X-ray imaging apparatus and X-ray tube

Abstract

The present invention provides an X-ray imaging apparatus and X-ray tube that can reduce artifacts caused by a limited number of imaging angles while suppressing the increase in imaging time required to acquire projected image data. [Solution] This X-ray imaging apparatus 100 comprises an X-ray tube 1 including a first electron irradiation unit 10a and a second electron irradiation unit 10b, a detector 2, a subject placement unit 3, a rotation mechanism 4, and a control unit 21. The control unit 21 performs the following controls: for each of the multiple imaging angles 6, it controls the simultaneous irradiation of electrons from the first electron irradiation unit 10a and the second electron irradiation unit 10b; and it controls the first relative focal position 7a of the first electron irradiation unit 10a at the first imaging angle 6a, the second relative focal position 7b of the second electron irradiation unit 10b at the first imaging angle 6a, the third relative focal position 7d of the first electron irradiation unit 10a at the second imaging angle 6b, and the fourth relative focal position 7e of the second electron irradiation unit 10b at the second imaging angle 6b, so as not to overlap with each other.

Description

Technical Field

[0005] ,

[0001] The present invention relates to an X-ray imaging apparatus and an X-ray tube.

Background Art

[0002] Conventionally, X-ray imaging apparatuses have been known (see, for example, Patent Document 1).

[0003] In the above Patent Document 1, an X-ray CT imaging apparatus (X-ray imaging apparatus) that performs CT (Computed Tomography) imaging of a subject is disclosed. The X-ray CT imaging apparatus includes an X-ray tube, a detector, a subject placement unit on which the subject is placed, and a computer (control unit). The X-ray tube irradiates X-rays toward the subject that rotates together with the subject placement unit. The detector detects the X-rays irradiated from the X-ray tube. The computer generates a CT image based on a plurality of projection image data acquired by the detector. The X-ray tube includes a single cathode element (electron irradiation unit) and a target. By irradiating electrons from the cathode element toward the focal position on the target, X-rays are emitted from the focal point (focal position) on the target toward the detector.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although not disclosed in Patent Document 1 mentioned above, in an X-ray CT imaging device (X-ray imaging device), when generating a CT image, multiple projection image data are acquired by imaging the subject from various shooting angles. To generate a high-resolution CT image, a sufficient number of shooting angles (views) of projection image data are required, but the time required to acquire a sufficient number of projection image data angles increases. If the number of shooting angles remains small without increasing the time required to acquire projection image data, artifacts caused by the small number of shooting angles (few views) occur in the reconstructed image (CT image). Therefore, it is desirable to reduce artifacts caused by a small number of shooting angles while suppressing the increase in the time required to acquire projection image data.

[0006] This invention was made to solve the above-mentioned problems, and one objective of this invention is to provide an X-ray imaging apparatus and X-ray tube that can reduce artifacts caused by a small number of imaging angles while suppressing an increase in the imaging time required to acquire projection image data. [Means for solving the problem]

[0007] X-ray imaging apparatus comprising: an X-ray tube including at least a first electron irradiation unit and a second electron irradiation unit that irradiate electrons to different focal positions of a target; a detector that detects X-rays emitted from the X-ray tube; a subject placement unit disposed between the X-ray tube and the detector on which a subject is placed; a rotation mechanism that rotates either the imaging unit including the X-ray tube and the detector or the subject placement unit to change the imaging angle of the subject; and a control unit that acquires multiple projection image data at each of multiple imaging angles from the detector and generates a CT image based on the acquired multiple projection image data, wherein the control unit performs the following controls for each of the multiple imaging angles: simultaneous irradiation of electrons from the first electron irradiation unit and the second electron irradiation unit; and control that the first relative focal position of the first electron irradiation unit with respect to the subject at the first imaging angle, the second relative focal position of the second electron irradiation unit with respect to the subject at the first imaging angle, the third relative focal position of the first electron irradiation unit with respect to the subject at the second imaging angle, and the fourth relative focal position of the second electron irradiation unit with respect to the subject at the second imaging angle, so as not to overlap with each other. Furthermore, an X-ray tube used in an X-ray imaging apparatus that acquires multiple projection image data at multiple shooting angles and generates a CT image based on the acquired multiple projection image data, comprising at least a first electron irradiation unit and a second electron irradiation unit that simultaneously irradiate electrons at different focal positions of a target, wherein the distance between the first focal point of the first electron irradiation unit and the second focal point of the second electron irradiation unit and the number of focal points on the target are preset so that the first relative focal position of the first electron irradiation unit with respect to the subject at the first shooting angle, the second relative focal position of the second electron irradiation unit with respect to the subject at the first shooting angle, the third relative focal position of the first electron irradiation unit with respect to the subject at the second shooting angle, and the fourth relative focal position of the second electron irradiation unit with respect to the subject at the second shooting angle do not overlap with each other. [Effects of the Invention]

[0008] In the above-described X-ray imaging apparatus, electrons are simultaneously irradiated from multiple electron irradiation units, including the first and second electron irradiation units, to different focal positions of the target for each of the multiple imaging angles. This allows for the acquisition of multiple projection image data corresponding to the number of electron irradiation units for each imaging angle. Therefore, the number of projection image data acquired can be increased without increasing the imaging time. Furthermore, by making the first to fourth relative focal positions different so as not to overlap, the imaging angles of the subject in the projection image data acquired for each imaging angle can be made different from each other, corresponding to the number of electron irradiation units. Thus, projection image data at different imaging angles can be acquired in each of the multiple acquired projection image data. As a result, a sufficient number of imaging angles (views) of projection image data can be acquired in the increased number of projection image data. For these reasons, artifacts caused by a small number of imaging angles can be reduced while suppressing the increase in imaging time required to acquire projection image data. Here, in this specification, relative focal position means the relative position of the focal point formed on the target in the X-ray tube, which rotates relatively around the subject, with respect to the subject. The rotation of the subject mounting section or the X-ray tube by the rotation mechanism changes the relative focal position of the first electron irradiation section and the second electron irradiation section with respect to the subject. Furthermore, in the above-mentioned X-ray tube, electrons are simultaneously irradiated from multiple electron irradiation units, including the first and second electron irradiation units, to different focal positions of the target for each of the multiple imaging angles. This allows for the acquisition of multiple projection image data corresponding to the number of electron irradiation units for each imaging angle. Therefore, the number of projection image data acquired can be increased without increasing the imaging time. In addition, since the distance between the first focal point of the first electron irradiation unit and the second focal point of the second electron irradiation unit, and the number of focal points on the target are predetermined so that the first to fourth relative focal positions do not overlap, projection image data at different imaging angles can be acquired for each of the multiple projection image data acquired. Therefore, a sufficient number of imaging angles (views) of projection image data can be acquired in the increased number of projection image data. For these reasons, artifacts caused by a small number of imaging angles can be reduced while suppressing the increase in imaging time required to acquire projection image data. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing the overall configuration of an X-ray imaging apparatus according to one embodiment. [Figure 2] This diagram illustrates a configuration in which electrons are irradiated simultaneously from multiple electron irradiation units. [Figure 3] This is a schematic diagram illustrating the configuration of multiple electron emission units. [Figure 4] This diagram illustrates the positional relationship of relative focal points in one embodiment. [Figure 5] This diagram illustrates the relative positional relationship of the focal points in the first comparative example. [Figure 6] This figure illustrates the number of relative focal points and the positional relationship between them in one embodiment. [Figure 7] This diagram illustrates the number of relative focal points and their positional relationships in the second comparative example. [Figure 8]This is a flowchart illustrating the X-ray image acquisition and reconstruction processes. [Figure 9] This figure illustrates the comparison between the tomographic images obtained by the X-ray imaging apparatus in the third and fourth comparative examples and the tomographic images obtained by the X-ray imaging apparatus in one embodiment. [Figure 10] These are enlarged sections and graphs illustrating the comparison between tomographic images obtained by the X-ray imaging apparatus in the third and fourth comparative examples and tomographic images obtained by the X-ray imaging apparatus in one embodiment. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below with reference to the drawings.

[0011] First, with reference to Figures 1 to 3, the overall configuration of an X-ray imaging apparatus 100 according to one embodiment will be described.

[0012] As shown in Figure 1, the X-ray imaging apparatus 100 is a device that captures an X-ray image of the subject 90 and generates a CT image 82. The X-ray imaging apparatus 100 of this embodiment is used, for example, for non-destructive testing. The subject 90 to be inspected is not particularly limited as long as it is an object other than a living organism. The X-ray imaging apparatus 100 acquires projection image data 81 (X-ray image data) of the subject 90 from the entire circumference of the subject mounting section 3 on which the subject 90 is placed, and constructs a tomographic image based on the acquired projection image data 81.

[0013] The X-ray imaging apparatus 100 comprises an X-ray tube 1, a detector 2, a subject placement unit 3, a rotation mechanism 4, and a control device 20. The X-ray tube 1 and the detector 2 constitute an imaging unit 5 that captures X-ray images.

[0014] The X-ray tube 1 is configured to irradiate the subject 90 placed on the subject placement unit 3 with X-rays 70. The X-ray tube 1 is configured to generate X-rays 70 when a high voltage is applied. The X-ray tube 1 faces the detector 2 through the subject placement unit 3. The X-ray tube 1, the subject placement unit 3, and the detector 2 are arranged side by side in the horizontal direction. In the present embodiment, the X-ray tube 1 is configured as a micro-focus X-ray tube with a focal size in microns. Note that the X-ray tube 1 may be configured as an X-ray tube with a focal size in millimeters.

[0015] As shown in FIG. 2, the X-ray tube 1 includes a plurality of electron irradiation units 10. Each of the plurality of electron irradiation units 10 simultaneously irradiates electrons 71 to different focal positions 13 on the target 11. In the present embodiment, the X-ray tube 1 includes a first electron irradiation unit 10a, a second electron irradiation unit 10b, and a third electron irradiation unit 10c. Each of the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c simultaneously irradiates electrons 71 to different focal positions 13 on the target 11. The details of the configuration of the X-ray tube 1 will be described later.

[0016] The detector 2 is configured to detect the X-rays 70 emitted from the X-ray tube 1. The X-rays 70 emitted from the X-ray tube 1 pass through the subject 90 and enter the detection surface of the detector 2. The detector 2 is configured to convert the detected X-rays 70 into an electrical signal. Thereby, an X-ray image reflecting the transmission of the X-rays 70 in the subject 90 is obtained. The detector 2 is, for example, an FPD (Flat Panel Detector). The detector 2 is composed of a plurality of conversion elements (not shown) and pixel electrodes (not shown) arranged on the plurality of conversion elements. The plurality of conversion elements and pixel electrodes are arranged in a matrix within the detection surface at a predetermined period (pixel pitch).

[0017] The detector 2 is configured to simultaneously detect the X-ray 70 based on the electrons 71 irradiated by the first electron irradiation unit 10a, the X-ray 70 based on the electrons 71 irradiated by the second electron irradiation unit 10b, and the X-ray 70 based on the electrons 71 irradiated by the third electron irradiation unit 10c. The detector 2 converts the X-ray 70 based on the first electron irradiation unit 10a, the X-ray 70 based on the second electron irradiation unit 10b, and the X-ray 70 based on the third electron irradiation unit 10c into electrical signals. The detection signal (image signal) including the first detection signal (first image signal) of the X-ray 70 based on the first electron irradiation unit 10a, the second detection signal (second image signal) of the X-ray 70 based on the second electron irradiation unit 10b, and the third detection signal (third image signal) of the X-ray 70 based on the third electron irradiation unit 10c is sent to the image processing unit 23 described later.

[0018] The subject placement unit 3 is disposed between the X-ray tube 1 and the detector 2 and is configured to place the subject 90. The subject placement unit 3 is constituted by a subject stage on which the subject 90 is placed.

[0019] The rotation mechanism 4 rotates one of the imaging unit 5 including the X-ray tube 1 and the detector 2 and the subject placement unit 3. Thereby, the rotation mechanism 4 is configured to change the imaging angle 6 (see FIG. 2) of the subject 90. The rotation mechanism 4 rotates one of the imaging unit 5 and the subject placement unit 3 around the rotation axis 4a. The rotation axis 4a is orthogonal to a straight line (representative line of the X-ray beam) from the X-ray tube 1 through the subject 90 on the subject placement unit 3 and toward the detector 2. In the present embodiment, the rotation axis 4a passes through the subject placement unit 3 and extends along the vertical direction.

[0020] In the present embodiment, the rotation mechanism 4 rotates the subject placement unit 3 around the rotation axis 4a in the horizontal plane. The rotation mechanism 4 does not rotate the imaging unit 5. The rotation mechanism 4 includes a motor (not shown) and a speed reducer (not shown) for rotating the subject placement unit 3.

[0021] As the subject mounting section 3 rotates, the subject 90 placed on the subject mounting section 3 rotates around the rotation axis 4a in the horizontal plane. This rotation changes the shooting angle 6 (see Figure 2) of the subject 90. The shooting angle 6 is the relative angle between the subject 90 and the shooting section 5. In this embodiment, the shooting angle 6 is the angle of the subject mounting section 3 around the rotation axis 4a, with the origin angle (initial angle) of the rotation mechanism 4 being 0 degrees. Figure 2 shows an example of the subject mounting section 3 being rotated from the origin angle to a certain shooting angle 6. The rotation mechanism 4 can rotate the subject mounting section 3 to any angle so that the subject 90 is positioned at any shooting angle 6.

[0022] As shown in Figure 1, the control device 20 includes a control unit 21, a storage unit 25, and an input / output unit 26. The control device 20 is configured, for example, by a PC (personal computer). The control device 20 is connected to a display device 27 and an input device 28.

[0023] The control unit 21 is a computer including a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The control unit 21 performs predetermined control when the CPU executes a predetermined program 80. Functionally, the control unit 21 includes a main control unit 22, an image processing unit 23, and a shooting control unit 24. That is, the control unit 21 functions as the main control unit 22, the image processing unit 23, and the shooting control unit 24 when the CPU executes a predetermined program 80. Note that the image processing unit 23 and the shooting control unit 24 are examples of the "control unit" in the claims.

[0024] The main control unit 22 executes the program 80 stored in the memory unit 25 to set the imaging conditions in the X-ray imaging apparatus 100 and to control the start and stop of imaging.

[0025] The image processing unit 23 acquires multiple projection image data 81 from the detector 2 for each of the multiple shooting angles 6. In this embodiment, the image processing unit 23 acquires from the detector 2, for each of the shooting angles 6, a first detection signal obtained by converting X-rays 70 based on the first electron irradiation unit 10a into an electrical signal, a second detection signal obtained by converting X-rays 70 based on the second electron irradiation unit 10b into an electrical signal, and a third detection signal obtained by converting X-rays 70 based on the third electron irradiation unit 10c into an electrical signal. The image processing unit 23 generates projection image data 81 from the acquired first detection signal, generates projection image data 81 from the acquired second detection signal, and generates projection image data 81 from the acquired third detection signal. In other words, for each of the shooting angles 6, the image processing unit 23 generates projection image data 81 from each of the first to third detection signals of the detector 2. As described above, by changing the shooting angle 6 of the subject 90 with the rotation mechanism 4, an X-ray image of the subject 90 is captured by the imaging unit 5, including the first to third electron irradiation units 10c, at each of the multiple preset shooting angles 6. The projected image data 81 is X-ray image data based on each of the first to third detection signals acquired for each shooting angle 6.

[0026] The acquisition of projected image data 81 based on the first to third detection signals for each of the six shooting angles is performed over a predetermined angular range. The predetermined angular range is 360 degrees (one rotation). However, the predetermined angular range is not limited to 360 degrees (one rotation); it is not particularly limited as long as it is 180 degrees (half rotation) or more. Furthermore, the multiple shooting angles 6 are angles set at equal angular intervals obtained by dividing the predetermined angular range (360 degrees (one rotation)) by the number of shooting angles.

[0027] As shown in Figure 4(c), the first relative focal position 7a of the first electron irradiation unit 10a with respect to the subject 90 at the first shooting angle 6a, the second relative focal position 7b of the second electron irradiation unit 10b with respect to the subject 90 at the first shooting angle 6a, the third relative focal position 7c of the third electron irradiation unit 10c with respect to the subject 90 at the first shooting angle 6a, the fourth relative focal position 7d of the first electron irradiation unit 10a with respect to the subject 90 at the second shooting angle 6b, the fifth relative focal position 7e of the second electron irradiation unit 10b with respect to the subject 90 at the second shooting angle 6b, and the sixth relative focal position 7f of the third electron irradiation unit 10c with respect to the subject 90 at the second shooting angle 6b are different so as not to overlap with each other.

[0028] In other words, the shooting angles 6 of the subject 90 in the projected image data 81 based on each of the first to third detection signals of the first shooting angle 6a are different from each other, the shooting angles 6 of the subject 90 in the projected image data 81 based on each of the first to third detection signals of the second shooting angle 6b are different from each other, and in all cases, the shooting angles 6 of the subject 90 in the projected image data 81 based on each of the first to third detection signals of the first shooting angle 6a and the shooting angles 6 of the subject 90 in the projected image data 81 based on each of the first to third detection signals of the second shooting angle 6b are different from each other.

[0029] The numbers assigned to the relative focal positions 7 are, for the sake of explanation, numbers assigned sequentially according to the number of electron irradiation units 10. Therefore, the fourth relative focal position 7d in this embodiment is an example of the "third relative focal position of the first electron irradiation unit with respect to the subject at the second shooting angle" in the claims, and the fifth relative focal position 7e in this embodiment is an example of the "fourth relative focal position of the second electron irradiation unit with respect to the subject at the second shooting angle" in the claims.

[0030] As shown in Figure 1, the image processing unit 23 is configured to generate a CT image 82 based on multiple acquired projection image data 81. The image processing unit 23 generates the CT image 82 by performing a reconstruction process on a set of projection image data 81 (called a projection dataset) based on each of the first to third detection signals for each of the 360-degree imaging angles 6. The CT image 82 is an image that reflects the three-dimensional structure of the subject 90 and is reconstructed by computation from X-ray images (projection image data 81) based on each of the first to third detection signals for each of the multiple imaging angles 6. The CT image 82 can take the form of a tomographic image, a three-dimensional stereoscopic image, or other forms of the subject 90.

[0031] The imaging control unit 24 controls the operation of the X-ray tube 1 and the rotation mechanism 4. Specifically, the imaging control unit 24 controls the simultaneous irradiation of electrons 71 from the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c for each of the multiple imaging angles 6.

[0032] Furthermore, the shooting control unit 24 controls the first relative focal position 7a of the first electron irradiation unit 10a with respect to the subject 90 at the first shooting angle 6a, the second relative focal position 7b of the second electron irradiation unit 10b with respect to the subject 90 at the first shooting angle 6a, the third relative focal position 7c of the third electron irradiation unit 10c with respect to the subject 90 at the first shooting angle 6a, the fourth relative focal position 7d of the first electron irradiation unit 10a with respect to the subject 90 at the second shooting angle 6b, the fifth relative focal position 7e of the second electron irradiation unit 10b with respect to the subject 90 at the second shooting angle 6b, and the sixth relative focal position 7f of the third electron irradiation unit 10c with respect to the subject 90 at the second shooting angle 6b, so that they do not overlap with each other.

[0033] The storage unit 25 is configured to include a volatile memory device and a non-volatile memory device. The storage unit 25 stores the program 80, various setting information (not shown) related to X-ray image acquisition of the X-ray imaging device 100, and so on. The storage unit 25 stores multiple acquired projection image data 81 and CT images 82 generated based on those projection image data 81.

[0034] The input / output unit 26 is composed of various interfaces for inputting and outputting signals to and from the control device 20. The input / output unit 26 is connected to the display device 27 and the input device 28. The display device 27 is, for example, a liquid crystal display. The input device 28 includes a keyboard and a mouse. The image processing unit 23 acquires detection signals (image signals) from the detector 2 via the input / output unit 26. The main control unit 22 transmits instructions such as starting or stopping shooting to the shooting control unit 24 via the input / output unit 26.

[0035] (Configuration of an X-ray tube) As shown in Figure 2, the X-ray tube 1 includes a target 11 and a plurality of electron irradiation units 10. The target 11 and the plurality of electron irradiation units 10 are housed in a vacuum vessel 12.

[0036] The X-ray tube 1 is configured to generate X-rays 70 from the target 11 by applying a voltage between the electron irradiation unit 10, which is the cathode, and the target 11, which is the anode, thereby irradiating electrons 71 from the electron irradiation unit 10 and causing the irradiated electrons 71 to collide with the target 11.

[0037] The multiple electron irradiation units 10 are configured to irradiate electrons 71 at different focal positions 13 on the target 11. In this embodiment, there are three electron irradiation units 10: a first electron irradiation unit 10a, a second electron irradiation unit 10b, and a third electron irradiation unit 10c. The number of multiple electron irradiation units 10 is not particularly limited. The number of electron irradiation units 10 in the X-ray tube 1 may be, for example, two or four or more. Each of the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c is arranged in a plane of rotation perpendicular to the rotation axis 4a of the rotation mechanism 4.

[0038] Each of the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c simultaneously irradiates electrons 71 toward different focal positions 13 of the target 11. Each of the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c simultaneously irradiates electrons 71 at each of the multiple imaging angles 6, based on the control of the imaging control unit 24. The first electron irradiation unit 10a irradiates electrons 71 toward the first focal position 13a (first focus) of the target 11. This causes X-rays 70 to be emitted toward the detector 2 from the first focal position 13a corresponding to the first electron irradiation unit 10a. The second electron irradiation unit 10b irradiates electrons 71 toward the second focal position 13b (second focus) of the target 11. This causes X-rays 70 to be emitted toward the detector 2 from the second focal position 13b corresponding to the second electron irradiation unit 10b. The third electron irradiation unit 10c irradiates electrons 71 toward the third focal position 13c (third focus) of the target 11. As a result, X-rays 70 are emitted toward the detector 2 from the third focal position 13c corresponding to the third electron irradiation unit 10c.

[0039] The first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c are positioned such that the distance from the first focal position 13a (first focal point) to the rotation axis 4a passing through the subject mounting unit 3, the distance from the second focal position 13b (second focal point) to the rotation axis 4a passing through the subject mounting unit 3, and the distance from the third focal position 13c (third focal point) to the rotation axis 4a passing through the subject mounting unit 3 are approximately equal. Therefore, the distance from each of the first to ninth relative focal positions (7a to 7i) to the rotation axis 4a passing through the subject mounting unit 3 is approximately equal.

[0040] In other words, as shown in Figure 4(b), the shooting control unit 24 is configured to arrange the first to ninth relative focal positions (7a to 7i) in an arc, at different positions that do not overlap with each other, with respect to the rotation axis 4a of the rotation mechanism 4, as the shooting angle 6 changes.

[0041] As shown in Figure 3, the X-ray tube 1 includes an electron irradiation unit moving mechanism 14. The electron irradiation unit moving mechanism 14 is configured to change the distance between the first electron irradiation unit 10a and the second electron irradiation unit 10b, and the distance between the second electron irradiation unit 10b and the third electron irradiation unit 10c. The electron irradiation unit moving mechanism 14 is configured to move at least two of the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c in a direction substantially perpendicular to the optical axis direction of the X-ray 70 and the rotation axis 4a of the rotation mechanism 4. The electron irradiation unit moving mechanism 14 includes motors for moving the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c.

[0042] The structure of the target 11 is not particularly limited. The target 11 may be either a reflective target or a transmission target. A reflective target has a surface that is inclined at an angle to the electrons 71, and is a type of target that emits X-rays 70 so that they are reflected by the inclined surface in a direction different from the direction in which the electrons 71 are coming. A transmission target has a pair of (front and back) surfaces that are perpendicular to the electrons 71, and is a type of target that emits X-rays 70 from the other surface so that they pass through the target 11 upon collision of electrons 71 with one surface. Furthermore, the target 11 may be fixed in place in the vacuum vessel 12, or it may be rotated by a drive source such as a motor. That is, the X-ray tube 1 may have a so-called rotating anode type structure.

[0043] One target 11 is provided for each of the multiple electron irradiation units 10. One target 11 is provided for the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c. The focal positions 13 of each of the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c are dispersed on the surface of the target 11.

[0044] Figure 3 shows a more detailed configuration example of the electron irradiation unit 10 and target 11. Figure 3 shows an example of a transmission type target. In Figure 3, the X-ray tube 1 includes an electron source unit 16 having a plurality of cold cathode electron sources 15 arranged in a plane. Each of the plurality of electron irradiation units 10 is composed of different groups of the plurality of cold cathode electron sources 15.

[0045] The electron source unit 16 is formed by applying semiconductor manufacturing technology to create an array of numerous cold cathode electron sources 15 on a substrate 17. The substrate 17 is a flat plate made of silicon, glass, or the like. A group composed of some of the multiple cold cathode electron sources 15 arranged in the array constitutes one electron irradiation unit 10.

[0046] A group constituting one of the multiple electron irradiation units 10 consists of one or more cold cathode electron sources 15 that irradiate electrons 71 to the same focal point 13 on the target 11. One electron irradiation unit 10 includes one or more cold cathode electron sources 15. One electron irradiation unit 10 includes, for example, 100 or more or 1000 or more cold cathode electron sources 15. When one electron irradiation unit 10 is composed of multiple cold cathode electron sources 15, the collection of electrons 71 irradiated from each of the multiple cold cathode electron sources 15 constituting the electron irradiation unit 10 forms the electrons 71 irradiated from the electron irradiation unit 10. The electrons 71 are irradiated to one focal point 13 on the target 11. X-rays 70 are generated from the focal point 13 on the target 11 by the collision of the electrons 71. The spot (point-like region) where the electrons 71 collide at the focal point 13 becomes the focal point of the X-rays 70. The imaging control unit 24 (see Figure 1) controls the power supply 18 to apply a predetermined voltage between the cathode electrode (not shown) and the target 11.

[0047] (Control of the arrangement of the 1st to 9th relative focal points by the shooting control unit) The imaging control unit 24 is configured to simultaneously irradiate electrons 71 to the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c, each directed toward different focal positions 13 of the target 11. As a result, the detector 2 detects the first to third detection signals, and the image processing unit 23 generates projection image data 81 based on each of the first to third detection signals.

[0048] Referring to Figures 4 and 5, the positional relationship of the first to ninth relative focal positions (7a to 7i) will be explained. Figure 4(a) is a schematic diagram showing the first focal position 13a (first focal point), the second focal position 13b (second focal point), and the third focal position 13c (third focal point), the subject 90, and the detector 2 as viewed from the vertical direction in an example of this embodiment. Figure 4(b) is a schematic diagram showing the positional relationship of the first to ninth relative focal positions (7a to 7i) in an example of this embodiment. Figure 4(c) is an enlarged view of part A of Figure 4(b). Furthermore, Figure 5(a) is a schematic diagram showing the first focal position 13a (first focal point), the second focal position 13b (second focal point), and the third focal position 13c (third focal point), the subject 90, and the detector 2 as viewed from the vertical direction in the first comparative example; Figure 5(b) is a schematic diagram showing the positional relationship of the first to ninth relative focal positions (79a to 79i) in the first comparative example; and Figure 5(c) is an enlarged view of part B of Figure 5(b).

[0049] As shown in Figure 5(c) relating to the first comparative example, the second relative focal position 79b at the first shooting angle 6a overlaps with the fourth relative focal position 79d at the second shooting angle 6b. Also, the third relative focal position 79c at the first shooting angle 6a overlaps with the fifth relative focal position 79e at the second shooting angle 6b and the seventh relative focal position 79g at the third shooting angle 6c. Furthermore, the sixth relative focal position 79f at the second shooting angle 6b overlaps with the eighth relative focal position 79h at the third shooting angle 6c.

[0050] In other words, in the first comparative example, the shooting angle 6 of the projected image data 81 based on the first detection signal originating from the first electron irradiation unit 10a at the first shooting angle 6a, the shooting angle 6 of the projected image data 81 based on the second detection signal originating from the second electron irradiation unit 10b, and the shooting angle 6 of the projected image data 81 based on the third detection signal originating from the third electron irradiation unit 10c, and the shooting angle 6 of the projected image data 81 based on the first detection signal originating from the first electron irradiation unit 10a at the second shooting angle 6b, and the second detection signal originating from the second electron irradiation unit 10b The same projection image data 81 is included in the following cases: the shooting angle 6 of the projected image data 81, the shooting angle 6 of the projected image data 81 based on the third detection signal originating from the third electron irradiation unit 10c, and the shooting angle 6 of the projected image data 81 based on the first detection signal originating from the first electron irradiation unit 10a, the shooting angle 6 of the projected image data 81 based on the second detection signal originating from the second electron irradiation unit 10b, and the shooting angle 6 of the projected image data 81 based on the third detection signal originating from the third electron irradiation unit 10c at the third shooting angle 6c. In this case, these projection image data 81 at the same shooting angle 6 can be said to be substantially the same, and therefore the number of shooting angles 6 in the projected image data 81 cannot be increased.

[0051] In contrast, in the X-ray imaging apparatus 100 according to this embodiment, as shown in the example in Figure 4(c), the first to ninth relative focal positions (7a to 7i) are all located in different positions without overlapping. Therefore, the number of imaging angles 6 in the projected image data 81 can be increased. The imaging control unit 24 controls the relative focal positions 7 in the first imaging angle 6a (first relative focal position 7a, second relative focal position 7b, and third relative focal position 7c), the second imaging angle 6b (fourth relative focal position 7d, fifth relative focal position 7e, and sixth relative focal position 7f), and the third imaging angle 6c (seventh relative focal position 7g, eighth relative focal position 7h, and ninth relative focal position 7i) to be different from each other without overlapping.

[0052] Specifically, the shooting control unit 24 is configured to make the first to ninth relative focal positions (7a to 7i) different so as not to overlap with each other by adjusting at least one of the following: the distance between focal points p (see Figure 3) between the first focal point (first focal position 13a) of the first electron irradiation unit 10a and the second focal point (second focal position 13b) of the second electron irradiation unit 10b; the distance between focal point and subject d (see Figure 2) between the first focal point (first focal position 13a) and the subject 90; the number of shooting angles 6 (number of views) v; the rotation angle range θ by the rotation mechanism 4; the number of focal points N in the target 11; and the number of relative focal position 7 m, including the second relative focal position 7b, that exist between the first relative focal position 7a and the second relative focal position 7b.

[0053] Here, the distance p between the first focal point (first focal position 13a) of the first electron irradiation unit 10a and the second focal point (second focal position 13b) of the second electron irradiation unit 10b is arranged to be approximately equal to the distance p between the second focal point (second focal position 13b) of the second electron irradiation unit 10b and the third focal point (third focal position 13c) of the third electron irradiation unit 10c. Therefore, the distance p between the focal points may also be the distance p between the second focal point (second focal position 13b) of the second electron irradiation unit 10b and the third focal point (third focal position 13c) of the third electron irradiation unit 10c.

[0054] Furthermore, the focal-subject distance d between the first focal point (first focal position 13a) and the subject 90, the focal-subject distance d between the second focal point (second focal position 13b) and the subject 90, and the focal-subject distance d between the third focal point (third focal position 13c) and the subject 90 are configured to be approximately equal. Therefore, the focal-subject distance d may also be the focal-subject distance d between the second focal point (second focal position 13b) or the third focal point (third focal position 13c) and the subject 90. Also, the number m of relative focal positions 7 may be the number m of relative focal positions 7 that include the third relative focal position 7c, which is located between the second relative focal position 7b and the third relative focal position 7c.

[0055] More specifically, the imaging control unit 24 is configured to make the first to ninth relative focal positions (7a to 7i) different so that they do not overlap with each other, based on the following equation (1).

number

[0056] In this embodiment, the number of focal points N in the target 11 is 3 and is stored as a fixed value in the storage unit 25. In addition, before the shooting unit 5 starts shooting the subject 90, the user can set the magnification ratio, rotation angle range θ, and the number of shooting angles 6 (views) v of the subject 90 in the projected image data 81 using the input device 28. The shooting control unit 24 acquires the information of the fixed value of the number of focal points N in the target 11 stored in the storage unit 25, and the information of the magnification ratio, rotation angle range θ, and the number of shooting angles 6 v of the subject 90 in the projected image data 81 that has been input by the user via the input device 28.

[0057] Here, the inter-focal distance p corresponds to the distance between adjacent electron irradiation units 10 in the plurality of electron irradiation units 10. The imaging control unit 24 acquires information on the inter-focal distance p based on the distance between the first electron irradiation unit 10a and the second electron irradiation unit 10b.

[0058] Furthermore, the focal distance between subjects d corresponds to the magnification ratio of the subject 90 in the projected image data 81, which can be set by the user. The shooting control unit 24 receives information on the magnification ratio of the subject 90 in the projected image data 81 via input from the user through the input device 28, and obtains information on the focal distance between subjects d from the information on the magnification ratio of the subject 90 in the projected image data 81. The method for obtaining information on the focal distance between subjects d based on the information on the magnification ratio of the subject 90 in the projected image data 81 is not particularly limited and can be obtained by various methods as appropriate.

[0059] The shooting control unit 24 acquires parameters other than the acquired information, such as those satisfying equation (1), based on the fixed value information of the number of focal points N, the information acquired based on user input, and the above equation (1). As an example, the shooting control unit 24 acquires a value for the distance between focal points p and a value for the number of relative focal points 7, including the second relative focal point 7b, which exists between the first relative focal point 7a and the second relative focal point 7b, such that the above equation (1) is satisfied.

[0060] The imaging control unit 24 adjusts the inter-focal distance p and the number m of relative focal positions 7 based on the value of the inter-focal distance p obtained by the calculation of equation (1) above, and the value of the number m of relative focal positions 7 that include the second relative focal position 7b, which is located between the first relative focal position 7a and the second relative focal position 7b.

[0061] Specifically, the imaging control unit 24 moves the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c via the electron irradiation unit moving mechanism 14 so that the distance p between the first focal point (first focal position 13a) of the first electron irradiation unit 10a and the second focal point (second focal position 13b) of the second electron irradiation unit 10b, and the distance p between the second focal point (second focal position 13b) of the second electron irradiation unit 10b and the third focal point (third focal position 13c) of the third electron irradiation unit 10c become the acquired distance p, and the number m of relative focal positions 7, including the second relative focal position 7b, that exist between the first relative focal position 7a and the second relative focal position 7b become the acquired number m of relative focal positions 7.

[0062] After the first electron irradiation unit 10a, the second electron irradiation unit 10b, and the third electron irradiation unit 10c are moved by the electron irradiation unit movement mechanism 14 via the imaging control unit 24, the main control unit 22 receives an input operation from the user via the input device 28 to start imaging by the imaging unit 5, and then starts imaging by the imaging unit 5.

[0063] (Relative focal position number) Referring to Figures 6(a) to (d), the number m of relative focal positions 7, including the second relative focal position 7b, which lies between the first relative focal position 7a and the second relative focal position 7b, will be explained. Note that the number m of relative focal positions 7, including the second relative focal position 7b, which lies between the first relative focal position 7a and the second relative focal position 7b, is the same as the number m of relative focal positions 7, including the third relative focal position 7c, which lies between the second relative focal position 7b and the third relative focal position 7c.

[0064] In an example of controlling the arrangement of the first to ninth relative focal positions (7a to 7i) by the shooting control unit 24 described above, the shooting control unit 24 acquires the value of the distance between focal points p and the value of a number m of relative focal position 7, which includes the second relative focal position 7b, located between the first relative focal position 7a and the second relative focal position 7b, based on the above equation (1). Figures 6(a) to (d) show an example of the positional relationship between the first to sixth relative focal positions (7a to 7f), the seventh relative focal position 7g of the first electron irradiation unit 10a with respect to the subject 90 at the third shooting angle 6c, the eighth relative focal position 7h of the second electron irradiation unit 10b with respect to the subject 90 at the third shooting angle 6c, and the ninth relative focal position 7i of the third electron irradiation unit 10c with respect to the subject 90 at the third shooting angle 6c, based on the value of a number m of relative focal position 7 and the value of the distance between focal points p acquired by the above equation (1). In one example of the relative focal position 7, the distance d between focal subjects is 75 mm, the number v of the shooting angle 6 is 100, the rotation angle range θ is 180 degrees, and the number N of focal points at target 11 is 3.

[0065] Figure 6(a) shows an example of the positional relationship between the 1st to 9th relative focal positions (7a to 7i) when the number m of the relative focal position 7 obtained by the above equation (1) is 1 and the interfocal distance p is 0.78 mm. As shown in Figure 6(a), the number m of the relative focal position 7, including the 5th relative focal position 7e, which is located between the 4th relative focal position 7d and the 5th relative focal position 7e at the 2nd shooting angle 6b, is 1. In this case, the 1st to 3rd relative focal positions (7a to 7c) at the 1st shooting angle 6a, the 4th to 6th relative focal positions (7d to 7f) at the 2nd shooting angle 6b, and the 7th to 9th relative focal positions (7g to 7i) at the 3rd shooting angle 6c are all different from each other and do not overlap.

[0066] Figure 6(b) shows an example of the positional relationship between the 1st to 9th relative focal positions (7a to 7i) when the number m of the relative focal position 7 obtained by the above equation (1) is 2 and the interfocal distance p is 1.57 mm. As shown in Figure 6(b), the number m of the relative focal position 7, including the 5th relative focal position 7e, which is located between the 4th relative focal position 7d and the 5th relative focal position 7e at the 2nd shooting angle 6b, is 2. In this case as well, the 1st to 3rd relative focal positions (7a to 7c) at the 1st shooting angle 6a, the 4th to 6th relative focal positions (7d to 7f) at the 2nd shooting angle 6b, and the 7th to 9th relative focal positions (7g to 7i) at the 3rd shooting angle 6c are all different from each other and do not overlap.

[0067] Figure 6(c) shows an example of the positional relationship between the 1st to 9th relative focal positions (7a to 7i) when the number m of the relative focal position 7 obtained by the above equation (1) is 4 and the interfocal distance p is 3.14 mm. As shown in Figure 6(c), the number m of the relative focal position 7, including the 5th relative focal position 7e, which is located between the 4th relative focal position 7d and the 5th relative focal position 7e at the 2nd shooting angle 6b, is 4. In this case as well, the 1st to 3rd relative focal positions (7a to 7c) at the 1st shooting angle 6a, the 4th to 6th relative focal positions (7d to 7f) at the 2nd shooting angle 6b, and the 7th to 9th relative focal positions (7g to 7i) at the 3rd shooting angle 6c are all different from each other and do not overlap.

[0068] Figure 6(d) shows an example of the positional relationship between the 1st to 9th relative focal positions (7a to 7i) when the number m of the relative focal position 7 obtained by the above equation (1) is 5 and the interfocal distance p is 3.92 mm. As shown in Figure 6(d), the number m of the relative focal position 7, including the 5th relative focal position 7e, which is located between the 4th relative focal position 7d and the 5th relative focal position 7e at the 2nd shooting angle 6b, is 5. In this case as well, the 1st to 3rd relative focal positions (7a to 7c) at the 1st shooting angle 6a, the 4th to 6th relative focal positions (7d to 7f) at the 2nd shooting angle 6b, and the 7th to 9th relative focal positions (7g to 7i) at the 3rd shooting angle 6c are all different from each other and do not overlap.

[0069] In the example shown in Figures 6(a) to (d), where the value of the interfocal distance p and the value of the number m of relative focal positions 7, including the second relative focal position 7b, which is located between the first relative focal position 7a and the second relative focal position 7b, are obtained based on the above equation (1), the projection image data 81 based on the first detection signal originating from the first electron irradiation unit 10a, the projection image data 81 based on the second detection signal originating from the second electron irradiation unit 10b, and the projection image data 81 based on the third detection signal originating from the third electron irradiation unit 10c, for the first to third shooting angles 6c, do not include projection image data 81 for the same shooting angle 6.

[0070] Note that in equation (1) above, the remainder when the number m of the relative focal position 7 is divided by the number of focal points N (3 in the above example) at target 11 is not 0. In contrast, as in the second comparative example shown in Figure 7, when the number m of the relative focal position 79 is 3, the remainder when the number m (3) of the relative focal position 79 is divided by the number of focal points N (3) at target 11 is 0. In this case, the second relative focal position 79b at the first shooting angle 6a and the fourth relative focal position 79d at the second shooting angle 6b overlap. Also, the third relative focal position 79c at the first shooting angle 6a, the fifth relative focal position 79e at the second shooting angle 6b, and the seventh relative focal position 79g at the third shooting angle 6c overlap. Furthermore, the sixth relative focal position 79f at the second shooting angle 6b and the eighth relative focal position 79h at the third shooting angle 6c overlap. In other words, the projected image data 81 based on the third detection signal originating from the third electron irradiation unit 10c at the first shooting angle 6a, the projected image data 81 based on the second detection signal originating from the second electron irradiation unit 10b at the second shooting angle 6b, and the projected image data 81 based on the first detection signal originating from the first electron irradiation unit 10a at the third shooting angle 6c are all the same projected image data 81 at the same shooting angle 6.

[0071] (Reconstruction process) A brief explanation will be given of the reconstruction process performed by the image processing unit 23 (see Figure 1) using multiple projection image data 81.

[0072] The data used in the reconstruction process will now be described. The storage unit 25 of the control device 20 (see Figure 1) stores the program 80 executed by the image processing unit 23 and multiple projection image data 81. Each of the multiple projection image data 81 is stored associated with the shooting angle 6 at the time the projection image data 81 was acquired, information about the electron irradiation unit 10 (information identifying whether it is the first electron irradiation unit 10a, the second electron irradiation unit 10b, or the third electron irradiation unit 10c), and information about the relative focal position 7. The storage unit 25 also stores the generated CT image 82.

[0073] Here, the detector 2 simultaneously detects, for each of the multiple imaging angles 6, the X-rays 70 emitted from the first focal spot corresponding to the first electron irradiation unit 10a and transmitted through the subject 90, the X-rays 70 emitted from the second focal spot corresponding to the second electron irradiation unit 10b and transmitted through the subject 90, and the X-rays 70 emitted from the third focal spot corresponding to the third electron irradiation unit 10c and transmitted through the subject 90. In other words, the detection signal (image signal) acquired by the detector 2 is an overlapping detection signal (image signal) of X-rays 70 emitted from the first, second, and third focal spots, respectively, so general analytical CT reconstruction methods such as filtered back projection cannot be applied.

[0074] Therefore, in this embodiment, reconstruction processing is performed using the iterative approximation method. The image processing unit 23 iteratively calculates the contribution rate from each of the first, second, and third focal points using the iterative approximation method. As a result, the image processing unit 23 can obtain the detection signal (image signal) of the X-ray 70 emitted from the first focal point, the detection signal (image signal) of the X-ray 70 emitted from the second focal point, and the detection signal (image signal) of the X-ray 70 emitted from the third focal point from the detection signal (image signal) in which the X-rays 70 emitted from each of the first, second, and third focal points overlap. Therefore, a high-quality reconstructed image can be generated. The method of obtaining detection signals (image signals) for each focal point from overlapping detection signals (image signals) of X-rays 70 emitted from each of multiple focal points using the iterative approximation method is a known technique disclosed, for example, in "Daniel F. Yu, Jeffrey A. Fessler, Edward P. Ficaro, “Maximum-Likelihood Transmission Image Reconstruction for Overlapping Transmission Beams” IEEE transactions on medical imaging 19.11 (2000): p.1094-1105," so a detailed explanation is omitted here.

[0075] As a result of the reconstruction process using the iterative approximation method, the image processing unit 23 generates a CT image 82 of the subject 90.

[0076] (X-ray image acquisition and reconstruction processing) Referring to Figure 8, the X-ray image acquisition and reconstruction processes performed by the control unit 21 will be explained. Note that the order of the processing steps can be reversed or performed simultaneously, as long as they do not conflict with each other.

[0077] In step S1, the shooting control unit 24 receives input from the storage unit 25 or from the user via the input device 28 to acquire at least one of the following: information on the distance between focal points p, information on the distance between focal subjects d, information on the number v of the shooting angle 6, information on the rotation angle range θ, information on the number N of focal points in the target 11, and information on the number m of relative focal positions 7. The process then proceeds to step S2.

[0078] In step S2, the imaging control unit 24 acquires parameters other than the above information that satisfy equation (1) based on the acquired information and equation (1) above. After that, the process proceeds to step S3.

[0079] In step S3, the imaging control unit 24 performs adjustments based on parameters other than the information obtained by the calculation of equation (1) above. After that, the process proceeds to step S4.

[0080] In step S4, the main control unit 22 receives an operation input from the user via the input device 28 and transmits a signal to the imaging control unit 24 instructing it to start the imaging operation. The imaging control unit 24, upon receiving the signal from the main control unit 22, controls the X-ray tube 1 and the rotation mechanism 4 to start imaging the subject 90. The imaging control unit 24 then captures projection image data 81 within a predetermined angular range. After that, the process proceeds to step S5.

[0081] In step 5, the image processing unit 23 performs reconstruction processing based on each projection image data 81 included in the projection dataset. The process then proceeds to step S7.

[0082] In step 6, the image processing unit 23 stores the generated CT image 82 in the storage unit 25. After that, the processing is terminated.

[0083] (Comparison with Comparative Examples 3 and 4) Referring to Figures 9(a) to 9(c), the comparison results between the tomographic images obtained by the X-ray imaging apparatus in the third and fourth comparative examples and the tomographic images obtained by the X-ray imaging apparatus 100 in this embodiment will be explained.

[0084] Note that the subject 90 shown in Figures 9(a) to 9(c) is the same subject 90. The subject 90 is a cylindrical sample made of resin, and contains material or voids with a low X-ray absorption coefficient 70 inside the subject 90. The upper images in Figures 9(a) to 9(c) are tomographic images along the horizontal direction of the cylindrical subject 90. The lower images in Figures 9(a) to 9(c) are difference images between the tomographic image in the upper image and the image of the cross-section obtained by cutting the cylindrical subject 90 at the position corresponding to the tomographic image. In other words, the lower images in Figures 9(a) to 9(c) are images in which artifacts 93 have been extracted from the tomographic image in the upper image.

[0085] Figure 9(a) shows a tomographic image acquired by the X-ray imaging apparatus in the third comparative example. The X-ray imaging apparatus in the third comparative example is equipped with a single-focus X-ray tube consisting of a target and a single electron irradiation unit. In the upper and lower parts of Figure 9(a), radially extending streaky artifacts 93 can be seen, which are caused by the limited number of imaging angles (few views).

[0086] Furthermore, Figure 9(b) shows a tomographic image acquired by the X-ray imaging apparatus in the fourth comparative example. The X-ray imaging apparatus in the fourth comparative example is equipped with a three-focus X-ray tube consisting of a target and three electron irradiation units. However, unlike the X-ray imaging apparatus 100 in this embodiment, the X-ray imaging apparatus in the fourth comparative example does not perform control to ensure that the first to third relative focal point positions (7a to 7c) at the first imaging angle 6a, the fourth to sixth relative focal point positions (7d to 7f) at the second imaging angle 6b, and the seventh to ninth relative focal point positions (7g to 7i) at the third imaging angle 6c do not overlap with each other. In other words, the X-ray imaging apparatus in the fourth comparative example includes overlapping relative focal positions at the first to third relative focal positions (7a to 7c) at the first imaging angle 6a, the fourth to sixth relative focal positions (7d to 7f) at the second imaging angle 6b, and the seventh to ninth relative focal positions (7g to 7i) at the third imaging angle 6c. Therefore, in the upper and lower figures of Figure 9(b), numerous radially extending streaky artifacts 93 can be observed, which are caused by the small number of imaging angles (few views).

[0087] In contrast, Figure 9(c) is a tomographic image acquired by the X-ray imaging apparatus 100 in this embodiment. The imaging control unit 24 controls the first to third relative focal positions (7a to 7c) at the first imaging angle 6a, the fourth to sixth relative focal positions (7d to 7f) at the second imaging angle 6b, and the seventh to ninth relative focal positions (7g to 7i) at the third imaging angle 6c so that they do not overlap with each other. As a result, the upper and lower figures of Figure 9(c) show that, compared to Figure 9(a) in the third comparative example and Figure 9(b) in the fourth comparative example, there are virtually no radially extending streaky artifacts 93 caused by a smaller number of imaging angles (few views). Thus, the X-ray imaging apparatus 100 in this embodiment can reduce artifacts caused by a small number of imaging angles.

[0088] Furthermore, Figure 10(a) is an enlarged view of portion C in the upper part of Figure 9(a) relating to the third comparative example, Figure 10(b) is an enlarged view of portion D in the upper part of Figure 9(b) relating to the fourth comparative example, and Figure 10(c) is an enlarged view of portion E in the upper part of Figure 9(c) relating to this embodiment. Also, Figure 10(d) is a graph showing the pixel values ​​in the portion of line 91a to 91c in Figures 10(a) to 10(c). Comparing Figures 10(a) to 10(c), it can be confirmed that Figure 10(c) relating to this embodiment has fewer artifacts 93 than Figure 10(a) relating to the third comparative example and Figure 10(b) relating to the fourth comparative example. Also, from Figures 10(a) to (d), it can be confirmed that the contrast of the vertically elongated structure 92 is improved in the tomographic image acquired by the X-ray imaging apparatus 100 in this embodiment.

[0089] [Differentiation] It should be noted that the embodiments and examples disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims rather than by the above-described embodiments and examples, and includes all modifications (modifications) within the meaning and scope equivalent to the claims. For example, the X-ray tube may have a predetermined focal distance p between the first focal point of the first electron irradiation unit and the second focal point of the second electron irradiation unit, and the number of focal points N on the target, such that the first relative focal point position of the first electron irradiation unit with respect to the subject at the first imaging angle, the second relative focal point position of the second electron irradiation unit with respect to the subject at the first imaging angle, the third relative focal point position of the first electron irradiation unit with respect to the subject at the second imaging angle, and the fourth relative focal point position of the second electron irradiation unit with respect to the subject at the second imaging angle do not overlap with each other and are different. Furthermore, for example, the imaging control unit may be configured to individually control the electron irradiation from multiple electron irradiation units, and may be configured to select two or more of the multiple electron irradiation units to irradiate electrons simultaneously. In this case, the focal distance p can be appropriately changed according to the selected electron irradiation units, so an electron irradiation unit movement mechanism does not need to be provided. Furthermore, for example, the first to fourth relative focal points may be positioned on the contour of a polygon rather than on a circular arc centered on the rotation axis of the rotation mechanism, as long as they are in different positions that do not overlap with each other as the shooting angle changes. Furthermore, for example, the first electron irradiation unit and the second electron irradiation unit may be positioned so as to be offset vertically with respect to the rotation plane perpendicular to the rotation axis of the rotation mechanism. Furthermore, for example, the shooting control unit may be configured to make the first to ninth relative focal positions different so as not to overlap with each other by replacing at least one of the following parameters: the distance between focal points p, the distance between focal subjects d, the number of shooting angles v, the rotation angle range θ by the rotation mechanism, and the number of focal points N and the number of relative focal positions m on the target with another parameter, or by adding another parameter and adjusting at least one of these parameters. Furthermore, for example, X-ray imaging equipment may be used for medical purposes. In this case, the subject is a living organism being examined. Furthermore, for example, multiple electron irradiation units may be composed of a thermal cathode electron source.

[0090] [Pattern] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0091] (Item 1) An X-ray tube including at least a first electron irradiation section and a second electron irradiation section that irradiate electrons at different focal positions of a target, A detector for detecting X-rays emitted from the X-ray tube, A subject placement section is positioned between the X-ray tube and the detector, on which the subject is placed. A rotation mechanism that rotates one of the imaging unit, which includes the X-ray tube and the detector, and the subject placement unit, so as to change the imaging angle of the subject, The system includes a control unit that acquires multiple projection image data at each of the multiple shooting angles from the detector and generates a CT image based on the acquired multiple projection image data, The control unit, Control to simultaneously irradiate electrons from the first electron irradiation unit and the second electron irradiation unit for each of the multiple aforementioned shooting angles, An X-ray imaging apparatus that controls the first relative focal position of the first electron irradiation unit with respect to the subject at a first imaging angle, the second relative focal position of the second electron irradiation unit with respect to the subject at a first imaging angle, the third relative focal position of the first electron irradiation unit with respect to the subject at a second imaging angle, and the fourth relative focal position of the second electron irradiation unit with respect to the subject at a second imaging angle, so as not to overlap with each other. By simultaneously irradiating the target with electrons from multiple electron irradiators, including the first and second electron irradiators, at different focal positions for each of the multiple shooting angles, multiple projection image data can be acquired for each shooting angle, corresponding to the number of electron irradiators. Therefore, the number of projection image data acquired can be increased without increasing the shooting time. Furthermore, by making the first to fourth relative focal positions different so as not to overlap, the shooting angles of the subject in the projection image data acquired for each shooting angle can be made different for each of the multiple electron irradiators. Thus, projection image data at different shooting angles can be obtained in each of the multiple acquired projection image data. Therefore, a sufficient number of shooting angles (views) of projection image data can be acquired in the increased number of projection image data. For these reasons, artifacts caused by a small number of shooting angles can be reduced while suppressing the increase in shooting time required to acquire projection image data. (Item 2) The X-ray imaging apparatus according to item 1, wherein the control unit is configured to arrange the first relative focal position, the second relative focal position, the third relative focal position, and the fourth relative focal position at different, non-overlapping positions around the rotation axis of the rotation mechanism, and on an arc, in accordance with the change in the imaging angle. In this case, since the distance between each of the first to fourth relative focal points and the subject can be kept constant as the shooting angle changes, when generating a CT image based on projection image data acquired at each of the first to fourth relative focal points, the CT image can be generated more easily through reconstruction processing than when the distances between each of the first to fourth relative focal points and the subject are different. (Item 3) The X-ray imaging apparatus according to item 1 or 2, wherein the first electron irradiation unit and the second electron irradiation unit simultaneously irradiate electrons for each of the plurality of imaging angles based on the control of the control unit, and are arranged side by side in a plane of rotation perpendicular to the rotation axis of the rotation mechanism. In this case, since the first electron irradiation unit and the second electron irradiation unit can be arranged on the same plane at each of the first to fourth relative focal point positions corresponding to the change in the imaging angle, when generating a CT image based on the projection image data acquired at each of the first to fourth relative focal point positions, the CT image can be generated more easily through reconstruction processing compared to when the first electron irradiation unit and the second electron irradiation unit are not arranged on the same plane at each of the first to fourth relative focal points. (Item 4) The X-ray imaging apparatus according to any one of items 1 to 3, wherein the control unit adjusts at least one of the following: the distance between focal points between the first focal point of the first electron irradiation unit and the second focal point of the second electron irradiation unit; the distance between focal points or the second focal point and the subject; the number of imaging angles; the rotation angle range by the rotation mechanism; the number of focal points in the target; and the number of relative focal points, including the second relative focal point, that exist between the first relative focal point and the second relative focal point, thereby causing the first relative focal point, the second relative focal point, the third relative focal point, and the fourth relative focal point to be different so as not to overlap with each other. In this case, the control unit can easily make the first to fourth relative focal positions different so as not to overlap by adjusting at least one of the following: the distance between focal points, the distance between focal subjects, the number of shooting angles, the rotation angle range, the number of focal points, and the number of relative focal positions. As a result, a sufficient number of shooting angles (views) of projected image data can be acquired in the increased projected image data, thereby suppressing the increase in shooting time required to acquire projected image data, and easily reducing artifacts caused by a small number of acquired projected image data due to a small number of shooting angles. (Item 5) The X-ray imaging apparatus according to item 4, wherein the control unit is configured to make the first relative focal position, the second relative focal position, the third relative focal position, and the fourth relative focal position different from each other based on the following formula (1).

number

[0092] 1 X-ray tube 2 detectors 3. Subject placement section 4 Rotation mechanism 4a Rotation axis 5. Photography Department 6. Shooting angle 6a First shooting angle 6b Second shooting angle 6c Third shooting angle 7. Relative focal point 7a First relative focal point 7b Second relative focal point 7c 3rd relative focus position 7d Fourth relative focal point 7e 5th relative focus position 7f 6th relative focal point 7g Relative focal point 7 7h 8th relative focus position 7i 9th relative focal point 10 Electron irradiation section 10a 1st electron irradiation section 10b Second electron irradiation section 10c Third electron irradiation section 11 Targets 13 Focus position 13a 1st focus position 13b 2nd focus position 13c 3rd focal point 21 Control Unit 70 X-ray 71 electronic 81 Projected image data 82 CT images 90 Subjects 100 X-ray imaging equipment

Claims

1. An X-ray tube including at least a first electron irradiation section and a second electron irradiation section that irradiate electrons at different focal positions of a target, A detector for detecting X-rays emitted from the X-ray tube, A subject placement section is positioned between the X-ray tube and the detector, on which the subject is placed. A rotation mechanism that rotates one of the imaging unit, which includes the X-ray tube and the detector, and the subject placement unit, so as to change the imaging angle of the subject, The system includes a control unit that acquires multiple projection image data at each of the multiple aforementioned shooting angles from the detector and generates a CT image based on the acquired multiple projection image data, The control unit, Control to simultaneously irradiate electrons from the first electron irradiation unit and the second electron irradiation unit for each of the multiple aforementioned shooting angles, An X-ray imaging apparatus that controls the first relative focal position of the first electron irradiation unit with respect to the subject at a first imaging angle, the second relative focal position of the second electron irradiation unit with respect to the subject at a first imaging angle, the third relative focal position of the first electron irradiation unit with respect to the subject at a second imaging angle, and the fourth relative focal position of the second electron irradiation unit with respect to the subject at a second imaging angle, so as not to overlap with each other.

2. The X-ray imaging apparatus according to claim 1, wherein the control unit is configured to arrange the first relative focal position, the second relative focal position, the third relative focal position, and the fourth relative focal position at different positions that do not overlap with each other and are arranged on an arc, with respect to the rotation axis of the rotation mechanism, in accordance with the change in the imaging angle.

3. The X-ray imaging apparatus according to claim 1, wherein the first electron irradiation unit and the second electron irradiation unit simultaneously irradiate electrons for each of the plurality of imaging angles based on the control of the control unit, and are arranged side by side in a rotation plane perpendicular to the rotation axis of the rotation mechanism.

4. The X-ray imaging apparatus according to claim 1, wherein the control unit adjusts at least one of the following: the distance between focal points between the first focal point of the first electron irradiation unit and the second focal point of the second electron irradiation unit; the distance between focal points or the second focal point and the subject; the number of imaging angles; the range of rotation angles by the rotation mechanism; the number of focal points in the target; and the number of relative focal points, including the second relative focal point, that exist between the first relative focal point and the second relative focal point, thereby causing the first relative focal point, the second relative focal point, the third relative focal point, and the fourth relative focal point to be different from each other and not overlap.

5. The X-ray imaging apparatus according to claim 4, wherein the control unit is configured to make the first relative focal position, the second relative focal position, the third relative focal position, and the fourth relative focal position different from each other based on the following formula (1). [Math 3] Here, p is the distance between focal points, d is the distance between focal subjects, v is the number of shooting angles, θ is the rotation angle range by the rotation mechanism, N is the number of focal points in the target, and m is the number of relative focal points, including the second relative focal point, that exist between the first relative focal point and the second relative focal point.

6. The X-ray tube includes the target and at least the first electron irradiation unit and the second electron irradiation unit that irradiate electrons to different focal positions on the target, respectively. The X-ray imaging apparatus according to claim 1, wherein the detector is configured to simultaneously detect X-rays based on electrons irradiated by the first electron irradiation unit and X-rays based on electrons irradiated by the second electron irradiation unit.

7. An X-ray tube used in an X-ray imaging apparatus that acquires multiple projection image data at multiple shooting angles and generates a CT image based on the acquired multiple projection image data, It comprises at least a first electron irradiation unit and a second electron irradiation unit that simultaneously irradiate electrons at different focal positions of the target, An X-ray tube in which the distance between the first focal point of the first electron irradiation unit and the second focal point of the second electron irradiation unit, and the number of focal points on the target are set in advance so that the first relative focal point position of the first electron irradiation unit with respect to the subject at a first shooting angle, the second relative focal point position of the second electron irradiation unit with respect to the subject at a first shooting angle, the third relative focal point position of the first electron irradiation unit with respect to the subject at a second shooting angle, and the fourth relative focal point position of the second electron irradiation unit with respect to the subject at a second shooting angle do not overlap with each other and are different.

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