Imaging unit, radiation image acquisition system, and radiation image acquisition method

Abstract

This imaging unit comprises a housing having an incident window that allows radiation that has passed through an object to pass through, a scintillator having an input surface that inputs radiation that has passed through the incident window, and a line scan sensor having an imaging surface that captures scintillation light output from the input surface. The imaging unit further comprises a slit portion that is arranged between the incident window and the scintillator and forms a slit that guides the radiation that has passed through the incident window toward the input surface, and a 1x lens that is arranged between the scintillator and the line scan sensor and forms an image of scintillation light output from the input surface on the imaging surface of the line scan sensor.

Description

[Technical Field]

[0001] The present disclosure relates to an imaging unit, a radiation image acquisition system, and a radiation image acquisition method. [Background technology]

[0002] Conventionally, there is known a radiation detection device that includes a radiation source and a radiation detector, irradiates an object transported on a transport path disposed between the radiation source and the radiation detector with radiation, and converts the transmitted radiation into fluorescence (visible light) using a wavelength conversion member (see Patent Document 1). In this radiation detection device, the wavelength conversion member is supported by a support provided in a housing. The radiation that has transmitted through the object passes through an opening formed in a shielding member and is incident on the wavelength conversion member. The fluorescence emitted by the fluorescent layer of the wavelength conversion member passes through a light collecting body and is incident on the light receiving portion of the photoelectric conversion element. The radiation detector generates and outputs a two-dimensional radiation image signal of the object. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-141673 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional detectors described above, radiation passing through the aperture tends to spread. Therefore, the radiation irradiation range on the input surface of the wavelength conversion member (the substrate layer of the wavelength conversion member in the detector) becomes large, resulting in low resolution. In addition, the long working distance results in low sensitivity.

[0005] The present disclosure describes an imaging unit, a radiological image acquisition system, and a radiological image acquisition method that can improve resolution and sensitivity. [Means for solving the problem]

[0006] One aspect of the present disclosure is an imaging unit for acquiring a radiological image of an object being transported in a transport direction, comprising: a housing having an entrance window that allows radiation that has passed through the object to pass therethrough; a scintillator installed within the housing and having an input surface that inputs the radiation that has passed through the entrance window; a line scan sensor installed within the housing and having an imaging surface that images scintillation light output from the input surface; a slit member arranged between the entrance window and the scintillator and forming a slit that guides the radiation that has passed through the entrance window toward the input surface; and a 1:1 lens arranged between the scintillator and the line scan sensor that forms an image of the scintillation light output from the input surface on the imaging surface of the line scan sensor.

[0007] According to this imaging unit, radiation that has passed through an object passes through the entrance window of the housing and enters the housing. A slit member inside the housing guides the radiation toward the input surface of the scintillator. At this time, the slit in the slit member narrows (i.e., limits) the radiation irradiation area on the input surface of the scintillator. This improves resolution. A 1x1 lens used to form an image of scintillation light can shorten the working distance, thereby improving sensitivity. The 1x1 lens is, for example, positioned close to the input surface of the scintillator. Even in such cases, the influence of scattered radiation is reduced because the radiation irradiation area is narrowed by the slit.

[0008] The slit member may be positioned so that the slit is positioned in the normal direction to the input surface of the scintillator, and the 1:1 lens and line scan sensor may image and capture the scintillation light output in a direction inclined relative to the normal direction of the input surface. In this case, it is easy to place the 1:1 lens and line scan sensor close to the input surface. Desired imaging is possible from the viewpoints of improving resolution and sensitivity.

[0009] The slit member may be arranged so that the slit extends obliquely relative to the transport direction. Orienting the slit obliquely relative to the transport direction may increase the optical path of the radiation passing through the object, resulting in higher contrast in the acquired radiographic image.

[0010] The slit member may be arranged so that the slit is positioned in a direction inclined with respect to the normal direction of the input surface of the scintillator, and the 1:1 lens and the line scan sensor may form an image of the scintillation light output in a direction inclined with respect to the normal direction of the input surface. In this case, too, it is easy to bring the 1:1 lens and the line scan sensor close to the input surface.

[0011] The housing may have another entrance window that allows radiation transmitted through the object to pass therethrough, and the imaging unit may further include another slit member disposed between the other entrance window and the scintillator and forming another slit that guides the radiation that has passed through the other entrance window toward the input surface, the slit member and the other slit member being disposed so that the slit and the other slit respectively guide radiation from two different directions relative to the input surface of the scintillator. Radiation images based on radiation guided (incident) from the two different directions will be different images based on the difference in angle. This can improve the accuracy of various inspections. For example, by using a mechanical shutter in combination, two types of images can be acquired in a single imaging session, thereby shortening the inspection time.

[0012] The imaging unit may further include a cover member that holds the slit member and is detachably attached to the housing. By preparing multiple combinations of the cover member and the slit member held by the cover member and exchanging them as needed, the incident direction (incident angle) of radiation with respect to the input surface of the scintillator can be easily changed. For example, by changing the incident direction of radiation and performing multiple imaging operations, the accuracy of various inspections can be improved.

[0013] The slit member may be configured so that the width of the slit in the transport direction narrows as it approaches the input surface of the scintillator. In this case, the entrance portion of the slit can be widened, making it possible to change the incident direction (incident angle) of the radiation with respect to the input surface of the scintillator or to guide the radiation to the input surface in multiple incident directions.

[0014] The slit member, the 1:1 lens, and the line scan sensor may be rotatable within the housing around an axis extending along the input surface. In this case, the incident direction (incident angle) of the radiation with respect to the input surface of the scintillator can be easily changed. For example, by changing the incident direction of the radiation and performing multiple images, the accuracy of various inspections can be improved.

[0015] As another aspect of the present disclosure, there may be provided a radiological image acquisition system for acquiring a radiological image of an object, the radiological image acquisition system including: a radiation source that outputs radiation toward the object; a conveying device that conveys the object in a conveying direction and allows the radiation to pass therethrough; and any one of the imaging units described above, which is installed so that the radiation source and the entrance window are arranged on the same plane. With this radiological image acquisition system, the above-mentioned effects enable improvement in resolution and further improvement in sensitivity.

[0016] In the radiographic image acquisition system, the slit members of the conveying device and the imaging unit may be arranged so that the slit extends obliquely with respect to the conveying direction. Orienting the slit obliquely with respect to the conveying direction can lengthen the optical path of the radiation passing through the object. As a result, the contrast of the acquired radiographic image can be increased.

[0017] Yet another aspect of the present disclosure is a radiological image acquisition method for acquiring a radiological image of an object, the method including: a radiation output step of outputting radiation toward the object being transported in a transport direction; a radiation introduction step of allowing the radiation that has passed through the object to enter a housing through an entrance window and guiding the radiation toward an input surface of a scintillator through a slit formed in the housing; a scintillation light output step of inputting the radiation that has passed through the entrance window to the input surface of the scintillator, converting the input radiation into scintillation light, and outputting the scintillation light from the input surface; a scintillation light imaging step of forming an image of the scintillation light output from the input surface on an imaging surface of a line scan sensor using a 1:1 lens; and a scintillation light imaging step of imaging the scintillation light on the imaging surface of the line scan sensor.

[0018] According to this radiographic image acquisition method, radiation that has passed through the object passes through the entrance window of the housing and enters the housing. A slit member inside the housing guides the radiation toward the input surface of the scintillator. At this time, the slit of the slit member narrows (i.e., limits) the radiation irradiation area on the input surface of the scintillator. This improves resolution. The 1x1 lens used in the scintillation light imaging process can shorten the working distance, thereby improving sensitivity. The 1x1 lens is, for example, positioned close to the input surface of the scintillator. Even in such cases, the influence of scattered radiation is reduced because the radiation irradiation area is narrowed by the slit in the radiation introduction process.

[0019] In the radiation output step, the object is transported multiple times in the transport direction, and radiation is output toward the object from multiple different directions during the multiple transports. In the radiation introduction step, radiation is guided from multiple directions toward the input surface of the scintillator during the multiple transports. The radiation image acquisition method may further include an image processing step that performs image processing on the multiple captured images obtained in the scintillation light imaging step. Radiation images based on radiation guided (incident) from multiple directions will be different images based on differences in angle. This can improve the accuracy of various inspections. [Effects of the Invention]

[0020] According to some aspects of the present disclosure, resolution can be improved and, furthermore, sensitivity can be improved. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a perspective view showing a radiation image acquisition system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram showing a schematic configuration of the radiation image acquisition system shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the internal configuration of the imaging unit in FIG. [Figure 4] FIG. 4 is a diagram showing the arrangement of each part in the radiation image acquisition system of FIG. [Figure 5] 5(a) and 5(b) are diagrams showing the arrangement of each part in various modified examples of the radiation image acquisition system. [Figure 6] 6(a) and 6(b) are diagrams illustrating differences in the angle of incidence of radiation on an object. [Figure 7] 7(a) to 7(c) are diagrams showing the arrangement of each part in various modified examples of the radiation image acquisition system. [Figure 8] 8(a) and 8(b) are diagrams showing the internal configurations of various modified examples of the radiation image acquisition system. [Figure 9]9(a) and 9(b) are diagrams showing the internal configurations of various modified examples of the radiation image acquisition system. [Figure 10] 10(a) to 10(c) are diagrams showing the procedure for irradiating and capturing images from multiple directions. [Figure 11] FIG. 11 is a diagram showing the arrangement of each part in a modified example of the radiation image acquisition system. [Figure 12] FIG. 12 is a diagram showing the arrangement of each part in a modified example of the radiation image acquisition system. [Figure 13] FIG. 13 is a cross-sectional view showing an example of the internal configuration of an imaging unit corresponding to the modified example of FIG. [Figure 14] FIG. 14 is an enlarged cross-sectional view of a part of FIG. [Figure 15] 15(a) and 15(b) are diagrams showing the difference in the irradiation area and the imaging area depending on whether or not there is a slit member. [Figure 16] FIG. 16 is a table showing the measurement results of the radiation scattering test. [Figure 17] 17(a) to 17(c) are radiation images obtained in an imaging test using the sample. [Figure 18] 18(a) and 18(b) are radiographic images obtained in an imaging test using the sample. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, each drawing is created for explanatory purposes and is drawn to particularly emphasize the portions to be described. Therefore, the dimensional proportions of each component in the drawings do not necessarily correspond to the actual ones.

[0023] As shown in FIGS. 1 and 2 , a radiographic image acquisition system 1 according to one embodiment is an apparatus for acquiring a radiographic image of an object A. The radiographic image acquisition system 1 is a non-destructive inspection system capable of inspecting the object A without disassembling or destroying it. The object A contains, for example, a substance made of light elements. The radiographic image acquisition system 1 is applicable, for example, to fields such as food inspection, battery inspection, and electronic component inspection. In the field of food inspection, for example, sealed containers and packaging are inspected for the presence or absence of foreign objects trapped inside. The radiographic image acquisition system 1 is particularly excellent in the ability to discriminate substances made of light elements. Examples of such substances include food scraps, hair, plastic, insects, and bones in meat. The radiographic image acquisition system 1 is applicable, for example, to in-line X-ray inspection.

[0024] The radiation image acquisition system 1 includes a radiation source 2 that outputs radiation such as white X-rays toward an object A, a conveying device 20 that conveys the object A in a predetermined conveying direction D, a scintillator 6 that generates scintillation light in response to input radiation that has passed through the object A conveyed by the conveying device 20, a line scan sensor 3 that detects the scintillation light output from a radiation input surface 6a of the scintillator 6, and a computer 10 that controls several functions of the radiation image acquisition system 1 and creates radiation images. As described above, the radiation image acquisition system 1 is an X-ray imaging system that uses a scintillator surface observation method. The radiation image acquisition system 1 has excellent sensitivity to low-energy X-rays.

[0025] The radiation source 2 outputs a cone beam X-ray from an X-ray emission section. The radiation source 2 has a focal point 2a of the cone beam X-ray. The radiation source 2 may be, for example, a microfocus X-ray source or a millifocus X-ray source. The X-rays emitted from the radiation source 2 form a radiation flux. The radiation image acquisition system 1 is provided with a radiation source-side slit member 26 and a slit member 16 (see FIG. 2 ), so that the X-rays in an irradiation region 12, narrowed to a limited portion of the X-rays in the output region where the radiation flux exists, are input to the input surface 6a of the scintillator 6. The irradiation region 12 extends in a triangular (or fan) shape toward the scintillator 6 in the housing 15 of the imaging unit 30.

[0026] The conveying device 20 has, for example, two belt conveyors 21, 21 that move along a circular orbit, and the object A is placed or held on the conveying surface 21a of the belt conveyor 21. The belt conveyor 21 is a conveying stage or a conveying unit. The conveying device 20 is equipped with a driving source (not shown) that drives each belt conveyor 21. The conveying device 20 is configured to convey the object A at a constant speed in a conveying direction D. In this embodiment, the conveying direction D is horizontal. Between the two belt conveyors 21, 21, a gap C that allows X-rays to pass is provided at a position corresponding to the above-mentioned irradiation area 12. The gap C has a small, constant length (width) in the conveying direction D and extends straight in a horizontal detection width direction perpendicular to the conveying direction D. The conveying timing and conveying speed of the object A in the conveying device 20 are preset and controlled by the control unit 10a of the computer 10. The belt conveyor 21 does not need to have the gap C that allows X-rays to pass through, and the belt member of the belt conveyor 21 may be made of a radiotransparent material.

[0027] The radiological image acquisition system 1 can accommodate any type of conveying device 20. For example, the conveying direction D may be horizontal or may be inclined relative to the horizontal. The conveying direction D does not have to be linear, and may be, for example, curved. In this case, the conveying direction D may be a tangent to the conveying path of the object A at a portion that overlaps with the irradiation area 12. The conveying device 20 does not need to have a physical conveying surface 21a. For example, the conveying device 20 may convey the object A in a floating state using air. The conveying device 20 may also convey the object A by releasing it into the air. In this case, the conveying path of the object A may be, for example, parabolic.

[0028] The transport device 20 is not limited to a configuration having a belt conveyor 21. The transport device 20 may have, for example, a roller conveyor including multiple rollers. Because a roller conveyor does not have a belt, the influence of the belt can be eliminated. Another advantage over a belt conveyor is that gaps (slit-shaped openings) are formed between the rollers. Using a roller conveyor reduces X-ray attenuation caused by the belt. Considering the arrangement of the radiation source 2 and the arrangement of the irradiation area 12 (oblique irradiation), which will be described later, a roller conveyor can be effectively used. A roller conveyor is a transport means suitable for a radiological image acquisition system 1 in which sensitivity to low-energy X-rays is important. According to a configuration in which two or more belt conveyors are installed in the transport direction and X-rays are irradiated through the gap C between the belt conveyors, as in the present embodiment, the influence of the belt can be eliminated while using the belt conveyor 21.

[0029] As shown in FIGS. 1 to 3, the radiation image acquisition system 1 includes an imaging unit 30 installed along the conveying device 20. The imaging unit 30 is, for example, attached to the conveying device 20 and fixed to the conveying device 20. The imaging unit 30 may be attached to something other than the conveying device 20. The imaging unit 30 may be placed on a stand or the like. The imaging unit 30 is attached so as not to interfere with the rotation of the belt conveyor 21. The same applies when the conveying device 20 is a roller conveyor. The imaging unit 30 is arranged with a certain gap from the conveying part such as a belt conveyor or roller conveyor so as not to interfere with the movement of the conveying part.

[0030] The imaging unit 30 has a rectangular parallelepiped housing 15. The housing 15 has a rectangular parallelepiped housing main body 13 made of, for example, aluminum, and a lead cover 14 covering the outer surface (outer periphery) of the housing main body 13. The housing main body 13 houses each component of the imaging unit 30 in an internal space 15S. The lead cover 14 shields against radiation from outside the housing main body 13 so that it does not affect the internal space 15S of the imaging unit 30. The lead cover 14 may be disposed on the outside or inside of the housing 15. Another cover may be attached to the outside of the lead cover 14. From the standpoint of lead strength and ease of handling, it is preferable that another material be attached to the outside of the lead. The cover may be made of a material other than lead, such as tungsten, iron, stainless steel, or copper. Alternatively, a rubber-like material or a sheet-like material in which a heavy metal such as tungsten is contained in rubber (resin) may be used.

[0031] The housing body 13 is made of a material that can block X-rays, for example. The housing body 13 may be made of iron, stainless steel, or the like. The housing body 13 may include a protective material, which may be lead, tungsten, or copper. Alternatively, a rubber-like material or a sheet-like material containing a heavy metal such as tungsten in rubber (resin) may be used. The housing body 13 includes a top wall portion 13a and a bottom wall portion 13d that face each other in the vertical direction, a pair of first side walls 13b that face each other in the transport direction D, and a pair of second side walls 13c that face each other in a horizontal detection width direction perpendicular to the transport direction D. The imaging unit 30 is very small in size in the transport direction D of the housing body 13, resulting in a compact device. The transport direction D is parallel to the x direction parallel to the paper surface shown in the figure. The detection width direction is parallel to the y direction perpendicular to the paper surface shown in the figure. The up-down direction is parallel to the z direction parallel to the paper surface shown in the figure.

[0032] The upper wall portion 13a is disposed to face the conveying device 20. A top plate portion 14a of the lead cover 14 is attached to the upper wall portion 13a at a distance from the upper wall portion 13a. The top plate portion 14a is disposed parallel to the upper wall portion 13a. An aluminum support plate portion 13e is provided between the upper wall portion 13a and the top plate portion 14a to support a slit member 16 (described later). Note that the support plate portion 13e for supporting the slit member 16 may be made of metal such as stainless steel or iron. A pair of first side plate portions 14b of the lead cover 14 are attached to the outer surfaces of the pair of first side wall portions 13b. A pair of second side plate portions (not shown) of the lead cover 14 are attached to the outer surfaces of the pair of second side wall portions 13c. The lead cover 14 covers the entire surface of the housing main body 13 except for the bottom wall portion 13d. Note that the first side plate portion 14b is not shown in FIG. 1.

[0033] An entrance window 14f is formed in the top plate portion 14a of the lead cover 14 to allow X-rays transmitted through the object A to pass therethrough. The entrance window 14f has a small, constant length (width) in the x direction and extends straight in the y direction. The length of the entrance window 14f in the x direction may be determined by the width of the slit S in the slit member 16 (described later) or the width of the desired irradiation area 12 (thickness in the conveying direction D). The length of the entrance window 14f in the x direction is constant in the detection width direction (y direction) and the thickness direction (z direction) of the top plate portion 14a.

[0034] A through-hole 13g (see FIG. 3) having a constant length (width) in the x-direction and extending straight in the y-direction is formed in the support plate portion 13e at a position corresponding to the entrance window 14f. A slit member 16 for defining the irradiation area 12 is disposed and fixed in the through-hole 13g. The slit member 16 includes a first slit plate 17 and a second slit plate 18 that face each other with a small constant gap in the x-direction. The first slit plate 17 and the second slit plate 18 are made of, for example, copper. The gap between the first slit plate 17 and the second slit plate 18 is the width of the slit S formed by the slit member 16, which is equal to, for example, the length (width) of the entrance window 14f in the x-direction. The width of the slit S may be slightly different from the length (width) of the entrance window 14f in the x-direction. The upper end 16a of the slit member 16 is inserted into the through-hole 13g of the support plate portion 13e, and the upper end 16a is fixed to the support plate portion 13e. The support plate portion 13e supports the slit member 16 so that the slit S is continuous with the entrance window 14f. That is, the entrance end Sa of the slit S is directly connected to the entrance window 14f (for example, without a gap). Both ends of the first slit plate 17 and the second slit plate 18 in the y direction may be open or may be closed by another copper plate or the like.

[0035] The slit member 16 is installed in the housing 15. The slit member 16 is disposed between the entrance window 14f and the scintillator 6. The slit member 16 is inserted through an opening 13f formed in the upper wall portion 13a and hangs down toward the internal space 15S. The slit member 16 extends to the vicinity of the input surface 6a of the scintillator 6. The arrangement of the slit member 16 and the positional relationship between the slit member 16 and the scintillator 6 will be described later. Note that, for example, if the top plate portion 14a is not provided, the upper end of the slit member 16 may be exposed on the top surface of the housing 15 or may protrude upward from the housing 15. In that case, the upper end of the slit member 16 also serves as the entrance window.

[0036] As shown in FIGS. 1 and 2 , a radiation source-side slit member 26 that restricts the irradiation area 12 is provided for the radiation source 2. The radiation source-side slit member 26 has, for example, a pair of triangular copper plates. The pair of triangular copper plates face each other at a certain distance in the x direction to form a slit. Both ends of the radiation source-side slit member 26 in the y direction are closed, for example, by another copper plate. In the radiographic image acquisition system 1, the focal point 2a of the radiation source 2, the slit of the radiation source-side slit member 26, the gap C of the transport device 20, the entrance window 14f, and the slit S of the slit member 16 are installed so that they are all aligned on the same plane. These members restrict (limit) the X-ray irradiation area 12, so that only a portion of the X-rays output from the radiation source 2 pass through the object A and reach the input surface 6a of the scintillator 6. The irradiation region 12 is a quadrangular pyramidal region having a slight thickness in the x direction and defined by the inner circumferential surface of the radiation source side slit member 26, the inner wall surface of the entrance window 14f, and the inner wall surface of the slit member 16, for example.

[0037] As shown in Figures 2 and 3, the slit member 16 guides X-rays that have passed through the entrance window 14f toward the input surface 6a of the scintillator 6 through the slit S. The slit member 16 prevents X-rays from scattering in the internal space 15S of the housing 15. The input surface 6a of the scintillator 6 inputs X-rays that have passed through the slit member 16 and are within the irradiation area 12. Note that the "input surface 6a of the scintillator 6" refers only to the area that effectively contributes to the output of scintillation light. For example, the area of ​​the entire rectangular input surface 6a that is covered by the scintillator holder is not included in the "input surface 6a of the scintillator 6."

[0038] In the radiation image acquisition system 1, the imaging unit 30 is configured to capture an image of scintillation light output from the input surface 6a of the scintillator 6 in a direction inclined relative to the input surface 6a. The scintillator 6, the line scan sensor 3, and the equal-magnification lens 7 are installed within the housing 15. Furthermore, a shielding member 9 is attached between the line scan sensor 3 and the equal-magnification lens 7. The line scan sensor 3, the shielding member 9, and the equal-magnification lens 7 are integrated together. The line scan sensor 3, the shielding member 9, and the equal-magnification lens 7 are held by a bracket or the like (not shown) in the internal space 15S.

[0039] The scintillator 6 is held by, for example, a scintillator holder (not shown) and is arranged, for example, horizontally. The scintillator 6 is a flat wavelength conversion member. The scintillator 6 has a rectangular shape that is long in the detection width direction (y direction) (see FIG. 1). The scintillator 6 is made of, for example, Gd2O2S:Tb, Gd2O2S:Pr, CsI:Tl, CdWO4, CaWO4, Gd2SiO5:Ce, Lu 0.4 Gd 1.6 SiO5, Bi4Ge3O 12, Lu2SiO5:Ce, Y2SiO5, YAlO3:Ce, Y2O2S:Tb, YTaO4:Tm, YAG:Ce, YAG:Pr, YGAG:Ce, YGAG:Pr, GAGG:Ce, etc. The thickness of the scintillator 6 is set to an appropriate value depending on the energy band of the radiation to be detected, ranging from several μm to several mm. The scintillator 6 converts X-rays that have passed through the object A into visible light. X-rays with relatively low energy are converted at the input surface 6a of the scintillator 6 and output from the input surface 6a.

[0040] The line scan sensor 3 captures images of the object A as it moves and outputs radiation image data, which is one-dimensional image data. The line scan sensor 3 has an imaging surface 3a that captures the scintillation light output from the input surface 6a of the scintillator 6. The line scan sensor 3 is, for example, a general line sensor, a multi-line sensor, or an area image sensor capable of TDI (time delay integration) drive. The line scan sensor 3 is, for example, a CCD image sensor or a CMOS image sensor. The line scan sensor 3 has a configuration in which multiple light receiving elements, each arranged in a line in the pixel direction, are arranged in one or more rows in the column direction corresponding to the movement direction of the object A. The line scan sensor 3 has a scan direction corresponding to the transport direction D of the object A and a line direction perpendicular to the scan direction. This line direction is the pixel direction and is parallel to the y direction in FIG. 2. The scan direction corresponds to the column direction and is parallel to the z direction in FIG. 2. In the case of an area image sensor capable of TDI drive, the column direction is the same as the integration direction.

[0041] The line scan sensor 3 captures an image of the object A in accordance with the movement of the object A under the control of the control unit 10a. That is, the line scan sensor 3 captures an image on the imaging surface 3a in synchronization with the movement of the object A by the conveying device 20, and outputs radiation image data. This makes it possible to obtain a radiation image with a good S / N ratio. Note that, in order to synchronize the movement of the object A by the stage with the imaging by the line scan sensor, an encoder may be provided on the stage, and the line scan sensor 3 may be controlled by a signal from the encoder.

[0042] The scintillator 6 of this embodiment is disposed so that the input surface 6a is parallel to the transport direction D and the line direction. That is, the input surface 6a of the scintillator 6 is parallel to the xy plane.

[0043] The equal-magnification lens 7 is disposed between the scintillator 6 and the line scan sensor 3 and forms an image of the scintillation light output from the input surface 6a on the imaging surface 3a of the line scan sensor 3. The equal-magnification lens 7 has a magnification of 1x and can be realized, for example, by a gradient index lens (GRIN lens), a rod lens, or a rod lens array. The equal-magnification lens 7 is focused on the input surface 6a of the scintillator 6. Because the equal-magnification lens 7 has a deep depth of field, there is little out-of-focus blur even when imaging a phosphor at an oblique angle, which is advantageous for oblique imaging such as that of this embodiment. Furthermore, the equal-magnification lens 7 increases the degree of freedom in the arrangement and combination of the radiation source 2, object A, and line scan sensor 3.

[0044] The shielding member 9 is a radiation-shielding member that transmits scintillation light generated by the scintillator 6 and focused by the 1x1 lens 7, and blocks X-rays. The shielding member 9 is made of, for example, lead-containing glass, lead-free radiation-shielding glass containing heavy elements such as Sr, Ba, Ti, B, W, Si, Gd, and Zr, an FOP (fiber optic plate), or a radiation-shielding resin. The shielding member 9 is attached to the surface (surface of the protective resin) of the line scan sensor 3. The shielding member 9 reduces the effects of scattered X-rays.

[0045] As shown in Fig. 3, in the imaging unit 30 of the radiation image acquisition system 1, the slit member 16 is arranged so that the slit S is positioned in the direction of the normal B of the input surface 6a of the scintillator 6. The equal-magnification lens 7, the shielding member 9, and the line scan sensor 3 are arranged in a direction inclined with respect to the direction of the normal B of the input surface 6a. The equal-magnification lens 7 forms an image on the imaging surface 3a of the scintillation light output in a direction inclined with respect to the direction of the normal B of the input surface 6a. The line scan sensor 3 images the scintillation light output in a direction inclined with respect to the direction of the normal B of the input surface 6a.

[0046] The exit end Sb of the slit S formed by the slit member 16 is close to the input surface 6a of the scintillator 6. The tip surface 7a of the 1:1 magnification lens 7 is close to the input surface 6a of the scintillator 6. In the imaging unit 30, the slit member 16 and the 1:1 magnification lens 7 are arranged so that they are as close as possible to the input surface 6a of the scintillator 6. The slit member 16 extends to a position close to the input surface 6a of the scintillator 6, but not so close that it interferes with the imaging of scintillation light by the line scan sensor 3 and the 1:1 magnification lens 7. The distance from the exit end Sb of the slit S to the input surface 6a of the scintillator 6 is preferably, for example, less than 20 mm. The shorter the distance from the exit end Sb of the slit S to the input surface 6a of the scintillator 6, the better, and it is even more preferable if it is less than 5 mm. The lower ends of the two slit plates do not need to be aligned, and the distance from the scintillator to the slit plate on the 1x1 lens 7 side (first slit plate) and the slit plate on the opposite side (second slit plate) may be different.

[0047] The 1:1 lens 7 is positioned so that its tip surface 7a faces the irradiation area 12 on the scintillator 6 (see Figure 15(a)) and is close to the irradiation area 12, so as not to interfere with the scintillator 6 and the slit member 16.

[0048] The computer 10 includes, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and an input / output interface. The computer 10 includes a control unit 10a (control processor) that controls the radiation source 2 and the line scan sensor 3, and an image processing unit 10b (image processor) that creates a radiographic image of the object A based on the radiographic image data output from the line scan sensor 3. The image processing unit 10b receives the radiographic image data and performs predetermined processing, such as image processing, on the received radiographic image data. A display device 11 is connected to the computer 10. The image processing unit 10b outputs the created radiographic image to the display device 11. The control unit 10a controls the radiation source 2 based on values ​​of the tube voltage and tube current of the radiation source 2 that are stored based on user input or the like. The control unit 10a controls the line scan sensor 3 based on the exposure time of the line scan sensor 3 that are stored based on user input or the like. The control unit 10a and the image processing unit 10b may be separate processors or may be the same processor. The computer 10 may be programmed to execute the functions of the control unit 10a and the image processing unit 10b. The computer 10 may be configured with a microcomputer or an FPGA (Field-Programmable Gate Array).

[0049] Next, the operation of the radiation image acquisition system 1, i.e., the method for acquiring a radiation image, will be described. First, the object A is transported in the transport direction D using the transport device 20 (transport step). At the same time, radiation such as white X-rays is output from the radiation source 2 toward the object A (radiation output step). Next, the radiation that has passed through the object A is made to enter the housing 15 through the entrance window 14f and is guided toward the input surface 6a of the scintillator 6 via a slit S formed in the housing 15 (radiation introduction step). The radiation that has passed through the object A is input to the input surface 6a, where it is converted into scintillation light by the scintillator 6, and the scintillation light is output from the input surface 6a (scintillation light output step). The scintillation light output from the input surface 6a is then imaged on the imaging surface 3a of the line scan sensor 3 by the 1:1 lens 7 (scintillation light imaging step). Furthermore, the scintillation light is imaged on the imaging surface 3a of the line scan sensor 3 (scintillation light imaging step). The line scan sensor 3 outputs radiation image data obtained by imaging to the image processing unit 10b of the computer 10.

[0050] The image processing unit 10b of the computer 10 receives the radiation image data and performs predetermined processing such as image processing on the received radiation image data to create a radiation image (image creation step). The image processing unit 10b outputs the created radiation image to the display device 11. The display device 11 displays the radiation image output from the image processing unit 10b. Through the above steps, a radiation image obtained by observing the surface of the object A is obtained.

[0051] According to the imaging unit 30, radiological image acquisition system 1, and radiological image acquisition method of this embodiment, radiation transmitted through the object A passes through the entrance window 14f of the housing 15 and enters the housing 15. The slit member 16 in the housing 15 guides the radiation toward the input surface 6a of the scintillator 6. At this time, the slit S of the slit member 16 narrows (i.e., limits) the radiation irradiation area 12 on the input surface 6a of the scintillator 6. FIG. 15(a) shows the irradiation area 12 when the slit member 16 is provided, and FIG. 15(b) shows the irradiation area 12 when the slit member 16 is not provided. As is clear from FIGS. 15(a) and 15(b), the irradiation area 12 on the input surface 6a of the scintillator 6 is limited to a narrower area by providing the slit member 16. Therefore, the imaging area formed by the 1:1 lens 7 is also narrow, similar to the irradiation area 12 shown in FIG. 15(a). If the radiation irradiation area 12 on the input surface 6a of the scintillator 6 is wide, the fluorescence emitted on the scintillator 6 crosstalks (mixes), resulting in a decrease in resolution. Furthermore, the resolution also decreases due to the effects of scattered radiation. Narrowing the radiation irradiation area 12 can prevent the resolution from decreasing due to crosstalk and scattered radiation. Therefore, narrowing the irradiation area 12 in this manner can improve the resolution. The 1:1 magnification lens 7 used in the scintillation light imaging process can shorten the working distance, thereby improving sensitivity. The 1:1 magnification lens 7 is positioned close to the input surface 6a of the scintillator 6. Even in such cases, the radiation irradiation area 12 is narrowed by the slit S during the radiation introduction process, reducing the effects of scattered radiation. The slit member 16 also serves the purpose of preventing exposure to the line scan sensor 3 and the 1:1 magnification lens 7. The installation of the slit member 16 and the 1:1 magnification lens 7 in the imaging unit 30 contributes to a compact unit.

[0052] As shown in Figure 4, the slit member 16 is positioned so that the slit S is positioned in the direction of the normal B to the input surface 6a of the scintillator 6, and the 1:1 lens 7 and line scan sensor 3 form an image of the scintillation light output in a direction inclined with respect to the direction of the normal B to the input surface 6a, and capture an image. This configuration makes it easy to place the 1:1 lens 7 and line scan sensor 3 close to the input surface 6a. Desired imaging is possible from the standpoints of improving resolution and sensitivity.

[0053] Furthermore, since the shielding member 9 is attached to the line scan sensor 3, the effect of suppressing scattered X-rays is achieved. FIG. 16 is a table showing the measurement results of a radiation scattering test. In this test, a lead cover 14 was installed around the housing main body 13, including the vicinity of the entrance window 14f. The number of pixels of scattered X-rays was measured in Examples 1 and 2, which were provided with a copper plate slit portion having a configuration similar to that of the slit member 16, and in a comparative example, which did not have a copper plate slit portion. As shown in FIG. 16, the proportion of scattered X-rays was reduced in Examples 1 and 2 compared to the comparative example, confirming the effect of the copper plate slit portion in reducing X-ray scattering. Furthermore, a difference in the proportion of scattered X-rays was confirmed between Example 1, which was provided with the shielding member 9, and Example 2, which did not have the shielding member 9. It was confirmed that the proportion of scattered X-rays was further reduced by providing the shielding member 9.

[0054] The radiation image acquisition system and imaging unit of the present disclosure may adopt various modified forms in addition to the forms shown in Figures 2 to 4. The modified forms of the present disclosure will be described below with reference to the respective drawings. Note that although the shielding member 9 is not shown in the following description, the shielding member 9 may be provided in any of the modified forms, similar to the imaging unit 30.

[0055] For example, as shown in FIG. 5(a), the slit member 16 may be disposed so that the slit S extends obliquely with respect to the transport direction D. In this radiographic image acquisition system 1A and imaging unit 30A, the slit member 16 is disposed so that the slit S is positioned in a direction oblique to the normal B of the input surface 6a of the scintillator 6, and the equal-magnification lens 7 and line scan sensor 3 form an image of the scintillation light output in the direction of the normal B of the input surface 6a and capture an image. As shown in FIGS. 6(a) and 6(b), by orienting the slit S obliquely with respect to the transport direction D, the optical path of the radiation passing through the object A can be lengthened. Assuming that the object A has a certain thickness (thickness in the direction perpendicular to the transport surface 21a), the optical path length Lb shown in FIG. 6(b) is longer than the optical path length La shown in FIG. 6(a). As a result, the contrast of the acquired radiographic image is increased.

[0056] 5(b), the slit member 16 may be arranged so that the slit S extends obliquely with respect to the transport direction D. In this radiological image acquisition system 1B and imaging unit 30B, the slit member 16 is arranged so that the slit S is positioned in a direction oblique to the normal B of the input surface 6a of the scintillator 6, and the equal-magnification lens 7 and line scan sensor 3 also form an image of the scintillation light output in a direction oblique to the normal B of the input surface 6a and capture an image. Even in this case, the contrast of the acquired radiological image is increased.

[0057] 17(a) to 17(c) show the results of a test to check whether or not a foreign object F (such as a hair) was caught in the sealed portion of a plastic bag containing sweets. As shown in the image of FIG. 17(a), when the slit member 16 was not provided, the foreign object F was not visible. However, as shown in the image of FIG. 17(b), when the slit member 16 was provided and X-rays were irradiated perpendicularly as shown in FIG. 4, the foreign object F was confirmed. Furthermore, as shown in the image of FIG. 17(c), when the slit member 16 was provided and X-rays were irradiated obliquely as shown in FIG. 5, the foreign object F was also confirmed. Note that in the images of FIGS. 17(b) and 17(c), the contrast in the images became clearer when the tube voltage of the radiation source 2 was reduced to 25 kV and the tube current was increased to 25 mA (100 kV and 15 mA, respectively, in FIG. 17(a)).

[0058] Figures 18(a) and 18(b) show the results of a test to check for the presence of foreign matter in the sealed portion of a plastic bag containing candy. As shown in the image of Figure 18(a), when a slit member 16 was provided and X-rays were irradiated perpendicularly as shown in Figure 4, a large packaging bag P1 and a small packaging bag P2 (the candy inside is shown in black) contained therein were confirmed. Furthermore, as shown in the image of Figure 18(b), when a slit member 16 was provided and X-rays were irradiated obliquely as shown in Figure 5, unevenness was confirmed in the large packaging bag P1, the small packaging bag P2 contained therein, and the sealed portion P3 of the larger packaging bag P1.

[0059] As shown in FIG. 7( a), the slit member 16 may be disposed so that the slit S extends obliquely with respect to the transport direction D. In this radiological image acquisition system 1C and imaging unit 30C, the transport direction D is inclined with respect to the input surface 6a of the scintillator 6. The slit member 16 is disposed so that the slit S is positioned in the direction of the normal B to the input surface 6a of the scintillator 6, and the equal-magnification lens 7 and line scan sensor 3 form an image of the scintillation light output in a direction inclined with respect to the normal B to the input surface 6a. Even in this case, the contrast of the acquired radiological image is high. In the radiological image acquisition system 1D and imaging unit 30D shown in FIG. 7( b), unlike the radiological image acquisition system 1C and imaging unit 30C, the orientation of the transport surface 21a is not changed, but the orientations of the radiation source 2 and imaging unit 30D are inclined. In other respects, they are similar to the radiological image acquisition system 1C and imaging unit 30C. In the radiographic image acquisition system 1E and the imaging unit 30E shown in FIG. 7(c), only the posture of the object A is inclined on the transfer surface 21a.

[0060] As shown in FIG. 8( a), the slit member 16 may be configured so that the width of the slit S in the transport direction D narrows as it approaches the input surface 6a of the scintillator 6. In this radiological image acquisition system 1F and imaging unit 30F, a pair of tapered first and second slit plates 17 and 18 widen the opening of the slit member 16, enabling normal and oblique incidence of X-rays within a single housing 15. An angle indicator 40 may also be installed within the housing 15 to easily visually confirm the angle of oblique incidence. The 1:1 lens 7 and line scan sensor 3 form an image of scintillation light output in a direction oblique to the normal B of the input surface 6a. Since the entrance portion of the slit S can be widened in this way, it is possible to change the incident direction (incident angle) of radiation with respect to the input surface 6a of the scintillator 6 or to guide radiation to the input surface 6a in multiple incident directions. To accommodate oblique incidence of X-rays, the housing 15 may be formed with another entrance window 14g, for example, that allows radiation transmitted through the object A to pass through. The entrance window 14g may be formed to match the arrangement of the second slit plate 18 (the inclined surface that defines the slit S). An opening and closing mechanism may be provided to appropriately open and close the entrance windows 14f and 14g. The opening and closing mechanism may operate in accordance with the timing of imaging by the line scan sensor 3.

[0061] As shown in FIG. 8(b), the slit member 16, the 1:1 magnification lens 7, and the line scan sensor 3 may be rotatable within the housing 15 about an axis L extending along the input surface 6a. In this radiographic image acquisition system 1G and imaging unit 30G, the angle between the irradiation area 12 of the radiation source 2 and the optical axis E of the line scan sensor 3 and the input surface 6a can be easily changed while the angle between these elements is fixed. For this reason, a rotation mechanism 50 is provided that can rotate the 1:1 magnification lens 7 and the line scan sensor 3 about the axis L. In other words, the incident direction (incident angle) of radiation with respect to the input surface 6a of the scintillator 6 can be easily changed. For example, by changing the incident direction of radiation and performing imaging multiple times, the accuracy of various inspections can be improved.

[0062] As shown in FIG. 9(a), the imaging unit 30H may further include a cover member 43 that holds the slit member 16 and is detachably attached to the housing. In this radiological image acquisition system 1H and imaging unit 30H, the slit member 16 is fixed to the L-shaped cover member 43 so that the slit S is oriented in the direction of the normal line B of the input surface 6a. By attaching an exchange unit 45H, which integrates these components, to the housing 15, imaging similar to that shown in FIG. 4 is possible. On the other hand, as shown in FIG. 9(b), the imaging unit 30J may further include a cover member 44 that holds the slit member 16 and is detachably attached to the housing. In this radiological image acquisition system 1J and imaging unit 30J, the slit member 16 is fixed to the L-shaped cover member 44 so that the slit S is oriented in a direction inclined with respect to the normal line B of the input surface 6a. By attaching an exchange unit 45J, which integrates these components, to the housing 15, imaging similar to that shown in FIG. 5(b) is possible. In this way, by preparing multiple types of combined parts consisting of a cover member and a slit member 16 held by the cover member and appropriately exchanging them, it is possible to easily change the incident direction (incident angle) of radiation with respect to the input surface 6a of the scintillator 6. For example, by changing the incident direction of radiation and taking images multiple times, it is possible to improve the accuracy of various inspections.

[0063] Alternatively, as shown in FIGS. 10(a) to 10(c), imaging may be performed by combining a radiological image acquisition system 1K and an imaging unit 30K arranged similarly to that shown in FIG. 4, a radiological image acquisition system 1L and an imaging unit 30L arranged similarly to that shown in FIG. 5(a), and a radiological image acquisition system 1M and an imaging unit 30M in which the slit member 16 is arranged symmetrically with respect to the radiological image acquisition system 1L and the imaging unit 30L with respect to the normal line B of the input surface 6a. That is, in the radiation output step, the object A may be transported multiple times in the transport direction D, and radiation may be output toward the object A from multiple different directions during the multiple transports. In the radiation introduction step, radiation may be introduced from multiple directions toward the input surface 6a of the scintillator 6 during the multiple transports. In this case, the radiological image acquisition method may further include an image processing step of processing the multiple captured images obtained in the scintillation light imaging step. Radiation images based on radiation introduced (incident) from multiple directions will be different depending on the angle. This improves the accuracy of various types of inspections. By increasing the number of combinations, imaging such as CT imaging is also possible. The tube voltage may be changed for different radiation sources 2, 2A.

[0064] As shown in FIG. 11 , the housing 15 may have another entrance window 14g that allows radiation transmitted through the object A to pass through. The imaging unit 30N may further include another slit member 16A disposed between the other entrance window 14g and the scintillator 6 and forming another slit SA that guides radiation that has passed through the other entrance window 14g toward the input surface 6a. The slit member 16 and the other slit member 16A are arranged so that the slit S and the other slit SA guide radiation from two different directions relative to the input surface 6a of the scintillator 6. Radiation images based on radiation guided (incident) from the two different directions will be different images based on the difference in angle. This can improve the accuracy of various inspections. For example, by using mechanical shutters 41 and 42 made of lead plates or the like in combination, two types of images can be acquired in a single imaging session, thereby shortening the inspection time. For example, the mechanical shutters 41 and 42 may be synchronized with the shutter of the line scan sensor 3. An opening / closing mechanism for opening and closing the entrance windows 14f, 14g may be provided, and this opening / closing mechanism may operate in accordance with the opening and closing timing of the mechanical shutters 41, 42 (imaging timing by the line scan sensor 3). By increasing the number of combinations, imaging such as CT imaging is also possible. The tube voltage may be changed for different radiation sources 2, 2A.

[0065] 12, the scintillator 6 may be disposed at an angle within the housing 15. In this radiation image acquisition system 1P and imaging unit 30P, the slit member 16 is disposed so that the slit S is positioned in a direction oblique to the normal B of the input surface 6a of the scintillator 6, and the equal-magnification lens 7 and line scan sensor 3 also form an image of the scintillation light output in a direction oblique to the normal B of the input surface 6a and capture an image. This configuration also makes it easy to bring the equal-magnification lens 7 and line scan sensor 3 close to the input surface 6a.

[0066] As explained above, it is known that images are different between normal incidence and oblique incidence of X-rays. Some things can be observed with normal incidence and some cannot, and some things can be observed with oblique incidence and some cannot. Furthermore, even with oblique incidence, the images will be different if the angle (direction) at which the X-rays are incident on object A is different. By processing these images, the accuracy of various inspections can be improved. As shown in the various variations above, a nearly infinite variety of combinations of normal incidence and oblique incidence can be realized by adopting all possible forms.

[0067] 13 and 14, a specific configuration example of an imaging unit 30R in which radiation is incident from a direction oblique to the input surface 6a of the scintillator 6 and the equal-magnification lens 7 and line scan sensor 3 form an image of scintillation light output in a direction oblique to the input surface 6a will be described. FIG. 13 is a cross-sectional view showing an example of the internal configuration of the imaging unit 30R. FIG. 14 is a cross-sectional view showing an enlarged portion of FIG. 13. The imaging unit 30R shown in FIG. 13 has a configuration similar to that of the imaging unit 30P shown in FIG. 12 in terms of the arrangement of the entrance window 14f, the scintillator 6, the radiation incident on the scintillator 6, the equal-magnification lens 7, and the line scan sensor 3.

[0068] Imaging unit 30R is configured to be able to capture an image of scintillation light output from input surface 6a of scintillator 6 in a direction inclined relative to input surface 6a. Scintillator 6, line scan sensor 3, and equal-magnification lens 7 are installed within housing 15. Average-magnification lens 7 is disposed between scintillator 6 and line scan sensor 3. Imaging unit 30R has a structure for holding scintillator 6, line scan sensor 3, and equal-magnification lens 7 in a predetermined positional relationship.

[0069] 13 and 14, the imaging unit 30R includes a holding member 60 that holds the 1:1 magnification lens 7 and the line scan sensor 3, a positioning member 70 that positions the scintillator 6, and a support member 80 that fits into the positioning member 70 and supports the scintillator 6. The holding member 60, positioning member 70, and support member 80 are attached to the housing main body 13 of the housing 15 and fixed at predetermined positions. Below, the configurations of the scintillator 6, the line scan sensor 3, and the 1:1 magnification lens 7, as well as the configuration for holding each of these components, will be described.

[0070] As shown in FIG. 13 , the holding member 60 is housed inside the housing main body 13. The holding member 60 has a positioning portion 61 that serves as a guide. The holding member 60 holds the 1:1 lens 7 at the positioning portion 61 of the holding member 60 facing the scintillator 6. The holding member 60 also holds the line scan sensor 3 at a base end 65 opposite the positioning portion 61. The holding member 60 holds the 1:1 lens 7 so that, for example, the tip surface (one end surface) 7 a of the 1:1 lens 7 is perpendicular to the x-direction. The holding member 60 holds the line scan sensor 3 so that, for example, the imaging surface 3 a of the imaging unit 31 is perpendicular to the x-direction. As shown in FIG. 14 , the imaging unit 31 of the line scan sensor 3 is held by a main body 32 attached to a base 33. A portion of the base 33 and the main body 32 are fitted into the base end 65 of the holding member 60.

[0071] As shown in FIGS. 13 and 14 , the positioning member 70 is incorporated into the housing main body 13 at a position directly below the entrance window 14f. The positioning member 70 is made of a metal such as copper. The positioning member 70 has a first through-hole 74 through which radiation passes and a second through-hole 75 through which scintillation light converted by the scintillator 6 and output from the scintillator 6 passes. The first through-hole 74 is formed, for example, along the yz plane, and the second through-hole 75 is formed, for example, along the xy plane. The lengths of the first through-hole 74 and the second through-hole 75 in the y direction are longer than the length of the scintillator 6 in the y direction. The first through-hole 74 and the second through-hole 75 communicate with each other through a space extending in the y direction. The positioning member 70 has a mounting surface 77 that extends at an angle relative to the first through-hole 74, i.e., the radiation passage path. The mounting surface 77 is inclined, for example, at 45° relative to the xy plane. The scintillator 6 is pressed against the mounting surface 77 by a support member 80. A space where the first through-hole 74 and the second through-hole 75 intersect is open to this mounting surface 77. The input surface 6a of the scintillator 6 faces this opening 70d. By appropriately setting the tilt angle of the mounting surface 77, the angle of the input surface 6a relative to the radiation input to the input surface 6a and the angle of the input surface 6a relative to the imaging surface 3a are determined. The tilt angle (45°) of the mounting surface 77 described above is merely an example, and the mounting surface 77 may be tilted at another angle relative to the xy plane.

[0072] The first through-hole 74 forms a slit through which radiation passes. The entrance window 14f of the top plate 14a, the through-hole 13g of the support plate 13e, and the opening 13f of the upper wall 13a are aligned in the z-direction with a fixed length in the x-direction. The first through-hole 74 is aligned in a straight line with the entrance window 14f, the through-hole 13g, and the opening 13f. The first through-hole 74 guides X-rays that have passed through the entrance window 14f toward the input surface 6a of the scintillator 6. The positioning member 70 prevents X-rays from scattering in the internal space of the housing 15. The input surface 6a of the scintillator 6 receives X-rays (radiation) within the irradiation region 12 (see FIG. 12) that have passed through the first through-hole 74 of the positioning member 70.

[0073] The 1:1 magnification lens 7 has a known configuration, but the following describes important features of the imaging unit 30R. The 1:1 magnification lens 7 has a rectangular parallelepiped shape. The 1:1 magnification lens 7 has a structure in which, for example, numerous cylindrical lens bodies (lenses) 8 are arranged in a row and held by a lens holder 7b. The arrayed lens bodies 8 allow the 1:1 magnification lens 7 to form images on the input surface 6a of the scintillator 6 and the imaging surface 3a of the line scan sensor 3, respectively. The distal end surface 7a and the proximal end surface (other end surface) 7c of the 1:1 magnification lens 7 in the lens length direction are parallel to each other and each form a flat surface. Both end surfaces of the lens body 8 are exposed at the distal end surface 7a and the proximal end surface 7c and are flush with both end surfaces of the lens holder 7b. In the 1:1 magnification lens 7, adjacent lens bodies 8 are arranged so that their images overlap. Because the lens bodies 8 are arranged in an array, there is no difference in brightness between the center and edges of the array, and lens distortion does not occur at the edges. In the equal-magnification lens 7, the working distance on the distal end surface 7a side and the working distance on the opposite side correspond to the distance between the input surface 6a and the distal end surface 7a and the distance between the proximal end surface 7c and the imaging surface 3a, respectively, as shown in Fig. 14. In other words, the conjugate length of the equal-magnification lens 7 corresponds to the distance between the input surface 6a and the imaging surface 3a.

[0074] 14, in the imaging unit 30R, the radiation passage path formed by the first through-holes 74 is disposed so as to be inclined with respect to the normal direction to the input surface 6a of the scintillator 6. The equal-magnification lens 7, the shielding member 9, and the line scan sensor 3 are disposed in a direction inclined with respect to the normal direction to the input surface 6a. The equal-magnification lens 7 forms an image on the imaging surface 3a of the scintillation light output in a direction inclined with respect to the normal direction to the input surface 6a. The line scan sensor 3 captures an image of the scintillation light output in a direction inclined with respect to the normal direction to the input surface 6a.

[0075] The shielding member 9 is, for example, a plate-like member provided on the line scan sensor 3, but may also be a block-like member provided across the space between the imaging surface 3a of the line scan sensor 3 and the base end surface 7c of the 1:1 magnification lens 7. In other words, a gap may be formed between the shielding member 9 and the 1:1 magnification lens 7, but no gap is required.

[0076] The positioning member 70 has a locking plate portion 79 that contacts the side surface of the housing body 13, and a main body portion 70a that is disposed within the housing body 13. A first through-hole 74 and a second through-hole 75 are formed in the main body portion 70a. The main body portion 70a is disposed between the entrance window 14f and the scintillator 6, and is a slit member that forms a slit that guides radiation that has passed through the entrance window 14f toward the input surface 6a. A rectangular recess 70c, for example, is formed in the main body portion 70a, and the positioning portion 61 of the holding member 60 is fitted into this recess 70c. In this way, the holding member 60 is fitted into and fixed within the housing body 13 relative to the positioning member 70 that is fixed to the housing body 13.

[0077] The positioning member 70 has a first positioning portion 71 that positions the scintillator 6 by contacting the input surface 6a of the scintillator 6. The first positioning portion 71 is formed as part of the mounting surface 77 and has a flat surface. The first positioning portion 71 comes into surface contact with, for example, the input surface 6a of the scintillator 6.

[0078] The support member 80 fitted into the positioning member 70 supports the scintillator 6. The support member 80 has a support surface 82 facing the mounting surface 77 on which the first positioning portion 71 is formed. The inclination angle of the support surface 82 is equal to the inclination angle of the mounting surface 77, and therefore the support surface 82 is parallel to the mounting surface 77. The support member 80 holds the scintillator 6 between the mounting surface 77 and the support surface 82. The support member 80 is fixed to the positioning member 70 by appropriate fixing means such as screws or bolts so that a gap 89 between the mounting surface 77 and the support surface 82 (the distance in the normal direction of the support surface 82) can be adjusted.

[0079] The positioning member 70 has a second positioning portion 72 that positions the imaging surface 3a by contacting with the tip surface 7a of the 1:1 magnification lens 7. The second positioning portion 72 is formed as part of the side surface 76 that faces the holding member 60, and has a flat surface. The second positioning portion 72 comes into surface contact with the tip surface 7a of the 1:1 magnification lens 7, for example.

[0080] In the imaging unit 30R, a single positioning member 70 positions the scintillator 6 with a first positioning portion 71 and the 1:1 lens 7 with a second positioning portion 72. Because the scintillator 6's 6a contacts the first positioning portion 71, the positional accuracy of the input surface 6a can be easily ensured even if the thickness of the scintillator 6 changes. Therefore, the distance between the line scan sensor 3 and the input surface 6a of the scintillator 6 can be maintained constant. This configuration eliminates the need to consider the positional accuracy of different components, providing an advantage over conventional detectors. The distance between the input surface 6a of the scintillator 6 and the tip surface 7a of the 1:1 lens 7 is also maintained constant, ensuring the accuracy of the focal length (the working distance of the 1:1 lens 7).

[0081] In the imaging unit 30R, the main body 70a of the positioning member 70 forms a slit for guiding radiation to the scintillator 6. There is no need to separately provide the above-mentioned slit member 16 (first slit plate 17 and second slit plate 18). That is, the slit is formed by the positioning member 70, which positions the input surface 6a of the scintillator 6 and the tip surface 7a of the 1:1 lens 7. A second through-hole 75, which is an optical path for scintillation light, is also formed. Furthermore, the holding member 60, which holds the line scan sensor 3, is fitted into the positioning member 70 and positioned. This makes it possible to easily achieve an arrangement similar to that of the imaging unit 30P shown in FIG. 12.

[0082] 13, the substrate and the like are arranged in a space extending in the x direction (transport direction D) from the position of the line scan sensor 3, but even in such an imaging unit 30R, the size of the housing main body 13 in the Z direction can be reduced. In addition, the layout of various members in the housing 15 can be changed depending on the application or installation location of the imaging unit, the required surrounding layout, etc.

[0083] 1 to 12 (imaging units 30, 30A to 30H, 30J to 30N, and 30P) described above, a structure using at least one of a positioning member 70, a support member 80, and a holding member 60, i.e., a structure similar to that of imaging unit 30R, may be applied. When the positioning member 70 is used, the main body 70a of the positioning member 70 may have a slit formed therein for guiding radiation to the scintillator 6. In that case, the slit member 16 may be omitted.

[0084] For example, the range in which the slit member 16 is provided may be smaller than that in the above embodiment, and may be a part of the range from the entrance window 14f to the input surface 6a of the scintillator 6.

[0085] The material used for the slit member 16 is not limited to copper plate, but may be aluminum, stainless steel, iron, lead, or the like. The surface of the aluminum, iron, stainless steel, or lead material may be covered with copper by, for example, attaching copper foil or a copper plate to the surface of the slit member 16. The slit member 16 may also be formed from a plurality of materials. The same applies to the radiation source-side slit member 26. The radiation source-side slit member 26 may be omitted. Copper has the property of being less likely to generate scattered radiation, and using copper is advantageous in terms of reducing scattered radiation and the associated noise in the sensor.

[0086] The shielding member 9 may be omitted. In that case, a 1x1 lens is attached directly to the line scan sensor 3. In the above embodiment, the scintillation light emitted from the input surface 6a of the scintillator 6 is imaged. However, in addition to this, the scintillation light emitted from the surface opposite to the input surface 6a of the scintillator 6 may also be imaged. In this case, the scintillator 6 may be made up of a plurality of scintillators, and a member that blocks the scintillation light may be inserted between the plurality of scintillators. [Industrial Applicability]

[0087] According to some aspects of the present disclosure, resolution can be improved and, furthermore, sensitivity can be improved. [Explanation of symbols]

[0088] 1...radiation image acquisition system, 3...line scan sensor, 3a...imaging surface, 6...scintillator, 6a...input surface, 7...equal magnification lens, 9...shielding member, 13...housing body, 14...lead cover, 14f...entrance window, 14g...another entrance window, 15...housing, 16...slit member, 16A...another slit member, 17...first slit plate, 18...second slit plate, 20...conveying device, 21a...conveying surface, 30...imaging unit, 26...radiation source side slit member, 70...positioning member (slit member), B...normal (to the input surface of the scintillator), C...gap, D...conveying direction, E...optical axis (of the line scan sensor), S...slit, SA...another slit.

Claims

1. An imaging unit for acquiring a radiographic image of an object being transported in a transport direction, a housing having an entrance window through which radiation transmitted through the object passes; a scintillator disposed within the housing and having an input surface for inputting the radiation that has passed through the entrance window; a line scan sensor installed within the housing and having an imaging surface that captures an image of scintillation light output from the input surface; a slit member disposed between the entrance window and the scintillator, the slit forming a slit for guiding the radiation that has passed through the entrance window toward the input surface; a unity-magnification lens disposed between the scintillator and the line scan sensor, the unity-magnification lens forming an image of the scintillation light output from the input surface onto the imaging surface of the line scan sensor; The slit member is configured so that the width of the slit in the transport direction becomes narrower as it approaches the input surface of the scintillator.

2. the slit member is arranged so that the slit is positioned in a normal direction of the input surface of the scintillator, The imaging unit according to claim 1 , wherein the equal-magnification lens and the line scan sensor form an image of the scintillation light output in a direction inclined with respect to the normal direction of the input surface.

3. The imaging unit according to claim 1 , wherein the slit member is disposed so that the slit extends obliquely with respect to the transport direction.

4. the slit member is arranged so that the slit is positioned in a direction inclined with respect to a normal direction of the input surface of the scintillator, The imaging unit according to claim 1 , wherein the equal-magnification lens and the line scan sensor form an image of the scintillation light output in a direction inclined with respect to the normal direction of the input surface.

5. 5. The imaging unit according to claim 1, further comprising a cover member that holds the slit member and is detachably attached to the housing.

6. An imaging unit for acquiring a radiographic image of an object being conveyed in a conveying direction, comprising: a housing having an entrance window through which radiation transmitted through the object passes, and another entrance window through which radiation transmitted through the object passes; a scintillator disposed within the housing and having an input surface for inputting the radiation that has passed through the entrance window; a line scan sensor installed within the housing and having an imaging surface that captures an image of scintillation light output from the input surface; a slit member disposed between the entrance window and the scintillator, the slit forming a slit for guiding the radiation that has passed through the entrance window toward the input surface; another slit member disposed between the another entrance window and the scintillator, and forming another slit for guiding the radiation that has passed through the another entrance window toward the input surface; a unity-magnification lens disposed between the scintillator and the line scan sensor, the unity-magnification lens forming an image of the scintillation light output from the input surface onto the imaging surface of the line scan sensor; An imaging unit, wherein the slit member and the other slit member are arranged so that the slit and the other slit respectively guide the radiation from two different directions relative to the input surface of the scintillator.

7. An imaging unit for acquiring a radiographic image of an object being conveyed in a conveying direction, comprising: a housing having an entrance window through which radiation transmitted through the object passes; a scintillator disposed within the housing and having an input surface for inputting the radiation that has passed through the entrance window; a line scan sensor installed within the housing and having an imaging surface that captures an image of scintillation light output from the input surface; a slit member disposed between the entrance window and the scintillator, the slit forming a slit for guiding the radiation that has passed through the entrance window toward the input surface; a unity-magnification lens disposed between the scintillator and the line scan sensor, the unity-magnification lens forming an image of the scintillation light output from the input surface onto the imaging surface of the line scan sensor; An imaging unit in which the slit member, the equal-magnification lens, and the line scan sensor are rotatable within the housing about an axis extending along the input surface.

8. A radiation image acquisition system for acquiring a radiation image of an object, comprising: a radiation source that outputs the radiation toward the target; a conveying device that conveys the object in the conveying direction and transmits the radiation; 8. A radiation image acquisition system comprising: an imaging unit according to claim 1, wherein the imaging unit is installed so that the radiation source and the entrance window are disposed on the same plane.

9. The radiation image acquisition system according to claim 8 , wherein the slit members of the conveying device and the imaging unit are arranged so that the slits extend obliquely with respect to the conveying direction.

10. A radiological image acquisition method for acquiring a radiological image of an object, comprising: a radiation output step of outputting radiation toward the object being transported in a transport direction; a radiation introducing step of allowing the radiation that has passed through the object to enter a housing through an entrance window and guiding the radiation toward the input surface of the scintillator through a slit that is formed in the housing so as to narrow in width in the transport direction as the slit approaches the input surface of the scintillator; a scintillation light output step of inputting the radiation that has passed through the slit to an input surface of a scintillator, converting the input radiation into scintillation light, and outputting the scintillation light from the input surface; a scintillation light imaging step of forming an image of the scintillation light output from the input surface on an imaging surface of a line scan sensor using an equal-magnification lens; a scintillation light imaging step of imaging the scintillation light on the imaging surface of the line scan sensor.

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