Abstract:
A method of detecting ionizing radiation is provided. The method includes detecting ionizing radiation using a detector assembly having a pixelated semiconductor substrate, each pixel including a central region and a region of variable response, each pixel further including at least one anode, the detector assembly including a grid electrode coupled to a first surface of the semiconductor substrate such that the grid electrode circumscribes the central region of at least one pixel anode, the detector assembly further including a cathode coupled to a second surface of the semiconductor substrate, the method comprising, measuring a first signal between the at least one pixel anode and the cathode wherein the anode is electrically biased with respect to the cathode, measuring a second signal between the grid electrode and the cathode wherein the grid electrode is electrically biased with respect to the cathode, combining the magnitude of the first signal and the magnitude of the second signal to obtain a total signal from the semiconductor substrate, and outputting the total signal.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation in part of U.S. application Ser. No. 11/175,695, filed Jul. 6, 2005 and entitled “METHOD AND APPARATUS OF DETECTING IONIZING RADIATION”, the complete subject matter of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Embodiments of the present invention relate generally to imaging systems using pixilated detectors, and more particularly to pixilated semiconductor detectors in imaging systems. 
     Imaging devices, such as gamma cameras and computed tomography (CT) imaging systems, are used in the medical field to detect radioactive emission events emanating from a subject, such as a patient and to detect transmission x-rays not attenuated by the subject, respectively. An output, typically in the form of an image that graphically illustrates the distribution of the sources of the emissions within the object and/or the distribution of attenuation of the object is formed from these detections. An imaging device may have one or more detectors that detect the number of emissions, for example, gamma rays in the range of 140 keV, and may have one or more detectors to detect x-rays that have passed through the object. Each of the detected emissions and x-rays is typically referred to as a “count,” but the detected emissions may also be counted together as a ‘signal current’. The detector also determines the number of counts received at different spatial positions. The imaging device then uses the count tallies to determine the distribution of the gamma sources and x-ray attenuators, typically in the form of a graphical image having different colors or shadings that represent the processed count tallies. 
     A pixilated semiconductor detector, for example, fabricated from cadmium zinc telluride (CZT), may provide an economical method of detecting the gamma rays and x-rays. However, a low energy tail on the energy spectrum resulting from the CZT interaction with the radiation may interfere with the ability to distinguish detection of direct gamma rays and direct x-rays from detection of gamma rays and x-rays that have scattered in the subject before contacting the CZT. The tail may result in part from a different response of the semiconductor material in the regions between the pixels. Because of the low electric field of the semiconductor between the pixel anodes, electrons arrive late to the anode, resulting in “ballistic deficit”. A low energy tail on the energy spectrum may also result from low hole mobility or trapping that causes charge integration derived from the pixel with respect to the common cathode to be incomplete. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment a method of detecting ionizing radiation is provided. The method includes detecting ionizing radiation using a detector assembly having a pixelated semiconductor substrate, each pixel including a central region and a region of variable response, each pixel further including at least one anode, the detector assembly including a grid electrode coupled to a first surface of the semiconductor substrate such that the grid electrode circumscribes the central region of at least one pixel anode, the detector assembly further including a cathode coupled to a second surface of the semiconductor substrate, the method comprising, measuring a first signal between the at least one pixel anode and the cathode wherein the anode is electrically biased with respect to the cathode, measuring a second signal between the grid electrode and the cathode wherein the grid electrode is electrically biased with respect to the cathode, combining the magnitude of the first signal and the magnitude of the second signal to obtain a total signal from the semiconductor substrate, and outputting the total signal. 
     In another embodiment an imaging system that includes a semiconductor detector is provided. The imaging system includes a pixilated semiconductor substrate responsive to ionizing radiation, the substrate including a first surface pixilated with at least one pixel anode, a grid electrode coupled to the pixilated surface, the grid electrode circumscribing a central region of the at least one pixel anode, and a cathode coupled to a second surface of the pixelated surface, the cathode substantially covering the second surface, and a controller configured to, measure a first signal between the at least one pixel anode and the cathode by applying a first bias voltage to the at least one pixel anode, measure a second signal between the grid electrode and the cathode by applying a second bias voltage to the grid electrode wherein the second bias voltage is less than the first bias voltage, and combine the magnitude of the first signal and the magnitude of the second signal to obtain a total signal from the semiconductor substrate. 
     In still another embodiment a radiation detector is provided. The radiation detector includes a semiconductor substrate comprising at least one pixel anode defined in a first surface of the substrate, the at least one pixel anode configured to receive a first bias voltage, a cathode electrically coupled to a second surface of the substrate, the cathode substantially covering the substrate, a grid electrode coupled to the first surface, the grid electrode circumscribing a central region of the at least one pixel anode and configured to receive a second bias voltage, a first measurement circuit configured to measure a first signal, a second measurement circuit configured to measure a second signal, and a summing circuit configured to combine the magnitude of the output of the first measurement circuit and the magnitude of the output of the second measurement circuit, the combination proportional to a total charge in the pixel volume. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph that illustrates an exemplary energy spectrum of a single pixel of a pixilated CZT detector exposed to substantially unscattered 140 keV gamma rays; 
         FIG. 2  is a cross-sectional view of an exemplary radiation detector having a plurality of pixilated semiconductor detector elements; and 
         FIG. 3  is a perspective view of an exemplary radiation detector including a plurality of anodes and a grid electrode surrounding the plurality of anodes. 
         FIG. 4  illustrates a top plan view of a detector formed in accordance with an alternative embodiment. 
         FIG. 5  illustrates a top plan view of a detector formed in accordance with an alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a graph  50  that illustrates an exemplary energy spectrum of a single pixel of a pixilated CZT detector exposed to substantially unscattered 140 keV gamma rays. Graph  50  includes an x-axis graduated in units of keV and a y-axis representative of an amount of total counts or count rate observed at each keV level. An energy spectrum peak  52  centered about 140 keV represents the gamma rays that have been absorbed substantially within a central region portion of a single pixel. The distribution of signal amplitudes of these events is approximately Gaussian. However, a significant number of gamma rays are also detected in the portion of the energy response spectrum that tails toward the lower energies. This tail effect is caused, in part, by Compton scattering, by gamma ray absorption events that do not confine all charge creation to within a single pixel and by non-ideal charge collection. Because the illustrated response function represents the distribution of measured signals from only a single pixel, charge that is lost from the pixel and shared with adjacent pixels is not included in the response function. As a result, gamma ray absorption events in which the charge collection is incomplete due to less than ideal charge collection, such as, charge sharing with other pixels, are lost from the peak region and contribute to the low energy tailing. 
       FIG. 2  is a cross-sectional elevation view of an exemplary imaging device detector  100  and includes a plurality of pixilated semiconductor detector elements  102  that may be used in connection with, for example, localizing a radiation interaction event in the detector  100 . Detector  100  includes a detector substrate  104 . Detector  100  may be formed of a radiation responsive semiconductor material, for example, cadmium zinc telluride (CZT) crystals. Detector elements  102  may be formed of the substrate  104  by pixelating a corresponding plurality of pixel electrodes coupled to a first surface  110  of detector substrate  104  (shown as a lower surface). A cross-sectional size and shape of detector elements  102  and a spacing between each of the detector elements  102  facilitates determining a location and size of each pixilated detector element  102 . Specifically each pixilated detector element  102  is located proximate a second surface  112  (shown as an upper surface) of detector substrate  104  in substantial alignment with a longitudinal axis  114  of a corresponding pixel electrode  108 . Each pixilated detector element  102  includes a central region  116 , bounded by useful limits  118 , defining an operating portion, and a region of variable response  119 . Central region  116  and region of variable response  119  extend substantially from surface  110  to surface  112 . In the exemplary embodiment, a grid electrode  111 , having a substantially planar body is positioned to circumscribe central regions  116 . 
     Within central region  116 , pixilated detector element  102  has a substantially uniform and repeatable response characteristic to radiation incident on second surface  112 . Detector substrate  104  includes regions of variable response  119  in areas outside central region  116 . The region of variable response  119  exhibits a response characteristic to radiation that may be inconsistent or variable. An intrinsic spatial resolution of detector  100  may be defined by the size of, and the spacing between, each pixilated detector element  102 . Because pixilated detector elements  102  may be non-homogeneous in response and because central region  116  has a substantially uniform and repeatable response characteristic, collimator  106  may be formed to allow gamma and x-ray photons to interact with central region  116  and to block gamma and x-ray photons from reaching the region of variable response  119 . 
     In operation, photons  144 , for example emission gammas and transmission x-rays, from a source  140  are directed towards second surface  112 . Photons  144  pass between collimator septa  120  and exit collimator aperture  122 . Second surface  112  may be substantially covered by a relatively thin single cathode electrode  154 . First surface  110  has an array of small, between about one millimeters squared (mm 2 ) and about ten mm 2 , generally square pixel electrodes  108  configured as anodes. A voltage difference applied between pixel electrodes  108  and electrode  154  during operation generates a detector electric field in substrate  104 . The detector electric field may be, for example, about one kilovolts per centimeter to about five kilovolts per centimeter. Although pixel electrodes  108  are described in the exemplary embodiment as being generally square like the pixel, it should be understood that this exemplary shape is not limiting in other embodiments, in that other shapes of pixel electrodes  108  are contemplated. 
     When a photon is incident on substrate  104 , the photon generally loses all its energy in substrate  104  by ionization and leaves pairs of mobile electrons  156  and holes  158  in a small localized region of substrate  104 . As a result of the detector electric field, holes  158  drift toward cathode electrode  154  and electrons  156  drift toward pixel electrodes  108 , thereby inducing charges on pixel electrodes  108  and cathode electrodes  154 . The induced charges on pixel electrodes  108  are detected. The time is identified at which a photon was detected. It is also identified how much energy the detected photon deposited in the substrate  104  and where in the substrate  104  the photon interaction occurred. To facilitate optimum detection of gamma and x-ray photons, central region  116  should be in substantial alignment with apertures  122  and the relative dimensions of gap  132 , length  124 , aperture  122  and thickness  128  should be determined such that photons arriving at incident surface  142  are absorbed in collimator  106  or central region  116 . 
       FIG. 3  is a perspective view of an exemplary view of the detector  100 . Imaging device detector  100  includes detector substrate  104  with high voltage cathode electrode  154  covering substantially the entire second surface  112 . In the exemplary embodiment, grid electrode  111 , having apertures of width  420 , length  430 , and thickness  410  is placed to circumscribe the central regions of the detector elements  102  and corresponding pixel electrodes  108 . 
     Each pixel electrode  108  is electrically connected, over a lead or trace  441 , to a corresponding pre-amplifier  443 . The grid electrode  111  is electrically connected, over a lead or trace  451 , to a corresponding pre-amplifier  453 . Signals from the pixel electrodes  108  and from the grid electrodes  111  are amplified by corresponding pre-amplifiers  443  and  453  to produce measured signals  440  and  450 , respectively. The pre-amplifiers  443  and  453  amplify the incoming signals based on gain coefficients G 2  and G 1 , respectively, which may be adjusted. Optionally the preamplifiers  443  and  453  may be AC coupled or DC compensated to avoid saturation. Integrator components  445  and  455  may be provided in series with the preamplifiers  443  and  453  to integrate, over time, the signals on the leads  441  and  451 , respectively. The integrator components  445  and  455  may be provided before or after the preamplifiers  443  and  453 . Optionally the pre-amplifiers  443  and  453  constitute current to voltage converters which integrate current over a limited bandwidth. For example, integrators may be AC coupled. 
     The measured signals  440  and  450  are output by the preamplifiers  443  and  453 , and supplied to the input terminals of an operational amplifier  463 . The Op-Amp  463  combines magnitudes of the measured signals  440  and  450  to produce a corrected signal  460 . Optionally the measured signals  440  and  450  may be both positive, while one of the measures signals  440  and  450  is applied to a positive input of the Op-Amp  463  and the other of the measures signals  440  and  450  is applied to a negative input of the Op-Amp  463 . Alternatively, the measured signal  450  from the pixel electrode  108  may be positive, while the measured signal  440  from the grid electrode  111  may be negative. Thus, the corrected signal  460  represents the difference between the measured signals  440  and  450 . 
     Grid electrode  111  may have, applied to it, a potential (e.g., −20V) which is slightly lower than the potential of pixel electrodes  108  that may be at 0.0 volts. While in the present example, the pixel electrodes receive a bias voltage of 0.0 volts, alternatively the pixel electrodes may receive a non-zero bias voltage. Applying a negative voltage to grid electrode  111  has the effect of steering electrons  156  from the region of variable response  119  and directly to the pixel electrodes  108 , thereby reducing the ballistic deficit. Applying (negative) voltage to grid electrode  111  also has the effect of steering electrons from grid electrode  111  to pixel electrodes  108 , thereby separating the hole and electron signal induction on the pixel and grid electrodes  108  and  111 . 
     Applying voltage to grid electrode  111  thus has the effect of measuring the trapped signal by electromagnetic induction. According to the Ramo&#39;s Theorem, the signal induced on the pixel electrode is proportional to the distance that the charge carrier transits. A charge that transits half the total distance, for instance, will induce half the available signal in the pixel electrode. Optionally a slight bias voltage may be applied to grid electrode  111  to cause the induction of signal  440  by electromagnetic induction that is equal and opposite to the missing charge trajectory. Combining the magnitude value from grid electrode  111  to the measured signal  450  from a pixel electrode  108  results in a corrected signal  460  from moving electrons  156  and holes  158 , and those that have not been measured by direct means because of lost mobility. The combination is made with amplifier gain coefficient G 1  and G 2  that are adjusted empirically for details of the electrode shapes  108  and  111 . 
     In accordance with one embodiment the physical dimensions and geometry and electrical parameters of the detector  100  may be selected based on certain criteria to improve, and potentially optimize, certain aspects of the performance (e.g., sensitivity, specificity reduce signal to noise ratio, etc.). As an example, the dimensions and geometry of the detector may include selection of the size of each pixel electrode, or the selection of each grid electrode or sub-grid electrode relative to the number of pixel electrodes within the grid electrode or sub-grid electrode. As another example, the electrical properties may include selection of a relative gain ratio for the gains set on the pre-amplifiers  443  and  453 . By adjusting the relative gain ratio, the output of the amplifier  461  may become independent of a depth within the substrate, at which the photon interacts with the substrate. By way of example only the gain ratio G 2 /G 1  may be set to equal R, where R represents the area of the grid proportion. The relative gain ratio may be calibrated in order to improve the detector performance. The gain ratio calibration may be set based on experimental studies of different detector configurations. Alternatively the gain ratio calibration may be set based on the geometry of the pixel electrodes and the grid electrodes. 
     Following is an exemplary calculation for correcting the signal as described: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Electron charge = 
                 E 
               
               
                 total area of pixel anodes in a module = 
                 AP 
               
               
                 area of grid = 
                 AG 
               
               
                 area of grid proportion (per pixel)  
                 R = AG/(AG + AP) 
               
               
                 CZT slab thickness = 
                 t 
               
               
                 gamma is absorbed at depth 
                 d 
               
               
                 ‘work function for CZT’ 
                 W = 4.5eV/e 
               
               
                 γ energy for Tc 99m   
                 Eγ = 140 keV 
               
               
                 Absorption gives charge 
                 q = Eγ/W = 31ke 
               
               
                 Ramo&#39;s theorem gives electron  
                 E = q(t − d)/t 
               
               
                 induction on hit anode: 
                   
               
               
                 Hole Induction on anode plane 
                 H = −qd/t 
               
               
                 Hole induction on grid 
                 GH = (−qd/t)/R 
               
               
                 Output of Pre-1 (450) 
                 P1 = G1 E 
               
               
                 Output of Pre-2 (440) 
                 P2 = G2 GH 
               
               
                 Output of Op-amp 
                 O = P1 − P2 = (G1 E) − 
               
               
                   
                 (G2 GH) = G1 (q(t − d)/t) − 
               
               
                   
                 (G2/R) (−qd/t) 
               
               
                   
               
             
          
         
       
     
     The noise contribution can be calculated to optimize the grid size. Following is a sample calculation. For a typical preamp (e.g. Ortec 142C) the RMS noise Referred To Input (rti) for input C=2 nF is N≈7.5 ke. 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Noise goal (RMS) 
                 N = 3% for Tc 99m   
               
               
                 Grid Capacitance 
                 GC = (C/N) 0.03 Eγ = 250 pF 
               
               
                 Pixel Capacitance (measured on sample) 
                 PC = 3 pF 
               
               
                 Optimum Grid Size 
                 GS = GC/PC = 82 pixels = 
               
               
                   
                 9 × 9 pixels 
               
               
                   
               
             
          
         
       
     
     Because modules of the semi-conductor substrate are presently made of slabs comprising 8×8 arrays of pixels, this is a convenient size. 
     The above-described imaging device detectors provide a cost-effective and reliable means for examining a patient. More specifically the imaging system includes a grid electrode circumscribing the central regions of all anodes which is held at a potential slightly lower than the pixel anodes. When read out together, the problems of ballistic deficit and low charge mobility are corrected, thereby yielding full performance of the detector. 
     An exemplary embodiment of pixilated photon detector methods and apparatus are described above in detail.  FIG. 3  shows square pixel electrodes and grid openings but is not limited to square elements nor to the absolute or relative sizes illustrated. For example, round or oblong anodes and grid features and smaller or larger electrodes and/or grid openings may be used to facilitate reducing electric field emissions at sharp and/or corner features or different relative inductions. 
       FIG. 4  illustrates a detector  200  formed in accordance with an alternative embodiment. A top plan view of the detector  200  is shown in  FIG. 4  with the first surface  212  facing upward and an opposed second surface facing into the page (not shown). While not shown in  FIG. 4 , it is understood that the opposite (second) surface of the detector  200  also includes an electrode (e.g., a cathode electrode). The detector  200  includes a grid electrode  211  that is segmented into multiple sub-grid electrodes  221 - 229  provided on the first surface  212 . Each of the sub-grid electrodes  221 - 229  includes a plurality of apertures  230  there through. The apertures  230  through each sub-grid electrode  221 - 229  are arranged in an array that may be organized into rows  232  and columns  234 . The detector  200  also includes a plurality of pixel electrodes  208  (only a portion of which are shown) that are electrically joined to the first surface  212  of the detector  200 . The pixel electrodes  208  are positioned within, and electrically isolated from, the apertures  230  such that a corresponding one of the sub-grid electrodes  221 - 229  surrounds or circumscribes the corresponding array of pixel electrodes  208 . To simplify  FIG. 4 , only a small portion of the pixel electrodes  208  are shown and denoted by reference numbers. 
     The sub-grid electrodes  221 - 229  have edges  238 , where a portion of the edges  238  are positioned adjacent to edges of another sub-grid electrode  221 - 229  at grid-to-grid interfaces  236 . In the exemplary arrangement, edges  238  of the sub-grid electrodes  221 - 229  may abut against and directly engage one another. Alternatively, adjacent edges  238  of the sub-grid electrodes  221 - 229  may be spaced apart from one another on the first surface  212 . The grid-to-grid interfaces  236  extend parallel to the rows  232  and columns  234 . Optionally the sub-grid electrodes  221 - 229  may have alternative shapes and thus the grid-to-grid interfaces  236  may extend along alternative paths. 
     The pixel electrodes  208  may be categorized into different types based on the location of the pixel electrode  208  on the detector  100  and based on the location of the pixel electrode  208  with respect to other pixel electrodes  208 . To illustrate a potential categorization, a portion of the pixel electrodes  208  in  FIG. 4  are denoted by numeric labels ( 1 ,  2 , and  4 ). The labels  1 ,  2 , and  4  illustrate exemplary types into which particular pixel electrodes  208  may be categorized. Within the sub-grid electrode  221 , one of the pixel electrodes  208  (denoted as  4 ) is referred to as a bounded corner pixel electrode because it is located at a corner  244  that is bounded by three other sub-grid electrodes  222 ,  224  and  225 . Within the sub-grid electrode  222 , two pixel electrodes  208  (denoted at  4 ) represent bounded corner pixel electrodes, one of which is located at corner  246  that is bounded by three other sub-grid electrodes  221 ,  224  and  225  and the other of which is located at corner  247  that is bounded by three other sub-grid electrodes  225 ,  226  and  223 . 
     The sub-grid electrode  221  also includes a set of pixel electrodes (denoted at  2 ), referred to as edge pixel electrodes. The edge pixel electrodes  2  represent pixel electrodes that are located along an edge  240  that is positioned adjacent to, and bordered by, another sub-grid electrode  224 . The sub-grid electrode  221  also includes edge pixel electrodes  2  that are located along an edge  242  this is positioned adjacent and bordered by another sub-grid electrode  222 . The edge pixel electrodes  2  do not constitute corner electrodes  4 . The remainder of the pixel electrodes  208  surrounded by the sub-grid electrode  221 , that are not corner pixel electrodes  4  and are not edge pixel electrodes  2 , are referred to as center pixel electrodes (denoted at  1 ). 
     The sub-grid electrodes  221 - 229  are grouped into grid groups  264 - 267 . The grid groups  264 - 267  may include one or more sub-grid electrodes  221 - 229 . For example, grid electrodes  221 - 222  may be combined into one grid group  264 , while grid electrode  223  represents a separate grid group  266 . Sub-grid electrodes  224 ,  225 ,  227  and  228  are combined into another grid group  267 , and sub-grid electrodes  226  and  229  are combined into another grid group  265 . The sub-grid electrodes  226  and  229  in one grid group  265  are joined through leads  249  and  257  to pre-amplifiers  250  and  258 . The outputs of pre-amplifiers  250  and  258  are combined and provided to an input of a summing operational amplifier  260 . Each individual pixel electrode  208  surrounded by grid group  265  is joined through a corresponding lead (e.g.,  251 ,  255 ) to a corresponding individual pre-amplifier (e.g.,  252 ,  256 ). The outputs of each of the individual pre-amplifiers  252 ,  256  are supplied to inputs of corresponding summing amplifiers  254 ,  260 . The pre-amplifiers  250 ,  252 ,  256 ,  258  may be adjusted to have different desired gains in order to provide a weighted summation for each pixel electrode  208  and the corresponding sub-grid group  265  of sub-grid electrodes  226  and  229 . 
     Signals “s” and “g” are produced by pixel electrodes  208  and sub-grid electrodes  221 - 229  may be combined in different combinations to improve sensitivity. Different weights may be applied to pre-amplifiers associated with each type of pixel electrodes  208 . For example, center pixel output signal S 1  from each center pixel electrode  1  may be formed based on the equation S 1 =s 1 −a*g 1 , where s 1  represents the center pixel signal output over a corresponding lead  251  from the corresponding pixel electrode  208 ; g 1  represents the grid signal output  249  from the sub-grid electrode  226 ; and “a” represents a gain coefficient to be applied to the grid signal before summing the grid signal output and pixel signal. For example, side pixel output signal S 2  from a side pixel electrode  2  may be formed based on the equation S 2 =s 2 −b*g 1 −c*g 2 ; where s 2  represents the pixel signal output  255  from the corresponding pixel electrode  208 ; g 1  and g 2  represent the grid signal outputs  249  and  257  from the corresponding sub-grid electrodes  226  and  229 ; and “b” and “c” represent gain coefficients to be applied to the grid signal outputs  249  and  257  before summing the grid signal outputs  249  and  257  with the edge pixel signal  255 . 
     For example, corner pixel output signal S 4  from a corner pixel electrode  4  may be formed based on the equation S 4 =s 4 −d*g 1 −e*g 2 −e*g 3 −f*g 4 ; where s 4  represents the corner pixel signal output from a corresponding pixel electrode  208 ; g 1 , g 2  and g 3  represent the grid signal outputs from corresponding sub-grid electrodes in a grid group  267  (e.g.,  224 ,  225 ,  227  and  228 ); and “d”, “e” and “f” represent gain coefficients to be applied to the grid signal outputs before summing the grid signal outputs faith a corner edge pixel signal. 
       FIG. 5  illustrates a detector  300  formed in accordance with an alternative embodiment. A top plan view of the detector  300  is shown in  FIG. 5  with the first surface  312  facing upward and an opposed second surface (not shown). While not shown in  FIG. 5 , it is understood that an opposite (second) surface of the detector  300  also includes an electrode (e.g., a cathode electrode). The detector  300  includes a grid electrode  311  that is segmented into multiple sub-grid electrodes  321 - 330  provided on the first surface  312 . Each of the sub-grid electrodes  321 - 330  includes a plurality of apertures  331  there through. The apertures  331  through each sub-grid electrode  321 - 330  are arranged in an array organized into rows and columns. The detector  300  also includes a plurality of pixel electrodes  308  that are electrically joined to the first surface  312  of the detector  300 . The pixel electrodes  308  are positioned within the apertures  331  such that a corresponding one of the sub-grid electrodes  321 - 330  surrounds or circumscribes the pixel electrodes  308 . The sub-grid electrodes  321 - 323 , and  324 - 327  and  328 - 330  are arranged in rows that are shifted or offset with respect to one another. Thus, in the embodiment of  FIG. 5 , each sub-grid electrode  321 - 330  is bounded, at any given corner, by only two other sub-grid electrodes. 
     The pixilated photon detector components illustrated are not limited to the specific embodiment described herein, but rather, components of each pixilated photon detector and the gridded anode may be utilized independently and separately or repetitively from other components described herein. For example, the pixilated photon detector components described above may also be used in combination with different imaging systems and grid electrode  111  and related structures, G 2  are reduced in size to surround one or more pixel electrodes and is then repeated for each grouping. A technical effect of the embodiment of the systems and methods described herein include improving the semiconductor detector response energy spectrum by reducing the characteristic tail of the response by reducing the effect of ballistic deficit and by measuring, by electromagnetic induction, charges stuck in the detector material due to poor charge mobility. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.