WO2009042827A1

WO2009042827A1 - Variable pixel pitch x-ray imaging system

Info

Publication number: WO2009042827A1
Application number: PCT/US2008/077781
Authority: WO
Inventors: David S. Rundle
Original assignee: Ev Products, Inc.
Priority date: 2007-09-28
Filing date: 2008-09-26
Publication date: 2009-04-02

Abstract

In a system and method of radiographic imaging, photons passing through an aperture in a collimator strike intrinsic pixels of a pixilated energy discriminating radiation detector having an X, Y array of intrinsic pixels, wherein X ≥ 1 and Y ≥ 2. From the intrinsic pixels is electronically defined a plurality of composite pixels each of which includes at least a pair of adjacent intrinsic pixels. The outputs of the intrinsic pixels defining each composite pixel are electronically combined in response to the photons striking the intrinsic pixels to produce a composite output for the composite pixel.

Description

VARIABLE PIXEL PITCH X-RAY IMAGING SYSTEM

BACKGROUND OF THE INVENTION [0001J Field of the Invention

[0002] The present invention relates to X-ray photon counting linear arrays where the pixel width and pitch of each array can be selectively configured by using a collimator in combination with selective pixel summing. This enables a single linear array to support multiple pixel pitches and linear array configurations with multiple operational and manufacturing benefits. [0003] Description of Related Art

[0004] Heretofore, photon counting detector arrays, especially linear detector arrays, were implemented in systems that included one or more collimator apertures of fixed size. When positioned between a high energy photon source and an energy discriminating detector array, each collimator aperture permitted photons from the photon source to impinge on a predetermined surface area of one or more pixels of the detector array. In other words, the design of the detector array and the apertures of the collimator were typically designed in tandem to permit each pixel of the detector array to receive a pre-determined amount of radiation (photons) from the high energy photon source. Thus, a fixed relationship is established between the projection of the collimator aperture on the pixels of the detector array and the surface area of the detector array exposed to photons passing through the collimator aperture.

[0005 J Moreover, heretofore, each pixel of a prior art detector array was typically coupled to signal processing electronics that is capable of detecting an electrical pulse that is output by the pixel in response to each photon from the photon source striking the pixel. The charge generated in each pixel is output as electrical pulse which is processed by the signal processing electronics. For each pixel, the corresponding signal processing electronics determines whether the energy of the photon exceeds a threshold value and for all of the pixels accumulates the number of photon events occurring within a sample interval of time into a window or frame that can be processed, along with other windows or frames, into an image of the photons striking the detector array during the sample interval. [0006] A problem with the prior art arrangements of detector arrays, collimators and signal processing electronics is that typically the relationship between the pixels of the detector array and each collimator aperture is fixed as is the manner in which the output of each pixel is processed by signal processing electronics. An obvious disadvantage of such an arrangement is its inflexibility. It would, therefore, be desirable to provide a radiographic imaging system that overcomes the above problems and others.

SUMMARY OF THE INVENTION

[0007] The invention is a radiographic imaging system. The system includes means for outputting photons along a path and a pixilated energy discriminating radiation detector having an X, Y array of intrinsic pixels positioned for receiving photons traversing the path, wherein X > 1 and Y > 2. The system includes a collimator having an aperture positioned in the path whereupon photons received by the intrinsic pixels pass through the aperture. A controller is coupled to the output of each intrinsic pixel and is operative for defining from the intrinsic pixels a plurality of composite pixels. Each composite pixel is comprised of at least a pair of adjacent intrinsic pixels. The controller is further operative for combining the outputs of the intrinsic pixels defining each composite pixel in response to the photons striking the intrinsic pixels to produce a composite output for the composite pixel. [0008] Each intrinsic pixel can have a height (Y)-to-width (X) ratio of at least 2-to-l . [0009] The aperture can be sized whereupon an area of each intrinsic pixel that receives photons passing through the collimator aperture has a height (Y)-to-width (X) ratio of > 1-to l .

[0010] The pixilated energy discriminating radiation detector can be made from Cd_1-XZn_xTe, where (0 < x < 1).

[0011] The controller can be operative for defining a plurality of composite pixels, each of which is comprised of either a 4 x 4 array of intrinsic pixels, a 2 x 2 array of intrinsic pixels, a 1 x 2 array of intrinsic pixels or a 2 x 1 array of intrinsic pixels.

[0012] The invention is also a radiographic imaging method. The method includes (a) providing a pixilated energy discriminating radiation detector having an X, Y array of intrinsic pixels, wherein X > 1 and Y > 2; (b) causing photons to pass through an aperture in a collimator and strike the intrinsic pixels; (c) electronically defining from the intrinsic pixels a plurality of composite pixels, with each composite pixel comprised of at least a pair of adjacent intrinsic pixels; and (d) electronically combining the outputs of the intrinsic pixels defining each composite pixel in response to the photons striking the intrinsic pixels to produce a composite output for the composite pixel. [0013] Each composite pixel in step (c) can be comprised of one of the following: a 4 x 4 array of intrinsic pixels, a 2 x 2 array of intrinsic pixels, a 1 x 2 array of intrinsic pixels or a

2 x 1 array of intrinsic pixels.

[0014] Step (a) can further include each intrinsic pixel having a height (Y)-to- width (X) ratio of at least 2-to-l.

[0015] The aperture in step (b) can be sized whereupon an area of each intrinsic pixel that receives photons passing through the collimator aperture has a height (Y)-to-width (X) ratio

> 1-to-l.

[0016J The pixilated energy discriminating radiation detector is desirably made from

Cd_!-xZn_xTe, where (0 < x < 1).

[0017] The method can further include accumulating a count output by each of a plurality of intrinsic pixels that define a composite pixel in response to photons striking the intrinsic pixel; and combining the count accumulated for one of the intrinsic pixels that defines the composite pixel with the count accumulated for another one of the intrinsic pixels that defines the composite pixel.

[0018] The method can further include accumulating counts output by each of a plurality of intrinsic pixels that define a composite pixel in response to photons striking the intrinsic pixel into bins based on the energies of the striking photons; and combining the count accumulated in one of the bins for one of the intrinsic pixels that defines the composite pixel with the count accumulated in one of the bins for another one of the intrinsic pixels that defines the composite pixel.

[0019] Lastly, the invention is a radiographic imaging system. The system includes means for outputting photons along a path and a pixilated energy discriminating radiation detector disposed on the path. The pixilated energy discriminating radiation detector has an X, Y array of intrinsic pixels, wherein X > 1 and Y > 2. The system includes means for selectively blocking/passing photons disposed on the path. Said means for selectively blocking/passing includes an aperture for the passage of photons on the path that strike the intrinsic pixels.

The system also includes means for electronically defining from the intrinsic pixels a plurality of composite pixels, with each composite pixel comprised of at least a pair of adjacent intrinsic pixels. The system further includes means for electronically combining the outputs of the intrinsic pixels defining each composite pixel in response to the photons striking the intrinsic pixels to produce a composite output for the composite pixel. [0020] Each composite pixel can be comprised of one of the following: a 4 x 4 array of intrinsic pixels, a 2 x 2 array of intrinsic pixels, a 1 x 2 array of intrinsic pixels or a 2 x 1 array of intrinsic pixels.

[0021] Each intrinsic pixel can have a height (Y)-to- width (X) ratio of at least 2-to- 1. [0022] The aperture can be sized whereupon an area of each intrinsic pixel that the photons passing through the collimator aperture strike has a height (Y)-to- width (X) ratio > 1-to-l. [0023] The pixilated energy discriminating radiation detector can be made from Cd_1-xZn_xTe, where (0 < x < 1).

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Fig. 1 is a schematic of a radiographic imaging system in accordance with the present invention;

[0025] Fig. 2 is a view taken along line II - II of the pixilated energy discriminating radiation detector of the radiographic imaging system of Fig. 1 that includes a projection of a collimator aperture thereon that defines an area of each intrinsic pixel where photons strike to have a height (Y)-to- width (X) ratio of about 1-to-l, wherein the controller of the radiographic imaging system of Fig. 1 defines sets of the intrinsic pixels into: two composite pixels (2-1 and 2-2) each comprised of an array of 2 x 2 intrinsic pixels (P), two composite pixels (4-1 and 4-2) each comprised of an array of 1 x 2 intrinsic pixels P, two composite pixels (6-1 and 6-2) each comprised of an array of 2 x 1 intrinsic pixels P, and a 4 x 4 array (8-1, 8-2, 8-3 and 8-4) of intrinsic pixels P; and

[0026] Fig. 3 is a view taken along line III - III of the pixilated energy discriminating radiation detector of the radiographic imaging system of Fig. 1 that includes a projection of a collimator aperture thereon that defines an area of each intrinsic pixel where photons strike to have a height (Y)-to-width (X) ratio of greater than 1-to-l and, desirably, at least 2-to-l, wherein the controller of the radiographic imaging system of Fig. 1 defines sets of the intrinsic pixels into: one composite pixel (10) comprised of an array of 4 x 2 intrinsic pixels (P), one composite pixel (12) comprised of an array of 2 x 2 intrinsic pixels P, one composite pixel (14) comprised of an array of 1 x 2 intrinsic pixels P, two composite pixels (16-1 and 16-2) each comprised of an array of 2 x 1 intrinsic pixels P, and a 1 x 1 array (18-1 and 18-2) of intrinsic pixels P.

DETAILED DESCRIPTION OF THE INVENTION [0027] The invention will be described with reference to the accompanying figures where like reference numbers correspond to like elements.

[0028] With reference to Fig. 1 , a radiographic imaging system 20 includes a high energy photon source 22, such as, without limitation, an X-ray source or a gamma ray source, and at least one photon counting detector array 24 positioned in a transmission path 26 of photons output by photon source 22. A collimator 23 may be positioned between photon source 22 and detector array 24 for shaping, focusing and restricting the photons that impinge on detector array 24.

(0029] One or more controllers 28 can be provided and operative for controlling the operation of photon source 22 and for detecting and processing photon events detected by the radiation detection elements or pixels (described hereinafter) of detector array 24. The depiction in Fig. 1 of a single controller 28 coupled to photon source 22 and detector array 24 is not to be construed as limiting the invention since it is envisioned that any number of controllers 28, operating independently or in coordination with each other, can be utilized. [0030] Signal processing electronics 27 can be provided as standalone components, as an integral part of detector array 24, as an integral part of controller 28 (as shown in Fig. 1), or some combination thereof, as desired. In response to each photon from photon source 24 striking one of the pixels of detector array 24, a charge is generated thereby that is proportional to the energy of the photon. The charge generated in each pixel is output thereby as a current or voltage pulse which is processed by signal processing electronics 27. For each pixel, signal processing electronics 27 determines whether the energy of the photon exceeds one or more threshold values and for all of the pixels accumulates into one or more energy bins the number of photon events occurring within a sample interval of time into a window or frame that can be processed, along with other windows or frames, by controller 28 into an image of the photon striking detector array 24 during said sample interval. Said image can then be displayed on a display 29 under the control of controller 28. Inasmuch as suitable signal processing electronics are well known in the art, signal processing electronics 27 will not be described in detail herein for the purpose of simplicity.

[0031] With reference to Figs. 2 and 3 and with continuing reference to Fig. 1, detector array 24 desirably includes a linear array (X-Y array, where X is > 1 and Y is > 2) of intrinsic pixels P fabricated on an energy discriminating detector material, such as CdTe or CdZnTe, which can be utilized in combination with collimator 23 which includes a window or aperture through which photons from photon source 22 can pass and strike the pixels. In Figs. 2 and 3, the projection of different sized collimator apertures on detector array 24 are shown. [0032] The height (the Y direction in Figs. 2 and 3) of the intrinsic pixels P in detector array 24 are desirably oversized with respect to the largest pixel height desired during operation. To this end, the height of each intrinsic pixel P can be two or more times greater than its width or pitch (the X direction in Figs. 2 and 3). The height of each intrinsic pixel P in use to detect incoming photons can then be selected by changing the width of the collimator aperture.

[0033] In accordance with the present invention, the outputs of two or more intrinsic pixels P can be combined to form a composite pixel (discussed in greater detail hereinafter). The pitch (the center-to-center distance) between composite pixels of detector array 24 can be set to the smallest pitch desired during operation. Each intrinsic pixel P is connected to signal processing electronics 27 in a conventional fashion. The composite pixel pitch during operation is then set by selectively summing the outputs of multiple intrinsic pixels in a pattern that produces a composite pixel pitch that is a multiple of the intrinsic pixel pitch pattern. In this way, the data collected from each intrinsic pixel can be combined in various ways to produce a wide variety of composite pixel pitches and configurations from a single X-Y array, where X is > 1 and Y is > 2.

[0034] A benefit of this arrangement is that the effective count rate capacity of any composite pixel pitch that is a multiple of an intrinsic pixel pitch will be a multiple of the maximum count rate capacity of a single channel of single processing electronics 27 which provides pulse processing throughput via multiple channels (when summing is employed). [0035] In operation, the voltage or current pulse output by each intrinsic pixel P of detector array 24 in response to a radiation event (an incoming photon) is compared by a comparator (not shown), either directly or after amplification, to a threshold voltage or current. Voltage or current pulses below this threshold value are ignored. In contrast, a count of each voltage or current pulse exceeding this threshold value is accumulated by signal processing electronics 27 for processing by controller 28 in a manner known in the art. The counts accumulated from all the intrinsic pixels P of detector array 24 for a specific sample interval of time can be converted by controller 28 in a manner known in the art into an electronic version of an image which can be displayed as a visual image on display 29. [0036] When controller 28 combines the counts for a set or group of related intrinsic pixels P of detector array 24 operating as a composite pixel, the effective count rate of the set or group of pixels, now being treated as a single composite pixel, is a multiple of the number of intrinsic pixels P comprising the composite pixel times the maximum count rate for any intrinsic pixel P of the composite pixel. More on. this later. [0037] An additional benefit of combining intrinsic pixels of detector array 24 into a composite pixel is that the fault tolerance to dead and/or poor performing intrinsic pixels P of the composite pixel will be increased as the number of intrinsic pixels P summed is increased. For example, if the outputs of four 0.25 mm intrinsic pixels are summed to produce a single 0.5 mm composite pixel, a single dead intrinsic pixel P in the group of four intrinsic pixels P will produce a 25 percent decrease in the apparent sensitivity of the composite pixel that can be corrected with minimal or no impact on detection performance. With this in mind, intrinsic pixels can be selected to form composite pixels that maximize detector yields for any given configuration.

[0038] Detector array 24 (shown schematically in Figs. 2 and 3) can, in combination with controller 28 and collimator 23, be employed to combine the outputs of the intrinsic pixels in a variety of different ways. Thus, multiple combinations of intrinsic pixels can be supported by the same imaging system 20. For example, as shown in Fig. 2, controller 28 can combine two rows of 0.25 mm wide (pitch) intrinsic pixels P utilized with a 0.5 mm wide collimator aperture into a single row of 0.5 mm x 0.5 mm (X, Y) composite pixels 2 (composite pixels 2-1 and 2-2 in Fig. 1) each capable of counting at 4X the capability that controller 28 can count each intrinsic pixel P. In Fig. 2, each composite pixel 2 is comprised of 2 x 2 intrinsic pixels P as shown. Thus, for example, if each intrinsic pixel P of each composite pixel 2 is capable of outputting two million counts per second (MCPS) and controller 28 is capable of processing these counts, by combining intrinsic pixels P into a composite pixel 2 made up of four intrinsic pixels P would result in composite pixel 2 having an effective counting rate of 8 MCPS, or 8X the MCPS of each intrinsic pixel P.

[0039] In another example, controller 28 can combine two rows of 0.25 mm intrinsic pixels utilized with the 0.5 mm wide collimator aperture into a single row of 0.25 mm x 0.5 mm (X, Y) composite pixels 4 (composite pixels 4-1 and 4-2 in Fig. 1) having an effective counting rate of 2X the counting rate of each intrinsic pixel P.

[0040] In another example, controller 28 can combine two rows of 0.25 mm intrinsic pixels utilized with the 0.5 mm wide collimator aperture into two rows of 0.5 mm x 0.25 mm (X, Y) composite pixels 6 (composite pixels 6-1 and 6-2 in Fig. 1) having an effective counting rate of 2X the counting rate of each intrinsic pixel P.

[0041] Lastly, controller 28 can utilize two rows of 0.25 mm wide intrinsic pixels P used with the 0.5 mm wide collimator aperture as two rows of 0.25 mm x 0.25 mm (X, Y) pixels 8 (pixels 8-1, 8-2, 8-3 and 8-4 in Fig. 1) having a counting rate of IX. [0042] With reference to Fig. 3 and with continuing reference to Fig. 1, for different application requirements, collimators having smaller or larger apertures can be utilized to facilitate additional intrinsic pixel combinations and resolutions using the same detector array 24.

[0043] For example, as shown in Fig. 3, controller 28 can combine two rows of 0.25 mm wide pixels utilized with a 1 mm wide collimator aperture into a single row of 1 mm x 1 mm

(X, Y) composite pixels 10 having an effective counting rate of 16X the counting rate of each intrinsic pixel P. In Fig. 3, composite pixel 10 is comprised of 4 x 2 intrinsic pixels P as shown. Thus, for example, if each intrinsic pixel P of composite pixel 10 is capable of outputting two million counts per second (MCPS) and controller 28 is capable of processing these counts, by combining intrinsic pixels P into composite pixel 10 made up of eight intrinsic pixels P would result in composite pixel 10 having an effective counting rate of 16

MCPS, or 16X the MCPS of each intrinsic pixel P.

[0Θ44J In another example, controller 28 can combine two rows of 0.25 mm wide intrinsic pixels utilized with the 1 mm collimator aperture into a single row of 0.5 mm x 1 mm (X, Y) composite pixels 12 having an effective counting rate of 4X the counting rate of each intrinsic pixel P.

[0045J In another example, controller 28 can combine two rows of 0.25 mm wide intrinsic pixels P utilized with the 1 mm collimator aperture into a single row of 0.25 mm x 1 mm

(X, Y) composite pixels 14 having an effective counting rate of 2X the counting rate of each intrinsic pixel P.

[0046] In another example, controller 28 can combine two rows of 0.25 mm wide intrinsic pixels utilized with the 1 mm collimator aperture into two rows of 0.5 mm x 0.5 mm (X, Y) composite pixels 16 (composite pixels 16-1 and 16-2 in Fig. 3), each having an effective counting rate of 2Xthe counting rate of each intrinsic pixel P.

[0047] Lastly, controller 28 can utilize two rows of 0.25 mm wide intrinsic pixels used with the 1 mm collimator aperture as two rows of 0.25 mm x 0.5 mm (X₅ Y) composite pixels

18 (pixels 18-1 and 18-2 in Fig. 2), each having an effective counting rate of IX the counting rate.

[0048] In Figs. 2 and 3 and the foregoing description thereof, the intrinsic pixels P of a

10 x 2 (X, Y) pixel array were combined by controller 28 in various different manners to form different sized composite pixels. However, this is not to be construed as limiting the invention since it is envisioned that typically all of the intrinsic pixels P of the pixel array would be combined by controller 28 in the same manner during a specific imaging event. For example, in Fig. 2, all of the composite pixels would have the form of either composite pixel 2, 4, 6 or 8. Similarly, in Fig. 3, each composite pixel could have the form of either composite pixel 10 (where the pixel array was a 12 x 2 pixel array), 12, 14, 16, or 18. Thus, the fact that detector array 24 in Figs. 2 and 3 is shown as being combined into various combinations of composite pixels is not to be construed as limiting the invention. However, it is envisioned that for different imaging events, the pixels of each array can be combined differently. For example, in an imaging event where spatial resolution is desired, the outputs of intrinsic pixels P, e.g., 8 or 18, can be processed by controller 28 separately. In contrast, where it is desired to analyze the spectral content of the outputs of the pixels of each detector array, the intrinsic pixels P of detector array 24 can be combined in any suitable and/or desirable manner. For example, the intrinsic pixels P of detector array 24 can be arranged in the pattern of either composite pixel 2, 4 or 6 in Fig. 2, or 10, 12, 14 or 16 in Fig. 3. Moreover, it is envisioned that combinations of intrinsic pixels P and/or composite pixels can be formed by controller 28. For example, controller 28 can process the outputs of intrinsic pixels P of detector array 24 in Fig. 2 in any combination of intrinsic pixels 8 and/or composite pixels 2, 4 and/or 6. Similarly, controller 28 can process the output of intrinsic pixels P of detector array 24 in Fig. 3 in any combination of intrinsic pixels 18 and/or composite pixels 10, 12, 14 and/or 16.

10049] The outputs of intrinsic pixels 8 and/or composite pixels 2, 4 and/or 6 of detector array 24 in Fig. 2, and/or the outputs of intrinsic pixels 18 and/or composite pixels 10, 12, 14 and/or 16 of detector array 24 in Fig. 3 can be combined in any suitable and/or desirable manner. For example, each pulse output by each intrinsic pixel in response to an incident photon can be counted and accumulated by signal processing electronics 27 based on the amplitude of the pulse (which corresponds to the energy of the incident photon). Thus, for a particular sample interval, signal processing electronics 27 may have three (3) energy bins associated with a pixel - bin 1 for accumulating a first count of pulses output by the intrinsic pixel during the sample interval that have a peak amplitude greater than a first threshold but less than a second threshold; bin 2 for accumulating a second count of pulses output during the sample interval that have a peak amplitude that is greater than the second threshold but less than a third threshold; and bin 3 for accumulating a third count of pulses output during the sample interval that have a peak amplitude that is greater than the third threshold. [0050] The count accumulated for each bin for each intrinsic pixel can then be processed by controller 28 in any suitable and/or desirable manner. For example, for each intrinsic pixel, the counts accumulated in bins 1-3 during the sample interval may be summed together to realize an image on display 29 having improved spatial resolution at the expense of spectral information. Controller 28 can then process the counts summed together for each intrinsic pixel to produce a corresponding image on display 29.

[0051] Alternatively, the counts summed together for the bins of each two or more intrinsic pixels that form a composite pixel can be combined (summed) by controller 28 across said two or more intrinsic to form a corresponding image on display 29. For example, the counts accumulated in bins 1-3 of a first intrinsic pixel forming a composite pixel can be summed with the counts accumulated in bins 1 -3 of a second intrinsic pixel forming a composite pixel [0052] In another example, the counts accumulated in like bins of a number of adjacent intrinsic pixels can be summed across the intrinsic pixels that form a composite pixel to realize an image on display 29 having improved spectral information at the expense of spatial resolution. For example, for a composite pixel formed from a first and second intrinsic pixel, the count accumulated in bin 1 of the first intrinsic pixel can be summed with the count accumulated in bin 1 of a second intrinsic pixel; the count accumulated in bin 2 for the first intrinsic pixel can be summed with the count accumulated in bin 2 for the second intrinsic pixel; and the count accumulated in bin 3 for the first intrinsic pixel can be summed with the count accumulated in bin 3 for the second intrinsic pixel. Controller 28 can then process the counts summed across the intrinsic pixels forming each composite pixel for each bin, e.g., the sum of the counts in bin 1 of the first and second intrinsic pixels, to produce a corresponding image on display 29.

[0053] In another example, summing of counts can occur in any combination within a pixel and/or across pixels. For example, for intrinsic pixels having three bins each, the counts in bins 1 and 2 of each intrinsic pixel can be summed together to determine a so-called sum within the intrinsic pixel. Then, the thus determined sum within a first intrinsic pixel can be added to the sum determined within a second intrinsic pixel to produce a composite sum for the composite pixel comprised of the first and second intrinsic pixels (i.e., the sum of the counts of bins 1 and 2 for the first and second intrinsic pixels). Also or alternatively;, the count accumulated in bin 3 for the first intrinsic pixel can be added to the count accumulated in bin 3 for the second intrinsic pixel (across pixels) for the composite pixel formed by the first and second pixels.

[0054] Because the counts of each pixel (intrinsic or composite) are accumulated in bins, controller 28 can manipulate the counts in each bin in any one or a number of suitable and/or desirable combination to produce one or more desired images on display 29. Accordingly, the foregoing description of summing counts for (within) and/or across pixels is not to be construed as limiting the invention. To this end, numerous combinations of summed counts within a pixel and/or across pixels is envisioned.

[0055] As can be seen, selective collimation and intrinsic pixel summing can be utilized to enable detector array 24 to have multiple composite pixel pitches and configurations.

Technical advantages include:

[0056] • A single common array of intrinsic pixels can support multiple composite pixel pitches;

[0057] • A single array of intrinsic pixels can support both one and two row composite pixel linear array configurations;

(0058] • Increased effective count rate capability via combining the counts of multiple intrinsic pixels;

[0059] • Increased fault tolerance (detector yield) for dead or poor performing intrinsic pixels (when summing); and

(0060] • Increased intrinsic pixel surface areas for higher bonding yields while maintaining small pitch.

[0061] The present invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

THE INVENTION CLAIMED IS:

1. A radiographic imaging system comprising: means for outputting photons along a path; a pixilated energy discriminating radiation detector having an X, Y array of intrinsic pixels positioned for receiving photons traversing the path, wherein X > 1 and Y > 2; a collimator having an aperture positioned in the path whereupon photons received by the intrinsic pixels pass through the aperture; and a controller coupled to the output of each intrinsic pixel and operative for defining from the intrinsic pixels a plurality of composite pixels, with each composite pixel comprised of at least a pair of adjacent intrinsic pixels, the controller operative for combining the outputs of the intrinsic pixels defining each composite pixel in response to the photons striking the intrinsic pixels to produce a composite output for the composite pixel.

2. The system of claim 1 , wherein each intrinsic pixel has a height (Y)-to» width (X) ratio of at least 2-to-l.

3. The system of claim 2, wherein the aperture is sized whereupon an area of each intrinsic pixel that receives photons passing through the collimator aperture has a height (Y)- to- width (X) ratio of 1-to-l.

4. The system of claim 2, wherein the aperture is sized whereupon an area of each intrinsic pixel that receives photons passing through the collimator aperture has a height (Y)- to- width (X) ratio greater than 1-to-l.

5. The system of claim 1, wherein the pixilated energy discriminating radiation detector is made from Cd ^_xZn_xTe, where (0 < x < 1).

6. The system of claim 1, wherein the controller is operative for defining a plurality of composite pixels, each of which is comprised of either a 4 x 4 array of intrinsic pixels, a 2 x 2 array of intrinsic pixels, a 1 x 2 array of intrinsic pixels or a 2 x 1 array of intrinsic pixels.

7. A radiographic imaging method comprising:

(a) providing a pixilated energy discriminating radiation detector having an X, Y array of intrinsic pixels, wherein X > 1 and Y > 2;

(b) causing photons to pass through an aperture in a collimator and strike the intrinsic pixels;

(c) electronically defining from the intrinsic pixels a plurality of composite pixels, with each composite pixel comprised of at least a pair of adjacent intrinsic pixels; and

(d) electronically combining the outputs of the intrinsic pixels defining each composite pixel in response to the photons striking the intrinsic pixels to produce a composite output for the composite pixel.

8. The method of claim 1, wherein each composite pixel in step (c) is comprised of one of the following: a 4 x 4 array of intrinsic pixels; a 2 x 2 array of intrinsic pixels; a 1 x 2 array of intrinsic pixels; or a 2 x 1 array of intrinsic pixels.

9. The method of claim 7, wherein step (a) further includes each intrinsic pixel having a height (Y)-to-width (X) ratio of at least 2-to-l.

10. The method of claim 9, wherein the aperture in step (b) is sized whereupon an area of each intrinsic pixel that receives photons passing through the collimator aperture has a height (Y)-to- width (X) ratio > 1-to-l .

11. The method of claim 7, wherein the pixilated energy discriminating radiation detector is made from Cdi_-xZn_xTe, where (0 < x < 1).

12. The method of claim 7, further including: accumulating a count output by each of a plurality of intrinsic pixels that defines a composite pixel in response to photons striking the intrinsic pixel; and combining the count accumulated for one of the intrinsic pixels that defines the composite pixel with the count accumulated for another one of the intrinsic pixels that defines the composite pixel.

13. The method of claim 7, further including: accumulating counts output by each of a plurality of intrinsic pixels that define a composite pixel in response to photons striking the intrinsic pixel into bins based on the energies of the striking photons; and combining the count accumulated in one of the bins for one of the intrinsic pixels that defines the composite pixel with the count accumulated in one of the bins for another one of the intrinsic pixels that defines the composite pixel.

14. A radiographic imaging system comprising: means for outputting photons along a path; a pixilated energy discriminating radiation detector disposed on the path, said pixilated energy discriminating radiation detector having an X, Y array of intrinsic pixels, wherein X > 1 and Y > 2; means for selectively blocking/passing photons disposed on the path, said means for selectively blocking/passing including an aperture for the passage of photons on the path that strike the intrinsic pixels; means for electronically defining from the intrinsic pixels a plurality of composite pixels, with each composite pixel comprised of at least a pair of adjacent intrinsic pixels; and means for electronically combining the outputs of the intrinsic pixels defining each composite pixel in response to the photons striking the intrinsic pixels to produce a composite output for the composite pixel.

15. The system of claim 14, wherein each composite pixel is comprised of one of the following: a 4 x 4 array of intrinsic pixels; a 2 x 2 array of intrinsic pixels; a 1 x 2 array of intrinsic pixels; or a 2 x 1 array of intrinsic pixels.

16. The system of claim 14, wherein each intrinsic pixel has a height (Y)-to- width (X) ratio of at least 2-to-l.

17. The system of claim 16, wherein the aperture is sized whereupon an area of each intrinsic pixel that the photons passing through the collimator aperture strike has a height (Y)- to-width (X) ratio > 1-to-l .

18. The system of claim 14, wherein the pixilated energy discriminating radiation detector is made from Cd _I-J[Zn_xTe, where (0 < x < 1).