Sensor layout for direct converter detector

Abstract

A system and method includes an array of sensors electrically coupled to a material capable of converting gamma rays into electrical charges, wherein a distance between a center of a first sensor and a center of each sensor immediately adjacent to the first sensor is substantially equal. A signal is collected from each sensor immediately adjacent to the first sensor, and one of a plurality of logical sub-pixels of the first sensor is determined based on the signals collected from each sensor immediately adjacent to the first sensor.

Description

[0001] Cross-referencing of related patent applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 912,875, filed October 9, 2019, the contents of which are incorporated herein by reference for all purposes. Background Technology

[0003] Direct converter gamma-ray detectors use materials such as zinc cadmium telluride (CZT) to directly convert received gamma rays into electrical charges. Typically, an anode bonded to the surface of the conversion material defines a detector pixel. The anode collects the charge, which is then used to locate the impacting gamma ray relative to the defined pixel.

[0004] Typical detector designs use a square anode grid to define the detector pixels. To increase the inherent resolution of such systems, algorithms such as Anger logic are implemented to locate gamma rays at subpixel positions. However, conventional anode grids exhibit suboptimal noise characteristics, which directly limits the inherent resolution of the detector. Due to the lack of isotropy in the anode plane, the positioning of gamma rays at subpixel locations is also not optimal. For example, the uncertainty in subpixel positioning at the edges of the collecting anode is less than that at the center.

[0005] The desired system is to reduce the inhomogeneity of noise and / or uncertainty in the sensor region of a direct converter detector. Attached Figure Description

[0006] Figure 1 This is a view of a direct converter detector sensor array according to some embodiments;

[0007] Figure 2 This is a view of the components of a direct converter detector according to some embodiments;

[0008] Figure 3 The diagram illustrates the operation of a direct converter detector according to some embodiments;

[0009] Figure 4 This is a flowchart of a process for generating an image using a direct converter detector according to some embodiments;

[0010] Figure 5 Subpixel positioning according to some embodiments is described;

[0011] Figure 6 Subpixel positioning according to some embodiments is described;

[0012] Figure 7 This is a view of a direct converter detector sensor array according to some embodiments;

[0013] Figure 8 This is a view of a direct converter detector sensor array according to some embodiments; and

[0014] Figure 9 The illustration shows components of a SPECT imaging system according to some embodiments. Detailed Implementation

[0015] The following description is provided to enable anyone in the art to make and use the described embodiments, and illustrates the best mode contemplated for carrying out the described embodiments. However, various modifications should still be apparent to those skilled in the art.

[0016] Some embodiments employ direct converter detector sensors, which exhibit lower capacitance and a higher signal-to-noise ratio compared to conventional sensors. In some embodiments, such capacitance can be achieved by reducing the sensor perimeter for a given sensor area. Lower capacitance and a higher signal-to-noise ratio result in reduced subpixel positioning uncertainty and improved intrinsic resolution.

[0017] Furthermore, some embodiments employ direct converter detector sensor arrays, which exhibit a more homogeneous electric field distribution and more uniform noise patterns and responses across sensor subpixels than conventional sensor arrays. This homogeneity and uniformity result in more uniform subpixel localization than previously available.

[0018] According to some embodiments, the distance between the centers of adjacent sensors in the sensor array is substantially uniform. Such an arrangement can provide a more homogeneous electric field distribution and a more uniform noise pattern and response compared to a square grid of sensors, where the distance from the center of one sensor to the center of an adjacent (e.g., N, S, E, W) sensor is not equal to the distance from the center of one sensor to the center of another adjacent (e.g., NE, NE, SE, SW) sensor.

[0019] According to some embodiments, the sensor array can consist of hexagonal sensors. By allowing the calculation of sub-pixel positions in three directions (e.g., a hexagonal grid pattern), such a sensor array can further improve the inherent resolution relative to conventional systems.

[0020] The reduction in nonlinearity can reduce the need for position-dependent localization corrections. Furthermore, since the two-dimensional position of the detector collimator septa can be resolved more accurately than in existing systems (e.g., sensors with square or rectangular patterns), the embodiments can reduce the need to align the septa with the physical sensor boundaries.

[0021] Figure 1This is a view of a portion of an array 100 of individual hexagonal shape sensors according to some embodiments. The sensors described herein may also be referred to in the art as anodes, pixels, or electrodes. Each hexagonal shape sensor is coupled to a dedicated signal line and does not make direct electrical contact with its adjacent sensors. Embodiments are not limited to the package arrangement of array 100 or the sensor shapes illustrated.

[0022] Compared to conventional sensors, the sensor of array 100 can exhibit lower capacitance and a higher signal-to-noise ratio. For example, due to the lower perimeter-to-area ratio of the hexagon, the sensor of array 100 can exhibit lower capacitance and a higher signal-to-noise ratio than a conventional square sensor with the same surface area. As described below, lower capacitance and a higher signal-to-noise ratio can lead to reduced subpixel positioning uncertainty and improved intrinsic resolution.

[0023] If the distance between the two parallel plates d Compared to A If the size is small enough, the separation distance can be calculated. d has area A The capacitance between the two parallel plates C , ,in, C Capacitance is measured in farads. A It is the overlapping area of ​​two boards, measured in square meters. It is the electrical constant of the material, and d This refers to the distance between the two plates, measured in meters. Considering each sensor is 4mm... 2 With an arbitrary detection area and an arbitrary sensor thickness of 5mm, the capacitance of a hexagonal sensor is 4-5% smaller than that of a square sensor, or 1.479pF for a square sensor and 1.415pF for a hexagonal sensor. Therefore, compared to a square-shaped sensor, the hexagonal-shaped sensor exhibits a larger signal-to-noise ratio and more uniform subpixel positioning uncertainty across the entire anode.

[0024] The largest contribution to the capacitance observed by a single sensor comes from the proximity of adjacent sensors, which is related to the perimeter of the pixels. Therefore, triangular, square, and hexagonal shape sensors exhibit successively decreasing capacitance for the same sensor area, primarily due to the successively decreasing perimeter per unit area for each shape. The perimeter of a square shape sensor is 88% of that of a triangular shape sensor, while the perimeter of a hexagonal shape sensor is 82% of that of a triangular shape sensor. Therefore, in ultra-low noise systems, hexagonal shape sensors can exhibit a superior signal-to-noise ratio compared to square and triangular shape sensors, which increases the inherent resolution of the system.

[0025] The distance between the centers of adjacent sensors in array 100 is substantially equal. In other words, each sensor in array 100 is substantially equidistant from each sensor immediately adjacent to it. As will be described below, such an arrangement can provide a more homogeneous electric field distribution and a more uniform noise pattern and response compared to a square grid of sensors. The hexagonal package of array 100 can also improve the inherent resolution relative to conventional systems, as will be described below, by allowing the computation of sub-pixel positions in three directions (e.g., a hexagonal grid pattern).

[0026] Figure 2 This is a schematic diagram of the components of a direct converter detector according to some embodiments. Detector 200 includes a sensor array 210, a cathode 220, and a direct conversion material 230 therebetween. Sensor array 210 may include an array of hexagonal or other shaped anodes as described herein. Cathode 220 may include a continuous layer that is generally transparent to gamma rays of energy to be detected by detector 200. Direct conversion material 230 may be composed of a single-crystal semiconductor material such as CZT or cadmium telluride (CdTe).

[0027] Figure 3 The diagram illustrates a detector 300 in one example of operation. Detector 300 can implement the structure of detector 200, including sensor array 310, cathode 320, direct conversion material 330, and as described above. Collimator 340 adjacent to cathode 320 is also shown. Collimator 340 can include a multifocal cone-beam collimator or a parallel-aperture collimator as known in the prior art.

[0028] Detector 300 is positioned to detect gamma rays 355 emitted from volume 350. Systems for facilitating the emission of gamma rays from a volume are known in the art, and particularly with respect to single-photon emission computed tomography (SPECT) imaging. Some of the gamma rays in gamma ray 355 are collimated by collimator 340 to define their response lines and filter out scattered or stray gamma radiation, and the collimated gamma rays pass through cathode 320 due to their transparency to cathode 320.

[0029] Gamma rays penetrate the direct conversion material 330 and interact with it to generate electron-hole pairs. The cathode 320 is maintained at a negative bias potential, while the sensors in the array 310 are maintained at a smaller repulsive potential. Therefore, positively charged holes drift towards the cathode 320, while negatively charged electrons drift towards the sensors in the array 310. When an electron approaches a given sensor in the array 310, a signal is induced at that sensor and its neighboring sensors.

[0030] After electrons are collected by a given sensor, the readout electronics 360 can use signals received from adjacent sensors to determine the sub-pixel position of the given sensor, at which gamma rays are assumed to have been received. As is known in the art, an image can then be generated using the sub-pixel positions where all gamma rays were received. As is also known in the art, multiple such images can be acquired from different angles around volume 350 and used to reconstruct a three-dimensional image of volume 350.

[0031] Examples are not limited to Figure 2 and Figure 3 structure or Figure 3 The orientation. For example, gamma rays can enter material 330 from any direction, but because the readout electronics 360 is located close to the sensor array 310, Figure 3 Such an orientation may be beneficial.

[0032] As described above, the capacitance of a sensor according to some embodiments can be smaller than the capacitance of another sensor with the same surface area. This reduction in capacitance, as seen in the readout electronics 360, reduces system noise and increases the signal-to-noise ratio.

[0033] Figure 4 This is a flowchart of a process according to some embodiments. Process 400 and other processes described herein can be performed using any suitable combination of hardware and software. The software program code embodying these processes can be stored by any non-transitory tangible medium, including hard disks, volatile or non-volatile random access memory, CDs, DVDs, flash drives, or magnetic tapes. Embodiments are not limited to the examples described below.

[0034] Initially, in S410, charge is received at the first sensor of the direct converter gamma-ray detector. As described above, the charge can consist of electrons from electron-hole pairs generated by the direct conversion material in response to the penetration of gamma rays. According to this example, the center of each sensor directly adjacent to the first sensor is substantially equidistant from the center of the first sensor. This physical property is determined by... Figure 1 The sensor array 100 is shown, but the embodiments are not limited thereto.

[0035] Next, in S420, the sub-pixels of the sensors are determined based on the electrical signals sensed at each sensor directly adjacent to the first sensor and corresponding to the charges received at the first sensor (i.e., generated by the same gamma-ray interactions). As is known in the art, the sensed signals on the sensors that collect the generated electrons are different from the signals sensed on adjacent non-collecting sensors. Therefore, the signals sensed on adjacent non-collecting sensors can be used to determine the sub-pixels or sub-regions of the collecting sensors, in which gamma-ray interactions are considered to have occurred. At this point, each sensor can be considered to define multiple logical sub-pixels.

[0036] The S420 can be implemented using Anger logic as known in the prior art, however, using a hexagonal grid instead of a Cartesian grid. Anger logic involves calculating the ratio between the sums of signals on opposite sensors. However, in a square-shaped sensor, the contribution of all sensors to the overall noise is not uniform. Specifically, sensors closer to the collection sensor—i.e., sensors N, S, E, and W—contribute more to the noise, while other adjacent sensors—i.e., sensors NE, NW, SE, and SW—are farther from the collection sensor and contribute less to the overall noise.

[0037] The resulting nonlinearity of the calculated ratio introduces greater uncertainty for events closer to the sensor center, where the ratio is almost flat and noise dominates the inherent resolution, especially if the signal-to-noise ratio is low. Because the calculated ratio is highly nonlinear, subpixel determination using a conventional sensor array requires nonlinear correction to calculate the estimated true interaction locations. Furthermore, using a square-shaped sensor, the ratio is typically calculated in two orthogonal directions, such as the XY direction, defined by sensors near the collection sensor.

[0038] Figure 5 The illustration shows the determination of subpixels at S420 according to some embodiments. The hexagonal-shaped sensor 500 is depicted as having 36 logical subpixels, but embodiments can define any number of subpixels for each sensor. Due to the hexagonal shape of the sensor and subpixels, the Anger ratio can be advantageously calculated in a hexagonal grid pattern with three directions, thereby improving the inherent resolution when using all coordinates. Specifically, the three-dimensional subpixel positions within sensor 510 for each gamma-ray event ( ) are collected. x , y , z It can be determined based on the signals induced on the opposite sets of two electrodes, such as regarding X i Figure 520 Y i Figure 530 andZ i As shown in Figure 540, where K x , K y , K z and K 深度 It is a linear correction factor and a factor with “less” nonlinearity.

[0039] Figure 6 The illustration also shows the determination of sub-pixels of the collecting sensor 510 in S420 according to some embodiments. Figure 6 The determination uses an additional (i.e., a third) signal to calculate each coordinate value, which increases the signal-to-noise ratio while shifting the axis of the sub-pixel position, as in... X i Figure 620 Y i Figure 630 and Z i As shown in Figure 640.

[0040] The sub-pixel position can be determined using any suitable algorithm in S420. Furthermore, the sub-pixel position can also be determined using signals from one or more sensors that are not adjacent to the collecting sensor.

[0041] Returning to process 400, an image is then generated in S430 based on the determined sub-pixels. Assuming that S410 and S420, combining numerous gamma-ray interactions and the resulting collected charge, are performed in parallel numerous times, the image generated in S430 comprises image data of numerous sub-pixels. As described above, the generated image can include a two-dimensional image, which can be combined with other two-dimensional images to reconstruct a three-dimensional volume, as is known in the art.

[0042] Figure 7 The illustration shows a sensor array 700 according to some embodiments. The sensors in the sensor array 700 are circular. In this respect, for a given area of ​​any shape, a circle exhibits the smallest circumference. Therefore, for a given area, the circular sensor of array 700 exhibits the smallest capacitance of any sensor shape, resulting in the aforementioned corresponding advantages.

[0043] Furthermore, the sensors in array 700 are arranged in a hexagonal structure. Therefore, for any given sensor in array 700, the centers of all adjacent sensors are equidistant from the center of the given sensor. This characteristic provides reduced nonlinearity and increased consistency in positioning determinism for each sensor subpixel. Due to the number of non-charge collection regions between the individual sensors in array 700, sensor array 700 may exhibit lower sensitivity compared to array 100.

[0044] Figure 8 The illustration shows a sensor array 800 arranged in a hexagonal structure according to some embodiments. The sensors in sensor array 800 are square in shape and therefore exhibit a larger capacitance per unit area than the hexagonal and circular sensors described above. Due to the hexagonal packaging, for any given sensor in array 800, the centers of all adjacent sensors are equidistant from the center of the given sensor. Therefore, compared to a conventional square grid, sensor array 800 can provide reduced nonlinearity and increased consistency in positioning determinism for each sensor subpixel. Sensor array 800 may also exhibit lower sensitivity compared to array 100 due to the number of non-charge collection regions between the individual sensors in array 800.

[0045] Figure 9 The illustration shows a SPECT system 900 that can implement one or more direct converter detectors as described above. System 900 includes a bench 902 to which one or more detectors 904a, 904b can be attached. Each of detectors 904a, 904b detects gamma photons (i.e., emission data) emitted by a radioactive isotope within a volume 906 on a bed 908.

[0046] Bed 908 is capable of moving volume 906 along axis A and / or axis B. At the corresponding bed position (i.e., imaging position), a portion of volume 906 is positioned between direct converter detectors 904a, 904b to capture emission data from that body portion. Direct converter detectors 904a, 904b may employ sensor arrays as described herein and may be coupled to multifocal cone-beam collimators or parallel-aperture collimators as known in the art.

[0047] The control system 920 may include any general-purpose or special-purpose computing system. Therefore, the control system 920 includes one or more processing units 922 and a storage device 930 for storing program code. The processing unit 922 is configured to execute processor-executable program code to cause the system 920 to operate as described herein. The storage device 930 may include one or more fixed disks, solid-state random access memory, and / or removable media (e.g., thumb drives) mounted in a corresponding interface (e.g., a USB port).

[0048] Storage device 930 stores the program code of system control program 932. One or more processing units 922 may execute system control program 932 in conjunction with SPECT system interface 940 to control motors, servo systems, and encoders, thereby causing detectors 904a, 904b to rotate along gantry 902, acquiring signals from sensor detectors 904a, 904b based on received gamma rays, and determining sub-pixel positions of gamma ray events (i.e., projected images) based on electrical signals as described herein. Event data 934 may be stored in memory 930. As is known, control program 932 may also be executed to reconstruct volume 936 from event data 934.

[0049] Terminal 950 may include a display device and an input device coupled to system 920. Terminal 950 may display any projected image or reconstructed volume stored in memory 930. In some embodiments, terminal 950 is a standalone computing device, such as, but not limited to, a desktop computer, laptop computer, tablet computer, and smartphone.

[0050] Each component of system 900 may include other elements necessary for its operation, as well as additional elements for providing functionality beyond those described herein.

[0051] Each functional component described herein may be implemented, at least in part, in computer hardware, in program code, and / or in one or more computing systems that execute program code as known in the art. Such computing systems may include one or more processing units that execute processor-executable program code stored in a memory system.

[0052] The foregoing diagrams illustrate a logical architecture for describing processes according to some embodiments, and actual implementations may include more or different components arranged in other ways. Other topologies may be used in conjunction with other embodiments. Furthermore, each component or device described herein may be implemented by any number of devices communicating via any number of other public and / or private networks. Two or more such computing devices may be located remotely to each other and may communicate with each other via one or more networks and / or dedicated connections of any known manner. Each component or device may include any number of hardware and / or software elements suitable for providing the functions described herein as well as any other functions. For example, any computing device used in an implementation of a system according to some embodiments may include a processor that executes program code such that the computing device operates as described herein.

[0053] All systems and processes discussed herein can be embodied in program code stored on one or more non-transitory computer-readable media. Such media may include, for example, hard disks, DVD-ROMs, flash drives, magnetic tapes, and solid-state random access memory (RAM) or read-only memory (ROM) storage units. Therefore, embodiments are not limited to any particular combination of hardware and software.

[0054] Those skilled in the art will appreciate that various adaptations and modifications can be configured for the above embodiments without departing from the claims. Therefore, it should be understood that the claims can be practiced in ways different from those specifically described herein.

Claims

1. A gamma-ray detector, comprising: Direct converter materials; The cathode is electrically coupled to the direct converter material; and Sensor array electrically coupled to direct converter material Each sensor in the sensor array is hexagonal in shape. The distance between the center of the first sensor in the sensor array and the center of each sensor immediately adjacent to the first sensor is equal, and The sub-pixels of the first sensor are determined based on the electrical signals sensed at each sensor directly adjacent to the first sensor and generated by the same gamma-ray interaction, wherein the sub-pixels are determined based on the ratio between the sums of the electrical signals on the opposite sensors.

2. The gamma ray detector according to claim 1, The sensors in the sensor array are arranged in a hexagonal structure.

3. The gamma ray detector according to claim 2, Each sensor in the sensor array is circular.

4. The gamma ray detector according to claim 2, Each sensor in the sensor array is square in shape.

5. The gamma ray detector according to claim 1, further comprising a collimator, The opening defined by the collimator is not aligned with the array of sensors.

6. A method for constructing a gamma-ray detector, comprising: Couple the cathode to the direct converter material; and Couple the sensor array to the direct converter material. Each sensor in the sensor array is equidistant from the center of each sensor immediately adjacent to it. Each sensor in the sensor array is hexagonal in shape, and The sub-pixels of the first sensor are determined based on the electrical signals sensed at each sensor directly adjacent to the first sensor and generated by the same gamma-ray interaction, wherein the sub-pixels are determined based on the ratio between the sums of the electrical signals on the opposite sensors.

7. The method according to claim 6, The sensors in the sensor array are arranged in a hexagonal structure.

8. The method according to claim 7, Each sensor in the sensor array is circular.

9. The method according to claim 7, Each sensor in the sensor array is square in shape.

10. The method of claim 6, further comprising: Install the collimator onto the detector. The opening defined by the installed collimator is not aligned with the array of sensors.

11. A method comprising: A first sensor from a sensor array electrically coupled to a material capable of converting gamma rays into electrical charge collects a first signal, wherein the center of the first sensor is equidistant from the center of each sensor immediately adjacent to the first sensor, and wherein the first sensor comprises a plurality of logical sub-pixels, and wherein each sensor in the sensor array is hexagonal in shape; Collect signals from each sensor immediately adjacent to the first sensor; and One of a plurality of sub-pixels is determined based on signals collected from each sensor immediately adjacent to the first sensor, wherein the sub-pixel of the first sensor is determined based on electrical signals sensed at each sensor directly adjacent to the first sensor and generated by the same gamma-ray interaction, wherein the sub-pixel is determined based on a ratio between the sums of electrical signals on opposite sensors.

12. The method according to claim 11, The sensors in the sensor array are arranged in a hexagonal structure.

13. The method according to claim 12, Each sensor in the sensor array is circular.

14. The method according to claim 12, Each sensor in the sensor array is square in shape.

15. The method of claim 11, wherein determining one of the plurality of sub-pixels comprises: Based on signals collected from each sensor immediately adjacent to the first sensor, the value of each of the three coordinates of the hexagonal grid is determined.

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