Image sensor with calibration mode

Abstract

An image sensor (9000) is disclosed herein, comprising two radiation detectors (100A, 100B) and a calibration pattern (101), wherein each of the radiation detectors (100A, 100B) comprises a flat surface to receive radiation from a radiation source. The flat surfaces (103A, 103B) of the radiation detectors (100A, 100B) are not coplanar. The image sensor (9000) can use the radiation detectors (100A, 100B) to capture images of two portions of the calibration pattern (101), respectively. The image sensor (9000) can determine two transformations (108A, 108B) of the radiation detectors (100A, 100B) based on the images of the portions of the calibration pattern (101), respectively. The image sensor (9000) can respectively use the radiation detectors (100A, 100B) to capture images of two parts (180A, 180B) of the scene (50), use the transformations (108A, 108B) to respectively determine projections (181A, 181B) of the images of the parts (180A, 180B) of the scene (50) on the image plane, and form an image of the scene (50) by stitching the projections (181A, 181B).

Description

[Background technology]

[0001] A radiation detector is a device that can be used to measure the flux, spatial distribution, spectrum, or other properties of radiation.

[0002] Radiation detectors can be used in many applications, one important application being imaging. Radiation imaging is a radiographic technique that can be used to reveal the internal structure of objects of inhomogeneous composition and opaque objects (e.g., the human body).

[0003] Early radiation detectors used for imaging included photographic plates and photographic films. Photographic plates can be glass plates with a light-sensitive emulsion coating. Although photographic plates were replaced by photographic films, they are still used in special cases because of the superior quality and extreme stability they offer. Photographic films can be plastic films (e.g., strips or sheets) with a light-sensitive emulsion coating.

[0004] In the 1980s, photoexcitable phosphor plates (PSP plates) became available. PSP plates contain phosphor materials with color centers in their lattices. When the PSP plates are exposed to radiation, the electrons excited by the radiation are trapped in the color centers until they are stimulated by a laser beam scanned over the surface of the PSP plates. When the laser scans the PSP plates, the trapped excited electrons emit light, which is collected by a photomultiplier tube, and the collected light is converted into a digital image. In contrast to photographic negatives and photographic films, PSP plates are reusable.

[0005] Another type of radiation detector is a radiation image intensifier. The components of a radiation image intensifier are usually sealed in a vacuum. Compared to photographic plates, photographic films, and PSP boards, radiation image intensifiers can produce real-time images, that is, no post-exposure processing is required to produce an image. The radiation first hits the input phosphor (e.g., cesium iodide) and is converted into visible light. The visible light then hits the photocathode (e.g., a thin metal layer containing cesium and antimony compounds) and causes electron emission. The number of electrons emitted is proportional to the intensity of the incident radiation. The emitted electrons are projected onto the output phosphor through an electron optic and cause the output phosphor to produce a visible light image.

[0006] Scintillators operate somewhat similarly to radiation image intensifiers in that the scintillator (e.g., sodium iodide) absorbs radiation and emits visible light, which can then be detected by a suitable image sensor. In the scintillator, the visible light diffuses and scatters in all directions, which reduces spatial resolution. Reducing the scintillator thickness helps improve spatial resolution, but also reduces the absorption of radiation. Therefore, scintillators must achieve a compromise between absorption efficiency and resolution.

[0007] Semiconductor radiation detectors largely overcome the above problems by converting radiation directly into electrical signals. A semiconductor radiation detector may include a semiconductor layer that absorbs radiation at a wavelength of interest. When a radiation particle is absorbed in the semiconductor layer, a plurality of carriers (e.g., electrons and holes) are generated and swept toward electrical contacts on the semiconductor layer under an electric field. The cumbersome thermal management required in currently available semiconductor radiation detectors (e.g., Medipix) may make semiconductor radiation detectors with larger areas and a large number of pixels difficult or impossible to produce. [Summary of the invention]

[0008] The present invention discloses an image sensor, which includes: a first radiation detector and a second radiation detector, each including a planar surface configured to receive radiation from a radiation source; and a calibration pattern; wherein the planar surface of the first radiation detector is not coplanar with the planar surface of the second radiation detector; wherein the image sensor is configured to use the first radiation detector and the second radiation detector to capture an image of a first portion of the calibration pattern and an image of a second portion of the calibration pattern, respectively; wherein the image sensor is configured to determine a first transformation of the first radiation detector based on the image of the first portion of the calibration pattern, and to determine a second transformation of the second radiation detector based on the image of the second portion of the calibration pattern; wherein the image sensor is configured to use the first radiation detector and the second radiation detector to capture an image of a first portion of a scene and an image of a second portion of the scene, respectively, use the first transformation to determine a first projection of the image of the first portion of the scene on an image plane, and use the second transformation to determine a second projection of the image of the second portion of the scene on the image plane, and then form an image of the scene by stitching the first projection and the second projection.

[0009] According to an embodiment, the calibration pattern has an inhomogeneous spatial distribution of radiation absorption.

[0010] According to an embodiment, the calibration pattern is a plane.

[0011] According to an embodiment, the image of the first portion of the calibration pattern comprises images of three features of the calibration pattern, wherein the positions of the three features relative to the calibration pattern are known.

[0012] According to an embodiment, said first transformation is an affine transformation.

[0013] According to an embodiment, the first radiation detector and the second radiation detector are configured to move relative to the radiation source.

[0014] According to an embodiment, the first radiation detector and the second radiation detector are configured to move relative to the radiation source by rotating or translating relative to the radiation source.

[0015] According to an embodiment, the first radiation detector comprises an array of pixels.

[0016] According to an embodiment, the first radiation detector is rectangular in shape.

[0017] According to an embodiment, the first radiation detector is hexagonal in shape.

[0018] A method is disclosed herein, which includes: using a first radiation detector to capture an image of a first portion of a calibration pattern using radiation from a radiation source; using a second radiation detector to capture an image of a second portion of the calibration pattern using the radiation; wherein the first radiation detector and the second radiation detector respectively include a planar surface configured to receive the radiation, and the planar surface of the first radiation detector is not coplanar with the planar surface of the second radiation detector; determining a first transformation of the first radiation detector based on the image of the first portion of the calibration pattern; determining a second transformation of the second radiation detector based on the image of the second portion of the calibration pattern; using the first radiation detector to capture an image of a first portion of a scene; using the second radiation detector to capture an image of a second portion of the scene; using the first transformation to determine a first projection of the image of the first portion of the scene on an image plane; using the second transformation to determine a second projection of the image of the second portion of the scene on the image plane; and forming an image of the scene by stitching the first projection and the second projection.

[0019] According to an embodiment, the calibration pattern has an inhomogeneous spatial distribution of radiation absorption.

[0020] According to an embodiment, the calibration pattern is a plane.

[0021] According to an embodiment, the image of the first portion of the calibration pattern comprises images of three features of the calibration pattern, wherein the positions of the three features relative to the calibration pattern are known.

[0022] According to an embodiment, said first transformation is an affine transformation.

[0023] A computer program product is disclosed herein, comprising a non-transitory computer-readable medium having instructions recorded thereon, wherein the instructions implement the method of any one of the above claims when executed by a computer.

Brief Description of the Drawings

[0024] Figure 1AA cross-sectional view schematically illustrates a portion of an image sensor according to an embodiment.

[0025] Figure 1B A perspective view schematically illustrates a portion of an image sensor including a calibration pattern between a radiation source and a radiation detector according to an embodiment.

[0026] Figure 1C A perspective view of the image sensor is schematically shown according to an embodiment, the image sensor capturing an image of the calibration pattern using radiation from a radiation source.

[0027] Figure 1D A perspective view of an image sensor is schematically shown according to an embodiment, the image sensor capturing an image of a scene using radiation from a radiation source.

[0028] Figure 2 The radiation detector capturing an image of a portion of a scene according to an embodiment is schematically illustrated.

[0029] 3A-3C schematically illustrate arrangements of the radiation detector in the image sensor according to an embodiment.

[0030] Figure 4 An image sensor with a plurality of hexagonal radiation detectors according to an embodiment is schematically illustrated.

[0031] Figure 5A A cross-sectional view of a radiation detector according to an embodiment is schematically shown.

[0032] Figure 5B A detailed cross-sectional view of the radiation detector according to an embodiment is schematically shown.

[0033] Figure 5C An alternative detailed cross-sectional view of the radiation detector according to an embodiment is schematically shown.

[0034] Figure 6 The radiation detector with a pixel array according to an embodiment is schematically illustrated.

[0035] Figure 7 The functional block diagram of the image sensor according to the embodiment is schematically shown.

[0036] Fig. 8A and Figure 8B Each schematically illustrates a movement of a radiation detector of an image sensor relative to a radiation source according to an embodiment.

[0037] Fig. 9 A flow chart of a method according to an embodiment is schematically shown.

[0038] Fig.10A system including an image sensor as described herein according to an embodiment is schematically shown, the system being suitable for medical imaging, such as chest radiography, abdominal radiography, etc.

[0039] Fig.11 A system comprising an image sensor as described herein is schematically shown according to an embodiment, the system being suitable for dental radiography.

[0040] Fig.12 A cargo scanning or non-intrusive inspection (NII) system including an image sensor as described herein is schematically illustrated according to an embodiment.

[0041] Fig.13 Another cargo scanning or non-intrusive inspection (NII) system including the image sensor described herein according to an embodiment is schematically illustrated.

[0042] Fig.14 A whole body scanning system including the image sensor described herein according to an embodiment is schematically illustrated.

[0043] Fig.15 A radiation computed tomography (radiation CT) system including an image sensor as described herein according to an embodiment is schematically illustrated.

[0044] Fig.16 An electron microscope including the image sensor described herein according to an embodiment is schematically illustrated.

[0045] Fig.17A and Fig. 17B Each schematically shows how Figure 5A , Figure 5B and Figure 5C The electronic system components of the radiation detector are shown in FIG.

[0046] Fig.18 Schematic diagram of the time variation of the current flowing through the electrode of the diode or through the electrical contact of the resistor exposed to radiation (upper curve) according to the embodiment, the current being caused by the carriers generated by the radiation particles incident on the radiation absorbing layer, and the corresponding time variation of the electrode voltage (lower curve). [Specific implementation method]

[0047] Figure 1A Schematically shows a cross-sectional view of a portion of an image sensor 9000 according to an embodiment. The image sensor 9000 includes a plurality of radiation detectors (eg, a first radiation detector 100A, a second radiation detector 100B). The image sensor 9000 may have a support 107 with a curved surface 102. Figure 1AAs shown in the example of , the multiple radiation detectors can be arranged on the support 107, for example, on the curved surface 102. The first radiation detector 100A can have a first flat surface 103A configured to receive radiation from a radiation source 109. The second radiation detector 100B can have a second flat surface 103B configured to receive radiation from the radiation source 109. The first flat surface 103A and the second flat surface 103B can be non-coplanar. The radiation from the radiation source 109 may have passed through the flat surface 103A of the first radiation detector 100A or the flat surface 103B of the second radiation detector 100B before reaching it. Figure 1A The scene 50 shown (e.g., a portion of a human body) or Figure 1B The calibration pattern 101 shown. The calibration pattern 101 may be a plane. The calibration pattern 101 may have an inhomogeneous spatial distribution of radiation absorption. Figure 1B In the example, the calibration pattern 101 includes a first region 161 and a second region 162 in the center of the calibration pattern, wherein the first region 161 is made of a material having a low mass attenuation coefficient for radiation from the radiation source 109, and the second region 162 is made of another material having a high mass attenuation coefficient for radiation from the radiation source 109.

[0048] Figure 1C Schematically shows a perspective view of the image sensor 9000 according to an embodiment, wherein the image sensor 9000 uses radiation from the radiation source 109 to capture a partial image of the calibration pattern 101. Figure 1C In the example of FIG. 1 , radiation incident on the first region 161 of the calibration pattern 101 may pass through the calibration pattern 101 and be detected by the radiation detectors (eg, 100A, 100B, Figure 1C The radiation incident on the second area 162 of the calibration pattern 101 may be absorbed or blocked by the calibration pattern 101 to the greatest extent, and it may be inconspicuously received by the radiation detector 100. An image 104A of the first portion of the calibration pattern 101 and an image 104B of the second portion of the calibration pattern 101 are captured by the image sensor 9000 using the first radiation detector 100A and the second radiation detector 100B, respectively.

[0049] According to an embodiment, the image 104A includes an image (e.g., 105A, 105B, 105C) of three features (e.g., 106A, 106B, 106C) of the calibration pattern 101. The image is a projection of the three features onto the flat surface 103A by radiation incident on the calibration pattern 101. The positions of the three features on the calibration pattern 101 are known. By comparing the image (e.g., 105A, 105B, 105C) of the calibration pattern 101 and the features (e.g., 106A, 106B, 106C), a first transformation 108A for the first radiation detector 100A can be determined by the image sensor 9000. Using the first transformation 108A, the projection of any point of the calibration pattern 101 on the first flat surface 103A can be determined. The first transformation 108A can be represented by a matrix,

[0050]

[0051] , where r1, r2, r3, and r4 represent relative rotations between the three features and the three positions, t1 and t2 represent relative translations between the three features and the three positions, and p1 and p2 represent perspective transformations between the three features and the three positions. If the first transformation 108A is an affine transformation, p1 and p2 are equal to 0. That is, if the first transformation 108A is an affine transformation, it can be represented by the matrix

[0052]

[0053] A second transformation 108B for the second radiation detector 100B may be similarly determined by the image sensor 9000 based on the image 104B of the second portion of the calibration pattern 101. Using the second transformation 108B, the projection of any point of the second portion of the calibration pattern 101 on the second planar surface 103B may be determined. The second transformation 108B may be represented by a matrix,

[0054]

[0055] If the second transformation 108B is an affine transformation, it can be represented by the matrix

[0056]

[0057] Figure 1D Schematically shows a perspective view of the image sensor 9000 according to an embodiment, the image sensor 9000 uses radiation from the radiation source 109 to capture an image of the scene 50 and converts the image of the scene 50 into a projection on an image plane. Figure 1D In the example of , the image sensor 9000 uses the first radiation detector 100A to capture an image 180A of the first portion of the scene 50. Using the first transformation 108A, the image 180A of the first portion of the scene 50 is converted into a first projection 181A on an image plane. The image sensor 9000 also uses the second radiation detector 100B to capture an image 180B of the second portion of the scene 50. Using the second transformation 108B, the image 180B of the second portion of the scene 50 is converted into a second projection 181B on the image plane. The image sensor 9000 forms an image of the scene 50 by stitching the first projection 181A and the second projection 181B.

[0058] Figure 2 The schematic diagram shows that the image sensor 9000 can capture multiple images of various parts of the scene 50. Figure 2 In the example shown, the radiation detector 100 is moved to three positions A, B and C, for example, by using an actuator 500. The image sensor 9000 captures images 51A, 51B and 51C of portions of the scene 50 at positions A, B and C, respectively. The image sensor 9000 can stitch the images 51A, 51B and 51C of the portions to form an image of the scene 50. These images 51A, 51B and 51C of the portions can overlap each other for easy stitching. Each portion of the scene 50 appears in at least one of the images captured when the radiation detector is in multiple positions. That is, when the images of the portions are stitched together, the images of the portions can cover the entire scene 50.

[0059] The radiation detector 100 can be arranged in the image sensor 9000 in various ways. FIG3A schematically illustrates an arrangement according to an embodiment, wherein the radiation detector 100 is arranged in staggered rows. For example, the radiation detector 100A and the radiation detector 100B are in the same row, aligned in the Y direction, and have the same size; the radiation detector 100C and the radiation detector 100D are in the same row, aligned in the Y direction, and have the same size. The radiation detector 100A and the radiation detector 100B are staggered in the X direction relative to the radiation detector 100C and the radiation detector 100D. According to an embodiment, the distance X2 between two adjacent radiation detectors 100A and radiation detectors 100B in the same row is greater than the width X1 of a radiation detector in the same row (i.e., the X-direction dimension, i.e., the extension direction of the row) and less than twice the width X1. The radiation detectors 100A and 100E are in the same column, aligned in the X direction, and have the same size; the distance Y2 between two adjacent radiation detectors 100A and 100E in the same column is less than the width Y1 (i.e., the Y-direction dimension) of one radiation detector in the same column. This arrangement allows Figure 7 The imaging of the scene shown, and the image of the scene can be obtained by stitching images of three parts of the scene captured at three positions spaced apart in the X direction.

[0060] FIG3B schematically illustrates another arrangement according to an embodiment, wherein the radiation detectors 100 are arranged in a rectangular grid. For example, the radiation detector 100 may include radiation detectors 100A, 100B, 100E, and 100F arranged exactly as in FIG3A , without radiation detectors 100C, 100D, 100G, or 100H in FIG3A . This arrangement allows imaging of a scene by taking images of portions of the scene at six locations. For example, three locations spaced apart in the X direction, and another three locations spaced apart in the X direction and spaced apart from the first three locations in the Y direction.

[0061] Other arrangements are also possible. For example, in FIG3C , the radiation detector 100 may span the entire width of the image sensor 9000 in the X direction, and the distance Y2 between two adjacent radiation detectors 100 is less than the width Y1 of one radiation detector. Assuming that the width of the radiation detector in the X direction is greater than the width of the scene in the X direction, the image of the scene can be obtained by stitching together images of two parts of the scene captured at two positions spaced apart in the Y direction.

[0062] The radiation detectors 100 described above have any suitable size and shape. According to an embodiment, at least some of the radiation detectors are rectangular in shape. According to an embodiment, Figure 4As shown, at least some of the radiation detectors are hexagonal in shape.

[0063] Figure 5A A cross-sectional view of a radiation detector 100 according to an embodiment is schematically shown. The radiation detector 100 may be used in the image sensor 9000. The radiation detector 100 may include a radiation absorption layer 110 and an electronic layer 120 (e.g., an ASIC) for processing or analyzing an electrical signal of incident radiation generated in the radiation absorption layer 110. In an embodiment, the radiation detector 100 does not include a scintillator. The radiation absorption layer 110 may include a semiconductor material, such as silicon, germanium, GaAs, CdTe, CdZnTe or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the radiation energy of interest. The flat surface of the radiation absorption layer 110 at the distal end of the electronic layer 120 is configured to receive radiation.

[0064] like Figure 5B As shown in the detailed cross-sectional view of the radiation detector 100 in FIG. 1 , the radiation absorbing layer 110 according to an embodiment may include one or more diodes (e.g., pin or pn) composed of one or more discrete regions 114 of a first doping region 111 and a second doping region 113. The second doping region 113 may be separated from the first doping region 111 by an optional intrinsic region 112. The discrete regions 114 are separated from each other by the first doping region 111 or the intrinsic region 112. The first doping region 111 and the second doping region 113 have opposite types of doping (e.g., the first doping region 111 is p-type and the second doping region 113 is n-type, or the first doping region 111 is n-type and the second doping region 113 is p-type). Figure 5B In the example in , each discrete region 114 of the second doped region 113 together with the first doped region 111 and the optional intrinsic region 112 form a diode. Figure 5B In the example of FIG. 1 , the radiation absorbing layer 110 includes a plurality of diodes having the first doping region 111 as a common electrode. The first doping region 111 may also have discrete portions.

[0065] When a radiation particle strikes the radiation absorption layer 110 including a diode, the radiation particle may be absorbed and generate one or more carriers through several mechanisms. A radiation particle may generate 10 to 100,000 carriers. The carriers may drift toward an electrode of one of the diodes under an electric field. The electric field may be an external electric field. The electrical contact 119B may include discrete portions, each of which is in electrical contact with the discrete region 114. In an embodiment, the carriers may drift in different directions so that the carriers generated by a single radiation particle are not substantially shared by two different discrete regions 114 ("substantially not shared" here means that less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of these carriers flow to a discrete region 114 different from the remaining carriers). The carriers generated by the radiation particles incident around the footprint of one of the discrete regions 114 are not substantially shared by another discrete region 114. A pixel 150 associated with a discrete region 114 may be a region surrounding the discrete region 114, wherein substantially all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99%) of the charge carriers generated by radiation particles incident therein at an incident angle of 0° flow toward the discrete region 114. That is, less than 2%, less than 1%, less than 0.1%, or less than 0.01% of the charge carriers flow outside the pixel.

[0066] like Figure 5C As shown in an alternative detailed cross-sectional view of the radiation detector 100 in FIG. 1 , the radiation absorbing layer 110 according to an embodiment may include a resistor having a semiconductor material such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof, but does not include a diode. The semiconductor may have a high mass attenuation coefficient for the radiation energy of interest.

[0067] When a radiation particle strikes the radiation absorption layer 110 including a resistor but not a diode, the radiation particle may be absorbed and generate one or more carriers through several mechanisms. A radiation particle may generate 10 to 100,000 carriers. The carriers may drift toward the electrical contact 119A and the electrical contact 119B under an electric field. The electric field may be an external electric field. The electrical contact 119B includes discrete portions. In an embodiment, the carriers may drift in different directions so that the carriers generated by a single radiation particle are not substantially shared by two different discrete portions of the electrical contact 119B ("substantially not shared" here means that less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of these carriers flow to discrete portions that are different from the remaining carriers). The carriers generated by the radiation particles incident around the footprint of one of the discrete portions of the electrical contact 119B are not substantially shared by another discrete portion of the electrical contact 119B. A pixel 150 associated with one of the discrete portions of the electrical contact 119B may be a region surrounding the discrete portion where substantially all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99%) of the charge carriers generated by radiation particles incident therein at an incident angle of 0° flow toward the discrete portion of the electrical contact 119B. That is, less than 2%, less than 0.5%, less than 0.1%, or less than 0.01% of the charge carriers flow outside the pixel associated with one of the discrete portions of the electrical contact 119B.

[0068] The electronic layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by radiation particles incident on the radiation absorbing layer 110. The electronic system 121 may include analog circuits such as filter networks, amplifiers, integrators, comparators, or digital circuits such as microprocessors and memories. The electronic system 121 may include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system 121 may include an amplifier dedicated to each of the pixels and a microprocessor shared among all pixels. The electronic system 121 may be electrically connected to the pixels via a through hole 131. The space between the through holes may be filled with a filling material 130, which may increase the mechanical stability of the connection between the electronic layer 120 and the radiation absorbing layer 110. Other bonding techniques may make it possible to connect the electronic system 121 to the pixels without using through holes.

[0069] Figure 6It is schematically shown that the radiation detector 100 (for example, the first radiation detector 100A, the second radiation detector 100B, and the third radiation detector 100C) can have an array of pixels 150. The array can be a rectangular array, a honeycomb array, a hexagonal array, or any other suitable array. Each of the pixels 150 can be configured to detect radiation particles incident thereon, measure the energy of the radiation particles, or both. For example, each pixel 150 can be configured to count the number of radiation particles incident thereon and whose energy falls into multiple bins over a period of time. All of the pixels 150 can be configured to count the number of radiation particles in multiple energy bins incident thereon over the same period of time. Each pixel 150 can have its own analog-to-digital converter (ADC), which is configured to digitize an analog signal representing the energy of the incident radiation particles into a digital signal. The ADC can have a resolution of 10 bits or more. Each of the pixels 150 can be configured to measure its dark current, for example, before or at the same time as each radiation particle is incident thereon. Each of the pixels 150 may be configured to subtract the contribution of the dark current from the energy of the radiation particle incident thereon. The pixels 150 may be configured to operate in parallel. For example, while one pixel 150 is measuring an incident radiation particle, another pixel 150 may be waiting for a radiation particle to arrive. The pixels 150 may, but need not, be individually addressable.

[0070] In an embodiment, the radiation detector 100 (e.g., 100A and 100B) of the image sensor 9000 can be moved to multiple positions relative to the radiation source 109. The image sensor 9000 can capture images of multiple portions of the scene 50 from the radiation source 109 at the multiple positions, respectively, by using the radiation detector 100 and the radiation. The image sensor 9000 can stitch these images to form an image of the entire scene 50. Figure 7 As shown, the image sensor 9000 according to an embodiment may include an actuator 500, and the actuator 500 is configured to move the radiation detector 100 to a plurality of positions. The actuator 500 may include a controller 600. The actuator 500 is configured to move the calibration pattern 101 together with the radiation detector 100. The plurality of positions of the radiation detector 100 may be determined by the controller 600. The controller 600 may be configured to determine and store the transformations (e.g., 108A and 108B) of the radiation detector 100, and determine the projection using the transformations.

[0071] Fig. 8A and Figure 8BEach schematically illustrates the movement of the radiation detector 100 (eg, 100A and 100B) relative to the radiation source 109 according to an embodiment. Fig. 8A and Figure 8B In the example of , only a portion of the image sensor 9000 having a first radiation detector 100A and a second radiation detector 100B is shown. The first radiation detector 100A and the second radiation detector 100B may be arranged on a bracket 107. The relative position of the first radiation detector 100A with respect to the second radiation detector 100B remains the same at multiple positions. When the first radiation detector 100A moves from one position to another position in multiple positions, the relative position of the first radiation detector 100A with respect to the second radiation detector 100B may but does not have to remain the same. The first radiation detector 100A and the second radiation detector 100B may be rotatable around a first axis 501 relative to the radiation source 109. As Fig. 8A As shown in the example, the first radiation detector 100A and the second radiation detector 100B rotate from position 503A to position 503B relative to the radiation source 109 around the first axis 501. The first axis 501 may be parallel to the first planar surface 103A of the first radiation detector 100A and the second planar surface 103B of the second radiation detector 100B. The radiation source may be on the first axis 501. The first radiation detector 100A and the second radiation detector 100B may rotate around a second axis 502 relative to the radiation source 109. The second axis 502 is different from the first axis 501. For example, the second axis 502 may be perpendicular to the first axis 501. Fig. 8A As shown in the example of FIG. 5 , the first radiation detector 100A and the second radiation detector 100B may be rotated from a position 503A to a position 503C around the second axis 502 . The radiation source 109 may be on the second axis 502 .

[0072] like Figure 8B As shown in the example of FIG. 5 , the first radiation detector 100A and the second radiation detector 100B are translated from position 506A to position 506B along a first direction 504 relative to the radiation source 109. The first radiation detector 100A and the second radiation detector 100B may be translated along a second direction 505. The second direction 505 is different from the first direction 504. For example, the second direction 505 may be perpendicular to the first direction 504. Figure 8BAs shown in the example of , the first radiation detector 100A and the second radiation detector 100B can be translated from position 506A to position 506C along the second direction 505. The first direction 504 or the second direction 505 can be parallel to either the first planar surface 103A or the second planar surface 103B, or parallel to both, or not parallel to either. For example, the first direction 504 can be parallel to the first planar surface 103A, but not parallel to the second planar surface 103B.

[0073] Fig. 9 A flow chart of a method according to an embodiment is schematically illustrated. In step 151, a first image 104A of a first portion of the calibration pattern 101 is captured by using the first radiation detector 100A, and a second image 104B of a second portion of the calibration pattern 101 is captured by using the second radiation detector 100B, and in step 152, a first transformation 108A of the first radiation detector 100A is determined based on the image 104A of the first portion of the calibration pattern 101, and a second transformation 108B of the second radiation detector 100A is determined based on the image 104B of the second portion of the calibration pattern 101. The image 104A of the first portion of the calibration pattern 101 includes images of three features in the calibration pattern 101, whose positions relative to the calibration pattern are known. By comparing the positions of the three features in the captured image and in the calibration pattern 101, the first transformation 108A can be determined as an affine transformation. In step 153, an image 180A of a first portion of a scene 50 is captured using the first radiation detector 100A, and an image 180B of a second portion of the scene 50 is captured using the second radiation detector 100B. In step 154, a first projection 181A of the image of the first portion of the scene 50 on an image plane is determined using the first transformation 108A, and a second projection 181B of the image of the second portion of the scene 50 on an image plane is determined using the second transformation 108B. In step 155, an image of the entire scene 50 is formed by stitching the first projection 181A and the second projection 181B. A computer program product includes a non-transitory computer-readable medium having instructions recorded thereon, and the instructions, when executed by a computer, can implement the method as described above.

[0074] The image sensor 9000 described above can be used in various systems as follows.

[0075] Fig.10A system is schematically shown, the system comprising an image sensor 9000 as described in FIG. 1 to FIG. 8. The system can be used for medical imaging, such as chest radiography, abdominal radiography, etc. The system comprises a radiation source 1201. The radiation emitted from the radiation source 1201 penetrates an object 1202 (e.g., a human body part such as a chest, a limb, an abdomen), is attenuated to varying degrees by the internal structure of the object 1202 (e.g., bones, muscles, fat, organs, etc.), and is projected to the image sensor 9000. The image sensor 9000 forms an image by detecting the intensity distribution of the radiation.

[0076] Fig.11 A system is schematically shown, the system including an image sensor 9000 as described in Figures 1-8. The system can be used for medical imaging such as dental radiography. The system includes a radiation source 1301. The radiation emitted from the radiation source 1301 penetrates an object 1302 that is part of the oral cavity of a mammal (e.g., a human). The object 1302 may include the maxilla, the upper jaw, the teeth, the mandible, or the tongue. The radiation is attenuated to varying degrees by different structures of the object 1302 and is projected onto the image sensor 9000. The image sensor 9000 forms an image by detecting the intensity distribution of the radiation. Teeth absorb more radiation than caries, infections, and periodontal ligaments. The radiation dose received by dental patients is usually very small (approximately 0.150mSv for a full mouth series).

[0077] Fig.12 A cargo scanning or non-intrusive inspection (NII) system is schematically shown, the system including an image sensor 9000 as described in FIGS. 1-8. The system can be used to inspect and identify cargo in a transportation system, such as containers, vehicles, ships, luggage, etc. The system includes a radiation source 1401. Radiation emitted from the radiation source 1401 may be backscattered from an object 1402 (e.g., a transportation container, a vehicle, a ship, etc.) and projected to the image sensor 9000. Different internal structures of the object 1402 may backscatter radiation differently. The image sensor 9000 forms an image by detecting the intensity distribution of the backscattered radiation and / or the energy of the backscattered radiation particles.

[0078] Fig.13Another cargo scanning or non-intrusive inspection (NII) system is schematically shown, the system includes an image sensor 9000 as described in Figures 1-8. The system can be used for luggage inspection at public transportation stations and airports. The system includes a radiation source 1501. The radiation emitted from the radiation source 1501 can penetrate a piece of luggage 1502, be attenuated to varying degrees by the contents of the luggage, and be projected to the image sensor 9000. The image sensor 9000 forms an image by detecting the intensity distribution of the transmitted radiation. The system can reveal the contents of the luggage and identify prohibited items on public transportation, such as firearms, narcotics, sharp objects, and flammable items.

[0079] Fig.14 A whole body scanner system is schematically shown, the system comprising an image sensor 9000 as described in Figures 1 to 8. The whole body scanner system can detect objects on the human body for security inspection without physically removing clothing or making physical contact. The whole body scanner system is capable of detecting non-metallic objects. The whole body scanner system comprises a radiation source 1601. The radiation emitted from the radiation source 1601 may be backscattered from the inspected person 1602 and objects thereon, and projected to the image sensor 9000. The object and the human body may backscatter radiation differently. The image sensor 9000 forms an image by detecting the intensity distribution of the backscattered radiation. The image sensor 9000 and the radiation source 1601 may be configured to scan a person in a linear or rotational direction.

[0080] Fig.15 A radiation computed tomography (radiation CT) system is schematically shown. The radiation CT system uses computer-processed radiation to produce tomographic images (virtual "slices") of specific areas of the scanned object. The tomographic images can be used for diagnostic and therapeutic purposes in various medical disciplines, or for flaw detection, failure analysis, metrology, assembly analysis, and reverse engineering. The radiation CT system includes an image sensor 9000 and a radiation source 1701 as described in Figures 1-8. The image sensor 9000 and the radiation source 1701 can be configured to rotate synchronously along one or more circular or spiral paths.

[0081] Fig.16An electron microscope is schematically shown. The electron microscope includes an electron source 1801 (also referred to as an electron gun), which is configured to emit electrons. The electron source 1801 may have various emission mechanisms, such as thermal ions, photocathode, cold emission or plasma sources. The emitted electrons pass through an electron optical system 1803, which may be configured to shape, accelerate or focus the electrons. The electrons then reach a sample 1802, and an image sensor may form an image therefrom. The electron microscope may include an image sensor 9000 as described in Figures 1-8, which is used to perform energy dispersive radiation spectroscopy (EDS). EDS is an analytical technique for elemental analysis or chemical characterization of a sample. When the electrons are incident on a sample, they cause the sample to emit characteristic radiation. The incident electrons may excite electrons in the inner shell of atoms in the sample, ejecting them from the shell while creating electron holes where the electrons were previously located. Electrons from the outer, higher energy shells then fill the holes, and the energy difference between the higher energy shell and the lower energy shell may be released in the form of radiation. The amount and energy of radiation emitted from the sample can be measured by the image sensor 9000 .

[0082] The image sensor 9000 described herein may also have other applications, such as radiation telescopes, mammography, industrial radiation defect detection, radiation microscopes or radiation microphotography, radiation casting inspection, radiation nondestructive testing, radiation weld inspection, radiation digital subtraction angiography, etc. It may be suitable to use the image sensor 9000 to replace photographic plates, photographic films, PSP films, radiation image intensifiers, scintillators, or another semiconductor radiation detector.

[0083] Fig.17A and Fig. 17B Each shows a component diagram of an electronic system 121 according to an embodiment. The electronic system 121 may include a first voltage comparator 301 , a second voltage comparator 302 , a counter 320 , a switch 305 , an optional voltage meter 306 , and a controller 310 .

[0084] The first voltage comparator 301 is configured to compare the voltage of at least one of the electrical contacts 119B with a first threshold value. The first voltage comparator 301 may be configured to monitor the voltage directly, or to calculate the voltage by integrating the current flowing through the electrical contact 119B over a period of time. The first voltage comparator 301 may be controllably activated or deactivated by the controller 310. The first voltage comparator 301 may be a continuous comparator. That is, the first voltage comparator 301 may be configured to be continuously activated and continuously monitor the voltage. The first voltage comparator 301 may be a clocked comparator. The first threshold value may be 1-5%, 5-10%, 10%-20%, 20-30%, 30-40% or 40-50% of the maximum voltage that an incident radiation particle can generate on the electrical contact 119B. The maximum voltage may depend on the energy of the incident radiation particle, the material of the radiation absorbing layer 110 and other factors. For example, the first threshold may be 50 mV, 100 mV, 150 mV or 200 mV.

[0085] The second voltage comparator 302 is configured to compare the voltage with a second threshold. The second voltage comparator 302 may be configured to monitor the voltage directly, or to calculate the voltage by integrating the current flowing through the diode or electrical contact over a period of time. The second voltage comparator 302 may be a continuous comparator. The second voltage comparator 302 may be controllably enabled or disabled by the controller 310. When the second voltage comparator 302 is disabled, the power consumption of the second voltage comparator 302 may be less than 1%, less than 5%, less than 10% or less than 20% of the power consumption when the second voltage comparator 302 is enabled. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the term "absolute value" or "modulus" |x| of a real number x is a non-negative value of x regardless of its sign. That is, The second threshold value may be 200%-300% of the first threshold value. For example, the second threshold value may be 100mV, 150mV, 200mV, 250mV, or 300mV. The second voltage comparator 302 and the first voltage comparator 301 may be the same component. That is, the system 121 may have one voltage comparator that may compare a voltage to two different threshold values ​​at different times.

[0086] The first voltage comparator 301 or the second voltage comparator 302 may include one or more operational amplifiers or any other suitable circuits. The first voltage comparator 301 or the second voltage comparator 302 may have a high speed to allow the system 121 to operate under a high flux of incident radiation particles. However, having a high speed usually comes at the expense of power consumption.

[0087] The counter 320 is configured to record at least a number of radiation particles incident on the pixel 150 including the electrical contact 119B. The counter 320 can be a software component (e.g., a number stored in a computer memory) or a hardware component (e.g., 4017 IC and 7490 IC).

[0088] The controller 310 may be a hardware component such as a microcontroller and a microprocessor. The controller 310 is configured to start a time delay from when the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold (e.g., the absolute value of the voltage increases from an absolute value below the first threshold to a value equal to or exceeding the absolute value of the first threshold). Absolute values ​​are used here because the voltage can be negative or positive, depending on whether the cathode voltage or the anode voltage of the diode is used or which electrical contact is used. The controller 310 may be configured to keep the second voltage comparator 302, the counter 320, and any other circuits not required for the operation of the first voltage comparator 301 disabled before the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold. The time delay may expire before or after the voltage becomes stable (i.e., the rate of change of the voltage is substantially zero). The phrase "the rate of change is substantially zero" means that the time variation is less than 0.1% / ns. The phrase "substantially non-zero rate of change" means that the temporal variation of the voltage is at least 0.1% / ns.

[0089] The control 310 may be configured to start the second voltage comparator during the time delay (including the start and expiration). In an embodiment, the controller 310 is configured to start the second voltage comparator at the start of the time delay. The term "start" means to put a component into an operating state (e.g., by sending a signal such as a voltage pulse or a logic level, by providing power, etc.). The term "disable" means to put a component into a non-operating state (e.g., by sending a signal such as a voltage pulse or a logic level, by cutting off power, etc.). The operating state may have a higher power consumption than the non-operating state (e.g., 10 times higher, 100 times higher, 1000 times higher). The controller 310 itself may be disabled until the absolute value of the output voltage of the first voltage comparator 301 equals or exceeds the absolute value of the first threshold value before starting the controller 310.

[0090] If the second voltage comparator 302 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold during the time delay, the controller 310 may be configured to increase at least one of the numbers recorded by the counter 320 by one.

[0091] The controller 310 may be configured to cause the optional voltmeter 306 to measure the voltage when the time delay expires. The controller 310 may be configured to cause the electrical contact 119B to be connected to electrical ground to reset the voltage and discharge any carriers accumulated on the electrical contact 119B. In an embodiment, the electrical contact 119B is connected to electrical ground after the time delay expires. In an embodiment, the electrical contact 119B is connected to electrical ground for a limited reset period. The controller 310 may cause the electrical contact 119B to be connected to electrical ground by controlling the switch 305. The switch may be a transistor, such as a field effect transistor (FET).

[0092] In an embodiment, the system 121 is free of analog filter networks (eg, RC networks). In an embodiment, the system 121 is free of analog circuits.

[0093] The voltmeter 306 may feed its measured voltage to the controller 310 as an analog or digital signal.

[0094] The system 121 may include an integrator 309 electrically connected to the electrical contact 119B, wherein the integrator is configured to collect current carriers from the electrical contact 119B. The integrator 309 may include a capacitor in the feedback path of the operational amplifier. The operational amplifier configured in this way is called a capacitive transimpedance amplifier (CTIA). CTIA has a high dynamic range by preventing the operational amplifier from saturating and improves the signal-to-noise ratio by limiting the bandwidth in the signal path. The carriers from the electrical contact 119B accumulate on the capacitor over a period of time ("integration period"). After the integration period expires, the capacitor voltage is sampled by the ADC 306 and then reset by a reset switch. The integrator 309 may include a capacitor directly connected to the electrical contact 119B.

[0095] Fig.18Schematically showing the time variation of the current flowing through the electrical contact 119B caused by the carriers generated by the radiation particles incident on the pixel 150 including the electrical contact 119B (upper curve) and the corresponding time variation of the voltage of the electrical contact 119B (lower curve). The voltage may be the integral of the current with respect to time. At time t0, the radiation particles hit the pixel 150, the carriers begin to be generated in the pixel 150, the current begins to flow through the electrical contact 119B, and the absolute value of the voltage of the electrical contact 119B begins to increase. At time t1, the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold value V1, the controller 310 starts the time delay TD1 and the controller 310 may deactivate the first voltage comparator 301 at the start of the TD1. If the controller 310 is deactivated before time t1, the controller 310 is activated at time t1. During the TD1, the controller 310 activates the second voltage comparator 302. As used herein, the term "during" a time delay means the start and the expiration (i.e., the end) and any time in between. For example, the controller 310 may enable the second voltage comparator 302 when the TD1 expires. If during the TD1, the second voltage comparator 302 determines that the absolute value of the voltage at time t2 is equal to or exceeds the absolute value of the second threshold value V2, the controller 310 waits for the voltage to stabilize. The voltage at time t e Stable, at this time all the carriers generated by the radiation particles drift out of the radiation absorption layer 110. s , the time delay TD1 expires. At time t e At or after the time, the controller 310 causes the voltmeter 306 to digitize the voltage and determine in which bin the energy of the radiation particle falls. The controller 310 then increases the number recorded by the counter 320 corresponding to the bin by one. Fig. 9 In the example, the time t s At the time t e That is, TD1 expires after all carriers generated by the radiation particles drift out of the radiation absorption layer 110. If the time t cannot be easily measured e , TD1 can be selected empirically to allow sufficient time to collect substantially all of the carriers generated by the radiation particle, but TD1 cannot be too long, otherwise there is a risk that another carrier generated by the incident radiation particle will be collected. That is, TD1 can be selected empirically so that time t s At time t e After that. Time t s Not necessarily at time t e Afterwards, since once V2 is reached, the controller 310 may ignore TD1 and wait for time t eTherefore, the rate of change of the difference between the voltage and the dark current contribution to the voltage is e The controller 310 may be configured to disable the second voltage comparator 302 upon expiration of TD1 or at time t2 or any time in between.

[0096] At time t e The voltage of is proportional to the number of carriers generated by the irradiated particle, which is related to the energy of the irradiated particle. The controller 310 may be configured to determine the energy of the irradiated particle by using the voltmeter 306.

[0097] After TD1 expires or is digitized by the voltmeter 306 (whichever is later), the controller 310 connects the electrical contact 119B to the electrical ground 310 for a reset period RST to allow the accumulated carriers on the electrical contact 119B to flow to the ground and reset the voltage. After RST, the system 121 is ready to detect another incident radiation particle. If the first voltage comparator 301 is disabled, the controller 310 can activate it at any time before the expiration of RST. If the controller 310 is disabled, it can be activated before the expiration of RST.

[0098] Although various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for illustrative purposes and are not intended to be limiting, and the true scope and spirit of the invention should be determined by the claims herein.

Claims

1. An image sensor, comprising: a first radiation detector and a second radiation detector each including a planar surface configured to receive radiation from a radiation source; and calibration patterns; wherein the planar surface of the first radiation detector is not coplanar with the planar surface of the second radiation detector; wherein the image sensor is configured to capture an image of a first portion of the calibration pattern and an image of a second portion of the calibration pattern using the first radiation detector and the second radiation detector, respectively; wherein the image sensor is configured to determine a first transform of the first radiation detector based on an image of the first portion of the calibration pattern and to determine a second transform of the second radiation detector based on an image of the second portion of the calibration pattern; The image sensor is configured to capture an image of a first portion of a scene and an image of a second portion of the scene using the first radiation detector and the second radiation detector, respectively, determine a first projection of the image of the first portion of the scene on an image plane using the first transformation, determine a second projection of the image of the second portion of the scene on the image plane using the second transformation, and form an image of the scene by stitching the first projection and the second projection.

2. The image sensor of claim 1, wherein the calibration pattern has a non-uniform spatial distribution of radiation absorption. The image sensor of claim 1 , wherein the calibration pattern is a plane.

4. The image sensor of claim 1, wherein the image of the first portion of the calibration pattern comprises images of three features of the calibration pattern, wherein positions of the three features relative to the calibration pattern are known.

5. The image sensor of claim 1, wherein the first transformation is an affine transformation. 6 . The image sensor of claim 1 , wherein the first radiation detector and the second radiation detector are configured to move relative to the radiation source. 7 . The image sensor of claim 6 , wherein the first radiation detector and the second radiation detector are configured to move relative to the radiation source by rotating or translating relative to the radiation source.

8. The image sensor of claim 1, wherein the first radiation detector comprises a pixel array.

9. The image sensor of claim 1, wherein the first radiation detector is rectangular in shape.

10. The image sensor of claim 1, wherein the first radiation detector is hexagonal in shape.

11. A method for acquiring a scene image, comprising: capturing an image of a first portion of the calibration pattern using radiation from the radiation source using a first radiation detector; capturing an image of a second portion of the calibration pattern using the radiation using a second radiation detector; wherein the first radiation detector and the second radiation detector each include a planar surface configured to receive the radiation, and the planar surface of the first radiation detector is not coplanar with the planar surface of the second radiation detector; determining a first transformation of the first radiation detector based on an image of the first portion of the calibration pattern; determining a second transform of the second radiation detector based on an image of the second portion of the calibration pattern; capturing an image of a first portion of a scene using the first radiation detector; capturing an image of a second portion of the scene using the second radiation detector; determining a first projection of an image of the first portion of the scene on an image plane using the first transformation; determining a second projection of an image of the second portion of the scene on the image plane using the second transformation; as well as An image of the scene is formed by splicing the first projection and the second projection.

12. The method of claim 11, wherein the calibration pattern has a non-uniform spatial distribution of radiation absorption. The method of claim 11 , wherein the calibration pattern is a flat surface.

14. The method of claim 11, wherein the image of the first portion of the calibration pattern comprises an image of three features of the calibration pattern, wherein the positions of the three features relative to the calibration pattern are known. The method of claim 11 , wherein the first transformation is an affine transformation.

16. A computer program product comprising a non-transitory computer-readable medium having instructions recorded thereon, the instructions implementing the method of any one of claims 11-15 when executed by a computer.

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