CT device

Abstract

The FCD is set according to the shape of the object to be inspected and the set scan area, achieving optimal resolution. [Solution] The CT device 100 includes an inspection table 1 on which an object to be inspected A is placed and which moves and rotates the object to be inspected A, a radiation source 2 which irradiates the object to be inspected A with a radiation beam B, a detector 3 which is provided facing the radiation source A across the object to be inspected A, and a critical distance FCD which is the minimum distance required for the object to be inspected A not to come into contact with the radiation source 2 during rotation in a distance FCD between a focal point F of the radiation source 2 and the center of the object to be inspected A. L a scan area distance calculation unit 86 that calculates a scan area distance FCDs, which is the distance between the focal point F of the radiation source 2 and the center of the object A to be inspected in the set scan area S; and L and a comparison unit 87 which compares the scanning area distance FCDs with the shooting distance FCD to determine the shooting distance FCD, and an examination table control unit 81 which controls the examination table 1 to move the object A closer to and farther from the radiation source 2 based on the shooting distance FCD determined by the comparison unit 87 during imaging.

Description

[Technical field]

[0001] An embodiment of the present invention relates to a CT device. [Background technology]

[0002] Industrial CT devices are widely used to inspect small electronic components such as lithium-ion batteries with high resolution. In this CT device, a radiation source that irradiates radiation, such as an X-ray beam, and a detector that detects the X-ray beam from the radiation source with two-dimensional resolution are arranged facing each other. A rotatable inspection table is provided between the radiation source and the detector. The object to be inspected is placed on the inspection table, which rotates during imaging and is irradiated with radiation in all directions.

[0003] Generally, the distance between the focal point of the radiation source and the center of rotation of the object to be inspected is called the FCD. Since the shorter the FCD, the higher the resolution, the object to be inspected may be brought as close as possible to the radiation source to be photographed.

[0004] If the object to be photographed has a shape with a high aspect ratio, such as a rectangle or ellipse, the object can be brought closer to the radiation source when the short side faces the radiation source, but needs to be moved away when the long side faces the radiation source. Therefore, it is necessary to grasp the shape of the object to be photographed and change the FCD during photography according to the shape of the object. Therefore, a method is known in which the dimension d from the center of rotation of the object A to the end is calculated, and the object is moved closer to or farther from the radiation source according to the dimension d. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2024-71371 A Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, when taking an image, the scan area is set in advance. The FCDs required according to the size of the set scan area must be calculated separately from the shape of the object to be inspected. If this FCDs exceeds the dimension d of the object to be inspected, controlling the FCD according to the dimension d of the object to be inspected will result in a problem that the scan area will become too small.

[0007] An embodiment of the present invention has been made to solve the above-mentioned problems, and its purpose is to provide a CT device that realizes an FCD according to the shape of the object to be inspected and a set scan area, thereby achieving optimal resolution. [Means for solving the problem]

[0008] A CT apparatus according to an embodiment of the present invention is a CT apparatus for imaging an object to be inspected while rotating the object to be inspected, comprising: an inspection table on which the object to be inspected is placed and which moves and rotates the object to be inspected; a radiation source which irradiates a radiation beam onto the object to be inspected; a detector which is provided facing the radiation source across the object to be inspected; and a critical distance FCD which is a minimum distance required for the object to not come into contact with the radiation source during rotation in a distance FCD from a focus of the radiation source to a center of the object to be inspected. L a scan area distance calculation unit that calculates a scan area distance FCDs, which is a distance between the focus of the radiation source and the center of the object to be inspected, required in a set scan area; L and a comparison unit which compares the scan area distance FCDs with the scanning area distance FCDs to determine a shooting distance which becomes the distance FCD when performing imaging, and an examination table control unit which controls the examination table to move the object to be inspected closer to and away from the radiation source based on the shooting distance determined by the comparison unit during imaging. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a side view diagrammatically illustrating a CT apparatus according to an embodiment. [Diagram 2] FIG. 1 is a plan view illustrating a CT apparatus according to an embodiment. [Diagram 3] FIG. 2 is a block diagram showing a configuration of a control unit. [Figure 4] 5 is a flowchart showing a method of calculating a shooting distance FCD in the embodiment. [Diagram 5] FIG. 13 is a diagram showing a state in which an ROI is set on a fluoroscopic image. [Figure 6] FIG. 13 is a diagram showing the distance from the center of rotation to an end of an object to be inspected. [Figure 7] 13 is a graph showing the relationship between the limit distance FCDL and the rotation angle. [Figure 8] 8 is a graph showing the relationship between the limit distance FCDL and the rotation angle when the graph in FIG. 7 is shifted by 90 degrees. [Figure 9] 13 is a graph showing the relationship between the rotation angle and the limit distance FCDL when a predetermined distance is added. [Figure 10] FIG. 13 is a diagram showing settings of a scan area. [Figure 11] 11 is a graph showing the shooting distance when the scan area distance FCDs is longer than the maximum value of the limit distance FCDL. [Figure 12] 11 is a graph showing the shooting distance when the scan area distance FCDs is shorter than the minimum value of the limit distance FCDL. [Figure 13] 13 is a graph showing the shooting distance when the scan area distance FCDs is equal to or greater than the minimum value and equal to or less than the maximum value of the limit distance FCDL. [Figure 14] 1A and 1B are diagrams showing fluoroscopic images before and after enlargement, in which (a) is the fluoroscopic image before enlargement, and (b) is the fluoroscopic image after enlargement. [Figure 15] FIG. 13 is a side view showing a schematic diagram of a modified CT apparatus. [Figure 16] 13A and 13B are diagrams showing a method of moving an object to be inspected in a modified example. [Figure 17] 13A and 13B are diagrams showing the trajectory of movement of the center of rotation of an object to be inspected in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Embodiment] Hereinafter, a CT device according to an embodiment will be described in detail with reference to the drawings. Fig. 1 is a side view that shows a schematic diagram of the CT device according to the embodiment. Fig. 2 is a plan view that shows a schematic diagram of the CT device according to the embodiment.

[0011] The CT device 100 is a device used for non-destructive inspection of an object A to be inspected. The CT device 100 irradiates the periphery of the object A to be inspected with a radiation beam B that passes through the object A to detect the amount of radiation attenuated by passing through the object A. Then, based on this detection result, a CT image is generated which is a cross-sectional image of the object A to be inspected. The CT device 100 also generates a 3D image from the generated multiple CT images. The object A to be inspected has a shape with a high aspect ratio, for example, a cylindrical shape that is an ellipse when viewed from the direction of the rotation axis C. In this embodiment, the object A to be inspected is moved toward or away from the radiation source 2 according to the shape of the object A to be inspected during imaging.

[0012] As shown in FIG. 1, the CT apparatus 100 includes an examination table 1, a radiation source 2, a detector 3, a filter unit 4, a camera 5, a display unit 6, an input unit 7, and a control unit 8. The examination table 1 is a table having a mounting surface on which an object to be inspected A is placed. The examination table 1 is movable in a direction parallel to the mounting surface or in a direction perpendicular to the mounting surface. The examination table 1 is also rotatable about a rotation axis C that is perpendicular to the mounting surface. The examination table 1 rotates and moves the object to be inspected A during imaging. The examination table 1 includes a rotating table 11, a lifting mechanism 12, a Y mechanism 13, and an X mechanism 14.

[0013] The object A to be inspected is placed on the turntable 11. The object A to be inspected is placed on the turntable 11 so that a rotation axis C of the turntable 11 is coaxial with the center of the object A to be inspected. The turntable 11 is formed, for example, by an actuator including a drive source such as a motor, and is provided rotatable about a rotation axis C that is perpendicular to the surface on which the object is placed. While the radiation beam B is being irradiated, the turntable 11 rotates, so that the radiation beam B is irradiated in all directions on the object A to be inspected. A sample table may be provided on the turntable 11, and the object A to be inspected may be placed on the sample table.

[0014] The lifting mechanism 12 is provided below the rotary table 11. A ball screw mechanism driven by a servo motor can be used as the lifting mechanism 12. The lifting mechanism 12 is movable in a direction perpendicular to the mounting surface. That is, the height of the object A to be inspected can be adjusted by moving the lifting mechanism 12 in a direction perpendicular to the mounting surface.

[0015] Y mechanism 13 is provided below lifting mechanism 12. For example, a ball screw mechanism driven by a servo motor can be used as Y mechanism 13. Y mechanism 13 is movable in a direction parallel to the placement surface and perpendicular to the optical axis of radiation beam B (hereinafter also referred to as the Y direction).

[0016] X mechanism 14 is provided below Y mechanism 13. For X mechanism 14, a ball screw mechanism driven by a servo motor, for example, can be used. X mechanism 14 is movable in a direction parallel to the optical axis of radiation beam B (hereinafter also referred to as the X direction). X mechanism 14 is configured to be able to move inspection table 1, radiation source 2, and detector 3 independently. By moving object A by X mechanism 14, object A is brought closer to or away from radiation source 2.

[0017] The radiation source 2 irradiates, for example, a radiation beam B that penetrates the object A to be inspected. The radiation beam B is a bundle of radiation that spreads in a cone shape with a fan angle and a cone angle, with the focus F of the radiation source 2 as its apex. In this embodiment, the radiation source 2 is, for example, a reflective or transmissive microfocus X-ray tube or nanofocus X-ray tube, and the radiation beam B is an X-ray beam. Note that the radiation beam B is not limited to an X-ray beam, and any beam that penetrates the object A to be inspected, such as gamma rays, can be used. The radiation source 2 is supported by a support frame 21. The radiation source 2 can be moved in the X direction by an X mechanism 14.

[0018] The detector 3 is provided facing the radiation source 2 with the inspection table 1 and the object to be inspected A sandwiched between them. The detector 3 is provided so that the center of the imaging area coincides with the optical axis of the radiation source 2. The detector 3 detects a two-dimensional distribution of radiation intensity attenuated according to the transmission path of the radiation beam B, and outputs a fluoroscopic image. The detector 3 is configured by, for example, a flat panel detector (FPD). The detector 3 is supported by a support frame 31. The distance between the detector 3 and the object to be inspected A is adjusted by the X-mechanism 14.

[0019] The filter unit 4 is disposed in a position between the object A and the radiation source 2 and close to the radiation source 2. The filter unit 4 is a thin plate member having a thickness of about several mm. The filter unit 4 is a metal plate made of copper, aluminum, iron, or an alloy containing these. A plurality of filter units 4 are provided, and the filter units 4 are made of different materials and have different thicknesses.

[0020] The filter unit 4 is provided so as to be movable by a moving mechanism (not shown). For example, a ball screw mechanism driven by a servo motor can be used as the moving mechanism. The moving mechanism moves the filter unit 4 selected by the user onto the optical axis of the radiation source 2. The filter unit 4 arranged on the optical axis is irradiated with a radiation beam B, and the radiation beam B that has passed through the filter unit 4 is irradiated onto the object A to be inspected. By transmitting the radiation beam through the filter unit 4, the occurrence of metal artifacts is suppressed.

[0021] The CT device 100 may also include a collimator (not shown). The collimator is a device that limits the path and incident area of ​​the radiation beam B. The collimator is made of a material with a high specific gravity and high shielding ability, such as tungsten or molybdenum. The collimator is provided between the radiation source 2 and the object A to be inspected, symmetrically above and below the optical axis of the radiation beam B from the radiation source 2.

[0022] The camera 5 is provided above the turntable 11. That is, the camera 5 is provided facing the turntable 11 with the object to be inspected A sandwiched between them. The camera 5 is, for example, a CCD camera. The camera 5 captures an image of the object to be inspected A from above the object to be inspected A.

[0023] The display unit 6 is, for example, a monitor such as a liquid crystal display or an organic EL display. The display unit 6 displays various images of the object A, such as a fluoroscopic image, a CT image, and a 3D image, an imaging area, an imaging time, imaging conditions, and the like.

[0024] The input unit 7 can use a keyboard, a mouse, a touch panel, etc. The input unit 7 accepts various operations such as menu selection for actual photography or test photography, correction of photography time and photography conditions, manual operation of the movement mechanism, start of photography, and selection of a part of the inspection object A to be observed.

[0025] The control unit 8 is composed of a computer and a driver circuit. The computer is composed of a storage such as an HDD or SSD, a RAM, a CPU, etc. The control unit 8 controls each component of the CT device 100. The control unit 8 is connected to the input unit 7, and a user causes the control unit 8 to control each component of the CT device 100 via the input unit 7.

[0026] Fig. 3 is a block diagram showing the configuration of the control unit 8. As shown in Fig. 3, the control unit 8 has an examination table control unit 81, a radiation source control unit 82, a reconstruction unit 83, a camera control unit 84, a limit distance calculation unit 85, a scan area distance calculation unit 86, a comparison unit 87, and a magnification ratio calculation unit 88.

[0027] The inspection table control unit 81 controls the turntable 11, the lifting mechanism 12, the Y mechanism 13, and the X mechanism 14. By controlling the inspection table control unit 81, the object A placed on the inspection table 1 can be aligned with the optical axis of the radiation beam B, and the object A can be rotated once during irradiation with the radiation beam B. In addition, by moving the inspection table 1 under the control of the inspection table control unit 81, the distance FCD between the focus F of the radiation source 2 and the center of the object A can be adjusted. In other words, the object A can be moved closer to or farther away from the radiation source 2 during imaging. Based on the result of the comparison unit 87, the inspection table control unit 81 controls the X mechanism 14 during imaging to change the distance FCD.

[0028] The radiation source control unit 82 controls the radiation source 2 to irradiate the inspection object A with the radiation beam B. That is, under the control of the inspection table control unit 81 and the radiation source control unit 82, the inspection object A is irradiated with the radiation beam B in all directions.

[0029] The reconstruction unit 83 reconstructs the CT imaging region contained in the radiation beam B based on the number of fluoroscopic images obtained in 360-degree directions for the number of views. The reconstruction unit 83 transmits the fluoroscopic images to the limit distance calculation unit 85. When the magnification ratio calculation unit 88 has calculated a magnification ratio, the reconstruction unit 83 performs reconstruction taking into account the calculated magnification ratio. The reconstruction unit 83 reconstructs a plurality of cross-sectional images that are continuously arranged at equal intervals in a direction perpendicular to the placement surface of the object A to be inspected, and forms three-dimensional data from the plurality of cross-sectional images. The three-dimensional data can be displayed on the display unit 6 in MPR (Multi-planer Reconstruction) display or the like.

[0030] The camera control unit 84 controls the camera 5. The camera control unit 84 controls the position and image capturing timing of the camera 5. The camera control unit 84 transmits data captured by the camera 5 to a scan area distance calculation unit 86.

[0031] The limit distance calculation unit 85 calculates the limit distance FCD based on the fluoroscopic image of the object A. L Calculate the critical distance FCD. Lis the minimum distance required for the inspection object A not to come into contact with the radiation source 2 during rotation in the distance FCD. L Calculate.

[0032] The limit distance calculation unit 85 calculates the limit distance FCD L A predetermined distance α may be added to the predetermined distance α. For example, if there is a distance between the focal point F of the radiation source 2 and the window of the radiation source 2 through which radiation is emitted, this length may be added as the predetermined distance α. Furthermore, in order to form a small gap between the radiation source 2 and the object to be inspected A, the length of this gap may be added as the predetermined distance α.

[0033] The scan area distance calculation unit 86 sets a scan area on the image captured by the camera 5. The scan area may be set by the user using the input unit 7, or the scan area distance calculation unit 86 may automatically set an optimal scan area from the image captured by the camera 5.

[0034] The scan area distance calculation unit 86 calculates a diameter Sa of the set scan area. Then, the scan area distance calculation unit 86 calculates a scan area distance FCDs between the focal point F of the radiation source 2 and the center of the object A, which is required in the set scan area.

[0035] The comparison unit 87 compares the limit distance FCD calculated by the limit distance calculation unit 85. L and the scan area distance FCDs calculated by the scan area distance calculation unit 86 to determine the shooting distance FCD at each rotation angle. The shooting distance FCD is the distance between the focal point F of the radiation source 2 and the center of the object A when actually performing imaging. More specifically, the comparison unit 87 compares the limit distance FCD L The minimum distance FCD Lmin and maximum distance FCD Lmax Compare the scan area distances FCDs with the minimum distance FCD Lmin FCD is the limit distance between 0 and 360 degrees of rotation. LThe maximum distance FCD is the shortest distance among the Lmax FCD is the limit distance between 0 and 360 degrees of rotation. L The comparison unit 87 determines the distance FCD during rotation based on the comparison result, and transmits the determined imaging distance FCD to the examination table control unit 81. L If a predetermined distance α is added to the object distance FCD, the distance obtained by adding the predetermined distance α to the object distance FCDs is compared to determine the object distance FCD.

[0036] The magnification ratio calculation unit 88 calculates the magnification ratio based on the shooting distance FCD determined by the comparison unit 87. Specifically, when the distance FCD changes during shooting, the magnification ratio calculation unit 88 calculates the magnification ratio so that the magnification ratio of the captured image is the same. The magnification ratio calculation unit 88 calculates the magnification ratio at each rotation angle based on the shooting minimum distance FCDmin, which is the shortest shooting distance FCD, so that the magnification ratio is the same as the shooting minimum distance FCDmin.

[0037] [Operation] Next, calculation of the shooting distance FCD in this embodiment will be described with reference to the flowchart in Fig. 4. First, the CT device 100 acquires a perspective image of the object A to be inspected (step S01). The turntable 11 is rotated, and the radiation source 2 irradiates the object A with a radiation beam B in all directions, thereby acquiring a perspective image.

[0038] The acquired perspective image is displayed on the display unit 6. As shown in Fig. 5, the perspective image is displayed in an ellipse. The user draws a rectangular ROI circumscribing the perspective image displayed on the display unit 6 (step S02).

[0039] Based on the rectangular ROI, the limit distance calculation unit 85 calculates the number of pixels dg from the center of rotation at a rotation angle of 0 degrees to the end of the ROI (step S03). Then, based on the number of pixels dg, the limit distance calculation unit 85 calculates the distance d from the rotation axis C shown in FIG. 6 to the end of the object A to be inspected (the end 90 degrees before the radiation beam is irradiated). The limit distance calculation unit 85 calculates the distance d (mm) by the following formula (1). This distance d is the limit distance FCD. L (Step S04).

[0040] (Formula 1) TIFF0007610070000002.tif17101dpm: Dimensions per pixel

[0041] The limit distance calculation unit 85 calculates the limit distance FCD in all directions of the object A, that is, from a rotation angle of 0 degrees to 360 degrees. L In this embodiment, the limit distance calculation unit 85 calculates the limit distance FCD at intervals of 45 degrees. L The limit distance calculation unit 85 calculates the limit distance FCD at the rotation angle of 0 degrees to 360 degrees, as shown in the graph of FIG. L Calculate the limit distance FCD L It is preferable that the pitch of the rotation angle for calculating the limit distance FCD is small. L The pitch of the rotation angle for calculating the limit distance FCD is preferably, for example, 45 degrees rather than 90 degrees. L By calculating the above, the dimensions of the object A to be inspected can be calculated with high accuracy.

[0042] However, the limit distance FCD calculated as above L is the distance calculated when the object is located 90 degrees away from the radiation beam as shown in FIG. 6. Therefore, the critical distance FCD calculated at the position facing the radiation source 2 is L In order to position the object A in the corresponding portion, it is necessary to shift by 90 degrees. If the graph in FIG. 7 is shifted by 90 degrees, it will look like FIG. 8.

[0043] The limit distance calculation unit 85 calculates the limit distance FCD L (Step S05). The predetermined distance α is stored in advance in a storage unit (not shown) in order to provide a slight gap between the focal point F of the radiation source 2 and the window of the radiation source 2 through which radiation is emitted, and between the radiation source 2 and the object to be inspected A. L 9, the distance increases by the predetermined distance α at each rotation angle. The limit distance calculation unit 85 calculates the limit distance FCD by adding the predetermined distance α. L Let us assume that.

[0044] Next, the scan area distance calculation unit 86 sets a scan area (step S06). For example, as shown in Fig. 10, the scan area distance calculation unit 86 sets a circular scan area S on the image captured by the camera 5. The scan area distance calculation unit 86 calculates a diameter Sa of the scan area S. The diameter Sa (mm) may be calculated based on the number of pixels on the image.

[0045] Then, the scan area distance calculation unit 86 calculates the scan area distance FCDs based on the diameter Sa and the following formula (2) (step S07).

[0046] (Formula 2) TIFF0007610070000003.tif25145D: Vertical length of detector 3 FDD: Distance between the focal point F of the radiation source 2 and the detector 3

[0047] It should be noted that steps S06 and S07 do not necessarily have to be performed after steps S01 to S05. That is, steps S06 and S07 may be performed before steps S01 to S05, or may be performed simultaneously with steps S01 to S05.

[0048] Critical Distance FCD L After the calculation of the scan area distance FCDs is completed, the comparison unit 87 calculates the limit distance FCD LThe comparison unit 87 compares the scan area distance FCDs with the limit distance FCD (step S08). L The minimum distance FCD Lmin and maximum distance FCD Lmax and scan area distances FCDs.

[0049] The comparison unit 87 determines the shooting distance FCD based on the comparison result (step S09). As shown in FIG. 11, when the scan area distance FCDs is greater than or equal to the maximum distance FCD Lmax In the above cases, the limit distance FCD L If the shooting distance FCD is set to FCDs, the scan area S will become small. Therefore, the comparison unit 87 determines the scan area distance FCDs as the shooting distance FCD during shooting (see the thick solid line in FIG. 11). In this case, since the shooting distance FCD is constant, the object A does not move toward or away from the radiation source 2 during shooting.

[0050] On the other hand, as shown in Fig. 12, the scan area distance FCDs is the minimum distance FCD Lmin In the following cases, if the scan area distance FCDs is set as the shooting distance FCD, the object A comes into contact with the radiation source 2. Therefore, the comparison unit 87 uses the limit distance FCD L is determined as the shooting distance FCD (see the thick solid line in FIG. 12).

[0051] Also, as shown in Fig. 13, the scan area distance FCDs is the minimum distance FCD Lmin Longer than maximum distance FCD Lmax If it is shorter than the critical distance FCD L If only one of the limit distance FCDs and the scan area distance FCDs is used as the imaging distance, the object A may come into contact with the radiation source 2 or the scan area S may become small depending on the rotation angle. L For the part where FCDs is less than the scan area distance FCDs, the scan area distance FCDs is determined as the shooting distance FCD, and the limit distance FCD L The part where is greater than the scan area distance FCDs is the limit distance FCD Lis determined as the shooting distance FCD (see the thick solid line in FIG. 13). That is, the limit distance FCD L In the area where the scanning area distance FCDs is less than the scanning area distance FCDs, the shooting distance FCD is constant, and the limit distance FCD L In the area where the scan area distance FCDs is greater than or equal to the limit distance FCD L The shooting distance FCD changes based on this.

[0052] When the shooting distance FCD is determined, the magnification ratio calculation unit 88 calculates the magnification ratio (step S10). As shown in Fig. 12 and Fig. 13, when the shooting distance FCD changes with the rotation of the turntable 11, the size of the generated perspective image differs depending on the rotation angle. Therefore, the magnification ratio calculation unit 88 calculates the magnification ratio at each rotation angle based on the shooting distance FCD.

[0053] Specifically, the magnification ratio calculation unit 88 calculates the magnification ratio at each rotation angle so that the magnification ratio is the same as the magnification ratio of the minimum shooting distance FCDmin with the shortest shooting distance FCD. The magnification ratio calculation unit 88 calculates the magnification ratio based on the following formula (3). Therefore, as shown in Fig. 14, even a small fluoroscopic image can be enlarged to generate a fluoroscopic image of the same size. Note that, as shown in Fig. 11, when the shooting distance FCD is constant, the magnification ratio calculation unit 88 does not need to calculate the magnification ratio.

[0054] (Formula 3) TIFF0007610070000004.tif23148

[0055] After the calculation of the magnification ratio is completed, imaging is started (step S11). That is, the inspection table control unit 81 controls the X mechanism 14 so as to achieve the shooting distance FCD determined by the comparison unit 87. That is, the inspection table control unit 81 controls the X mechanism 14 so that, for an object A having a high aspect ratio, when the long side portion is positioned on the optical axis of the radiation beam B, the object A moves away from the radiation source 2, and when the short side portion is positioned on the optical axis of the radiation beam B, the object A moves closer to the radiation source 2.

[0056] When the imaging of the object A is completed, the reconstruction unit 83 generates a CT image based on the perspective images corresponding to the number of views obtained in the 360-degree direction (step S13). At this time, the reconstruction unit 83 generates the perspective images based on the magnification ratio calculated by the magnification ratio calculation unit 88, and generates a CT image.

[0057] [effect] As described above, the CT apparatus 100 of this embodiment includes the inspection table 1 on which the object A to be inspected is placed and which moves and rotates the object A to be inspected, the radiation source 2 which irradiates the object A with a radiation beam B, the detector 3 which is provided facing the radiation source 2 across the object A to be inspected, and a critical distance FCD which is the minimum distance required for the object A to not come into contact with the radiation source 2 during rotation in the distance FCD between the focal point F of the radiation source 2 and the center of the object A to be inspected. L a scan area distance calculation unit 86 that calculates a scan area distance FCDs, which is the distance between the focal point F of the radiation source 2 and the center of the object A to be inspected in the set scan area S; and L and the scan area distance FCDs to determine the shooting distance FCD, and an examination table control unit 81 to control the examination table 1 during imaging so as to move the object A closer to and farther away from the radiation source 2, based on the shooting distance FCD determined by the comparison unit 87.

[0058] In this manner, the CT apparatus 100 of this embodiment determines the critical distance FCD corresponding to the shape of the object A to be inspected. L The shooting distance FCD is determined based on the scan area distance FCDs required according to the scan area S. Therefore, imaging can be performed at the optimal shooting distance FCD without the scan area S becoming smaller. This makes it possible to generate high-quality CT images with optimal resolution.

[0059] The limit distance calculation unit 85 calculates the limit distance FCD L The comparison unit 87 adds a predetermined distance α to the limit distance FCD L and the scan area distances FCDs to determine the object distance FCD.

[0060] This creates a spatial margin of the predetermined distance α between the object to be inspected A and the radiation source 2. This effectively prevents the object to be inspected A from coming into contact with the radiation source 2 during rotation. In addition, if there is a certain distance between the focal point of the radiation source 2 and the window through which the radiation beam B is irradiated, the predetermined distance α is set based on this distance, and the limit distance FCD is set as follows: L By adding a predetermined distance α to the above, contact between the object A and the radiation source 2 can be prevented.

[0061] The system further includes a magnification ratio calculation unit 88 that calculates the magnification ratio of the perspective image at each rotation angle. When the shooting distance FCD changes depending on the rotation angle, the magnification ratio calculation unit calculates the magnification ratio so that the magnification ratio becomes the same as that of the perspective image captured at the minimum shooting distance FCDmin, which is the shortest among the shooting distances FCD.

[0062] When the shooting distance FCD changes, the magnification ratio of the fluoroscopic image of the object A to be photographed also changes. Therefore, the magnification ratio calculation unit 88 calculates the magnification ratio for each rotation angle based on the minimum shooting distance FCDmin. This makes each fluoroscopic image the same size, and a CT image can be generated based on this. Also, since the resolution is highest (one pixel size is small) at the minimum shooting distance FCDmin, an image can be generated according to this high resolution.

[0063] [Variations]

[0064] (1) In the above embodiment, the user draws the circumscription of the object A on the perspective image, but the ROI may be drawn automatically. That is, the limit distance calculation unit 85 may draw the ROI by processing the perspective image, and calculate the number of pixels dg based on the drawn ROI. This eliminates the need for drawing by the user, improving productivity.

[0065] (2) In the above embodiment, the limit distance calculation unit 85 draws the ROI on the perspective image, calculates each value such as the number of pixels dg, and calculates the limit distance FCD LHowever, it is not necessary to calculate based on the fluoroscopic image. For example, the critical distance FCD at each rotation angle L The user may visually determine the scan area. In this case, the user also visually sets the scan area. The comparison unit 87 compares each set value with the limit distance FCD calculated by the limit distance calculation unit 85. L and the imaging distance FCD is determined by taking it as the scan area distance FCDs calculated by the scan area distance calculation unit 86. This eliminates the need to create a fluoroscopic image before imaging, and therefore eliminates the need to irradiate X-rays.

[0066] (3) During imaging, the helical scan method may be applied, in which the object A is rotated and elevated while imaging is continued, thereby shortening the imaging time.

[0067] (4) The inspection table 1 may have an XY table 15 on a turntable 11 as shown in Fig. 15. An object A to be inspected is placed on the XY table 15. The XY table 15 moves the object A to be inspected in the X direction or the Y direction. The XY table 15 rotates in conjunction with the rotation of the turntable 11. The inspection table control unit 81 controls the XY table 15 based on the shooting distance FCD determined by the comparison unit 87 to move the object A to be inspected.

[0068] Specifically, as shown in FIG. 16, the XY table 15 is used to move the object A to a shooting distance FCD while locating the rotation center Ac of the object A on the optical axis of the radiation beam irradiated from the radiation source 2. Specifically, as shown in FIG. 16(a), when the rotation angle is 0 degrees, the rotation center Ac of the object A is coaxial with the rotation axis C. At this time, the long side direction of the object A is arranged parallel to the optical axis. When the rotation table 11 starts to rotate, the object A rotates so that the short side direction of the object A becomes parallel to the optical axis. As shown in FIG. 16(b), when the rotation table 11 rotates 45 degrees, the XY table 15 also rotates 45 degrees. At this time, the rotation center Ac of the object A is located at a position closer to the radiation source 2 than when the rotation angle is 0 degrees (a position closer to the radiation source 2 by a distance of 1 / 2 the radius from the rotation axis C). 16(c), when the rotation angle reaches 90 degrees, the center of rotation Ac of the object A is closest to the radiation source 2. That is, the shooting distance FCD becomes the minimum shooting distance FCDmin.

[0069] Then, when the rotation angle is between 90 degrees and 180 degrees, the object A rotates so that the long side direction is parallel to the optical axis, so that the rotation center Ac of the object A moves away from the radiation source 2 and is located coaxially with the rotation axis C at a rotation angle of 180 degrees, as shown in Figs. 16(d) and (e). Furthermore, when the rotation angle is between 180 degrees and 270 degrees, the object A rotates so that the short side direction is parallel to the optical axis again, so that the rotation center Ac of the object A moves in a direction approaching the radiation source 2 and is closest to the radiation source 2 at a rotation angle of 270 degrees, which is the minimum imaging distance FCDmin, as shown in Figs. 16(f) and (g). When the rotation angle is between 270 degrees and 360 degrees, the object A rotates so that the long side direction is parallel to the optical axis, so that the rotation center Ac of the object A moves away from the radiation source 2 and returns to the position of the rotation angle of 0 degrees at a rotation angle of 360 degrees, as shown in Figs. 16(h) and (i). When the locus of the rotation center Ac of the object A to be inspected on the XY table 15 is plotted at rotation angles from 0 to 360 degrees, the result is as shown in FIG.

[0070] In this way, the position of the object A to be inspected may be moved by the XY table 15, rather than by the X mechanism 14.

[0071] (5) The pitch of the rotation angle when capturing the fluoroscopic images does not need to be equal, and may be changed according to the shape of the object A to be inspected. That is, in the object A to be inspected, the pitch of the rotation angle may be large, for example, 45 degrees, for a part with a simple shape, and the pitch of the rotation angle may be small, for example, 10 degrees, for a part with a complex shape. This allows the dimensions of the object A to be calculated more accurately, and an image with high image quality precision can be generated while preventing contact between the object A to be inspected and the radiation source 2. Also, for example, for parts with simple shapes, even if the pitch of the rotation angle is large, the effect on image quality is small. Therefore, the total number of views can be reduced, and the scan time can be shortened.

[0072] (Other embodiments) In this specification, an embodiment of the present invention has been described, but this embodiment is presented as an example and is not intended to limit the scope of the invention. The above-mentioned embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. The embodiment and its modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and gist of the invention. [Explanation of symbols]

[0073] 100 CT equipment 1 Examination table 11 Rotating table 12 Lifting mechanism 13 Y mechanism 14X mechanism 2 Radiation source 21 Support frame 3. Detector 31 Support frame 4. Filter section 5. Camera 6 Display section 7 Input section 8. Control Unit 81 Examination table control unit 82 Radiation Source Control Section 83 Reconstruction part 84 Camera control unit 85 Limit distance calculation section 86 Scan area distance calculation unit 87 Comparison Section 88 Magnification ratio calculation section

Claims

1. A CT apparatus for photographing an object while rotating the object, an inspection table on which the object to be inspected is placed and which moves and rotates the object to be inspected; a radiation source that irradiates the object to be inspected with a radiation beam; a detector disposed opposite the radiation source across the object to be inspected; A critical distance FCD is a minimum distance required for the object to not come into contact with the radiation source during rotation, in the distance FCD between the focus of the radiation source and the center of the object to be inspected. Ｌ A limit distance calculation unit that calculates a scan area distance calculation unit that calculates a scan area distance FCDs, which is a distance between a focal point of the radiation source and a center of the object to be inspected in a set scan area; The limit distance FCD Ｌ a comparison unit for comparing the scan area distance FCDs with the distance FCDs to determine a photographing distance that is the distance FCD when photographing; an inspection table control unit that controls the inspection table to move the object to and from the radiation source based on the imaging distance determined by the comparison unit during imaging; A CT apparatus comprising:

2. The limit distance calculation unit calculates the limit distance FCD based on the size of the ROI circumscribing the drawn fluoroscopic image. Ｌ The CT apparatus according to claim 1, wherein the calculation is performed by:

3. The CT apparatus according to claim 2 , wherein the ROI is drawn by the limit distance calculation unit.

4. The limit distance calculation unit calculates the limit distance FCD Ｌ Add a preset distance to The comparison unit is a limit distance FCD Ｌ 4. The CT apparatus according to claim 1, wherein the imaging distance is determined by comparing a distance obtained by adding the predetermined distance to the imaging distance FCDs with a scan area distance FCDs.

5. a magnification ratio calculation unit that calculates a magnification ratio of a perspective image at each rotation angle, 4. The CT apparatus according to claim 1, wherein the magnification ratio calculation unit calculates the magnification ratio so that the magnification ratio becomes the same as that of a fluoroscopic image captured at the shortest distance among the shooting distances when the shooting distance changes depending on a rotation angle.

Images