Method and system for reducing internal scatter crosstalk

Abstract

To provide a system and a method for reducing scatter crosstalk in a photon-counting computed tomography system sensor.SOLUTION: A system is provided for a computed tomography system. The computed tomography system includes a gantry configured to rotate around an axis of rotation and a detector array comprising of a plurality of photon-counting computed tomography (PCCT) detector units configured to rotate around the axis of rotation by the gantry, wherein a stacking axis of at least one of the plurality of PCCT detector arrays is positioned at an angle with respect to the axis of rotation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION Embodiments of the subject matter disclosed herein relate to systems and methods for reducing scattering crosstalk within photon-counting computed tomography sensors. [Background technology]

[0002] A photon-counting computed tomography (PCCT) detection unit can include multiple sensors, each of which can be subdivided into multiple sensor subunits (e.g., pixels). A patient can be positioned between an X-ray source and a PCCT detection unit. X-rays scatter off the patient and travel away from the patient, where they are detected by the PCCT detection unit. The active material of the sensor is a semiconductor (e.g., silicon), which directly converts the energy of incident X-ray photons into an electrical signal. A source of noise in PCCT images can be signals from X-ray photons that are further scattered from the sensor and converted into an electrical signal. An anti-scatter grid can be placed between the sensors of a PCCT detection unit to absorb X-ray photons scattered between the sensors. However, the anti-scatter grid does not prevent internal scattering between sensor subunits within the sensor of a PCCT detection unit. Internal scattering can result in stochastic noise, which is difficult to correct and can result in loss of detail in the collected images. Summary of the Invention

[0003] In one embodiment, a computed tomography system includes a gantry configured to rotate about an axis of rotation; A detector array including a plurality of photon-counting computed tomography (PCCT) detector units configured to be rotated by the gantry about an axis of rotation, wherein a stacking axis of at least one PCCT detector array among the plurality of PCCT detector arrays is positioned at an angle to the axis of rotation.

[0004] It should be understood that the foregoing Summary of the Invention is provided to introduce, in a simplified form, some concepts that are further described in the Detailed Description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims. Moreover, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or anywhere in this disclosure. [Brief explanation of the drawings]

[0005] The invention can be better understood from the following description of non-limiting embodiments, taken in conjunction with the accompanying drawings, in which: [Figure 1] 1 shows a perspective view of a CT imaging system in accordance with one or more embodiments of the present disclosure. [Figure 2] 1 shows a block schematic diagram of an exemplary CT imaging system in accordance with one or more embodiments of the present disclosure. [Figure 3] 1 shows a diagram of a sensor of a photon counting computed tomography (PCCT) detector unit. [Figure 4] FIG. 1 shows a first perspective view of the scatter associated with the sensor of the PCCT detector unit. [Figure 5] FIG. 10 shows a second perspective view of the scatter associated with the sensor of the PCCT detector unit. [Figure 6] FIG. 1 shows a first embodiment of an array of PCCT detector units. [Figure 7] FIG. 10 shows a second embodiment of an array of PCCT detector units. [Figure 8] FIG. 10 shows a third embodiment of an array of PCCT detector units. [Figure 9] FIG. 10 shows a fourth embodiment of an array of PCCT detector units. [Figure 10] 1 shows a flowchart of an example method for correcting internal scatter of a PCCT detector array. [Figure 11] 1 shows a PCCT sensor stack with guard rings. [Figure 12] 1 shows a PCCT sensor stack. [Figure 13] FIG. 1 shows a first perspective view of a sensor of a PCCT detector unit including an adhesive. [Figure 14] FIG. 10 shows a second perspective view of an example of a sensor of a PCCT detector unit including an adhesive. [Figure 15] 1 shows a diagram of the sensor of the PCCT detection unit including the trench. [Figure 16] FIG. 1 illustrates an example process flow for forming trenches in a sensor. [Figure 17] 1 shows an alternative example of a trench included on two sides of the wafer. [Figure 18] FIG. 1 is a perspective view of a sensor including a trench / blocking layer combination. DETAILED DESCRIPTION OF THE INVENTION

[0006] The following description relates to a system and method for correcting internal scattering in a photon-counting computed tomography (PCCT) detector unit. Computed tomography (CT) uses x-rays to examine a subject (e.g., a patient). An example of a CT imaging system is shown in Figures 1-2. X-rays are scattered from the subject and collected on an array of detectors positioned directly opposite the x-ray source. In some examples, the detectors can be conventional detectors including a ceramic material and a photodetector, where energy from the x-rays can cause the ceramic material to emit low-energy photons. The low-energy photons are converted by the photodetector into electrical signals, which are used to form an image. Improved image quality can be achieved by using a photon-counting detector including a semiconductor configured to absorb energy from scattered x-rays and directly convert it into electrical signals. A common source of noise in a PCCT detector unit is the electrical signal resulting from additional scattering of x-rays between and within the sensors of the PCCT detector unit. An example of a sensor for a PCCT detector unit is shown in Figure 3. X-ray scattering between sensors of a PCCT detector unit can be suppressed by an anti-scatter grid disposed between the sensors of the PCCT detector unit, as shown in FIG. 4. However, subunits of a sensor may still be subject to internal scattering between the subunits, as shown in FIG. 5. As an example, an array of PCCT detector units can be adapted to allow internal scattering crosstalk to be corrected by an image processing system. Exemplary embodiments of PCCT detector arrays are shown in FIGS. 6-9. An exemplary flowchart of a method for reducing internal scattering crosstalk using the array of PCCT detector units of FIGS. 6-9 is shown in FIG. 10. Additionally or alternatively, the PCCT detector unit can be configured to further reduce the occurrence of internal scattering by adding foils of X-ray absorbing material, as shown in FIGS. 11-12, and / or by strategies to reduce the solid angle of scattered X-rays (such as by adding adhesive and / or X-ray absorbing material, as shown in FIGS. 13-14).Additionally, the PCCT detector unit may incorporate X-ray absorbing material therein as trenches separating one or more pixels of the sensor. Examples of sensors including trenches are shown in Figures 15-18.

[0007] Referring now to FIG. 1 , an exemplary CT system 100 configured for CT imaging is shown. In particular, the CT system 100 is configured to image a subject 112 (e.g., a patient, an inanimate object, one or more manufactured parts, and / or foreign objects present in the body, such as a dental implant, a stent, and / or a contrast agent). In one embodiment, the CT system 100 includes a gantry 102, which may further include at least one X-ray source 104 configured to emit an X-ray radiation beam 106 (see FIG. 2 ) used to image the subject 112 residing on a table 114. Specifically, the X-ray source 104 is configured to emit the X-ray radiation beam 106 toward a detector array 108 located on the opposite side of the gantry 102. While a single X-ray source 104 is shown in FIG. 1 , in certain embodiments, multiple X-ray sources and multiple detectors may be used to emit multiple X-ray radiation beams and acquire projection data at different energy levels corresponding to the patient. In some embodiments, the X-ray source 104 can achieve dual-energy gemstone spectral imaging (GSI) through rapid kilovolt peak voltage (kVp) switching. In some embodiments, the X-ray detector used is a photon-counting detector capable of distinguishing between X-ray photons of different energies. In other embodiments, two sets of X-ray sources and detectors are used, one set at low kVp and the other at high kVp, to generate dual-energy projections. Thus, it should be understood that the methods described herein can be implemented with single-energy and dual-energy collection techniques.

[0008] In certain embodiments, the CT system 100 further includes an image processor unit 110 including one or more processors configured to reconstruct an image of a target volume of the object 112 using an iterative image reconstruction method or an analytical image reconstruction method. For example, the image processor unit 110 may reconstruct an image of the target volume of the patient using an analytical image reconstruction method (such as filtered back projection (FBP)). In another example, the image processor unit 110 may reconstruct an image of the target volume of the object 112 using an iterative image reconstruction method (such as advanced statistical iterative reconstruction (ASIR), conjugate gradient (CG), maximum likelihood expectation maximization (MLEM), model-based iterative reconstruction (MBIR), etc.). As described further herein, in some examples, the image processor unit 110 may use an analytical image reconstruction method (such as FBP) in addition to an iterative image reconstruction method.

[0009] In some CT imaging system configurations, an X-ray source emits a cone-shaped beam of X-ray radiation that is collimated to lie within an XYZ plane of a Cartesian coordinate system, commonly referred to as the "imaging plane." The X-ray radiation beam passes through the object being imaged (such as a patient or subject). After being attenuated by the object, the X-ray radiation beam impinges on an array of detector elements. The intensity of the attenuated X-ray radiation beam received by the detector array depends on the attenuation of the X-ray radiation beam by the object. Each detector element in the array produces a separate electrical signal that is a measurement of the attenuation of the X-ray beam at the detector location. The attenuation measurements from all detector elements are acquired separately to generate a transmission profile.

[0010] In some CT systems, the x-ray source and detector array rotate with a gantry within the imaging plane and around the object to be imaged, constantly changing the angle at which the x-ray beam intersects the object. A group of x-ray radiation attenuation measurements (e.g., projection data) from the detector array at a given gantry angle is called a "view." A "scan" of an object includes a set of views made at different gantry angles (view angles) during one revolution of the x-ray source and detector.

[0011] The X-ray source 104 includes an anode and a cathode. Electrons emitted by the cathode (e.g., electrons emitted by energizing the cathode) are intercepted by a target located at or near the anode. Electrons intercepted by the target release energy in the form of X-rays, which travel toward the detector array 108. The area at the target plane that receives electrons from the cathode and forms the emitted X-rays may be referred to herein as a "focal spot." The emitted X-rays may be focused on a portion of the scanned object 204 by an "effective focal spot." The size of the effective focal spot may depend on the angle of the actual focal spot (e.g., relative to the target plane). For example, a small effective focal spot is desirable when scanning a small area, while a large effective focal spot is desirable when scanning a large area.

[0012] In some embodiments, an x-ray generating system including the x-ray source 104 can move and / or shape the focal spot. For example, the x-ray generating system can increase or decrease the size of the focal spot. Furthermore, in some embodiments, the x-ray generating system can generate a compound focal spot. A compound focal spot is a combination of two or more individual focal spots. For example, two individual focal spots located apart from each other can be combined to generate a single compound focal spot.

[0013] FIG. 2 illustrates an exemplary imaging system 200 similar to the CT system 100 of FIG. 1. According to aspects of the present disclosure, the imaging system 200 is configured to image a subject 204 (e.g., subject 112 of FIG. 1). In one embodiment, the imaging system 200 includes a detector array 108 (see FIG. 1). The detector array 108 further includes a plurality of detector units 202 that sense an X-ray radiation beam 106 (see FIG. 1) passing through the subject 204 (e.g., a patient) and acquire corresponding projection data. In some embodiments, the detector array 108 can be fabricated in a multi-slice configuration including a plurality of detector units 202, where one or more additional rows of detector units 202 are arranged in a parallel configuration to acquire projection data. In an exemplary embodiment, the detector units 202 can be PCCT detector units arranged as further described below with respect to FIGS. 6-9. Such an arrangement can correct for internal scattering crosstalk in CT images.

[0014] In certain embodiments, imaging system 200 is configured to move to different angular positions around object 204 to acquire desired projection data. Thus, gantry 102 and the components mounted on gantry 102 may be configured to rotate about center of rotation 206 to acquire projection data at different energy levels, for example. Alternatively, in embodiments in which the projection angle relative to object 204 changes as a function of time, the mounted components may be configured to move along a general curve rather than along the arc of a circle.

[0015] As the X-ray source 104 and detector array 108 rotate, the detector array 108 collects data of the attenuated X-ray beam. The data collected by the detector array 108 is pre-processed and calibrated to adjust the data to represent the line integrals of the attenuation coefficients of the scanned object 204. The processed data is commonly referred to as a projection. In some embodiments, the individual detectors or detector units 202 of the detector array 108 may include photon-counting detectors that register individual photon interactions into one or more energy bins. It should be understood that the methods described herein may also be implemented with energy-integrating detectors.

[0016] The acquired set of projection data can be used for reference material decomposition (BMD). During BMD, the measured projections are converted into a set of material density projections. The material density projections can be reconstructed to form a pair or set of material density maps or images of each reference material (e.g., bone, soft tissue) and / or a contrast agent map. The density maps or density images can be correlated in order to form a 3D volumetric image of the reference material (e.g., bone, soft tissue, and / or contrast agent) within the imaged volume.

[0017] Once reconstructed, the reference material images produced by the imaging system 200 reveal internal features of the subject 204, which are represented by the densities of two or more reference materials. The density images can be displayed to show these features. In traditional approaches to diagnosing diseases, such as pathologies, and broader medical phenomena, a radiologist or physician examines hard copies or displayed density images to identify specific features of interest. Such features include lesions, the size and shape of particular anatomical structures or organs, and other features identifiable from the images based on the skill and knowledge of the individual medical practitioner.

[0018] In one embodiment, imaging system 200 includes a control mechanism 208 that controls the movement of components, such as the rotation of gantry 102 and the operation of x-ray source 104. In some embodiments, control mechanism 208 further includes an x-ray controller 210 configured to provide power and timing signals to x-ray source 104. Additionally, control mechanism 208 includes a gantry motor controller 212 configured to control the rotational speed and / or position of gantry 102 based on imaging requirements.

[0019] In certain embodiments, the control mechanism 208 further includes a data acquisition system (DAS) 214 configured to sample analog data received from the detector elements 202 and convert the analog data to digital signals for further processing. The data sampled and digitized by the DAS 214 is transmitted to a computer or computing device 216 that includes one or more processors. In one example, the computing device 216 stores the data in a storage device or mass storage 218. The storage device 218 may be any type of non-transitory memory, including, for example, a hard disk drive, a floppy disk drive, a compact disk read / write (CD-R / W) drive, a digital versatile disk (DVD) drive, a flash drive, and / or a solid-state storage drive.

[0020] Additionally, the computing device 216 provides commands and parameters to one or more of the DAS 214, the X-ray controller 210, and the gantry motor controller 212 to control system operations (e.g., data acquisition and / or data processing). In certain embodiments, the computing device 216 controls system operations based on operator input. The computing device 216 receives operator input, including commands and / or scanning parameters, for example, through an operator console 220 operably coupled to the computing device 216. The operator console 220 may include a keyboard (not shown) or a touch screen to enable an operator to specify commands and / or scanning parameters.

[0021] 2 shows one operator console 220, two or more operator consoles may be coupled to imaging system 200, for example, to input or output system parameters, request exams, plot data, and / or view images. Additionally, in certain embodiments, imaging system 200 may be coupled to multiple displays, printers, workstations, and / or similar devices located either locally or remotely, for example, within a facility or hospital, or at entirely different locations, through one or more configurable wired and / or wireless networks (e.g., the Internet and / or virtual private networks, wireless telephone networks, wireless local area networks, wired local area networks, wireless wide area networks, wired wide area networks, etc.).

[0022] In one embodiment, for example, imaging system 200 includes or is coupled to a Picture Archiving and Communication System (PACS) 224. In an exemplary implementation, PACS 224 is further coupled to a remote system (such as a radiology information system, a hospital information system, and / or an internal or external network (not shown)) to allow an operator at another location to provide commands and parameters and / or access image data.

[0023] The computing device 216 uses operator-supplied and / or system-defined commands and parameters to operate a table motor controller 226, which may control the table 114, which may be a motorized table. In particular, the table motor controller 226 may move the table 114 so that the subject 204 is properly positioned in the gantry 102 to acquire projection data corresponding to a target volume of the subject 204.

[0024] As mentioned above, the DAS 214 samples and digitizes the projection data acquired by the detector unit 202. The image reconstructor 230 then performs high-speed reconstruction using the sampled and digitized x-ray data. While FIG. 2 illustrates the image reconstructor 230 as a separate entity, in certain embodiments, the image reconstructor 230 may form part of the computing device 216. Alternatively, the image reconstructor 230 may not be present in the imaging system 200; instead, the computing device 216 may perform one or more functions of the image reconstructor 230. Furthermore, the image reconstructor 230 may be located locally or remotely and may be operably connected to the imaging system 200 using a wired or wireless network. In particular, in one exemplary embodiment, the computational resources of a “cloud” network cluster may be used for the image reconstructor 230.

[0025] In one embodiment, image reconstructor 230 stores the reconstructed image in storage device 218. Alternatively, image reconstructor 230 may transmit the reconstructed image to computing device 216 for generating patient information useful for diagnosis and evaluation. In certain embodiments, computing device 216 may transmit the reconstructed image and / or patient information to a display or display device 232 communicatively coupled to computing device 216 and / or image reconstructor 230. In some embodiments, the reconstructed image is transmitted from computing device 216 or image reconstructor 230 to storage device 218 for short-term or long-term storage.

[0026] Referring now to FIG. 3 , a partial view of a photon-counting detector element 300 of a PCCT detector unit is shown. A reference axis 350 is provided, including the x-axis, y-axis, and z-axis. The reference axis 350 is used to compare views of each portion of the PCCT detector unit shown in FIGS. 3-5 , 11 , and 12 . The photon-counting detector element 300 can be a non-limiting embodiment of the detector elements of the detector unit 202 of FIG. 2 , where multiple rows of the detector elements 300 can be arranged in a stacked, parallel configuration along a stacking direction 320 parallel to the z-axis to form a detector unit (e.g., detector array 108) for acquiring projection data, as described above.

[0027] The photon-counting detector element 300 includes a sensor 302, which may be electronically coupled to a printed circuit board (PCB) 316. The PCB 316 includes connections 318 for the detector element 300 to readout electronics. An application specific integrated circuit (ASIC) 312 may be mounted on the PCB 316, which together with the readout electronics forms part of the DAS (e.g., DAS 214) of the PCCT system.

[0028] In various embodiments, the sensor 302 may be embedded in a chip made of a semiconductor material (such as silicon). The width of the chip (e.g., width along the z-axis) may be one pixel at an edge 311 of the sensor 302. Multiple sensors may be embedded along the surface of the chip and extend along the length of the chip. The sensor 302 may be configured to count photons that impinge on the edge 311 of the sensor 302. Specifically, for each pixel (e.g., subsensor) 309 along the edge 311, one or more sensor segments 305 may be embedded in a column 303 extending below each pixel 309 and oriented in the direction 307 of the incident X-ray beam 301 (e.g., vertically in FIG. 3 ). Each sensor segment 305 in each column 303 has a width of approximately one pixel at the surface of the sensor 302, which coincides with the pixel 309 at the edge 311 corresponding to the associated column 303. Each sensor segment 305 in each column 303 can count the number of photons of the incident x-ray beam 301 that strike the edge 311 at the corresponding pixel 309 .

[0029] In other words, each column 303 may include multiple sensor segments 305 that overlap in the vertical direction 307 of the column 303. For example, each column 303 (shown vertically) may include a first segment at a first vertical location 304, a second segment at a second vertical location 306, and so on. In the embodiment shown in FIG. 3, each column 303 includes two sensor segments 305. In other embodiments, each column 303 may include three, four, or other numbers of segments 305. The size of each segment 305 in a column 303 may be the same, or each segment 305 in a column 303 may be different. For example, the first segment 305 in a column 303 may be larger than the second segment 305 in the column 303. The third segment 305 in a column 303 may be smaller than the second segment 305 in the column 303.

[0030] Each segment 305 may be electrically coupled to an ASIC 312 mounted on a PCB 316. In various embodiments, each segment 305 of the sensor 302 may be electrically coupled to a sensor bond pad 310 of the sensor 302 through a PCCT sensor trace 308. The sensor bond pad 310 may be electrically coupled to the ASIC 312 through a wire bond 314.

[0031] Each segment 305 can detect multiple incident photons of the X-ray beam 301. When the X-ray beam 301 strikes the sensor 302 at a pixel 309, the X-ray beam 301 can pass through multiple overlapping (e.g., vertically arranged) segments 305 in the corresponding column 303. As the X-ray beam 301 passes through each segment 305 in the column 303, multiple photons contained in the X-ray beam 301 can be detected by the segments 305.

[0032] For example, the exemplary X-ray beam 301 may be incident on a first segment 305 at a first vertical position 304 of the column 303, and the first segment 305 may detect a first number of photons of the exemplary X-ray beam 301. The first number of photons may be less than the total number of photons of the exemplary X-ray beam 301, and a second number of photons of the total number of photons may pass through the first segment 305 without being detected. The second number of photons of the exemplary X-ray beam 301 that pass through the first segment 305 (undetected) may be incident on a second segment 305 at a second vertical position 306 of the column 303. The second segment 305 may detect a third number of photons of the exemplary X-ray beam 301. The third number of photons may be less than the second number of photons, and a fourth number of photons may pass through the second segment 305 without being detected. A fourth number of photons of the exemplary X-ray beam 301 that pass through the second segment 305 may then be incident on a third segment 305 at a third vertical position in the column 303, and so on. Thus, the total number of detected photons of the exemplary X-ray beam 301 can be estimated by summing the number of photons detected by each vertically stacked segment 305 of the column 303.

[0033] The number of photons detected in each vertically overlapping segment 305 in column 303 may vary. For example, in some cases, all photons of exemplary X-ray beam 301 may be detected by a first segment 305, and none of the photons of exemplary X-ray beam 301 may be detected by a second segment 305. In other cases, a large percentage of the photons of exemplary X-ray beam 301 may be detected by a first segment 305, a smaller percentage of the photons of exemplary X-ray beam 301 may be detected by a second segment 305 than the first segment 305, a smaller percentage of the photons of exemplary X-ray beam 301 may be detected by a third segment 305 than the second segment 305, and so on. Some photons of exemplary X-ray beam 301 may not be detected by any of the segments 305 in column 303, and the total number of detected photons may not equal the total number of photons of exemplary X-ray beam 301.

[0034] When a photon strikes segment 305, an analog electrical signal is generated and transmitted via sensor trace 308 and sensor bond pad 310 to ASIC 312. The analog electrical signal is proportional to the amount of energy in the photon. ASIC 312 can convert the analog electrical signal to a digital signal by counting the occurrence of photon hits with a counter. Furthermore, ASIC 312 can identify the energy imparted by the photon by comparing the magnitude of the electrical signal with one or more preset thresholds. Specifically, ASIC 312 can include multiple comparators, each of which outputs a trigger signal that increments a corresponding digital counter by one when the analog signal exceeds a signal level threshold associated with the comparator. Each comparator of the multiple comparators can have a different signal level threshold. For example, ASIC 312 may include thresholds for a first comparator having a first signal level threshold; a second comparator having a second signal level threshold, the second signal level threshold being greater than the first signal level threshold; a third comparator having a third signal level threshold, the third signal level threshold being greater than the second signal level threshold; and so on, up to the maximum energy level of the spectrum of photons. The difference between the thresholds defines an energy range or bin. Thus, the number of photons whose energy falls within each bin can be recorded by ASIC 312. These photon count numbers are transmitted by ASIC 312 to PCB 316 via connection 318 for use in image reconstruction. Alternatively, ASIC 312 may first perform additional operations on the numeric count information (such as summing the individual photon counts of the bins in a given column) to generate a total number of photon counts.

[0035] Noise in PCCT detected images can result from photons incident on the sensor 302 not interacting with the object being imaged or interacting with other components of the CT imaging system before reaching the sensor 302. For example, rather than being absorbed by the sensor 302, photons can scatter from the sensor 302 and be absorbed by an adjacent sensor in the PCCT detector unit. An anti-scatter grid can prevent scattering crosstalk between sensors, as shown in FIG. 4.

[0036] Referring to FIG. 4 , a side view of a PCCT detector unit 402 as viewed from the x-axis is shown. The PCCT detector unit 402 can include multiple sensors 302 stacked in the stacking direction 320. Each sensor 302 can be included in a detector (e.g., a photon-counting detector element 300). FIG. 4 illustrates the sensor 302, omitting other components of the detector element 300 for clarity. The anti-scatter grid 404 includes multiple fins 406. Each fin of the multiple fins 406 can be disposed between two adjacent sensors 302 in the stacking direction 320. The fins 406 can extend such that their height along the y-axis is at least equal to the height of the sensors 302 along the y-axis. In some examples, the thickness of the fins 406 in the stacking direction can be thinner than the thickness of the sensors 302 in the stacking direction, although other relative thicknesses of the fins 406 and the sensors 302 can also be considered. The fins 406 can be formed of a metal or metal alloy capable of absorbing scattered X-ray photons. For example, the fins 406 may comprise sheets of tungsten (W) or a tungsten alloy. Additionally, the fins 406 may be adhered to the sensors 302 with an epoxy located between the fins 406 and the sensors 302. In this manner, X-rays scattered from one sensor 302 are absorbed by the intervening fins of the anti-scatter grid 404 and do not reach adjacent fins. The sensor stack 401 includes multiple sensors 302 and multiple fins 406, with the fins 406 located between the sensors 302.

[0037] Graph 408 shows intensity as a function of position on the z-axis. The x-axis values ​​of graph 408 correspond to a diagram of the PCCT detector unit 402. Plot 410 shows peaks corresponding to the incident X-ray beam 301, indicated by the arrow. The incident X-rays may interact with one sensor 302. Scattering from one sensor 302 to an adjacent sensor is substantially absorbed by the intervening fin 406, and no signal intensity is recorded by the adjacent sensor. Thus, plot 410 shows peaks with a peak width approximately equal to the width of one sensor 302. Note that plot 410 is an approximation of the signal intensity; even though the fin 406 blocks most of the X-rays scattered in the z-direction, secondary peaks may occur in the z-direction. Furthermore, the width of the peaks may not be greater than the width of one sensor 302.

[0038] Referring now to FIG. 5, a side view of the PCCT detector unit 402 is shown as viewed from the stacking axis (e.g., the z-axis). As viewed from the stacking axis, the surface of one sensor 302 in the xy plane is shown to include pixels arranged in rows, with each pixel including a subsensor. Also shown in FIG. 5 is a collimator 502. The collimator can be positioned in front of the PCCT detector unit 402, between the object being imaged and the PCCT detector unit 402. The incident X-ray beam 301 may interact with the collimator before reaching the PCCT detector unit 402. The collimator 502 directs diffuse X-ray scatter from the object in a single direction toward the PCCT detector unit 402. The collimator directs divergent X-ray scatter from the object in a single direction toward the PCCT detector unit 402. In this way, X-ray scatter can be reduced by the collimator before reaching the PCCT detector unit 402. However, within each sensor 302, scattering in the X direction may not be prevented.

[0039] X-rays can interact with pixels of the sensor 302. Graph 504 shows intensity as a function of x-axis position on the sensor 302. Plot 506 shows peaks corresponding to pixels that absorbed incident X-rays. Plot 506 shows a broad distribution of intensities around the peak, which corresponds to the intensities recorded at pixels adjacent to the pixel that interacted with the X-rays. The intensities at the neighboring pixels can be attributed to scattering of the X-rays within the sensor 302. The broad curve in plot 506 can be a source of noise, reducing the resolution of the acquired image and can also cause spectral contamination, leading to contamination of material images (e.g., one material contaminating another material image).

[0040] The internal scatter shown in FIG. 5 may not be mitigated by the anti-scatter grid shown in FIG. 4, which merely blocks scatter between sensors, not within each sensor. Therefore, scatter may occur in one of several directions orthogonal to the x-rays. For example, scatter of x-rays traveling in the y direction toward the PCCT detector unit 402 is reduced in the z direction, but not in the x direction. Therefore, an image with sufficient resolution may not be obtained due to scatter of x-rays in the x direction. The arrangement of the PCCT detector unit 402 can be strategically adapted (e.g., positioned) to determine which signals are due to internal scatter and can be removed from the image by an image processing system without further modification of the PCCT detector unit 402.

[0041] As described above with respect to Figure 2, the PCCT detector units may be arranged in an arc around the circumference of the gantry. Conventionally, each PCCT detector unit may be arranged such that the stacking axis of the PCCT detector unit is parallel to the rotation axis of the gantry. Figures 6-9 show embodiments in which at least one PCCT detector unit among the plurality of PCCT detector units is arranged such that the stacking axis of the PCCT detector unit is at least partially tangent to the circumference of the gantry and at an angle to the rotation axis of the gantry.

[0042] A first embodiment of a detector array 602 is shown schematically in FIG. 6 . FIG. 6 also shows the positions of an x-ray source 604 and an object 606 being imaged. The detector arrays of FIGS. 6-9 may be examples of detector arrays included in a computed tomography system (such as CT system 100 of FIGS. 1-2 ). In some examples, the object 606 may be a patient. A reference axis 601, including x, y, and z axes, is shown to allow comparison between the embodiments shown in FIGS. 6-9 . X-rays 607 may be emitted from the x-ray source 604 in an imaging direction parallel to the y-axis. The emitted x-rays may be emitted from the x-ray source 604 outside the imaging direction, interact with the object 606, and impinge on the detector array 602. The x-ray source 604 and the detector array 602 may each be rotated around the object by a gantry (omitted for clarity) about an axis of rotation parallel to the axis indicated by point 603.

[0043] The detector array 602 may include a plurality of horizontally oriented PCCT detector units 608 and a plurality of vertically oriented PCCT detector units 610. For example, the same number of horizontally oriented PCCT detector units 608 as vertically oriented PCCT detector units 610 may be provided. The horizontally oriented PCCT detector units 608 are oriented such that the stacking axis of the PCCT detector unit (e.g., the PCCT detector unit 402 in FIGS. 4 and 5 ) is disposed horizontally with respect to the object 606 and is at an angle with respect to the rotation axis. For example, the horizontally oriented PCCT detector units 608 may be oriented such that the stacking axis of the PCCT detector unit (e.g., the PCCT detector unit 402 in FIGS. 4 and 5 ) is perpendicular to the object 606 and parallel to the rotation axis. The vertically oriented PCCT detector units 610 may be oriented such that the stacking axis of the PCCT detector unit (e.g., the PCCT detector unit 402 in FIGS. 4 and 5 ) is perpendicular to the object 606 and parallel to the rotation axis. The vertically oriented PCCT detector unit 610 can be rotated 90° about the imaging axis relative to the horizontally oriented PCCT detector unit 608. In this manner, the stacking axis of the vertically oriented PCCT detector unit 610 can be perpendicular to the stacking axis of the horizontally oriented PCCT detector unit 608.

[0044] At each detection angle, scattered x-rays can be detected by both the vertically oriented PCCT detector units 610 and the horizontally oriented PCCT detector units 608, as opposed to current configurations that include a single row of vertically oriented PCCT detector units 610. FIG. 6 shows that for a given detection angle, the horizontally oriented PCCT detector units 608 are positioned closer to the object 606 than the vertically oriented PCCT detector units 610. In this manner, incident x-rays at a given detection angle reach both the vertically oriented and horizontally oriented detector units and can be detected by both detector units. In an alternative example, the positions can be swapped, with the vertically oriented PCCT detector units 610 positioned closer to the object 606 than the horizontally oriented PCCT detector units 608. In other examples, the orientation of the PCCT detector unit closest to the object 606 can be alternated between vertical and horizontal. In such examples, x-rays can be incident on both the vertically oriented PCCT detector units 610 and the horizontally oriented PCCT detector units 608 and can be detected by both detector units. Additionally, a collimator (such as collimator 502 in FIG. 5) can be placed between array 602 and object 606. In this manner, scattering of the x-rays can be reduced by the collimator before they are detected and can be further reduced by the vertical placement of the PCCT detector units in array 602.

[0045] Scatter noise that is horizontal to the object 606 can be blocked by the anti-scatter grid of the horizontally oriented PCCT detector unit 608. Scatter noise that is perpendicular to the object 606 can be blocked by the anti-scatter grid of the vertically oriented PCCT detector unit 610. By including detectors of both orientations at each detection angle, a combined image can be formed in which signals generated by detectors of both orientations are considered true signals and signals recorded at one orientation are considered noise. The combined image can be free of noise signals, thereby improving image resolution.

[0046] In some cases, the high count rate of x-ray photons impinging on the PCCT detector units may necessitate the use of alternative means of analyzing acquired images. For example, the signal recorded at each pixel of the sensor is a convolution of the primary photon signal (e.g., signal due to scattering from the imaged object) with the signal scattered from neighboring pixels (e.g., noise). The convolution may extend in the Z direction for the horizontally oriented detector units 608 and in the X direction for the vertically oriented detector units 610. In some cases, these convolutions may be less computationally intensive and / or simpler than those resulting from a conventional vertically oriented sensor arrangement. A filter kernel for spectrally deconvolving the scatter-corrupted signal may be utilized to output a noise-reduced image. The filter kernels for the vertically oriented detector units 610 and the horizontally oriented detector units 608 may be constructed differently to account for both the direction of scatter and spectral beam hardening.

[0047] Furthermore, with regard to beam hardening, image processing can adjust the images acquired by the detector array 602 to take into account that low energy x-rays are absorbed by PCCT detector units located closer to the object 606 before reaching PCCT detector units located further from the object 606. In this way, the x-rays are hardened by the PCCT detector units closest to the object 606 before reaching the PCCT detector units farthest from the object 606.

[0048] As an alternative means of adjusting the hardening x-rays, a detector array 702, as shown in FIG. 7, may be used. The detector array 702 may include alternating horizontally oriented PCCT detector units 608 and vertically oriented PCCT detector units 610. The horizontally oriented PCCT detector units 608 and vertically oriented PCCT detector units 610 may be positioned approximately equidistant from the object 606. Furthermore, a collimator (such as the collimator 502 in FIG. 5) may be positioned between the array 602 and the object 606. In this manner, scattering of x-rays may be reduced by the collimator before detection and may be further reduced by the configuration of the PCCT detector units in the detector array 702. In a single-row arrangement, scattered x-rays at a given detection angle may be detected by a single detector unit. Therefore, in this configuration, x-rays may be detected by either the horizontally oriented detector units 608 or the vertically oriented detector units. For example, x-rays may be detected by either the horizontally oriented PCCT detector units 608 or the vertically oriented PCCT detector units 610. Furthermore, this alternating pattern allows for overall noise reduction in image processing. For example, a first image can be generated by combining signals from the horizontally oriented PCCT detector unit 608, and a second image can be generated by combining signals from the vertically oriented PCCT detector unit 610. Because of their interleaved arrangement, the first and second images may lack data. Therefore, the first and second images may be incomplete as separate images. However, image processing methods can construct a continuous image from the first and second images. Construction of the continuous image can be performed after the images have been corrected for spectral differences and convolution of scattering noise, as described above. In lower count rate scenarios, image processing methods can further determine which signals are noise from a comparison of the first and second images and filter them to generate a low-noise image. Furthermore, in high count rate techniques, deconvolution techniques using filter kernels, such as those described above, can be used to correct for scattering noise.

[0049] 10, a flowchart of a method 1000 for correcting for internal scatter in a PCCT detector array that includes two differently oriented PCCT detector units is shown. For example, the method 1000 can be used to generate high-resolution images from sensors in the detector arrays shown in FIGS. 6 and 7, where some PCCT detector units are oriented horizontally and some PCCT detector units are oriented vertically.

[0050] The method 1000 includes receiving first pixel intensities from a first orientation detector, at 1002. For example, the first orientation detector may be a horizontal orientation detector (such as the horizontal orientation PCCT detector unit 608 of FIGS. 6 and 7).

[0051] Method 1000 proceeds to 1004. At 1004, second pixel intensities are received from a corresponding second orientation detector. For example, the second orientation detector can be a vertical orientation detector (such as the vertical orientation PCCT detector unit 610 in FIGS. 6 and 7). Furthermore, the corresponding second orientation detector can be positioned adjacent to the first orientation detector. For example, the first orientation detector and the second orientation detector can be aligned at a detection angle such that x-rays first pass through the first orientation detector and then pass through the second orientation detector, as shown in FIG. 6. Alternatively, the first orientation detector and the second orientation detector can be aligned side by side, with the first orientation detector detecting x-ray scatter at a different detection angle than the second orientation detector.

[0052] At 1005, the method 1000 includes correcting pixel intensities to account for spectral and efficiency differences between the detectors in the first and second orientations. For example, correcting for spectral differences can include correcting for if the detector is preferentially exposed to hard or soft x-rays. As another example, the efficiency of photon-to-electrical signal conversion may differ between each PCCT detector unit, and the efficiency differences may be known (e.g., stored in a look-up table) and can be corrected for.

[0053] The method 1000 includes combining the intensities of the detectors in the first orientation and the second orientation to output an image at 1006. By combining the intensities of the detectors in the first orientation and the second orientation, the combined image may have a reduced noise level compared to an image acquired with a single orientation.

[0054] In a low count rate example, combining the intensities of the first and second detectors can include comparing the intensities as a function of time for each of the first and second detectors at 1008. For example, the intensity at a pixel of the first detector can be compared with the intensity at a corresponding pixel of the second detector. If the pixel intensities of the first and second detectors are determined to match, determining the match can include the computing device determining that the pixel intensities match if the intensities are within a threshold difference (e.g., a tolerance). The threshold difference can be predetermined and programmed into the computing device. If the pixel intensities are determined to match, the pixel intensities are maintained. Matching pixel intensities can indicate that the intensity is due to x-rays scattered from the object and not blocked by an anti-scatter grid in either the first or second detector. Because the pixel intensities obtained from the two differently oriented PCCT detector units match, the signal can be considered not to be noise due to internal scattering. Therefore, the intensity can be maintained and used to generate an image. If it is determined that the pixel intensities do not match, the pixel intensities are decreased. Because the pixel intensities obtained from the two PCCT detector units with different orientations do not match (e.g., are not within a threshold difference), the signal may be noise due to internal scattering. Therefore, the pixel intensities are decreased to reduce noise in the image obtained after processing. In some examples, decreasing the pixel intensities may include decreasing the pixel intensities to zero.

[0055] In an alternative example, such as when the count rate is high, method 1000 includes, at 1010, combining projection images at the intensity collected by a detector at a first orientation with projection images at the intensity collected by a corresponding detector at a second orientation (e.g., an adjacent or neighboring detector). In one example, the images can be combined in the Fourier domain by taking the X-direction frequency component from the projection images collected by a detector oriented to block scatter in the X direction and the Z-direction frequency component from the projection images collected by a detector oriented to block scatter in the Z direction. As another example, the images can be combined using a neural network trained to extract the least noisy features from each set of projection images.

[0056] Additionally or alternatively, combining the intensities includes deconvolving 1012 the scatter noise from the image collected by the detector at the first orientation and the image collected from the detector at the second orientation. Deconvolving can include deconvolving the scatter noise from the signal of the projection image. The deconvolution can be performed by a first deconvolution kernel configured to deconvolve the image from the detector at the first orientation and a second deconvolution kernel configured to deconvolve the image from the detector at the second orientation. In some examples, the deconvolution can occur before the spectral and efficiency data collection. In some embodiments, the corrected deconvolved images can be further combined as described above in step 1010. Method 1000 then ends.

[0057] Another alternative detector array 802 is shown in FIG. 8, which includes multiple non-orthogonally oriented PCCT detector units 804. The non-orthogonally oriented PCCT detector unit 804 can be the PCCT detector unit 402 of FIGS. 4 and 5 arranged as shown in FIG. 8. For example, the orientation of the non-orthogonally oriented PCCT detector unit 804 can be achieved by rotating the vertically oriented PCCT detector unit 610 about the y-axis so that the sensor (e.g., sensor 302 of FIGS. 3-5) is at a non-orthogonal angle (e.g., less than 90 degrees) to the incident x-rays. Additionally, the non-orthogonal PCCT detector unit 610 can be arranged such that the stack axis is at an angle to the axis of rotation. FIG. 8 illustrates the detector array 802 as viewed from the z-axis and the x-ray source 604 relative to the detector array 802, and also illustrates the detector array 802 as viewed from the y-axis. Each detector unit 804 can be rotated by approximately the same angle so that the sensors of the detector units are parallel, and the detector array 802 does not include detector units with other orientations. Furthermore, multiple detector units 804 can be arranged in plane contact. In this manner, noise can be reduced compared to detectors with conventional orientations. For example, in-plane scatter can be reduced at the expense of cross-plane scatter. Furthermore, including detectors with a single orientation rather than multiple orientations can simplify assembly and image reconstruction. In some embodiments, the detector orientation shown in FIG. 8 can be combined with other detector orientations (such as those shown in FIGS. 6 and 7). The detector orientation of FIG. 8 can be further used in constructing a combined image, as described above with respect to FIG. 10.

[0058] Another alternative detector array 902 is shown in FIG. 9 , which includes a single row of horizontally oriented PCCT detector units 608 spaced approximately equidistant from the object 606. There may be no detector units of other orientations in the detector array 902. In this manner, scattering in the X direction can be reduced. In some examples, XY slices of a 3D volume are particularly clinically important, and reducing X scattering can have a more positive effect on clinical outcomes than reducing Z scattering. In some examples, applying a scatter correction algorithm before reconstructing the image can reduce Z scattering in the detector array 902 in the final image. Furthermore, the scatter correction algorithm can be less computationally intensive than an algorithm configured to correct scattering in both the X and X directions. Additionally or alternatively, the image volume reconstructed after correcting for Z scattering can exhibit high image quality (e.g., improved resolution) not only in the transaxial plane (e.g., XY slice), but also in the coronal plane (e.g., XZ slice) and sagittal plane (e.g., YZ) plane.

[0059] Referring to FIG. 11 , the sensor 302 is shown with a guard ring 1102 surrounding the sensor 302. In other figures, the guard ring 1102 has been omitted from the illustration of the sensor 302 for clarity, but it is understood that any embodiment including the sensor 302 may include the guard ring 1102. The guard ring 1102 may be positioned in surface contact with the surface of the sensor 302 in the xy plane. The guard ring 1102 has a height 1104, a width 1106, and a thickness 1108. The height 1104 and width 1106 may vary depending on the dimensions of the sensor 302, while the thickness 1108 may remain constant regardless of the dimensions of the sensor stack 401. The guard ring 1102 may protect the sensing unit (e.g., a diode) from degradation, for example, when the sensing unit is incorporated into the detector unit 402 of FIG. 4 and used for imaging. For example, the guard ring may lower the potential of the sensor to prevent degradation of the diode. Additionally, the guardrails can protect the diode from leakage currents that originate from the sidewalls of the sensor 302 and flow inward toward the diode.

[0060] Referring to FIG. 12 , multiple sensor stacks 401 are shown with an incident X-ray beam 301. Furthermore, the multiple sensor stacks are aligned vertically, with their stacking axes oriented parallel (e.g., in the X direction). The sensor stack 401 of each detector unit 402 is wrapped with a metal foil 1204 made of a metal or metal alloy (e.g., tungsten or tungsten alloy foil) capable of absorbing scattered X-ray photons, and the surfaces in the xy plane and the yz plane can be covered with the metal foil. In FIG. 12 , for clarity, the metal foil 1204 is shown partially transparent. The surface in the xz plane of the sensor 302 is the surface on which the X-ray beam 301 impinges and can be left uncovered by the metal foil. Therefore, the metal foil 1204 can be in surface contact with at least four surfaces of each detector unit. In this manner, scattering in the z-direction is reduced by the fins 406, and scattering in the x-direction of adjacent PCCT detector units 402 (PCCT detector units adjacent in the x-direction) can be reduced by the metal foil. To further reduce scattering in this configuration, the x-direction dimension (e.g., the number of pixels) of the sensor 302 including the detector units 402 can be reduced and the number of detector units can be increased. In this manner, the number of boundaries between the detector units can be increased, thereby increasing the area where scattering is reduced. As shown in graph 504, plot 506 shows the peak in the x-direction when the sensor stack 401 is not wrapped with metal foil, and plot 1202 shows the peak in the x-direction when the sensor stack 401 is wrapped with metal foil. The peak in plot 1202 is narrower because the metal foil limits scattering in the x-direction. Therefore, scattering of X-rays is reduced compared to PCCT detector units without metal foil, and as a result, the metal foil allows for higher-resolution images.

[0061] An alternative example of a PCCT detector unit 1300 is shown in FIG. 13. In contrast to the PCCT detector unit 402, the PCCT detector unit 1300 may include fins (e.g., fins 406) disposed at every other connection between the sensors 302, rather than between each sensor 302. Instead of fins, an adhesive layer 1302 may be present between every other connection between the sensors 302 and adjacent sensors 302. The adhesive layer 1302 may be configured to ensure that the relative positions of the sensors 302 are fixed during installation of the PCCT detector unit and subsequent use of the PCCT detector unit. Furthermore, the adhesive layer 1302 may reduce or narrow the solid angle of the scattered X-rays in the x-y plane of each sensor 302. Narrowing the solid angle may shorten the distance that the internally scattered X-rays travel in the x-y plane of the sensor 302.

[0062] Conventionally, adhesive is applied in lines in the xy plane of each sensor, spaced along the x-axis of the sensor. However, if the adhesive is applied primarily along a single axis of the sensor 302, it may not be able to effectively reduce internal scattering in the x-direction. For example, while the cross-section shown in FIG. 13 includes an adhesive layer 1302, another cross-section of the PCCT detector unit 1300 (with adhesive lines in the x-direction) may have unfilled gaps between the sensors 302 and no adhesive.

[0063] An example of a sensor including an adhesive layer configured to reduce scattering of x-rays in the x-direction is shown in FIG. 14. A first sensor 1400 is shown including a diagonal adhesive pattern 1402. The diagonal adhesive pattern 1402 can include a plurality of diagonal adhesive lines 1404. Each diagonal adhesive line 1404 can be spaced apart and parallel to one another, such that the diagonal adhesive lines 1404 do not cross one another. A second sensor 1430 can include a mesh-like adhesive pattern 1432. The mesh-like adhesive pattern 1432 can include a plurality of vertical adhesive lines 1434 spaced apart and parallel to the y-axis, as well as a plurality of horizontal adhesive lines 1436 spaced apart and parallel to the x-axis. The vertical adhesive lines 1434 and horizontal adhesive lines 1436 can intersect at multiple points on the second sensor 1430 to form a mesh-like pattern. A third sensor 1460 can include a continuous adhesive layer 1462. The continuous adhesive layer 1462 may include an adhesive that extends continuously within the xy plane of the third sensor 1460. In each of the first sensor 1400, the second sensor 1430, and the third sensor 1460, the adhesive may not extend to the end of the sensor, and the adhesive or adhesive pattern may be disposed in the portion of the sensor that includes the sensor segment (e.g., sensor segment 305). In this manner, at least a portion of the adhesive layer may be present along a cross section perpendicular to the stacking direction in the portion of the sensor that includes the sensor segment (e.g., sensor segment 305). The pattern may be selected to balance the reduction in the solid angle in the x direction with the time and cost associated with applying additional adhesive during the manufacture of the PCCT detector unit.

[0064] Additionally or alternatively, the solid angle can be reduced in the x-direction by providing a layer of tungsten or other x-ray blocking material on the back surface of the detector (e.g., the surface on the side of the xy plane that does not contain the sensor segments 305). In some embodiments, the tungsten or tungsten alloy layer can be provided in a pattern similar to the adhesive pattern shown above with respect to FIG. 14. In some embodiments, the tungsten layer can be added as a foil. In another alternative, the tungsten layer can be deposited by an additive thin film technique (such as chemical vapor deposition).

[0065] Additionally or alternatively, a sensor of a PCCT detector unit (e.g., PCCT detector unit 402) can incorporate an X-ray shielding material into the sensor to block X-rays scattered in the X direction. Examples of incorporating an X-ray shielding material into a sensor are shown in FIGS. 15-17. Referring to FIG. 15, a sensor 302 is shown including trenches 1502 as viewed along a stacking axis (e.g., the z-axis). Each trench 1502 can be at least partially filled with a high atomic number X-ray blocking material. As an example, the X-ray blocking material can be tungsten metal. Alternatively, a post-collimator can be aligned with the trenches 1502 and extend into the sensor 302 to fill the trenches. As an example, the trenches 1502 can be provided between each pixel 309 of the sensor 302. Alternatively, the trenches 1502 can be provided between every other pixel or in other arrangements. Additionally, while the trench 1502 is shown in FIG. 15 as extending the entire length of the sensor 302 in the y-direction, in some embodiments, the length of the trench 1502 in the y-direction may be shorter than the length of the sensor. The trenches 1502 may be intermittently positioned to provide wiring paths. In this manner, the trenches 1502 may have a similar effect as the fins 406, but may block X-rays scattered in the x-direction rather than the z-direction. In some examples, the trenches 1502 may be configured to align with the fins 406. In this manner, the trenches 1502 may function as extensions of the fins 406. Furthermore, the PCCT detector unit may be configured with the trenches 1502 and fins 406 positioned in a manner selected to synergistically function in combination to minimize the amount of X-ray blocking material while maintaining the desired resolution in both the x- and y-directions of the X-ray image.

[0066] By incorporating the shielding material into the sensor, other aspects of the PCCT detector unit and image processing method may not require adjustment. Furthermore, because the trench 1502 is behind the post-collimator (e.g., with respect to the direction of x-ray travel), the geometric efficiency of the detector may not be affected. Because the x-ray blocking material may be a conductive metal, the trench 1502 may also be used to transmit a signal.

[0067] An exemplary embodiment of a process flow for forming trenches 1502 in sensor 302 is shown in FIG. 16. FIG. 16 shows a cross-sectional view of a wafer 1612 used to form sensors (such as sensor 302) of a PCCT detector unit. In an exemplary embodiment, wafer 1612 can be a silicon wafer. In a first step 1602, trenches 1502 can be formed in wafer 1612 after diodes 1610 are formed in wafer 1612 and before electrical wiring is formed. Diodes 1610 can include the active, photosensitive portion of the sensor. The first step 1602 includes etching wafer 1612 to form openings 1614. Openings 1614 can have a depth 1620 in the z-direction. In some examples, depth 1620 can be shallower than the thickness of wafer 1612 in the z-direction. In an alternative example, depth 1620 may be equal to the thickness of wafer 1612 in the z-direction, and opening 1614 may be formed as a via that extends completely through wafer 1612. Opening 1614 becomes a wall of trench 1502. By way of example, opening 1614 may be etched by direct reactive ion etching (DRIE), although other etching processes are contemplated.

[0068] An alternative example of wafer 1612 is shown in FIG. 17. In this alternative example, openings 1614 can be formed with openings on the same side as diodes 1610 and openings facing the opposite side of wafer 1612 in the z-axis. When filling the openings, both trenches 1502 and reverse trenches 1702 can be formed after openings 1614 are filled with X-ray blocking material. In one example, trenches 1502 and reverse trenches 1702 can be formed every other diode 1610 between diodes 1610. Forming trenches 1502 and reverse trenches 1702 helps reduce distortion of wafer 1612. Additionally, reverse trenches 1702 help shield X-ray scatter in the X-direction throughout the depth of the pixel.

[0069] In a second step 1604, an X-ray blocking material layer 1616 (such as tungsten) can be deposited on the wafer 1612. During deposition, the X-ray blocking material can fill each opening 1614 and extend over the surface of the wafer 1612. In an alternative embodiment, one or more openings 1614 can be left unfilled with the X-ray blocking material layer 1616. Alternatively, additional openings 1614 can be added after the X-ray material is deposited, thereby forming both unfilled and filled openings 1614. The openings 1614 that are not filled with the X-ray blocking material can prevent charge sharing between pixels of the sensor. After the second step 1604, the X-ray blocking material layer 1616 can be in face-to-face contact with the diode 1610. Deposition of the X-ray blocking material layer 1616 can be performed by an additive thin layer process. As an example, the X-ray blocking material layer 1616 can be deposited by chemical vapor deposition. In an alternative example, opening 1614 can be filled with a powdered x-ray blocking material (such as tungsten), and the powder can be sealed in place with a line of sealant (such as epoxy) that covers opening 1614 but not diode 1610. In such an example, opening 1614 can be tapered to facilitate powder filling. In other examples, the powdered x-ray blocking material and sealant can be applied in multiple layers within opening 1614 to avoid the formation of equipotentials.

[0070] In an alternative example shown in FIG. 18 , when the sensors 302 are stacked in a PCCT detection unit, gaps may remain between the sensors 302 in the stacking direction. A fluid filler material is injected from the side 1804, and the fluid filler material can wick between the sensors 302 and into the openings 1614. The fluid filler material can be made of an X-ray blocking material or contain a sufficient mass percentage of an X-ray blocking material. In this manner, a trench / shielding layer 1802 can be formed. In another example, an excess of fluid filler material can be applied to the surface of the sensor 302, and pressure can be applied to the sensor 302 in the direction indicated by arrow 1806 to force the fluid filler material into the openings 1614.

[0071] In a third step 1606, the x-ray blocking material layer 1616 may be removed from the surface of the wafer 1612 but remain in the openings 1614, thereby forming trenches 1502 in the wafer 1612. As an example, the x-ray blocking material layer 1616 may be removed from the surface by chemical mechanical polishing. In a fourth step 1608, a contact layer 1618 may be formed on the wafer 1612. After the fourth step 1608, the wafer 1612 may be prepared for assembly into a sensor (such as sensor 302).

[0072] A technical effect of method 1000 is to reduce the amount of noise in an x-ray image acquired by an array of PCCT detector units. The method uses existing sensor hardware and takes advantage of the relative positioning of the sensor hardware to reduce the amount of noise due to internal scattering. Additionally, the systems described herein may place x-ray absorbing elements within, around, and between sensors of the PCCT detector units to physically prevent crosstalk between pixels of the PCCT detector units.

[0073] The present disclosure also provides support for a computed tomography system including a gantry configured to rotate about a rotation axis, and a detector array including a plurality of photon-counting computed tomography (PCCT) detector units configured to be rotated by the gantry relative to the rotation axis, wherein a stacking axis of at least one PCCT detector unit of the plurality of PCCT detector units is arranged such that it is at an angle to the rotation axis. In a first system embodiment, the detector array includes a plurality of horizontally oriented PCCT detector units arranged such that their stacking axis is perpendicular to the rotation axis, and a plurality of vertically oriented PCCT detector units arranged such that their stacking axis is parallel to the rotation axis, wherein x-rays scattered at an angle are detected by both the vertically oriented PCCT detector units and the horizontally oriented PCCT detector units, and the plurality of vertically oriented detector units and the horizontally oriented detector units are equal in number. A second embodiment of the system optionally includes the first embodiment, wherein the detector array includes a plurality of horizontally oriented PCCT detector units arranged with a stack axis perpendicular to the rotation axis and disposed in front of a plurality of vertically oriented PCCT detector units arranged with a stack axis parallel to the rotation axis, wherein x-rays scattered at an angle toward one horizontally oriented PCCT detector unit of the plurality of horizontally oriented PCCT detector units also reach one vertically oriented PCCT detector unit of the plurality of vertically oriented PCCT detector units. A third embodiment of the system optionally includes one or both of the first and second embodiments, wherein the x-rays detected by the plurality of vertically oriented PCCT detector units are hardened with respect to the x-rays detected by the plurality of horizontally oriented PCCT detector units.A fourth example system optionally includes one or more of the first through third examples, wherein the detector array includes an alternating pattern of horizontally oriented PCCT detector units positioned with stacking axes perpendicular to the rotation axis and vertically oriented PCCT detector units positioned with stacking axes parallel to the rotation axis, and wherein x-rays scattered at an angle interact with one of the vertically oriented PCCT detector units and the horizontally oriented PCCT detector units. A fifth example system optionally includes one or more of the first through fourth examples, wherein the detector array includes a plurality of non-orthogonally oriented PCCT detector units with stacking axes parallel to each other and at an angle of less than 90 degrees with respect to the rotation axis. A sixth example system optionally includes one or more of the first through fifth examples, wherein the detector array includes a plurality of horizontally oriented PCCT detector units positioned such that a stacking axis is perpendicular to the rotation axis, but does not include a vertically oriented PCCT detector unit positioned such that a stacking axis is parallel to the rotation axis.A seventh example system optionally includes one or more of the first through sixth examples, wherein the system includes a controller configured to receive first pixel intensities from a first-oriented detector, receive second pixel intensities from a corresponding second-oriented detector, correct the first pixel intensities and the second pixel intensities to account for spectral differences and efficiency differences, and combine the intensities of the first-oriented detector and the second-oriented detector to form an image. An eighth embodiment of the system optionally includes one or more or each of the first to seventh embodiments, wherein the first orientation detector is positioned in front of the corresponding second orientation detector, and X-rays scattered at an angle to the detector array are detected by the first orientation detector and the corresponding second orientation detector.A ninth embodiment of the system optionally includes one or more or each of the first to eighth embodiments, wherein the first orientation detector is positioned adjacent to the corresponding second orientation detector such that the first orientation detector has a different detection angle than the corresponding second orientation detector.

[0074] The present disclosure also provides support for a photon-counting computed tomography (PCCT) detector unit. The photon-counting computed tomography (PCCT) detector unit includes a sensor stack including a plurality of sensors stacked along a stacking axis, and a metal foil in surface contact with four sides of the sensor stack, the four sides being perpendicular to faces of the plurality of sensors configured to receive x-rays. In a first embodiment of the system, the metal foil is tungsten or a tungsten alloy. In a second embodiment of the system, optionally including the first embodiment, the metal foil reduces x-ray scattering in a direction perpendicular to the stacking axis. In a third embodiment of the system, optionally including one or both of the first and second embodiments, the metal foil reduces scattering between adjacent PCCT detector units compared to a PCCT detector unit without the metal foil. In a fourth embodiment of the system, optionally including one or more or each of the first through third embodiments, the PCCT detector unit further includes fins present between adjacent sensors.

[0075] The present disclosure also provides support for a photon-counting computed tomography (PCCT) detector unit. The photon-counting computed tomography (PCCT) detector unit includes a plurality of sensors stacked in a stacking direction and an adhesive layer disposed between two adjacent sensors of the plurality of sensors, wherein at least a portion of the adhesive layer is present in a cross section perpendicular to the stacking direction of the plurality of sensors. In a first embodiment of the system, the system further includes a plurality of fins, each fin being present between two adjacent sensors. In a second embodiment of the system, optionally including the first embodiment, the adhesive layer includes a plurality of diagonal adhesive lines. In a third embodiment of the system, optionally including one or both of the first and second embodiments, the adhesive layer includes a plurality of vertical adhesive lines and a plurality of horizontal adhesive lines, and the plurality of vertical adhesive lines and the plurality of horizontal adhesive lines intersect. In a fourth embodiment of the system, optionally including one or more or each of the first to third embodiments, the adhesive layer includes a continuous adhesive layer.

[0076] In an alternative embodiment, the present disclosure also provides support for a computed tomography system including: a gantry configured to rotate about a rotation axis; and a detector array including a plurality of photon-counting computed tomography (PCCT) detector units configured to be rotated by the gantry relative to the rotation axis, wherein a stack axis of at least one of the plurality of PCCT detector units is positioned at an angle to the rotation axis. In a first embodiment of the system, the system includes a controller configured to receive first pixel intensities from a detector at a first orientation, receive second pixel intensities from a corresponding detector at a second orientation, correct the first pixel intensities and the second pixel intensities to account for spectral and efficiency differences, and combine projection images formed by the detector at the first orientation and the detector at the second orientation.

[0077] In an alternative embodiment, the present disclosure also provides support for a computed tomography system. The computed tomography system includes a gantry configured to rotate about an axis of rotation, and a detector array including a plurality of photon-counting computed tomography (PCCT) detector units configured to be rotated by the gantry relative to the axis of rotation, wherein a stack axis of at least one of the plurality of PCCT detector units is positioned at an angle to the axis of rotation. In a first embodiment of the system, the system includes a controller configured to receive first pixel intensities from a detector at a first orientation, receive second pixel intensities from a corresponding detector at a second orientation, correct the first pixel intensities and the second pixel intensities to account for spectral and efficiency differences, and deconvolve scatter noise from the detector at the first orientation using a first filter kernel and deconvolve scatter noise from the detector at the second orientation using a second filter kernel.

[0078] As used herein, elements or steps described in the singular and preceded by the words "a" or "an" should be understood not to exclude a plurality of such elements or steps, unless the exclusion of a plurality of such elements or steps is expressly stated. Furthermore, references to "one embodiment" of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Furthermore, unless expressly stated to the contrary, embodiments "comprising," "including," or "having" an element or elements having a particular characteristic may include additional such elements that do not possess that characteristic. The terms "including" and "in which" are used as shorthand for the terms "comprising" and "wherein," respectively. The terms "first," "second," and "third," etc., are used merely as labels and are not intended to impose numerical requirements or a specific positional order on the objects of these terms.

[0079] FIGS. 1-9 and 11-14 illustrate exemplary configurations of the relative placement of various components. When elements are shown as being in direct contact with or directly coupled to one another, they can, at least in one example, be said to be in direct contact with or directly coupled to one another. Similarly, elements shown as being in contact with or adjacent to one another are, at least in one example, in contact with or adjacent to one another. As one example, components in surface contact with one another can be said to be in surface contact. As another example, elements that are spaced apart from one another with only a space between them and no other components present can, at least in one example, be said to be spaced apart from one another with only a space between them and no other components present. As yet another example, elements shown above and below one another, opposite one another, or left and right from one another can be said to be shown above and below one another, opposite one another, or left and right from one another. Furthermore, as shown in the drawings, in at least one example, the uppermost element or point on an element can be said to be the “top” of the element, and the lowermost element or point on an element can be said to be the “bottom” of the element. As used herein, top / bottom, above / below, and above / below are relative to the vertical axis of the drawing and are used to describe the relative placement of elements in the drawing. Thus, an element shown above another element is, in one example, positioned vertically of the other element. As yet another example, the shapes of elements depicted in the drawing may be said to have those shapes (e.g., circular, straight, flat, curved, rounded, chamfered, angled, etc.). Furthermore, elements shown as intersecting one another may, in at least one example, be said to intersect or cross one another. Furthermore, an element shown within or outside another element may, in one example, be said to be within or outside of the other element.

[0080] This specification uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the relevant art to practice the invention (e.g., to make and use the devices or systems, and to perform the incorporated methods). The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not differ insubstantially from the literal language of the claims. [Explanation of symbols]

[0081] 100 CT System 102 Gantry 104 X-ray source 106 X-ray radiation beam 108 detector array 110 Image Processor Unit 112 specimens 114 Tables 200 Imaging System 204 specimens 206 Center of rotation 208 Control Mechanism 210 X-ray controller 212 Gantry motor controller 214 Data Acquisition System (DAS) 216 Computing Devices 220 Operator Console 226 Table Motor Controller 230 Image Reconstructor 232 display devices 301 X-ray beam 302 Sensors Column 303 304 First vertical position 306 Second vertical position 310 Sensor Bond Pad 311 Edge 312 Application Specific Integrated Circuits (ASICs) 314 Wire Bond 316 Printed Circuit Board (PCB) 318 Connection 320 Lamination direction 350 Reference axis 401 Sensor stack 404 Anti-Scatter Grid 408 graphs 410 Plot 502 Collimator 504 graphs 506 plots 601 Reference axis 603 points 604 X-ray source 606 Object 607 X-ray 702 detector array 902 detector array 1000 ways 1010 steps 1102 Guard Ring 1104 Height 1106 width 1202 plot 1204 Metal foil 1300 PCCT detector units 1302 Adhesive layer 1400 First Sensor 1402 adhesive pattern 1404 Adhesive Line 1430 Second Sensor 1432 adhesive pattern 1434 Vertical Adhesive Line 1436 Horizontal Adhesive Line 1460 Third Sensor 1462 No adhesive layer 1502 Trench 1602 First Step 1604 Second Step 1606 Third Step 1608 Fourth Step 1610 Diode 1612 wafers 1614 Opening 1616 X-ray blocking material layer 1618 Contact layer 1620 depth 1702 Reverse Trench 1802 layers 1804 Side 1806 Arrow 16012 wafers

Claims

1. 1. A computed tomography system comprising: a gantry configured to rotate about an axis of rotation; and a detector array including a plurality of photon-counting computed tomography (PCCT) detector units configured to be rotated by the gantry about an axis of rotation, wherein a stack axis of at least one PCCT detector unit of the plurality of PCCT detector units is positioned at an angle to the axis of rotation; 1. A computed tomography system comprising:

2. 2. The computed tomography system of claim 1, wherein the detector array includes a plurality of horizontally oriented PCCT detector units arranged such that their stacking axes are perpendicular to the rotation axis, and a plurality of vertically oriented PCCT detector units arranged such that their stacking axes are parallel to the rotation axis, and wherein X-rays scattered at a certain angle are detected by both the vertically oriented PCCT detector units and the horizontally oriented PCCT detector units, and the number of the vertically oriented detector units and the horizontally oriented detector units are the same.

3. 2. The computed tomography system of claim 1, wherein the detector array includes a plurality of horizontally oriented PCCT detector units arranged such that a stacking axis is perpendicular to the rotation axis, the plurality of horizontally oriented PCCT detector units being arranged in front of a plurality of vertically oriented PCCT detector units arranged such that a stacking axis is parallel to the rotation axis, and wherein X-rays scattered at an angle toward one of the horizontally oriented PCCT detector units also reach one of the vertically oriented PCCT detector units.

4. The computed tomography system of claim 3 , wherein x-rays detected by the plurality of vertically oriented PCCT detector units are hardened relative to x-rays detected by the plurality of horizontally oriented PCCT detector units.

5. 2. The computed tomography system of claim 1, wherein the detector array includes an alternating pattern of horizontally oriented PCCT detector units positioned with their stacking axes perpendicular to the rotation axis and vertically oriented PCCT detector units positioned with their stacking axes parallel to the rotation axis, and wherein x-rays scattered at a certain angle interact with one of the vertically oriented PCCT detector units and the horizontally oriented PCCT detector units.

6. 2. The computed tomography system of claim 1, wherein the detector array includes a plurality of non-orthogonally oriented PCCT detector units, stacking axes of the plurality of non-orthogonally oriented PCCT detector units being parallel to one another and at an angle of less than 90 degrees with respect to the axis of rotation.

7. 2. The computed tomography system of claim 1, wherein the detector array includes a plurality of horizontally oriented PCCT detector units positioned with their stacking axes perpendicular to the rotation axis, but does not include a vertically oriented PCCT detector unit positioned with their stacking axes parallel to the rotation axis.

8. a controller, the controller comprising: receiving a first pixel intensity from a detector in a first orientation; receiving second pixel intensities from a corresponding second orientation detector; correcting the first pixel intensity and the second pixel intensity to account for spectral differences and efficiency differences; and combining the intensity of the detector at the first orientation with the intensity of the detector at the second orientation to form an image.

2. The computed tomography system of claim 1 configured to perform:

9. 9. The computed tomography system of claim 8, wherein the first orientation detector is positioned in front of the corresponding second orientation detector, and x-rays scattered at an angle to the detector array are detected by the first orientation detector and the corresponding second orientation detector.

10. 9. The computed tomography system of claim 8, wherein the first orientation detector is positioned adjacent to the corresponding second orientation detector such that the first orientation detector has a different detection angle than the corresponding second orientation detector.

11. 1. A photon counting computed tomography (PCCT) detector unit comprising: a sensor stack including a plurality of sensors stacked along a stacking axis; and a metal foil in surface contact with four sides of the sensor stack, the four sides being perpendicular to a surface of the plurality of sensors configured to receive x-rays; A PCCT detector unit comprising:

12. The PCCT detector unit of claim 11, wherein the metal foil is tungsten or a tungsten alloy.

13. The PCCT detector unit of claim 11 , wherein the metal foil reduces X-ray scattering in a direction perpendicular to the stacking axis.

14. The PCCT detector unit of claim 11 , wherein the metal foil reduces scattering between adjacent PCCT detector units compared to a PCCT detector unit without the metal foil.

15. The PCCT detector unit of claim 11 , further comprising fins present between adjacent sensors.

16. 1. A photon counting computed tomography (PCCT) detector unit comprising: a plurality of sensors stacked in a stacking direction; and an adhesive layer disposed between two adjacent sensors of the plurality of sensors; Including, A PCCT detector unit, wherein at least a portion of the adhesive layer is present in a cross section perpendicular to the stacking direction of the plurality of sensors.

17. 17. The PCCT detector unit of claim 16, comprising a plurality of fins, each fin being located between two adjacent sensors.

18. The PCCT detector unit of claim 16 , wherein the adhesive layer includes a plurality of diagonal adhesive lines.

19. The PCCT detector unit of claim 16, wherein the adhesive layer includes a plurality of vertical adhesive lines and a plurality of horizontal adhesive lines, and the plurality of vertical adhesive lines and the plurality of horizontal adhesive lines intersect.

20. The PCCT detector unit of claim 16 , wherein the adhesive layer comprises a continuous adhesive layer.

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