coincidence between these ineffective areas, i.e. between the areas in the vicinity of the mid lines between the pixels  125 , and the areas immediately beneath the septa  210  of the collimator  204 . This overlap defines the registration of the collimator.  
         [0042]     It is therefore evident that maintaining constant pitch between pixels over the whole of the focal plane is very important for two reasons: 
    (i) For producing an image without deformations, and     (ii) For ensuring that the collimator is registered over the whole of the focal plane, to provide high detector efficiency.    
 
         [0045]     As explained hereinabove, in camera head  190 , the gaps  202  allow the desired insertion and replacement of modules  100  with normal production tolerances into the DCB  106 , or into sockets  110 . However, these gaps at the same time have the disadvantage that they prevent the maintenance of the desired constant pixel pitch over the whole active area of the camera, and thus result in deformed images with reduced sensitivity. The dead areas produced by the gaps  202  between adjacent modules further reduce the sensitivity of the head  190 .  
         [0046]     Reference is now made to  FIG. 3 , which is a composite schematic illustration of a camera head similar to that shown in  FIG. 2 , but incorporating a further preferred embodiment according to the present invention, which results in a solution for the above-mentioned disadvantage of the preferred embodiment shown in  FIG. 2 .  FIG. 3  shows the detector from two views. The upper part is a cross-sectional view from the side of a camera head  300  with collimator  302 . The lower part is a plan view of the same head  300 , but with the collimator  302  removed to show the pixelated detector array pattern. The relative positions between the views in the upper and lower parts of the drawing are correlated by means of the dashed arrows  336 .  
         [0047]     Collimator  302 , having holes  312  and septa  314 , is placed above the cathodes  316  of modules  308  that form the focal plane array of the camera. The collimator is such that the holes have a pitch  318  equal to pitch  320  of the pixels  304  on the detectors  322  in each of the modules  308 . In the plan view in the lower part of  FIG. 3 , the pixels  304  and edges  324  of detectors  322  are illustrated by broken lines to indicate that they are situated below the visible upper surface of the detectors. The pitch of the collimator holes and that of the pixels are preferably equal and constant over the whole of the camera-head  300 . Furthermore, this equality of pitch is preferably maintained between modules  308 . The maintenance of constant pixel pitch even between modules, where there is a gap  306 , can only be achieved by reducing the dimensions of those of the pixels situated along side-walls  307  of the modules. While the dimensions of the “inland” pixels can be expressed as  320 × 320 , where  320  is the pixel pitch, the dimensions of the side-wall pixels are given by  320 ×( 320 − 306 /2), where  306  is the gap dimension. Similarly, the dimensions of the corner pixels are given by ( 320 − 306 /2)×( 320 − 306 /2). According to this preferred embodiment of the present invention, it is the use of different sizes for the inland, the side-wall, and the corner pixels that enables the maintenance of constant pitch between modules and over the whole of the head, while still maintaining gaps between modules to enable easy replacement and fitting of the modules, and constant pitch, as described above in relation to  FIG. 2 .  
         [0048]     However, side-wall and corner pixels suffer from reduced performance due to surface effects. In addition, these pixels no longer have the square symmetry of the inland pixels. For the above reasons the performance of the side-wall and corner pixels is poor. It is possible to improve the performance of these pixels, and to even bring their performance back to the level of the inland pixels by applying insulated conductive bands  332  to side walls  307 , as described in U.S. Pat. No. 6,034,373, hereby incorporated by reference in its entirety, for “Semiconductor Radiation Detector with Reduced Surface Effects”, to some of the inventors in the present application. The use of the side-wall conductive bands  332  is an important feature for ensuring the performance of the camera according to the present invention.  
         [0049]     However, the conductive bands  332  are not an integral part of the detector material, but are additional components applied to the outer walls of the modules  308 , increasing their dimension. Consequently, the gaps  306  must be made large enough not only to allow the insertion of the modules  308  into the Detector Carrier Board  106  and their withdrawal therefrom, but they must also allow enough space to accommodate the conductive bands  332 .  
         [0050]     In the embodiment of  FIG. 3 , the modules  308  are shown also to include components equivalent to those described in the modules  100  shown in  FIG. 2 , including the PGA  326 , the PGA frame  328 , and the carrier plate  330 . The only essential way by which modules  308  differ from modules  100  of the embodiment shown in  FIG. 2  is by the additional insulated conductive bands  332 , and in the way that the side-wall and corner pixels of the detector differ from the inland pixels.  
         [0051]     The solid lines  334  in the plan view indicate the mid lines along which the septa  314  of collimator  302  are projected. In this configuration, the collimator is registered with respect to the pixels  304 , such that the unusable mid-line areas between pixels are those areas essentially screened by the septa, and optimum camera sensitivity is thus achieved thereby. In addition, the dead areas between separate modules  304 , comprised of the spaces themselves  306  and the conductive bands  332  surrounding the modules, are covered by the septa, such that these dead areas also do not cover any of the sensitive areas of the detector.  
         [0052]     The advantages of the camera head  300 , according to the various above-described preferred embodiments of the present invention, can thus be summarized in that: 
    (i) the camera head maintains constant pitch between pixels, thus avoiding deformation of the acquired image;     (ii) the camera head utilizes a collimator that is properly registered relative to the pixels, thus increasing the detection sensitivity;     (iii) the camera head minimizes detection loss due to dead areas produced by the inter-module gaps; and     (iv) the camera head allows the insertion and removal of the modules respectively into and out of the DCB or its sockets (not shown), while still maintaining the advantages mentioned in paragraphs (i) to (iii) above.    
 
         [0057]     Reference is now made to  FIG. 4 , which is a schematic drawing in enlargement of two modules  304  taken from the plan view of head  300  of  FIG. 3 , but shown with the collimator  302  in place. Two apertures  312  of the collimator have been schematically removed to show the exposed top surface of detectors  322 . The component parts of the array are labeled identically to those shown in  FIG. 3 . In addition, the insulating layer  400  is shown at the module side-walls, on top of which the conductive bands  332  are deposited.  
         [0058]     Although the methods and devices described herein mainly address the construction of X-ray and gamma ray detection and imaging cameras, the principles of the present invention can also be used in the construction of other systems comprising detector arrays, such as solid state cameras based on charge-coupled device (CCD) arrays and CMOS detector arrays.  
         [0059]     It will thus be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.