X-ray image acquisition device, x-ray image acquisition system, and x-ray image acquisition method

Abstract

This X-ray image acquisition device includes: a pixel unit having M (M is an integer of 2 or more) pixel arrays each including N (N is an integer of 2 or more) pixel parts for detecting an X-ray; a control unit that controls detection of an X-ray by the pixel unit; and a processing unit that generates an X-ray image of an object on the basis of the result of detecting the X-ray by the pixel unit. The control unit controls detection of an X-ray by the pixel unit so that the N pixel parts in each of the M pixel arrays sequentially detect the X-ray at a predetermined detection interval. When a value obtained by dividing an array pitch of the N pixel parts by a reference speed corresponding to the movement speed of the object is defined as a basic value, the detection interval is a value obtained by dividing the basic value by a pixel shift value that is an integer between 2 and N, inclusive.

Description

X-ray image acquisition device, X-ray image acquisition system, and X-ray image acquisition method

[0001] One aspect of the present disclosure relates to an X-ray image acquisition device, an X-ray image acquisition system, and an X-ray image acquisition method.

[0002] Patent Document 1 describes a line scan sensor that includes two pixel arrays that are diagonally offset from each other by half a pixel, and the data acquired by such a sensor can be processed to generate a high-resolution image.

[0003] U.S. Patent Application Publication No. 2022 / 0005157

[0004] On the other hand, there are cases where, for example, to inspect an object for foreign matter contamination, an object being transported in a predetermined direction is irradiated with X-rays, the X-rays that have passed through the object are sequentially detected by a line scan sensor, and a two-dimensional image of the object is generated based on the detection results. The inventors have found that in such cases, simply applying the above-mentioned sensor leaves room for improvement in terms of the degree of freedom in image acquisition and the resolution of the acquired image.

[0005] Therefore, one aspect of the present disclosure aims to provide an X-ray image acquisition device, an X-ray image acquisition system, and an X-ray image acquisition method that can improve the degree of freedom in image acquisition and increase the resolution of acquired images.

[0006] An X-ray image acquisition device according to one aspect of the present disclosure is [1] "an X-ray image acquisition device for acquiring an X-ray image of an object moving along a first direction, the X-ray image acquisition device comprising: a pixel unit having M pixel arrays (M is an integer of 2 or more) each including N pixel units (N is an integer of 2 or more) for detecting X-rays, the N pixel units being aligned along the first direction, and the M pixel arrays being aligned along a second direction intersecting the first direction; a control unit controlling the detection of X-rays by the pixel unit; and a processing unit generating the X-ray image of the object based on a result of the X-ray detection by the pixel unit, wherein the control unit controls the detection of X-rays by the pixel unit such that the N pixel units in each of the M pixel arrays sequentially detect the X-rays at a predetermined detection interval, and wherein, when a value obtained by dividing the arrangement pitch of the N pixel units in the first direction by a reference speed corresponding to the moving speed of the object along the first direction is taken as a basic value, the detection interval is a value obtained by dividing the basic value by a pixel deviation value which is an integer of 2 or more and N or less."

[0007] In this X-ray image acquisition device, N pixel units in each of M pixel arrays sequentially detect X-rays at a predetermined detection interval. The detection interval is set to a basic value obtained by dividing the arrangement pitch of the N pixel units by a reference speed corresponding to the moving speed of the object, and then dividing the basic value by a pixel deviation value, which is an integer between 2 and N. By generating an X-ray image of the object based on data detected at detection intervals shorter than the basic value, the X-ray image can be made high-resolution. Furthermore, while shifting the positions of two pixel arrays as in Patent Document 1 described above allows for high resolution, the resolution cannot be changed, resulting in low flexibility in image acquisition. In contrast, this X-ray image acquisition device allows for the detection interval to be changed by changing the pixel deviation value, thereby enabling the X-ray image to have a high resolution at a level corresponding to the pixel deviation value. This improves the flexibility in image acquisition. Furthermore, while blurring tends to reduce the resolution in the moving direction of the object during X-ray image acquisition, this X-ray image acquisition device can increase the resolution in the first direction by shortening the detection interval of the N pixel units arranged along the first direction, thereby advantageously achieving high resolution in the acquired image. Therefore, this X-ray image acquisition device can improve the degree of freedom in image acquisition and increase the resolution of the acquired images.

[0008] The X-ray image acquisition device according to one aspect of the present disclosure may be [2] "the X-ray image acquisition device according to [1], in which the pixel shift value is selected from integers of 2 or more and N or less in accordance with an input." In this case, the degree of freedom in image acquisition can be further improved. Note that N may be an integer of 3 or more.

[0009] The X-ray image acquisition device according to one aspect of the present disclosure may be [3] "the X-ray image acquisition device according to [1] or [2], wherein the control unit is configured to be able to set the detection interval to the basic value." In this case, the degree of freedom in image acquisition can be further improved.

[0010] The X-ray image acquisition device according to one aspect of the present disclosure may be [4] "the X-ray image acquisition device according to any one of [1] to [3], wherein the control unit controls the detection of the X-rays by the pixel units so that each of the N pixel units detects the X-rays for a period shorter than the basic value." In this case, the resolution of the X-ray image can be further increased.

[0011] The X-ray image acquisition device according to one aspect of the present disclosure may be [5] "the X-ray image acquisition device according to any one of [1] to [4], wherein the control unit controls the detection of the X-rays by the pixel units so that each of the N pixel units detects the X-rays a plurality of times during a detection period corresponding to the basic value." In this case, it is possible to increase the resolution of the X-ray image while suppressing a decrease in luminance of the X-ray image.

[0012] An X-ray image acquisition device according to one aspect of the present disclosure may be the X-ray image acquisition device described in any one of [1] to [5], wherein [6] "the processing unit processes output data that are detection results from the N pixel units such that the output data that have passed through the same region of the object are superimposed on each other to generate the X-ray image having a plurality of pixel regions, and the processing unit processes the output data such that, when generating the X-ray image, the output data that constitutes one of the pixel regions and that is different from the output data that constitutes a pixel region adjacent to the one pixel region is emphasized more than the output data other than the different output data, and the adjacent pixel region is the pixel region that is adjacent to the one pixel region on the earlier side of the detection timing in the direction corresponding to the first direction." In this case, it is possible to increase the resolution of the X-ray image while suppressing a decrease in brightness of the X-ray image.

[0013] An X-ray image acquisition system according to one aspect of the present disclosure is [7] "an X-ray image acquisition system including the X-ray image acquisition device according to any one of [1] to [6], an X-ray source that outputs the X-rays, and a transport unit that transports the object along the first direction." With this X-ray image acquisition system, for the reasons described above, it is possible to improve the degree of freedom in image acquisition and increase the resolution of the acquired images.

[0014] An X-ray image acquisition method according to one aspect of the present disclosure is [8] "an X-ray image acquisition method comprising: a detection step of irradiating X-rays onto an object moving along a first direction and detecting the X-rays that have passed through the object using a pixel unit; and a processing step of generating an X-ray image of the object based on a detection result in the detection step, wherein the pixel unit has M (M is an integer of 2 or more) pixel arrays each including N (N is an integer of 2 or more) pixel portions for detecting X-rays, the N pixel portions are aligned along the first direction, and the M pixel arrays are aligned along a second direction intersecting the first direction, wherein in the detection step, the N pixel portions in each of the M pixel arrays sequentially detect the X-rays at a predetermined detection interval, wherein a basic value is defined as a value obtained by dividing the arrangement pitch of the N pixel portions in the first direction by a reference speed corresponding to the moving speed of the object along the first direction, and the detection interval is a value obtained by dividing the basic value by a pixel deviation value which is an integer of 2 or more and N or less." According to this X-ray image acquisition method, for the reasons described above, it is possible to improve the degree of freedom in image acquisition and to increase the resolution of the acquired image.

[0015] According to one aspect of the present disclosure, it is possible to provide an X-ray image acquisition device, an X-ray image acquisition system, and an X-ray image acquisition method that can improve the degree of freedom in image acquisition and increase the resolution of acquired images.

[0016] [Correction based on Rule 91 18.06.2024] A diagram illustrating the configuration of an X-ray image acquisition system according to an embodiment. A diagram illustrating the configuration of an X-ray camera. A flowchart illustrating processing executed in an X-ray image acquisition device. A diagram illustrating a reference velocity. (a) and (b) are diagrams illustrating a normal TDI operation. (a) and (b) are diagrams illustrating a normal TDI operation. A diagram illustrating an addition process in a normal TDI operation. (a) and (b) are diagrams illustrating an operation when a pixel deviation value I is 4. (a) and (b) are diagrams illustrating an operation when a pixel deviation value I is 4. (a) and (b) are diagrams illustrating an addition process when a pixel deviation value I is 4. (a) and (b) are diagrams illustrating an operation when a pixel deviation value I is 3. (a) and (b) are diagrams illustrating an operation when a pixel deviation value I is 3. (a) and (b) are diagrams illustrating an addition process when a pixel deviation value I is 3. (a) and (b) are diagrams illustrating an addition process when a pixel deviation value I is 3. 10A and 10B are diagrams for explaining an operation when the pixel shift value I is 2. (a) and (b) are diagrams for explaining an operation when the pixel shift value I is 2. (a) and (b) are diagrams for explaining an operation when the pixel shift value I is 2. (a) and (b) are diagrams for explaining a first example of an addition process when the pixel shift value I is 2. (a) and (b) are diagrams for explaining a first example of an addition process when the pixel shift value I is 2. (b) are diagrams for explaining a second example of an addition process when the pixel shift value I is 2. (b) are diagrams for explaining a second example of an addition process when the pixel shift value I is 2. (c) are diagrams for explaining a first example of a configuration of a processing unit. (c) are diagrams for explaining a second example of a configuration of a processing unit. (c) are diagrams for explaining a third example of a configuration of a processing unit. (a) and (b) are diagrams for explaining an operation of a first modified example. (a) and (b) are diagrams for explaining an operation of a first modified example. (a) and (b) are diagrams for explaining an operation of a second modified example. (a) and (b) are diagrams for explaining an operation of a second modified example. (a) and (b) are diagrams for explaining an addition process in the second modified example. (b) are diagrams for explaining an addition process in the second modified example. 10A and 10B are diagrams illustrating an object and pixels in an assumed example, and are diagrams for explaining detection of an object in an assumed example.FIG. 10 is a diagram for explaining detection of an object in an assumed example. FIG. 11 is a diagram for explaining detection of an object in an assumed example. FIG. 12 is a diagram for explaining detection of an object in an assumed example. FIG. 13 is a diagram for explaining detection of an object in an assumed example. FIG. 14 is a diagram for explaining detection of an object in an assumed example. FIG. 15 is a diagram for explaining a first simulation result. FIG. 16 is a diagram for explaining a second simulation result. (a) and (b) are diagrams for explaining shortening of an exposure period. (b) are diagrams for explaining a third simulation result. (c) are diagrams for explaining additional simulation results. (d) are diagrams for explaining a modified example of shortening of an exposure period.

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted. [X-ray Image Acquisition System]

[0018] The X-ray image acquisition system 1 shown in Fig. 1 is a system for acquiring X-ray images of an object OJ being transported (moving) along a first direction X1. That is, the first direction X1 is the transport direction (movement direction) of the object OJ. The X-ray image acquisition system 1 includes an X-ray source 2, a transport unit 3, and an X-ray image acquisition device 4. The X-ray image acquisition device 4 includes an X-ray camera 5, a computer 6, a display unit 7, and an input unit 8.

[0019] The X-ray source 2 outputs X-rays. The transport unit 3 is, for example, a belt conveyor, and transports the object OJ placed on the belt along a first direction X1. The transport path of the transport unit 3 is set to pass through the irradiation range of the X-rays from the X-ray source 2. As an example, the object OJ is food, and the X-ray image acquisition system 1 is used to inspect whether or not foreign matter has been mixed into the object OJ.

[0020] As shown in FIG. 2 , the X-ray camera 5 includes a pixel unit 10 and a circuit unit 20. The X-ray camera 5 acquires an X-ray image of the object OJ by, for example, converting X-rays transmitted through the object OJ into scintillation light using a scintillator and detecting the scintillation light using the pixel unit 10. In this case, the X-ray camera 5 includes a scintillator disposed above the pixel unit 10 (between the pixel unit 10 and the transport unit 3). Alternatively, the pixel unit 10 may be configured as a direct conversion detector that directly converts incident X-rays into electrical signals without converting them into light. In this case, the scintillator is omitted. Examples of direct conversion detectors include compound semiconductor detectors such as CdTe detectors and CdZnTe detectors, and Si direct conversion detectors.

[0021] The pixel unit 10 and the circuit unit 20 are formed, for example, on a single chip and are integrated with each other. The pixel unit 10 has M pixel arrays 12 (M is an integer of 2 or more) each including N pixel units 11 (N is an integer of 2 or more) that perform photoelectric conversion. Each pixel unit 11 is formed, for example, in a square shape. Note that the pixel unit 10 and the circuit unit 20 may be formed on separate chips, and these chips may be electrically connected.

[0022] The N pixel units 11 are arranged in a line along the first direction X1 with a fixed interval (interval β) between them. The M pixel arrays 12 are arranged in a line along the second direction X2 that intersects with (is orthogonal to) the first direction X1 with a fixed interval between them. The A-th pixel unit 11 (A is an integer between 1 and N) of the M pixel arrays 12 is arranged in a line along the second direction X2. That is, in the pixel unit 10, N×M pixel units 11 are arranged in a matrix. The first direction X1 and the second direction X2 are, for example, directions perpendicular to the vertical direction.

[0023] N may be an integer equal to or greater than 8, or may be an integer equal to or greater than 16. The following description will be given using an example in which N and M are 4, but other values ​​of N and M may be used. Each pixel unit 11 is configured, for example, by a light-receiving element capable of detecting scintillation light. The light-receiving element is, for example, a photodiode made of silicon, but may also be a photodiode made of a compound semiconductor such as InGaAs or CdTe. The pixel unit 10 may be a multi-line sensor as shown in the example of FIG. 2, or an area sensor. The pixel unit 10 may be configured by a silicon photomultiplier (SiPM). An example of a SiPM is a multi-pixel photon counter (MPPC) (registered trademark).

[0024] The circuit unit 20 has a control unit 21 and a processing unit 22. The control unit 21 is configured, for example, by a microcomputer mounted on a chip, but may be configured by any circuit element such as an FPGA (Field-Programmable Gate Array). The control unit 21 controls the detection of X-rays by the pixel units 10. The processing unit 22 generates an X-ray image of the object OJ based on the results of X-ray detection by the pixel units 10. In other words, the processing unit 22 is an image processing unit that performs image processing. An example of a specific configuration of the processing unit 22 will be described later with reference to Figures 22 to 24. The circuit unit 20 (control unit 21 and processing unit 22) is electrically connected to each pixel unit 11, for example, via wiring 15.

[0025] The circuit unit 20 is electrically connected to the computer 6. The computer 6 includes, for example, a processor such as a CPU, and storage media such as a RAM and a ROM. The computer 6 controls the operation of each unit of the X-ray image acquisition system 1. For example, the computer 6 is electrically connected to the transport unit 3 and controls the operation of the transport unit 3. In this example, the control unit 21 is described as controlling the detection of X-rays by the pixel units 10, but the computer 6 may perform this control. That is, the computer 6 may function as the control unit. In this case, the control unit 21 may be omitted. Also, in this example, the processing unit 22 is described as generating an X-ray image of the object OJ based on the X-ray detection results by the pixel units 10, but the computer 6 may perform this generation. That is, the computer 6 may function as the processing unit. In this case, the processing unit 22 may be omitted. The control unit that controls the detection of X-rays by the pixel units 10 and the processing unit that generates the X-ray image of the object OJ based on the X-ray detection results by the pixel units 10 may be configured by a common element (for example, the computer 6).

[0026] The display unit 7 is, for example, a display connected to the computer 6, and displays various information on the screen. The input unit 8 is, for example, a mouse, a keyboard, etc. connected to the computer 6, and accepts user input operations. The display unit 7 and the input unit 8 may be configured as a touch display that integrates a display unit and an input unit, or as a smart device such as a smartphone or a tablet terminal. [X-ray Image Acquisition Method]

[0027] In the X-ray image acquisition method according to the embodiment, the X-ray source 2 irradiates the object OJ being transported along the first direction X1 with X-rays, and the pixel units 10 detect the X-rays that have passed through the object OJ (detection step). Subsequently, the processing unit 22 generates an X-ray image of the object OJ based on the detection results of the detection step (processing step). The processing step may be performed after the detection of the transmitted X-rays in the detection step is completed, or may be performed in parallel with the detection of the transmitted X-rays in the detection step.

[0028] Referring to FIG. 3 , the process executed by the X-ray image acquisition device 4 when acquiring an X-ray image will be outlined. First, an input for selecting a pixel shift value I is received (step S1). In this example, the pixel shift value I is an integer between 1 and N inclusive. The input is received, for example, by a user operating the input unit 8. The control unit 21 selects the pixel shift value I from integers between 1 and N inclusive in response to the input. Next, the control unit 21 sets a detection interval ΔT based on the pixel shift value I (step S2). Next, the control unit 21 sets whether or not to perform enhancement processing (step S3). As will be described later, enhancement processing may not be performed. Next, the control unit 21 controls the detection of X-rays by the pixel units 10 in each of the M pixel arrays 12 so that the N pixel units 11 sequentially detect X-rays at the detection interval ΔT (step S4). This results in acquisition of output data representing the detection results by each pixel unit 11. Next, the processing unit 22 generates an X-ray image of the object OJ based on the detection results of step S4 (step S5). Steps S1 to S4 are the detection step, and step S5 is the processing step. These steps will be described in detail below with reference to specific examples.

[0029] 5 to 7 are diagrams for explaining a normal TDI (Time Delay Integration) operation. This operation corresponds to the case where the pixel shift value I is 1. That is, when 1 is selected as the pixel shift value I in step S1, the X-ray image acquisition device 4 performs a normal TDI operation.

[0030] The left side of FIG. 5( a) shows the positional relationship between the object OJ and the pixel unit 10 at time T=t1, and the right side of FIG. 5( a) shows the imaging timings of lines 1, 2, 3, and 4. The positional relationship between the object OJ and the pixel unit 10 is shown on the left side, and the imaging timings of lines 1 to 4 are shown on the right side, as in FIG. 5( b), 6, 8, 9, 12, 13, 16, 17, and 25 to 28, which will be described later. Line 1 is a line of pixel units 11 formed by the first pixel units 11 of M pixel arrays 12 arranged along the second direction X2, and similarly, lines 2, 3, and 4 are lines of pixel units 11 formed by the second, third, and fourth pixel units 11 of M pixel arrays 12 arranged along the second direction X2. Hereinafter, the pixel arrays 12 will also be referred to as pixel arrays a, b, c, and d, respectively, as shown in FIG. 5( a).

[0031] As shown in FIG. 5A , in normal TDI operation, the detection interval ΔT (imaging interval) is set to (α + β) / (1 × V). That is, while in the X-ray image acquisition method according to the embodiment, the detection interval ΔT is set to (α + β) / (I × V), in this example, since I = 1, the detection interval ΔT is set to (α + β) / (1 × V). As shown in FIG. 2 , α is the width of the pixel unit 11 in the first direction X1. β is the distance in the first direction X1 between adjacent pixel units 11 in the first direction X1. (α + β) corresponds to the array pitch of the pixel units 11 in the first direction X1 (the distance between the centers of adjacent pixel units 11). The distance β may be zero, in which case the pixel units 11 are arranged without any gaps along the first direction X1. In this case, the array pitch is equal to the width α.

[0032] V is a reference velocity corresponding to the moving velocity V1 of the object OJ along the first direction X1 (determined based on the moving velocity V1). The reference velocity V will be described with reference to FIG. 4 . The reference velocity V may be the moving velocity V1 (conveying velocity) at which the object OJ is transported by the transport unit 3. Alternatively, the reference velocity V may be an apparent velocity V2 on the pixel unit 10, which takes into account the magnification rate of X-rays from the X-ray source 2 to the X-ray camera 5. The magnification rate is calculated by FDD / FOD. FOD (Focus to Object Distance) is the distance from the X-ray source 2 to the object OJ. FDD (Focus to Detector Distance) is the distance from the X-ray source 2 to the X-ray camera 5. The apparent velocity V2 is calculated by (FDD / FOD) × V1. Using the apparent velocity V2, which takes into account the magnification rate, as the reference velocity V enables more optimal image acquisition.

[0033] As described above, in the X-ray image acquisition method according to the embodiment, the detection interval ΔT is set to (α+β) / (I×V), where (α+β) is the array pitch of the pixel unit 11 and V is the reference velocity. In other words, if the value obtained by dividing the array pitch (α+β) by the reference velocity V is taken as the basic value, the detection interval ΔT is set to the value obtained by dividing the basic value (α+β) / V by the pixel deviation value I. In the normal TDI operation shown in FIGS. 5 to 7, I=1, and therefore the detection interval ΔT is set to the basic value itself.

[0034] As shown in FIG. 5( a), the detection result for line 1 during detection period 1, from start time T=t0 to time T=t1, is output as output data D11 from line 1. Output data Dpq is output data indicating the detection result for line p (p=1, 2, ..., N) during frame q (q=1, 2, ...) (detection period). As shown in FIG. 5( b), the detection results for each line during detection period 2, from time T=t1 to time T=t2, are output as output data D12 from line 1 and as output data D21 from line 2. The length of frame q is equal to the basic value (α+β) / V. In FIGS. 5( a) and 5(b), the portion of the object OJ corresponding to frame 1 is indicated by hatching. This also applies to FIGS. 6, 8, 9, 12, 13, 16, 17, and 25-28, which will be described later. In Figure 5(a), the part of object OJ corresponding to frame 1 is located above line 1, and in Figure 5(b), the part of object OJ corresponding to frame 1 is located above line 2, and the part of object OJ corresponding to frame 2 is located above line 1.

[0035] As shown in FIG. 6A, the detection results for each line during detection period 3 from time T=t2 to time T=t3 are output as output data D13 from line 1, output as output data D22 from line 2, and output as output data D31 from line 3. As shown in FIG. 6B, the detection results for each line during detection period 4 from time T=t3 to time T=t4 are output as output data D14 from line 1, output as output data D23 from line 2, output as output data D32 from line 3, and output as output data D41 from line 4. In this way, in the X-ray image acquisition device 4, the N pixel units 11 sequentially detect X-rays at detection intervals ΔT (step S4, detection step). This X-ray detection is performed simultaneously for each pixel array 12 (pixel arrays a to d).

[0036] 7 is a diagram for explaining the addition process in normal TDI operation. The addition process is performed by the processing unit 22. This addition process generates an X-ray image of the object OJ (step S5, processing step). As shown in FIG. 7, in the addition process, output data that are the detection results from the pixel unit 11 are processed so that output data that have passed through the same region of the object OJ are superimposed on each other, thereby generating an X-ray image of the object OJ.

[0037] The left side of FIG. 7 shows output data (output image) from lines 1 to 4. Output data Dpqr is output data for frame q (q = 1, 2, ...) from pixel array r (r = a, b, c, d) of line p (p = 1, 2, ..., N). Note that, for convenience, pixel array r is indicated by an alphabet, but the number of pixel arrays r may be any integer equal to or greater than 1, and may be, for example, 1536 pixels, 4608 pixels, or 6144 pixels. This also applies to FIGS. 10, 14, 18, and 20, which will be described later. As shown on the right side of FIG. 7, the output data from lines 1 to 4 are added together to generate an X-ray image of object OJ having a plurality of pixel regions 30.

[0038] 7 , for example, the value (pixel value) of the first pixel region 30 corresponding to pixel array a is D11a+D21a+D31a+D41a. The value of the second pixel region 30 corresponding to pixel array a is D12a+D22a+D32a+D42a. The value of the third pixel region 30 corresponding to pixel array a is D13a+D23a+D33a+D43a. The value of the fourth pixel region 30 corresponding to pixel array a is D14a+D24a+D34a+D44a. The value of the fourth pixel region 30 corresponding to pixel array d is D14d+D24d+D34d+D44d. In this way, with normal TDI operation, an X-ray image with four times the brightness can be generated compared to, for example, when an output image from a single line is simply used as an X-ray image.

[0039] 8 to 11 are diagrams for explaining the operation when the pixel shift value I is 4. That is, when 4 is selected as the pixel shift value I in step S1, the X-ray image acquisition device 4 performs the following operation.

[0040] 8A, when the pixel shift value I is 4, the detection interval ΔT is set to (α+β) / (4×V). As a result, as shown in FIGS. 8 and 9, detection (imaging) is performed at a detection interval ΔT that is shorter than that in the case of normal TDI operation (when the pixel shift value I is 1). For example, the detection results for each line in detection period 1 between time T=t3 and time T=t4 are output from line 1 as output data D11, from line 2 as output data D21, from line 3 as output data D31, and from line 4 as output data D41.

[0041] 10 and 11 are diagrams for explaining the addition process when the pixel shift value I is 4. In the normal TDI operation described above, the output data from lines 1 to 4 is X-ray output data from the same region on the object OJ, whereas when the pixel shift value I is 4, as shown on the left side of Fig. 10, the output data from lines 1 to 4 becomes X-ray output data from regions shifted from each other in the first direction X1 by ¼ of the width of the pixel portion 11 on the object OJ (¼ pixel shift).

[0042] As shown in Fig. 10, output data from lines 1 to 4 are added together to generate an X-ray image of an object OJ having a plurality of pixel regions 30. Fig. 11 shows the values ​​of each pixel region 30 corresponding to pixel array a. For example, the value (pixel value) of the first pixel region 30 corresponding to pixel array a is D11a+D21a+D31a+D41a. The value of the second pixel region 30 corresponding to pixel array a is D12a+D21a+D31a+D41a. The value of the third pixel region 30 corresponding to pixel array a is D12a+D22a+D31a+D41a. The value of the thirteenth pixel region 30 corresponding to pixel array a is D14a+D24a+D34a+D44a. 10 and 11, output data from all lines 1 to 4 is not acquired during the period from start time T=t0 to T=t3, and therefore, an X-ray image does not need to be generated for the range corresponding to this period. Similarly, output data from lines 1 to 4 are added for pixel arrays b to d.

[0043] In the above example, the output data from lines 1 to 4 were added together, but when adding output data from N lines, it is also possible to perform a filter process to multiply each output data by 1 / N and then add the filtered output data.

[0044] The emphasis process (step S3) will be described with reference to Figure 11. If it is set not to perform the emphasis process in step S3, the output data from lines 1 to 4 are added evenly (simple addition) as described above. On the other hand, if it is set to perform the emphasis process in step S3, the following emphasis process is performed to emphasize and add peculiar data from the output data from lines 1 to 4 (emphasis addition).

[0045] In FIG. 11 , peculiar data is indicated by a thick frame. The peculiar data is output data from a pixel region 30, and the output data from the pixel region 30 adjacent to the pixel region 30 has a detection timing in the direction corresponding to the first direction X1 that is earlier than the detection timing from the pixel region 30. For example, in the second pixel region 30, the output data D12a is different from the output data from the adjacent first pixel region 30. In this case, as a first example, the peculiar data may be multiplied by n (n is a value greater than 1), and the value of the second pixel region 30 may be calculated as nD12a+D21a+D31a+D41a. Alternatively, as a second example, data other than the peculiar data may be multiplied by m (m is a value greater than 0 and less than 1), and the value of the second pixel region 30 may be calculated as D12a+mD21a+mD31a+mD41a. Note that the first example is preferable from the viewpoint of increasing the value of the pixel region 30.

[0046] In the third pixel region 30, the output data D22a is different from the output data constituting the adjacent second pixel region 30. In this case, in the first example, the value of the third pixel region 30 may be D12a+nD22a+D31a+D41a. In the second example, the value of the third pixel region 30 may be mD12a+D22a+mD31a+mD41a. Similarly, in the first pixel region 30, in the first example, the value of the first pixel region 30 may be D11a+D21a+D31a+nD41a. In the second example, the value of the first pixel region 30 may be mD12a+mD21a+mD31a+D41a.

[0047] 12 to 15 are diagrams for explaining the operation when the pixel shift value I is 3. That is, when 3 is selected as the pixel shift value I in step S1, the X-ray image acquisition device 4 performs the following operation.

[0048] As shown in FIG. 12A, when the pixel shift value I is 3, the detection interval ΔT is set to (α+β) / (3×V). As a result, as shown in FIGS. 12 and 13, detection (imaging) is performed at a detection interval ΔT that is shorter than that in the case of normal TDI operation (when the pixel shift value I is 1). For example, the detection results of each line during the detection period from time T=t2 to time T=t3 are output from line 1 as output data D11, from line 2 as output data D21, and from line 3 as output data D31. When the pixel shift value I is 3, the output data from line 4 does not need to be used to generate an X-ray image. For example, the output data from line 4 does not need to be read out, or it does not need to be read out and then used.

[0049] 14 and 15 are diagrams for explaining the addition process when the pixel shift value I is 3. In the normal TDI operation described above, the output data from lines 1 to 4 is X-ray output data from the same region on the object OJ, whereas when the pixel shift value I is 3, as shown on the left side of Fig. 14, the output data from lines 1 to 3 becomes X-ray output data from regions shifted from each other in the first direction X1 by 1 / 3 of the width of the pixel portion 11 on the object OJ (1 / 3 pixel shift).

[0050] As shown in FIG. 14 , output data from lines 1 to 3 are added together to generate an X-ray image of an object OJ having a plurality of pixel regions 30. FIG. 15 shows values ​​for each pixel region 30 corresponding to pixel array a. For example, the value (pixel value) of the first pixel region 30 corresponding to pixel array a is D11a+D21a+D31a. The value of the second pixel region 30 corresponding to pixel array a is D12a+D21a+D31a. The value of the tenth pixel region 30 corresponding to pixel array a is D14a+D24a+D34a. As indicated by hatching in FIGS. 14 and 15 , output data from all lines 1 to 3 is not acquired during the period from start time T=t0 to T=t2, and therefore no X-ray image is generated for the range corresponding to that period. Also, in FIG. 15 , anomalous data is indicated by a thick frame. In the addition process when the pixel shift value I is 3, the peculiar data among the output data from lines 1 to 3 may also be emphasized and added.

[0051] 16 to 21 are diagrams for explaining the operation when the pixel shift value I is 2. That is, when 2 is selected as the pixel shift value I in step S1, the X-ray image acquisition device 4 performs the following operation.

[0052] 16(a), when the pixel shift value I is 2, the detection interval ΔT is set to (α+β) / (2×V). As a result, as shown in FIGS. 16 and 17, detection (imaging) is performed at a detection interval ΔT that is shorter than that in the case of normal TDI operation (when the pixel shift value I is 1). For example, the detection results for each line in detection period 1 between time T=t1 and time T=t2 are output from line 1 as output data D11 and from line 2 as output data D21.

[0053] 18 and 19 are diagrams for explaining a first example of the addition process when the pixel shift value I is 2. In the normal TDI operation described above, the output data from lines 1 to 4 is X-ray output data from the same region on the object OJ, whereas when the pixel shift value I is 2, as shown on the left side of Fig. 18 , the output data from lines 1 and 3 and the output data from lines 2 and 4 are X-ray output data from regions shifted from each other in the first direction X1 by 1 / 2 the width of the pixel portion 11 on the object OJ (1 / 2 pixel shift).

[0054] As shown in FIG. 18 , in the first example, output data from lines 1 to 4 are added together to generate an X-ray image of an object OJ having multiple pixel regions 30. FIG. 19 shows the values ​​of each pixel region 30 corresponding to pixel array a. For example, the value (pixel value) of the first pixel region 30 corresponding to pixel array a is D11a+D21a+D31a+D41a. The value of the second pixel region 30 corresponding to pixel array a is D12a+D21a+D32a+D41a. The value of the seventh pixel region 30 corresponding to pixel array a is D14a+D24a+D34a+D44a. As indicated by the hatching in FIGS. 18 and 19 , output data from all lines 1 to 4 is not acquired during the period from start time T=t0 to T=t1, and therefore, an X-ray image need not be generated for the range corresponding to that period. Also, in FIG. 19 , anomalous data is indicated by dashed hatching. Even in the addition process when the pixel shift value I is 2, peculiar data may be emphasized and added among the output data from lines 1 to 4. For example, the value of the first pixel region 30 corresponding to pixel array a may be D11a+nD21a+D31a+nD41a.

[0055] 20 and 21 are diagrams illustrating a second example of the addition process when the pixel shift value I is 2. In the second example, output data from lines 1 and 3, which are X-ray output data from the same region of the object OJ, are added to generate first data C1, and output data from lines 2 and 4, which are X-ray output data from the same region of the object OJ, are added to generate second data C2. The first data C1 and the second data C2 are then added to generate an X-ray image. In this case, as shown in FIG. 21 , the value of the first pixel region 30 corresponding to pixel array a is the sum of (D11a + D31a) of the first data C1 and (D21a + D41a) of the second data C2. In the first and second examples, the values ​​of each pixel region 30 in the generated X-ray image are the same. [Processing Unit]

[0056] FIG. 22 illustrates a first example of the configuration of the processing unit 22. In this first example, the processing unit 22 includes a single adder 51. The processing unit 22 includes an amplifier array 52, an ADC (Analog-to-Digital converter) array 53, an enhancement processing unit 54, and an adder memory 55. The amplifier array 52 includes M (four in this example) charge amplifiers connected to M pixel arrays 12, respectively, and converts charge signals output from the pixel units 11 of the corresponding pixel arrays 12 into voltage signals. The ADC array 53 includes M AD converters connected to the M charge amplifiers, respectively, and performs A / D conversion to convert the voltage signals output from the corresponding charge amplifiers into digital values. The enhancement processing unit 54 is a circuit element for performing the enhancement processing described above and is connected between the ADC array 53 and the adder memory 55. The enhancement processing unit 54 may be omitted. The adder memory 55 includes multiple memory areas and stores digital values ​​corresponding to the output data from each pixel unit 11. The processing unit 22 of the first example can perform the above-mentioned addition processing.

[0057] FIG. 23 is a diagram showing a second example of the configuration of the processing unit 22. In the second example, the processing unit 22 includes M (four in this example) adders 51 connected to M pixel arrays 12, respectively. Each adder 51 includes a charge amplifier 61, an enhancement processing unit 54, a switching element 62, N AD converters 63, and an output circuit 64. The charge amplifier 61 converts charge signals output from the pixel units 11 of the pixel array 12 into voltage signals. The charge amplifier 61 may be an amplifier array including M charge amplifiers. The enhancement processing unit 54 is connected between the charge amplifier 61 and the switching element 62. The enhancement processing unit 54 may be omitted. The switching element 62 is connected between the charge amplifier 61 and the N AD converters 63 and switches the connection state between the charge amplifier 61 and the N AD converters 63. The AD converters 63 convert the voltage signals output from the charge amplifiers 61 connected via the switching elements 62 into digital values. The output circuit 64 outputs the signals from the AD converters 63 to the outside. The processing unit 22 of the second example can also perform the above-described addition process.

[0058] FIG. 24 illustrates a third example of the configuration of the processing unit 22. In this third example, the processing unit 22 includes M (four in this example) adders 51 connected to M pixel arrays 12, respectively. Each adder 51 includes an enhancement processing unit 54, a switching element 62, N charge amplifiers 61, an ADC array 53, and an output circuit 64. The enhancement processing unit 54 is connected between the charge amplifier 61 and the switching element 62. The enhancement processing unit 54 may be omitted. The switching element 62 is connected between the N pixel units 11 and the N charge amplifiers 61, and switches the connection state between the N pixel units 11 and the N charge amplifiers 61. The ADC array 53 includes N AD converters connected to the N charge amplifiers 61, respectively, and converts the voltage signals output from the corresponding charge amplifiers 61 into digital values. The output circuit 64 outputs the signals from the ADC array 53 to the outside. The processing unit 22 of this third example can also perform the above-described addition process. [Operation and Effects]

[0059] In the X-ray image acquisition device 4, in each of the M pixel arrays 12, the N pixel units 11 sequentially detect X-rays at a predetermined detection interval ΔT. The detection interval ΔT is a basic value (α+β) / V obtained by dividing the arrangement pitch (α+β) of the N pixel units 11 by a reference velocity V corresponding to the moving velocity V1 of the object OJ, and then dividing the basic value (α+β) / V by the pixel deviation value I, i.e., (α+β) / (I×V). In other words, the detection interval ΔT can be set based on the arrangement pitch (α+β) of the N pixel units 11, the moving velocity V1 of the object OJ, and the pixel deviation value I. When the pixel deviation value I is an integer between 2 and N, the resolution of the X-ray image of the object OJ can be increased by generating the X-ray image based on data detected at a detection interval ΔT shorter than the basic value. Furthermore, while shifting the positions of the two pixel arrays as in the above-mentioned Patent Document 1 allows for increased resolution, the resolution cannot be changed, resulting in limited flexibility in image acquisition. In contrast, the X-ray image acquisition device 4 can change the detection interval ΔT by changing the pixel shift value I, and can increase the resolution of the X-ray image at a level corresponding to the pixel shift value I. This improves the degree of freedom in image acquisition. Furthermore, while blurring tends to reduce the resolution in the direction of movement of the object OJ when acquiring an X-ray image, the X-ray image acquisition device 4 can increase the resolution in the first direction X1 by shortening the detection interval ΔT of the N pixel units 11 arranged along the first direction X1, thereby favorably increasing the resolution of the acquired image. Details of this blurring will be described later. As described above, the X-ray image acquisition device 4 can improve the degree of freedom in image acquisition and increase the resolution of the acquired image.

[0060] The pixel deviation value I is selected from integers between 1 and N in accordance with the input, thereby further improving the degree of freedom in image acquisition.

[0061] The control unit 21 is configured to be able to set the detection interval ΔT to a basic value. That is, in the example described above, the pixel deviation value I can be set to 1, and normal TDI operation can be selected. This further improves the degree of freedom in image acquisition.

[0062] For example, if the pixel shift value I is N and the pixel unit 11 has N pixels, the resolution can be increased by a factor of N. However, since the detection interval ΔT is 1 / N compared to normal TDI operation (N = 1), even if N additions are performed, the SNR (signal-to-noise ratio) and CNR (contrast-to-noise ratio) cannot be improved. If the pixel shift value I is 1, the detection interval ΔT = (α + β) / V of normal TDI operation is maintained, and N additions are performed, thereby improving the SNR but not the resolution. By making the pixel shift value I selectable from 1 to N or 2 to N, the resolution and contrast can be adjusted. For example, if high resolution is required, the pixel shift value I can be set to a large value. However, if the SNR is likely to be low due to reasons such as a thick object OJ, the pixel shift value I can be set to a small value, thereby increasing the contrast and improving the SNR. The pixel shift value I may also be changed based on information about the object OJ, such as the type and thickness of the object OJ. Furthermore, the pixel deviation value I may be changed depending on imaging conditions such as the output of the X-ray source 2, the moving speed V1 of the object OJ, and the inspection recipe. The pixel deviation value I may be set based on information obtained by imaging the object OJ. For example, a threshold value for SNR or CNR may be set, and the pixel deviation value I may be set using the threshold value.

[0063] As an example, when N=12, by setting the pixel shift value I to 2, it is possible to achieve substantially six-stage addition and double the resolution. By setting the pixel shift value I to 3, it is also possible to achieve substantially four-stage addition and triple the resolution. By setting the pixel shift value I to 4, it is also possible to achieve substantially three-stage addition and quadruple the resolution. By setting the pixel shift value I to 5, it is also possible to achieve substantially two-stage addition and five-times the resolution. In this case, there is a period of no exposure or a period of no use as data. By setting the pixel shift value I to 12 and adding one stage at a time, it is also possible to achieve twelve-times the resolution.

[0064] Generally, in an image sensor, pixel size (pixel size) is related to the saturation charge amount, and reducing the pixel size reduces the saturation charge amount. That is, there is a trade-off between the saturation charge amount and the resolution. In contrast, the X-ray image detection method of the embodiment can increase the resolution without reducing the pixel size, thereby achieving both the saturation charge amount and the resolution. Furthermore, in a CdTe detector, improving the energy discrimination performance tends to increase the pixel size. Therefore, it is difficult to reduce the pixel size while maintaining the energy discrimination performance. In contrast, the X-ray image acquisition device 4 of the embodiment can increase the resolution without reducing the pixel size, thereby achieving both. Furthermore, while it is difficult to reduce the pixel size of a SiPM compared to other sensors, the X-ray image acquisition device 4 of the embodiment can increase the resolution regardless of the pixel size. Therefore, it is possible to increase the resolution even when the pixel unit 10 is configured using a SiPM.

[0065] In the X-ray image acquisition device 4, the processing unit 22 processes output data, which are detection results from the N pixel units 11, so that output data that have passed through the same region of the object OJ are superimposed on each other, thereby generating an X-ray image having multiple pixel regions 30. In generating the X-ray image, the processing unit 22 may process the output data so that, among the output data constituting one pixel region 30, output data that differs from output data constituting a pixel region 30 adjacent to the one pixel region 30 is emphasized more than the output data other than the different output data (enhancement processing). Here, the adjacent pixel region 30 is the pixel region 30 adjacent to the one pixel region 30 on the side where the detection timing in the direction corresponding to the first direction X1 is earlier. When performing the enhancement processing, it is possible to increase the resolution of the X-ray image while suppressing a decrease in brightness of the X-ray image.

[0066] The X-ray image acquisition system 1 includes an X-ray image acquisition device 4, an X-ray source 2 that outputs X-rays, and a transport unit 3 that transports an object OJ along a first direction X1. For the reasons described above, the X-ray image acquisition system 1 can improve the degree of freedom in image acquisition and increase the resolution of acquired images. [Modification]

[0067] 25 and 26 are diagrams for explaining the operation of the first modified example. In the first modified example, the control unit 21 controls the detection of X-rays by the pixel units 10 so that each of the N pixel units 11 detects X-rays for a period shorter than the basic value (α+β) / V. That is, in the examples shown in FIGS. 8 and 9 , each pixel unit 11 detects X-rays throughout the entire frame, but as in the examples shown in FIGS. 25 and 26 , each pixel unit 11 may detect X-rays for, for example, half the entire frame. During periods when X-rays are not detected, electric charges generated in the pixel units 11 may be removed, for example, by an electronic shutter or the like.

[0068] As in the above embodiment, the first modification also improves the degree of freedom in image acquisition and increases the resolution of the acquired image. Furthermore, because each of the N pixel units 11 detects X-rays for a period shorter than the basic value (α + β) / V, the resolution of the X-ray image can be further increased.

[0069] 27 and 28 are diagrams for explaining the operation of the second modified example. In the second modified example, the control unit 21 controls the detection of X-rays by the pixel unit 10 so that each of the N pixel units 11 detects X-rays multiple times during one frame corresponding to the basic value (α+β) / V. That is, in the examples shown in FIGS. 8 and 9 , each pixel unit 11 detects X-rays once during one frame, but as in the examples shown in FIGS. 27 and 28 , each pixel unit 11 may detect X-rays twice during one frame. In the examples of FIGS. 27 and 28 , each pixel unit 11 detects X-rays twice during one frame, during a first detection period and a second detection period.

[0070] 29 to 31 are diagrams for explaining the addition process in the case of the second modified example. For example, as shown in FIG. 29, output data in a first detection period is added to generate first data E1, and as shown in FIG. 30, output data in a second detection period is added to generate second data E2. Then, as shown in FIG. 31, the first data E1 and the second data E2 are added to generate an X-ray image. Note that although the sign "-1" added to the end of each data is omitted in FIG. 29, each data shown in FIG. 29 is output data in the first detection period. Similarly, although the sign "-2" added to the end of each data is omitted in FIG. 30, each data shown in FIG. 30 is output data in the second detection period.

[0071] As with the above embodiment, the second modified example also makes it possible to improve the degree of freedom in image acquisition and increase the resolution of acquired images. Furthermore, since each of the N pixel units 11 detects X-rays multiple times during one frame corresponding to the basic value (α+β) / V, it is possible to increase the resolution of the X-ray image while suppressing a decrease in brightness of the X-ray image. Note that X-rays are not limited to being detected twice during one frame, and it is sufficient to detect X-rays n times (n is an integer equal to or greater than 2) during one frame, in which case the length of the detection period should be 1 / n or less of the basic value. [Additional Explanation]

[0072] The X-ray image acquisition method of the embodiment will be further described with reference to Figures 32 to 39. As shown in Figure 32, it is assumed that X-rays are acquired from an object OJ moving along a first direction X1 by the pixel unit 11. In this assumed example, the size of the pixel unit 11 is 0.4 mm x 0.4 mm, and the object OJ moves 0.4 mm during the imaging of one line.

[0073] As shown in FIG. 33 , the object OJ is virtually divided into blocks A to O, each measuring 0.1 mm, along the first direction X1. At the start of imaging, blocks A to D are imaged. After moving 0.1 mm, blocks B to E are imaged. After moving 0.2 mm, blocks C to F are imaged. After moving 0.3 mm, blocks D to G are imaged. After moving 0.4 mm, blocks E to H are imaged. This completes imaging of one line. The output data for the first line is 0.5A + 1.5B + ​​2.5C + 3.5D + 3.5E + 2.5F + 1.5G + 0.5H. Here, for example, 0.5A means that, if the data corresponding to the entire length of each block is one unit, half of that, or 0.5 units, of data from block A is included. The data from block A is 0.5 units because, as the object OJ moves, only data from half the area of ​​block A is acquired. The output data for the second line is 0.5E+1.5F+2.5G+3.5H+3.5I+2.5J+1.5K+0.5L.

[0074] Thus, the output data for the first line includes data from a 0.8 mm region of blocks A to H. As described above, this is the reason why blurring tends to reduce the resolution in the movement direction of the object OJ when acquiring an X-ray image. That is, the imaging range (movement amount of the object OJ per line) during the imaging period is determined by the movement speed of the object OJ and the width (pixel height) of the pixel unit 11. Therefore, transport blurring occurs in the first direction X1, which is the movement direction (transport direction), and the resolution in the first direction X1 tends to be lower than the resolution in the second direction X2.

[0075] Consider a case where an X-ray image is used to inspect the presence or absence of a foreign object in the object OJ. As shown in FIG. 34, if a foreign object is present in block D, the brightness contrast is relatively high. For example, if the transmittance (X-ray transmittance) of block D is 0% due to the presence of a foreign object and the transmittance of the other blocks is 100%, the brightness when a foreign object is present in block D is 78% of the brightness when no foreign object is present in the object OJ. That is, as described above, the output data for the first line is 0.5A + 1.5B + ​​2.5C + 3.5D + 3.5E + 2.5F + 1.5G + 0.5H. If the data corresponding to the entire length of each block is defined as one unit, 16 units of data are included. If the contribution of block D (3.5 units) is set to 0, 12.5 units of data are included, so 12.5 / 16 is approximately 78%.

[0076] On the other hand, if a foreign object is present in block G, the contrast will be relatively small. For example, if the transmittance of block G is 0% and the transmittance of the other blocks is 100%, the luminance when a foreign object is present in block G will be 90% of the luminance when no foreign object is present in object OJ (14.5 / 16 ≒ 91%). In this way, the detection results will vary depending on the imaging timing. Similarly, below, the luminance when a foreign object is present in a certain range will be expressed as a ratio to the luminance when no foreign object is present in object OJ.

[0077] As shown in Figure 35, if foreign matter is present in blocks B to E, and we consider the same thing as above, the brightness will be 31% (5 / 16 ≒ 31%). On the other hand, if foreign matter is present in blocks E to H, the brightness will be 50% (8 / 16 = 50%). As such, even if foreign matter of the same size is present, the detection result will vary depending on the imaging timing. More specifically, if a foreign matter is present across the boundary of the pixel area 11, the contrast will be reduced.

[0078] In contrast to this, in the X-ray image acquisition method of the above embodiment, when the pixel shift value I is set to an integer greater than or equal to 2 and less than or equal to N, the contrast can be increased by generating an X-ray image using X-ray output data from areas that are shifted from each other in the first direction X1 by 1 / I of the width of the pixel portion 11 in the object OJ.

[0079] 36 , consider a case where two pixel units 11 are arranged with a shift of ½ the width of the pixel units 11 from each other (½ pixel shift). This corresponds to the case where the pixel shift value I is 2 in the above embodiment. In this case, the output data for the first line of the first pixel unit 11 is 0.5A + 1.5B + ​​2.5C + 3.5D + 3.5E + 2.5F + 1.5G + 0.5H, and the output data for the first line of the second pixel unit 11 is 0.5C + 1.5D + 2.5E + 3.5F + 3.5G + 2.5H + 1.5I + 0.5J.

[0080] In the example of FIG. 36 , when a foreign substance is present in block G, the brightness is 84% ​​(27 / 32 ≒ 84%). As described above, the contrast is greater than the 90% brightness obtained when an image is captured using a single pixel unit 11. Also, in the example of FIG. 36 , when a foreign substance is present in blocks E to H, the brightness is 37.5% (12 / 32 = 37.5%). As described above, the contrast is greater than the 50% brightness obtained when an image is captured using a single pixel unit 11. Therefore, by setting the pixel deviation value I to an integer between 2 and N, foreign substances can be detected effectively.

[0081] As shown in FIG. 37 , instead of exposing (detecting) the entire frame, it is possible to perform exposure only for a portion of the frame. The example in FIG. 37 corresponds to the first modified example described above. In the example in FIG. 37 , if the object OJ moves 0.4 mm, exposure is performed during the 0.3 mm movement period, and no exposure is performed during the remaining 0.1 mm movement period. In this case, the output data for the first line is 0.5A + 1.5B + ​​2.5C + 3D + 2.5E + 1.5F + 0.5G. If a foreign object is present in block D, the luminance is 75%. If a foreign object is present in block G, the luminance is 96%. If a foreign object is present in blocks B to E, the luminance is 21%. If a foreign object is present in blocks E to H, the luminance is 63%.

[0082] In this case, too, as in the case where the pixel shift value I is set to an integer greater than or equal to 2 and less than or equal to N in the X-ray image acquisition method of the above embodiment, the contrast can be increased by generating an X-ray image using X-ray output data from areas that are shifted from each other in the first direction X1 by 1 / I of the width of the pixel portion 11 in the object OJ.

[0083] As shown in Fig. 38, consider a case in which two pixel units 11 are arranged so as to be shifted from each other by half the width of the pixel units 11, as in the case of Fig. 36. In this case, the output data for the first line of the first pixel unit 11 is 0.5A + 1.5B + ​​2.5C + 3D + 2.5E + 1.5F + 0.5G, and the output data for the first line of the second pixel unit 11 is 0.5C + 1.5D + 2.5E + 3F + 2.5G + 1.5H + 0.5I.

[0084] In the example of FIG. 38 , when a foreign substance is present in block G, the luminance is 88%. As described above, the contrast is greater than the 96% luminance obtained when an image is captured using a single pixel unit 11. Also, in the example of FIG. 38 , when a foreign substance is present in blocks E to H, the luminance is 58%. As described above, the contrast is greater than the 63% luminance obtained when an image is captured using a single pixel unit 11. Therefore, by setting the pixel deviation value I to an integer between 2 and N, it is possible to effectively detect foreign substances. In particular, the contrast can be more effectively increased when exposure is performed for only a portion of a frame.

[0085] 39 shows an example in which the pixel area 11 is rectangular, the length (width) of the pixel area 11 in the first direction X1 is 0.6 mm, and the length of the pixel area 11 in the second direction X2 is 0.4 mm, and the object OJ moves 0.4 mm during imaging of one line. In this case, the output data for the first line is 0.5A + 1.5B + ​​2.5C + 3.5D + 4E + 4F + 3.5G + 2.5H + 1.5I + 0.5J, and the output data for the second line is 0.5E + 1.5F + 2.5G + 3.5H + 4I + 4J + 3.5K + 2.5L + 1.5M + 0.5N. Thus, the data for the first line starts from block A, and the data for the second line starts from block E. When generating an X-ray image by setting the pixel shift value I to an integer between 2 and N, the data for the first line of the second pixel area 11 preferably starts from block C. Therefore, it is preferable to set the pixel shift amount based on the movement amount of the object OJ, rather than the size of the pixel portion 11. [Simulation Results]

[0086] FIG. 40 is a diagram illustrating the results of the first simulation. In the first simulation, the sample resolution chart shown on the left side of FIG. 40 was analyzed. "Target" is the target image, "Original Image" is the image before reconstruction, and "Reconstruction" is the image after reconstruction. The diagram in the upper right of FIG. 40 shows the luminance value profile of the image shown on the left side of FIG. 40 in the conveyance direction. As shown in the luminance value profile, in the target image, the left end is set to 0 pixel, and the width, i.e., period, of the lp (line pair) (pair of white and black lines) changes every 50 pixels. Note that in the graph shown in the upper right of FIG. 40, a predetermined offset value is added to the luminance value to make it easier to grasp the lower end of the amplitude. This also applies to the graphs shown in the upper right of FIGS. 41 and 43, which will be described later.

[0087] In this analysis, reconstruction was performed using the method described in Figures 7A and 7B of Patent Document 1. Specifically, two images acquired with a shift of 1 / 2 the pixel width were enlarged using the nearest neighbor method, and then the pixels were shifted and added together to reconstruct a single image. While Patent Document 1 enlarges images in two mutually orthogonal directions, in this analysis, the images were enlarged in only one direction (the transport direction) and added together. Note that this analysis does not take into account the effects of transport blur, scintillator blur, afterglow blur, shot noise, and readout noise.

[0088] The table in the lower right of Figure 40 shows normalized values ​​obtained by dividing the amplitude of the luminance value at each lp by the amplitude of the luminance value of the target image. As shown in the table, by performing reconstruction, the amplitude of the original image was 0.20 within a range of lp of 4 pixels, but in the reconstructed image it was 0.50. This shows that the resolution can be improved by reconstructing one image from two images acquired with a shift of 1 / 2 the pixel width from each other.

[0089] 41 is a diagram for explaining the results of the second simulation. The second simulation differs from the first simulation in that transport blur was taken into account in the analysis. As shown in the table on the lower right of FIG. 41, when transport blur was taken into account, the count value was lower than when transport blur was not taken into account, and the improvement rate of resolution was reduced.

[0090] Fig. 42 is a diagram for explaining shortening of the exposure period. Instead of exposing over the entirety of one frame as shown in Fig. 42(a), it is possible to perform exposure for only a part of one frame as shown in Fig. 42(b). This shortening of the exposure period corresponds to the first modified example (Figs. 25 and 26) described above and the example in Fig. 37.

[0091] Figure 43 is a diagram illustrating the results of the third simulation. The third simulation differs from the second simulation in that the exposure period was shortened by half. As shown in the table in the lower right of Figure 43, when the exposure period was shortened by half (half exposure), the amplitude was larger than when the exposure period was not shortened (normal exposure). This shows that the resolution can be improved by shortening the exposure period.

[0092] Fig. 44 is a diagram for explaining additional simulation results. The bottom of the table in Fig. 44 shows the simulation results when the exposure period is shortened to 1 / 4. It can be seen from the table in Fig. 44 that the resolution can be increased as the exposure period is shortened.

[0093] FIG. 45 is a diagram illustrating a modified example of shortening the exposure period. As shown in FIG. 45, in this modified example, each pixel unit 11 detects X-rays twice during one frame. This modified example corresponds to the second modified example ( FIGS. 27 to 31 ). In this modified example, as in the second modified example, output data for each of the two exposure periods is summed to generate summed data, and the two resulting summed data are further summed to generate an X-ray image. As described above, simply shortening the exposure period can suppress the effects of transport blur, but this may result in a decrease in brightness. However, in this modified example, the exposure time can be substantially lengthened, thereby suppressing the effects of transport blur while suppressing a decrease in brightness.

[0094] The present disclosure is not limited to the above-described embodiment and modified examples. In the above-described embodiment, the pixel deviation value I can be selected from integers between 1 and N, but the pixel deviation value I may be selected from integers between 2 and N. In other words, 1 may not be selectable as the pixel deviation value I, and normal TDI operation may be selected. That is, the control unit 21 may not be configured to be able to set the detection interval ΔT to a basic value. The pixel deviation value I does not necessarily have to be selectable from multiple values, and may be a fixed value (e.g., N).

[0095] In the above embodiment, the M pixel arrays 12 are arranged along the second direction X2 perpendicular to the first direction X1. However, the M pixel arrays 12 may be arranged along a direction intersecting the first direction X1 at an angle other than perpendicular to the first direction X1. In each pixel array 12, the N pixel units 11 may be arranged so as to be shifted from one another in the second direction X2 perpendicular to the first direction X1. In this case, it is possible to improve the resolution not only in the first direction X1 but also in the second direction X2.

[0096] 1...X-ray image acquisition system, 2...X-ray source, 10...pixel unit, 3...transport unit, 4...X-ray image acquisition device, 11...pixel unit, 12...pixel array, 21...control unit, 22...processing unit, 30...pixel area, I...pixel deviation value, OJ...object, V...reference speed, V1...movement speed, X1...first direction, X2...second direction, ΔT...detection interval.

Claims

1. An X-ray image acquisition device for acquiring an X-ray image of an object moving along a first direction, comprising: a pixel unit having M pixel arrays (M is an integer of 2 or more) each including N pixel units (N is an integer of 2 or more) for detecting X-rays, the N pixel units being aligned along the first direction and the M pixel arrays being aligned along a second direction intersecting the first direction; a control unit that controls the detection of the X-rays by the pixel unit; and a processing unit that generates the X-ray image of the object based on a result of the X-ray detection by the pixel unit, wherein the control unit controls the detection of the X-rays by the pixel unit such that the N pixel units in each of the M pixel arrays sequentially detect the X-rays at a predetermined detection interval, and wherein, when a basic value is a value obtained by dividing an arrangement pitch of the N pixel units in the first direction by a reference speed corresponding to a moving speed of the object along the first direction, the detection interval is a value obtained by dividing the basic value by a pixel deviation value which is an integer of 2 or more and N or less.

2. The X-ray image acquisition device according to claim 1, wherein the pixel shift value is selected from integers between 2 and N inclusive in response to an input.

3. The X-ray image acquisition device according to claim 1 or 2, wherein the control unit is configured to be able to set the detection interval to the basic value.

4. An X-ray image acquisition device as described in claim 1 or 2, wherein the control unit controls the detection of the X-rays by the pixel units so that each of the N pixel units detects the X-rays for a period shorter than the basic value.

5. An X-ray image acquisition device as described in claim 1 or 2, wherein the control unit controls the detection of the X-rays by the pixel units so that each of the N pixel units detects the X-rays multiple times during a detection period corresponding to the basic value.

6. The processing unit processes output data that is the detection result of the N pixel units so that the output data that have passed through the same region in the object are superimposed on each other to generate the X-ray image having a plurality of pixel regions, and when generating the X-ray image, the processing unit processes the output data so that, among the output data constituting one of the pixel regions, the output data that is different from the output data constituting the pixel region adjacent to the one pixel region is emphasized more than the output data other than the different output data, and the adjacent pixel region is the pixel region adjacent to the one pixel region on the front side in terms of the detection timing in the direction corresponding to the first direction. The X-ray image acquisition device of claim 1 or 2.

7. An X-ray image acquisition system comprising: an X-ray image acquisition device according to claim 1 or 2; an X-ray source that outputs the X-rays; and a transport unit that transports the object along the first direction.

8. A method for acquiring an X-ray image, comprising: a detection step of irradiating an object moving along a first direction with X-rays and detecting the X-rays transmitted through the object by a pixel unit; and a processing step of generating an X-ray image of the object based on a detection result in the detection step, wherein the pixel unit has M pixel arrays (M is an integer of 2 or more) each including N pixel portions (N is an integer of 2 or more) for detecting X-rays, the N pixel portions being aligned along the first direction, and the M pixel arrays being aligned along a second direction intersecting the first direction, and in the detection step, the N pixel portions in each of the M pixel arrays sequentially detect the X-rays at a predetermined detection interval, wherein a basic value is a value obtained by dividing an arrangement pitch of the N pixel portions in the first direction by a reference speed corresponding to a moving speed of the object along the first direction, and the detection interval is a value obtained by dividing the basic value by a pixel deviation value which is an integer of 2 or more and N or less.

Images