X-ray imaging device

Abstract

To provide an X-ray imaging apparatus capable of inhibiting a rotation target from being damaged due to heat generation in collision of an electron beam with the rotation target, and inhibiting an acquired X-ray image from becoming unsharp due to variations in an incidence angle of the electron beam made incident on the rotation target.SOLUTION: An X-ray imaging apparatus 100 includes: an X-ray source 1 having a rotation target 11 supported rotatably around a rotation axis line 11b, and a plurality of electron beam emission parts 12 for emitting an electron beam 36 to each of a plurality of focal positions 14 with different distances from the rotation axis line in the rotation target, in which an incident angle θ of the electron beam emitted from each of the plurality of electron beam emission parts and made incident at a focal position of each of the plurality of electron beam emission parts in the rotation target is adjusted to be constant; a detector 2 for detecting an X-ray 10; an image processing unit 5 for generating an image; and an imaging control unit 6 for controlling the X-ray source so as to sequentially switch the plurality of electron beam emission parts and emit the electron beam.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an X-ray imaging apparatus, and more particularly to an X-ray imaging apparatus including an X-ray source having a rotating target and an electron emission unit.

Background Art

[0002] Conventionally, an X-ray imaging apparatus including an X-ray source having a rotating target and an electron emission unit has been known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses an X-ray imaging apparatus including an X-ray tube having an anode and a cathode. The anode is a rotating anode and includes a disk-shaped target. The target rotates about the central axis of the anode as the rotation center axis. X-rays are generated from the target when an electron beam from the cathode collides with the rotating target. The electron gun of the cathode includes a cathode that generates thermoelectrons, a grid electrode that focuses the thermoelectrons into a thin beam-shaped electron beam, and two deflection electrodes that electrostatically deflect the electron beam. By deflecting the electron beam by the deflection electrodes to deflect the target, the focal point is moved on the target along the inclined surface of the target in a direction orthogonal to the rotation direction of the target. By deflecting the electron beam and moving the focal point in a direction orthogonal to the rotation direction of the target, a plurality of spiral focal tracks are formed on the target. By increasing the substantial area of the focal point on the target, the electron beam current for generating X-rays of the X-ray tube that is allowed is increased.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The X-ray tube described in Patent Document 1 is thought to suppress damage to the target caused by heat generation due to electron beam collisions by deflecting the electron beam and moving the focal point in a direction perpendicular to the rotation direction of the target. Although not described in Patent Document 1, it is thought that when the electron beam is deflected, the incident angle of the electron beam irradiated from the electron source and incident on the focal point on the rotating target changes. When the electron beam is deflected and the focal point on the rotating target moves away from the central axis of the rotating target, it is thought that the incident angle of the electron beam incident on the focal point on the rotating target before deflection and the incident angle of the electron beam incident on the focal point on the rotating target after deflection will be different. As a result, the shape of the focal point before deflection and the shape of the focal point after deflection will be different, and the effect of aberration will be greater. Here, "aberration" indicates that the electron beam irradiated from the electron source is not focused to a single point on the rotating target by the deflection electrode. As a result, the more the focal point on the rotating target moves in a direction perpendicular to the rotation direction of the target due to the deflection of the electron beam, the more unclear the acquired X-ray image becomes. Therefore, it is desirable to suppress damage to the rotating target caused by heat generation due to electron beam collisions, while also suppressing the blurring of acquired X-ray images due to fluctuations in the incident angle of the electron beam incident on the rotating target.

[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 that can suppress damage to the rotating target caused by heat generation due to collision of electron beams with the rotating target, while also suppressing blurring of the acquired X-ray image due to fluctuations in the incident angle of the electron beams incident on the rotating target. [Means for solving the problem]

[0007] This invention 1The X-ray imaging apparatus in this context includes a rotating target supported so as to be rotatable around a rotation axis, and a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, and an X-ray source that is irradiated from each of the plurality of electron emission units and adjusted so that the incident angle of the electron beams incident at each of the plurality of electron emission units on the rotating target is constant, and from the X-ray source To the subject A detector that detects the emitted X-rays, In each of the multiple shooting angles detection vessel Based on the detection signal output from multiple It comprises an image processing unit that generates an image, and an imaging control unit that controls the X-ray source to sequentially switch between multiple electron emission units to irradiate with an electron beam. The image processing unit is configured to correct the position of the projected image of the subject in multiple images for multiple shooting angles based on electron beams irradiated from each of the multiple electron emission units. ru. Furthermore, the X-ray imaging apparatus in the second aspect of this invention includes a rotating target supported so as to be rotatable around a rotation axis, and a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, and comprises an X-ray source adjusted so that the incident angle of the electron beams irradiated from each of the plurality of electron emission units and incident at each of the focal positions of the plurality of electron emission units on the rotating target is constant, a detector that detects the X-rays emitted from the X-ray source, an image processing unit that generates an image based on the detection signal output from the detector, and an imaging control unit that controls the X-ray source to sequentially switch the plurality of electron emission units to irradiate electron beams, wherein the imaging control unit controls the X-ray source to sequentially switch the plurality of electron emission units to irradiate electron beams based on the remaining amount of electron beam irradiation time, which is the maximum time for which the rotating target can be continuously irradiated with electron beams irradiated from the electron emission units at the focal positions without being damaged by heat, and which is a previously acquired amount. Furthermore, the X-ray imaging apparatus in the third aspect of this invention includes a rotating target supported so as to be rotatable around a rotation axis, and a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, and an X-ray source adjusted so that the incident angle of the electron beams irradiated from each of the plurality of electron emission units and incident at each of the focal positions of the plurality of electron emission units on the rotating target is constant, a detector that detects the X-rays emitted from the X-ray source, an image processing unit that generates an image based on the detection signal output from the detector, an imaging control unit that controls the X-ray source to irradiate electron beams by sequentially switching the plurality of electron emission units, a subject mounting unit disposed between the X-ray source and the detector and supporting the subject, and a rotation mechanism that rotates the imaging unit including the X-ray source and the detector and the subject mounting unit relative to each other so as to change the imaging angle of the subject, wherein the plurality of electron emission units include a first electron emission unit and a second electron emission unit different from the first electron emission unit, and the imaging control unit is pre-acquired Based on the electron beam irradiation time, which is the maximum time that the target can be continuously irradiated with an electron beam from the electron emission unit to the focal position without being damaged by heat, the X-ray source is controlled to sequentially switch between multiple electron emission units to irradiate with an electron beam. The image processing unit generates multiple projection image data based on the detection signals at each of the multiple shooting angles, and generates a CT image based on the generated multiple projection image data. When the rotation mechanism rotates from the first shooting angle to the second shooting angle at one of the multiple shooting angles, the shooting control unit determines whether the remaining electron beam irradiation time at the focal position of the first electron emission unit that irradiated with an electron beam at the first shooting angle is shorter than the electron beam irradiation time at the focal position at the second shooting angle. If the shooting control unit determines that the remaining electron beam irradiation time at the first electron emission unit is shorter than the electron beam irradiation time at the second shooting angle, it controls the X-ray source to switch from the first electron emission unit to the second electron emission unit and irradiate with an electron beam. [Effects of the Invention]

[0008] An X-ray imaging apparatus in one aspect of the present invention includes, as described above, a rotating target supported so as to be rotatable around a rotation axis, a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, an X-ray source irradiated from each of the plurality of electron emission units and adjusted so that the incidence angle of the electron beam incident on each of the plurality of electron emission units on the rotating target is constant, and an imaging control unit that controls the X-ray source to sequentially switch the plurality of electron emission units to irradiate electron beams. By sequentially switching the plurality of electron emission units to irradiate electron beams, electron beams are irradiated at a plurality of focal positions on the rotating target at different distances from the rotation axis. By changing the focal positions on the rotating target, the heat-generating areas on the rotating target can be dispersed. Therefore, compared to the case where the same focal position on the rotating target continuously generates heat, the localized temperature rise on the rotating target can be reduced, thereby suppressing damage to the rotating target caused by heat generation due to electron beam collisions with the rotating target. Furthermore, by adjusting the incident angle of the electron beams, which are irradiated from each of the multiple electron emission units and incident on each of the multiple electron emission units on the rotating target at different focal positions, to remain constant, it is possible to suppress changes in the focal size at each of the multiple electron emission units. Therefore, the effects of aberrations caused by switching between electron emission units can be suppressed. As a result, it is possible to suppress damage to the rotating target caused by heat generation due to electron beam collisions, while also suppressing blurring of the acquired X-ray image due to fluctuations in the cathode-anode distance. [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 is a diagram illustrating the X-ray source and detector. [Figure 3] This is a schematic diagram illustrating the configuration of multiple electron emission units. [Figure 4]It is a schematic plan view for explaining a focal orbit on a rotating target. [Figure 5] It is a schematic view for explaining the configuration of a cold cathode electron source included in an electron emission section. [Figure 6] It is a first diagram for explaining the switching of the electron emission section. [Figure 7] It is a second diagram for explaining the switching of the electron emission section. [Figure 8] It is a third diagram for explaining the switching of the electron emission section. [Figure 9] It is a diagram showing various data stored in a storage unit. [Figure 10] It is a first diagram for explaining the correction of the change in the magnification of a subject. [Figure 11] It is a second diagram for explaining the correction of the change in the magnification of a subject. [Figure 12] It is a diagram for explaining the correction of the position of the projection image of a subject. [Figure 13] It is a flowchart for explaining the imaging operation of an X-ray imaging apparatus. [Figure 14] It is a flowchart for explaining the flow of reconstruction processing.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments embodying the present invention will be described based on the drawings.

[0011] (Overall Configuration of X-ray Imaging Apparatus) Referring to FIG. 1, the overall configuration of an X-ray imaging apparatus 100 according to an embodiment will be described.

[0012] As shown in FIG. 1, the X-ray imaging apparatus 100 is an apparatus for taking an X-ray CT image 56 of a subject 90. The X-ray imaging apparatus 100 of the present embodiment is used, for example, for non-destructive inspection purposes. In this case, the subject 90 is a sample to be inspected. Further, the X-ray imaging apparatus 100 of the present embodiment is used, for example, for medical purposes. In this case, the subject 90 is a living body to be inspected.

[0013] The X-ray imaging apparatus 100 comprises an X-ray source 1, a detector 2, a subject placement unit 3, a rotation mechanism 4, an image processing unit 5, and an imaging control unit 6. The X-ray source 1 and the detector 2 constitute an imaging unit 7 that captures X-ray images.

[0014] The X-ray source 1 is configured to irradiate the subject 90, which is placed in the subject placement section 3, with X-rays. The X-ray source 1 is configured to generate X-rays 10 when a high voltage is applied. The X-ray source 1 faces the detector 2 via the subject placement section 3. In this embodiment, the X-ray source 1, the subject placement section 3, and the detector 2 are arranged horizontally.

[0015] Detector 2 is configured to detect X-rays 10 emitted from X-ray source 1. The X-rays 10 emitted from X-ray source 1 pass through the object 90 and enter the detection surface of detector 2. Detector 2 is configured to convert the detected X-rays 10 into an electrical signal. This provides an X-ray image that reflects the transmission of X-rays 10 through the object 90. Detector 2 is, for example, an FPD (Flat Panel Detector). 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). The detection signal (image signal) from detector 2 is sent to image processing unit 5.

[0016] The subject placement section 3 is positioned between the X-ray source 1 and the detector 2 and is configured to support the subject 90. In this embodiment, the subject placement section 3 is composed of a subject stage on which the subject 90 is placed. The subject 90 may be placed in the subject placement section 3 via a holder (not shown) or the like for holding the subject 90.

[0017] The rotation mechanism 4 rotates the imaging unit 7, which includes the X-ray source 1 and the detector 2, relative to the subject placement unit 3. This allows the rotation mechanism 4 to change the imaging angle 40 of the subject 90. The rotation mechanism 4 rotates the imaging unit 7 and the subject placement unit 3 relative to each other around the rotation axis 4a. The rotation axis 4a is perpendicular to the straight line (representative line of the X-ray beam) from the X-ray source 1 through the subject 90 on the subject placement unit 3 to the detector 2. In this embodiment, the rotation axis 4a passes through the subject placement unit 3 and is aligned vertically.

[0018] The rotation mechanism 4 rotates at least one of the shooting unit 7 and the subject mounting unit 3 around the rotation axis 4a. In this embodiment, the rotation mechanism 4 rotates the subject mounting unit 3 in the horizontal plane around the rotation axis 4a. The rotation mechanism 4 does not rotate the shooting unit 7. The rotation mechanism 4 includes a motor (not shown) and a reduction gear (not shown) for rotating the subject mounting unit 3, which is the subject stage. In this embodiment, the subject mounting unit 3 and the rotation mechanism 4 constitute the rotating stage for the subject 90.

[0019] As the subject mounting section 3 rotates, the subject 90 supported by the subject mounting section 3 rotates around the rotation axis 4a in the horizontal plane. This rotation changes the shooting angle 40 (see Figure 2) of the subject 90. The shooting angle 40 is the relative angle between the subject 90 and the shooting section 7. In this embodiment, the shooting angle 40 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 40. 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 40.

[0020] Returning to Figure 1, the image processing unit 5 is located in the control unit 20. The control unit 20 is configured, for example, as a PC (personal computer). The control unit 20 comprises a main control unit 21, an image processing unit 5, a storage unit 22, and an input / output unit 23. The control unit 20 is connected to the display device 24 and the input device 25.

[0021] The main control unit 21 is composed of, for example, a processor such as a CPU (Central Processing Unit) or a circuit, and by executing an application program stored in the memory unit 22, it controls the setting of imaging conditions and the start and stop of imaging in the X-ray imaging apparatus 100.

[0022] The image processing unit 5 is comprised of a processor such as a GPU (Graphics Processing Unit) or an FPGA (Field-Programmable Gate Array) configured for image processing.

[0023] The image processing unit 5 acquires multiple projection image data 50 (see Figure 9) from the detector 2 for each of the multiple shooting angles 40. In other words, the image processing unit 5 generates projection image data 50 from the detection signal (image signal) of the detector 2 for each shooting angle. As described above, by changing the shooting angle 40 of the subject using the rotation mechanism 4, an X-ray image of the subject 90 is captured by the imaging unit 7 at each of the multiple preset shooting angles 40. The projection image data 50 is the data of the X-ray image acquired for each shooting angle.

[0024] The acquisition of projection image data 50 for each shooting angle 40 is performed over a predetermined angle range. The predetermined angle range is 360 degrees (1 rotation). In addition, the number of projection image data 50 acquired corresponds to the predetermined number of shooting angles (views). In this embodiment, the multiple shooting angles 40 are angles set at equal angle intervals obtained by dividing 360 degrees (1 rotation) by the number of shooting angles. Therefore, the multiple projection image data 50 are X-ray images acquired at each shooting angle 40 obtained by sequentially rotating the shooting unit 7 and the subject 90 relative to each other by a unit angle corresponding to the number of shooting angles.

[0025] The image processing unit 5 is configured to generate a CT image 56 (see Figure 9) based on multiple acquired projection image data 50 (see Figure 9). The image processing unit 5 generates the CT image 56 by performing a reconstruction process on a set of multiple projection image data 50 for each of the 360 ​​degrees of shooting angles (called a projection dataset). The CT image 56 is an image that reflects the three-dimensional structure of the subject 90 and is reconstructed by computation from multiple X-ray images (projection image data 50) taken at various shooting angles 40. The CT image 56 can take the form of a tomographic image, a three-dimensional stereoscopic image, or other forms of the subject 90.

[0026] The storage unit 22 is comprised of a volatile memory device and a non-volatile memory device. The storage unit 22 stores a program 51 (see Figure 9), various setting information 53 (see Figure 9) related to CT imaging of the X-ray imaging device 100, and the like. The storage unit 22 stores multiple acquired projection image data 50 (see Figure 9) and CT images 56 generated based on those projection image data 50.

[0027] The input / output unit 23 is composed of various interfaces for inputting and outputting signals to and from the control device 20. The input / output unit 23 is connected to the display device 24 and the input device 25. The display device 24 is, for example, a liquid crystal display. The input device 25 includes a keyboard and a mouse. The image processing unit 5 acquires detection signals (image signals) from the detector 2 via the input / output unit 23. The main control unit 21 transmits instructions such as starting or stopping shooting to the shooting control unit 6 via the input / output unit 23.

[0028] The imaging control unit 6 controls the operation of the X-ray source 1. The imaging control unit 6 also controls the operation of the rotation mechanism 4. The imaging control unit 6 consists of control equipment for the X-ray source 1, control equipment for the rotation mechanism 4, etc. When acquiring multiple projection image data 50 (see Figure 9), the imaging control unit 6 controls the irradiation of X-rays 10 from the X-ray source 1 and controls the irradiation to stop, and also controls the rotation mechanism 4 to sequentially position the subject 90 at multiple imaging angles 40.

[0029] (Configuration of the X-ray source) As shown in Figure 2, in this embodiment, the X-ray source 1 includes a rotating target 11 and a plurality of electron emission units 12. The rotating target 11 and the plurality of electron emission units 12 are housed in a vacuum vessel 13.

[0030] The X-ray source 1 is configured to emit an electron beam 36 from the electron emission unit 12, which is the cathode, and a rotating target 11, which is the anode, by applying a voltage between them, and to generate X-rays 10 from the rotating target 11 by causing the emitted electron beam 36 to collide with the rotating target 11.

[0031] The rotating target 11 has a disc shape. The rotating target 11 has an inclined surface 11a. The rotating target 11 is inclined to become thinner towards its periphery. The rotating target 11 is configured such that the X-rays 10 generated when the electron beam 36 collides with the inclined surface 11a are emitted in a direction different from the direction in which the electron beam 36 arrived. The rotating target 11 is supported so as to be rotatable around the rotation axis of the rotor 11c. The rotating target 11 is rotated around the rotation axis 11b by the rotor 11c. In other words, the X-ray source 1 has a so-called rotating anode type structure.

[0032] As shown in Figure 3, the multiple electron emission units 12 are configured to irradiate electron beams 36 to different focal positions 14 on the rotating target 11. The imaging control unit 6 individually controls the irradiation of electron beams 36 from the multiple electron emission units 12. The imaging control unit 6 selects one of the multiple electron emission units 12 to irradiate electron beams 36. The number of electron emission units 12 is not particularly limited. Figure 3 illustrates three electron emission units 12. The number of electron emission units 12 may be two or four or more. The three electron emission units 12 each emit electron beams 36 toward different focal positions 14 on the rotating target 11, causing X-rays 10 to be emitted toward the detector 2 from the focal positions 14 corresponding to each electron emission unit 12. As a result, the X-ray source 1 can emit X-rays from a number of different focal points (focal positions 14) equal to the number of electron emission units 12 that the X-ray source 1 has. Furthermore, from the viewpoint of dispersing the heat generated by the collision of the electron beam 36 with the rotating target 11, it is preferable to have a larger number of focal points on the rotating target 11. In other words, it is preferable to have a larger number of electron emission units 12.

[0033] Each of the multiple electron-emitting units 12 has a focal position 14 that is at a different distance from the rotation axis 11b on the rotating target 11. Each of the multiple electron-emitting units 12 has a focal position 14 that is aligned radially on the inclined surface 11a of the rotating target 11. That is, each of the multiple electron-emitting units 12 has a focal position 14 that is aligned away from the rotation axis 11b on the inclined surface 11a of the rotating target 11.

[0034] The electron beam 36 is irradiated onto one focal point 14 on the rotating target 11. Each focal point 14 is located at a constant distance from the rotating target 11 in the radial direction. The spot (point-like region) where the electron beam 36 collides at the focal point 14 becomes the focal point of the X-ray 10. As shown in Figure 4, multiple circular focal trajectories 37 are formed on the inclined surface 11a of the rotating target 11, each composed of a focal spot of one of the multiple electron emission units 12. In this embodiment shown in Figure 4, since there are three electron emission units 12 (see Figure 3), three focal trajectories 37 are formed. In Figure 4, the multiple focal trajectories 37 are represented by dashed lines. The distance between adjacent focal points 14 may be the same or different.

[0035] The adjacent focal ranges 14d on the rotating target 11 are positioned apart and do not overlap. In this specification, "focal range" refers to the spot where the electron beam 36 collides. The adjacent focal trajectories 37 on the rotating target 11 are also positioned apart and do not overlap. In this embodiment, the diameter of the focal spot (focal size) on the rotating target 11 is approximately 20 μm to 30 μm. The distance D1 between adjacent focal positions 14 on the rotating target 11 is approximately 1 mm. The diameter of the focal spot formed by the electron emission unit 12 is smaller than the distance D1 between adjacent focal positions 14. Because the adjacent focal ranges 14d are positioned apart and do not overlap, and because the diameter of the focal spot is smaller than the distance between adjacent focal positions 14, the effect of heat generated by an electron collision at one focal position 14 can be suppressed from extending to the adjacent focal range 14d.

[0036] Furthermore, as shown in Figure 2, the incident angle θ of the electron beam 36 irradiated from each of the multiple electron emission units 12 and incident on each of the focal positions 14 of the multiple electron emission units 12 on the rotating target 11 is adjusted to be constant. The incident angle θ refers to the angle between the incident direction of the electron beam 36 and the normal to each of the focal positions 14 of the multiple electron emission units 12 on the rotating target 11. In Figure 2, the incident direction of the electron beam 36 and the normal to the focal position 14 are shown to be the same. The incident angle θ of the electron beam 36 irradiated from each of the multiple electron emission units 12 and incident on the focal position 14 is the same regardless of which electron emission unit 12 is selected. In other words, the incident angle θ of the electron beam 36 irradiated from the electron emission unit 12a and incident at the focal position 14a, the incident angle θ of the electron beam 36 irradiated from the electron emission unit 12b and incident at the focal position 14b, and the incident angle θ of the electron beam 36 irradiated from the electron emission unit 12c and incident at the focal position 14c are adjusted to be constant relative to each other.

[0037] Specifically, the X-ray source 1 further includes a substrate 31 on which a plurality of electron-emitting units 12 are provided. The substrate 31 is a flat plate such as silicon or glass. The inclined surface 11a on the rotating target 11 where a plurality of focal positions 14 aligned radially are located is adjusted to be parallel to the surface of the substrate 31. Furthermore, the plurality of electron-emitting units 12 are provided on the substrate 31 such that the focal positions 14 of each of the plurality of electron-emitting units 12 are aligned radially on the rotating target 11. The electron beam 36 irradiated from the electron-emitting units 12 is configured to be incident perpendicular to the focal positions 14 on the inclined surface 11a of the rotating target 11. The axes 36a (electron beam axes) (see Figure 2) of the electron beams 36 irradiated from each of the plurality of electron-emitting units 12 are parallel to each other.

[0038] Figure 5 shows a more detailed configuration example of the electron emission unit 12 and the rotating target 11. The X-ray source 1 includes an electron source unit 15 having a plurality of cold cathode electron sources 30 arranged on a plane. Each of the plurality of electron emission units 12 is composed of different groups of the plurality of cold cathode electron sources 30.

[0039] The electron source unit 15 is formed by applying semiconductor manufacturing technology to create an array of numerous cold cathode electron sources 30 on a substrate 31. A group composed of some of the multiple cold cathode electron sources 30 arranged in the array constitutes one electron emission section 12.

[0040] A group constituting one of the multiple electron emission units 12 consists of one or more cold cathode electron sources 30 that irradiate electrons to the same focal point 14 on the rotating target 11. One electron emission unit 12 includes one or more cold cathode electron sources 30. One electron emission unit 12 includes, for example, 10 or more, 100 or more, or 1000 or more cold cathode electron sources 30. When one electron emission unit 12 is composed of multiple cold cathode electron sources 30, the collection of electrons emitted from each of the multiple cold cathode electron sources 30 constituting the electron emission unit 12 forms an electron beam 36 emitted from the electron emission unit 12. The electron beam 36 is irradiated to one focal point 14 on the rotating target 11.

[0041] Each cold cathode electron source 30 is a field emission electron source that emits electrons by tunneling effect from an emitter to which an electric field is applied. As shown in Figure 5, the cold cathode electron source 30 is, for example, a spint electron source. The spint electron source includes a cathode electrode 32 formed on a substrate 31, a tapered emitter 33 formed on the cathode electrode 32, and a gate electrode 35 formed on the insulating layer via an insulating layer 34 surrounding the emitter 33. When a predetermined extraction voltage is applied between the cathode electrode 32 and the gate electrode 35, a high electric field is generated at the tip of the emitter 33, and electrons are emitted from the tip of the emitter 33.

[0042] In a spint electron source, the emitter 33 is created by etching holes that penetrate the gate electrode 35 and the insulating layer 34, and then depositing the emitter material within the formed holes. The cold cathode electron source 30 may have a structure other than the spint type. For example, the emitter 33 may be formed from needle-shaped materials such as carbon nanotubes.

[0043] Furthermore, as shown in Figure 3, multiple electromagnetic lenses 38 are provided to focus the electron beam 36 from the emitter 33 (see Figure 5) of the electron emission unit 12. The electromagnetic lenses 38 are electromagnets utilizing coils and have magnetic poles (pole pieces) (not shown) that protrude toward the center of the holes in the coils. The electron beam 36 emitted from the field emission electron source 30 passes through the area (hole) surrounded by the pole pieces and collides with the target 11. Note that the lenses for focusing the electron beam 36 may be electrostatic lenses or other known lenses, rather than electromagnetic lenses 38.

[0044] The X-ray source 1 includes a switching unit 17 for individually controlling the voltage application to each electron emission unit 12 (group of cold cathode electron sources 30). The imaging control unit 6 (see Figure 1) controls the power supply to apply a predetermined voltage between the cathode electrode 32 (see Figure 5) and the rotating target 11. The imaging control unit 6 selectively connects the gate electrode (see Figure 4) of the cold cathode electron source 30 belonging to the selected electron emission unit 12 to the power supply and controls the switching unit 17 to apply a draw voltage to the gate electrode. As a result, an electron beam 36 is emitted from the group of cold cathode electron sources 30 belonging to the selected electron emission unit 12, and X-rays are emitted from the focal position 14 corresponding to the selected electron emission unit 12.

[0045] (Switching control of the electron emission section) In this embodiment, the imaging control unit 6 is configured to control the X-ray source 1 so as to sequentially switch between a plurality of electron emission units 12 to irradiate with an electron beam 36.

[0046] In this embodiment, the imaging control unit 6 controls the X-ray source 1 to switch the focal position 14 and irradiate the rotating target 11 with the electron beam 36 in order to prevent damage to the rotating target 11 caused by heat generation due to collision with the electron beam 36. That is, the imaging control unit 6 controls the X-ray source 1 to sequentially switch between a plurality of electron emission units 12. In this embodiment, the material of the rotating target 11 is tungsten. The melting point of tungsten is approximately 3420 degrees. The imaging control unit 6 controls the X-ray source 1 to sequentially switch between a plurality of electron emission units 12 so that the temperature of the focal position 14 irradiated with the electron beam 36 does not exceed approximately 3000 degrees. Note that the material of the rotating target 11 is not limited to tungsten, and known materials can be used.

[0047] As shown in Figure 2, the inside of the X-ray tube is in a vacuum state, and the rotating target 11 rotates at high speed in the rotating anode. Therefore, it is difficult to detect the temperature of the focal point 14 of the rotating target 11 in real time. For this reason, simulations and experiments are performed in advance to obtain information on the temperature rise of the rotating target 11. Conditions (parameters) related to the temperature rise of the rotating target 11 include the focal point size on the rotating target 11 and the radius of the focal trajectory 37 (see Figure 4), the shape and material of the rotating target 11, the rotation speed of the rotating target 11, the voltage applied to the X-ray source 1, and the irradiation time of the electron beam 36 by the electron emission unit 12. The shape and material of the rotating target 11 include the radius of the rotating target 11, the volume, the inclination angle of the inclined surface 11a with respect to the rotation axis 11b, and the density, thermal conductivity, and specific heat of the material. Based on the obtained information on the temperature rise of the rotating target 11, the irradiation time of the electron beam 36 under various conditions is set in advance. The irradiation time for the electron beam 36 is the maximum time that the rotating target 11 can be continuously irradiated with the electron beam 36 emitted from the electron emission unit 12 at a given focal point 14 without being damaged by heat. The set irradiation time for the electron beam 36 is stored in the storage unit 22 in advance. The imaging control unit 6 is configured to control the X-ray source 1 to irradiate with the electron beam 36 by sequentially switching between multiple electron emission units 12 based on the previously acquired irradiation time for the electron beam 36.

[0048] The irradiation time of the electron beam 36 varies depending on the imaging conditions. Furthermore, the irradiation time of the electron beam 36 differs for each of the multiple electron emission units 12. The focal trajectory 37 on the rotating target 11 (see Figure 4) becomes shorter as the distance between the focal position 14 and the rotation axis 11b decreases. Therefore, the irradiation time of the electron beam 36 is set to become shorter as the distance between the focal position 14 and the rotation axis 11b decreases.

[0049] The switching control of the electron emission unit 12 will be explained in detail with reference to Figures 6 to 8. Figure 6 shows an example in which the first electron emission unit 12a is selected at the first imaging angle 40a. Figure 7 shows an example in which the first electron emission unit 12a is selected at the second imaging angle 40b. Figure 8 shows an example in which the second electron emission unit 12b is selected at the third imaging angle 40c. As shown in Figure 6, the imaging control unit 6 selects one of the electron emission units 12, for example the first electron emission unit 12a, at the initial first imaging angle 40a, and controls the X-ray irradiation to be performed from the focal position 14a. The detector 2 acquires projection image data 50 at the first imaging angle 40a. After acquiring the projection image data 50, the imaging control unit 6 controls the rotation mechanism 4 to rotate the subject placement unit 3 by a unit angle to change from the first imaging angle 40a to the next second imaging angle 40b (see Figure 7).

[0050] The imaging control unit 6 then obtains the remaining time available for the electron beam 36 to irradiate the focal position 14a of the first electron emission unit 12a, which irradiated the electron beam 36 at the first imaging angle 40a. The remaining time available for the electron beam 36 is the time obtained by subtracting the irradiation time of the electron beam 36 at the first imaging angle 40a from the irradiation time of the electron beam 36 in the first electron emission unit 12a. The imaging control unit 6 then determines whether the remaining time available for the electron beam 36 in the first electron emission unit 12a is shorter than the irradiation time of the electron beam 36 at the second imaging angle 40b. The irradiation time refers to the time during which the electron beam 36 is irradiated at each imaging angle in order to acquire the projection image data 50.

[0051] Then, if the imaging control unit 6 determines that the remaining irradiation time of the electron beam 36 of the first electron emission unit 12a is shorter than the irradiation time of the electron beam 36 at the second imaging angle 40b, it selects an electron emission unit 12 different from the first electron emission unit 12a. In this embodiment, the second electron emission unit 12b is selected. That is, the imaging control unit 6 switches the electron emission unit 12 used at the second imaging angle 40b from the first electron emission unit 12a to the second electron emission unit 12b. The imaging control unit 6 irradiates with X-rays from the focal position 14b using the selected second electron emission unit 12b and acquires projection image data 50 at the second imaging angle 40b. After acquiring the projection image data 50, the imaging control unit 6 changes from the second imaging angle 40b to the next third imaging angle 40c (see Figure 8).

[0052] In response, if the imaging control unit 6 determines that the remaining irradiation time of the electron beam 36 of the first electron emission unit 12a is longer than the irradiation time of the electron beam 36 at the second imaging angle 40b, it selects the same first electron emission unit 12a at the second imaging angle 40b, as shown in Figure 7. The imaging control unit 6 irradiates with X-rays from the focal position 14a using the selected first electron emission unit 12a and acquires projection image data 50 at the second imaging angle 40b. After acquiring the projection image data 50, the imaging control unit 6 changes from the second imaging angle 40b to the next third imaging angle 40c (see Figure 8).

[0053] The imaging control unit 6 then obtains the remaining amount of time that the electron beam 36 can irradiate the focal position 14 of the first electron emission unit 12a or the second electron emission unit 12b that irradiated the electron beam 36 at the second imaging angle 40b. At the third imaging angle 40c, the imaging control unit 6 performs the same processing as performed at the second imaging angle 40b. That is, the imaging control unit 6 determines whether the remaining amount of time that the electron beam 36 can irradiate the electron beam 36 of the electron emission unit 12 that irradiated the electron beam 36 at the second imaging angle 40b is shorter than the irradiation time of the electron beam 36 at the third imaging angle 40c.

[0054] Then, if the imaging control unit 6 determines that the remaining irradiation time of the electron beam 36 of the electron emission unit 12 that irradiated with the electron beam 36 at the second imaging angle 40b is shorter than the irradiation time of the electron beam 36 at the third imaging angle 40c, it controls the X-ray source 1 to switch the electron emission unit 12 to the other electron emission unit 12 and irradiate with the electron beam 36. Figure 8 shows an example in which the electron beam 36 is irradiated after switching from the first electron emission unit 12a to the second electron emission unit 12b. Then, the imaging control unit 6 irradiates with X-rays from the focal position 14 using the switched electron emission unit 12 and acquires projection image data 50 at the third imaging angle 40c. After acquiring the projection image data 50, the imaging control unit 6 changes from the third imaging angle 40c to the next fourth imaging angle 40 (not shown).

[0055] In response, if the imaging control unit 6 determines that the remaining irradiation time of the electron beam 36 of the electron emission unit 12 that irradiated the electron beam 36 at the second imaging angle 40b is longer than the irradiation time of the electron beam 36 at the third imaging angle 40c, it controls the X-ray source 1 to irradiate the electron beam 36 using the same electron emission unit 12 that irradiated the electron beam 36 at the second imaging angle 40b. The imaging control unit 6 then irradiates the X-ray from the focal position 14 using the same electron emission unit 12 and acquires projection image data 50 at the third imaging angle 40c. After acquiring the projection image data 50, the imaging control unit 6 changes from the third imaging angle 40c to the next fourth imaging angle 40 (not shown).

[0056] The shooting control unit 6 (see Figure 1) is configured to control the rotation mechanism 4 so that it is positioned at each of the multiple shooting angles 40 obtained by dividing 360 degrees into a predetermined number of shooting angles. Therefore, the shooting control unit 6 repeats the above control for the number of shooting angles, causing the shooting unit 7 to capture multiple projection image data 50 for 360 degrees.

[0057] With this control, each time X-ray irradiation is performed to acquire projection image data 50 for each shooting angle, a decision is made whether or not to switch the selected electron emission unit 12 that was previously irradiated with the electron beam 36, based on the previously acquired irradiation time of the electron beam 36, and the electron beam 36 is irradiated from the electron emission unit 12 selected based on the decision result. With this control, an electron emission unit 12 is selected based on the irradiation time of the electron beam 36, and the electron beam 36 is irradiated by the selected electron emission unit 12.

[0058] In addition, when switching the electron emission unit 12, the imaging control unit 6 selects a second electron emission unit 12b that is different from the first electron emission unit 12a. In this embodiment, among a plurality of electron emission units 12 arranged in a certain direction on the substrate 31 to correspond to a plurality of focal positions 14 arranged radially on the rotating target 11, the imaging control unit 6 is configured to select different electron emission units 12 in a sequence of adjacent units in a certain direction.

[0059] (Reconstruction process) Next, we will explain the reconstruction process performed by the image processing unit 5 (see Figure 1) using multiple projection image data 50 (see Figure 9).

[0060] First, let's explain the data used in the reconstruction process. As shown in Figure 10, the memory unit 22 of the control device 20 (see Figure 1) pre-stores information 52 of the focal position 14 of each of the multiple electron emission units 12. Each focal position 14 on the surface of the rotating target 11 of the X-ray source 1 is determined based on the structural relationship between the multiple electron emission units 12 and the rotating target 11 and is known. The information of the focal position 14 is information that can identify the position coordinates in the spatial coordinate system used in the reconstruction process of the CT image 56 where each focal position 14 of the multiple electron emission units 12 is located.

[0061] Furthermore, the memory unit 22 stores SRD information 57 and SDD information 58. SRD information 57 is the Source to Rotation Center Distance (SRD) information, which is the distance from the focal position 14 of the rotating target 11 to the rotation axis 4a of the rotation mechanism 4 that rotates the subject mounting unit 3. SDD information 58 is the Source to Detector Distance (SDD) information, which is the distance from the focal position 14 of the rotating target 11 to the detector 2. A position measurement sensor (not shown) is provided on the subject stage on which the subject 90 is placed to detect the position of the rotation axis 4a of the rotation mechanism 4. A position measurement sensor (not shown) is provided on the support base (not shown) that supports the detector 2 to detect the position of the detection surface of the detector 2. Each projection image data 50 is stored in the memory unit 22 in association with the SRD information 57 and SDD information 58 obtained from each position detection sensor when the projection image data 50 is acquired.

[0062] The memory unit 22 stores the program 51 executed by the main control unit 21 and the image processing unit 5, as well as setting information 53. The setting information 53 specifies the switching order of the multiple electron emission units 12, the tube voltage, the number of imaging angles, the amount of movement of the focal position 14 in the Z direction (see Figure 13) associated with the switching of the electron emission units 12 (described later), and constant data for the reconstruction process. In addition, each projection image data 50 is stored in the memory unit 22 in association with the imaging angle 40 and emission unit identification information 54 at the time the projection image data 50 was acquired. The emission unit identification information 54 is information that identifies which of the multiple electron emission units 12 was used to acquire the projection image data 50. To generate one CT image 56, a set of projection image data 50 corresponding to the number of imaging angles set in the setting information 53 (hereinafter referred to as the projection data set) is stored in the memory unit 22. The memory unit 22 stores the generated CT image 56.

[0063] The image processing unit 5 (see Figure 1) is configured to generate a CT image 56 based on reconstruction information including projection dataset, focal position 14 information 52, SRD information 57, and SDD information 58, by executing a program 51 stored in the storage unit 22. The image processing unit 5 is configured to generate a CT image 56 by performing reconstruction processing that includes correction processing to correct the magnification of the subject 90 and the position of the projected image of the subject in each of the multiple projection image data 50.

[0064] In this embodiment, the focal position 14 is changed by switching the electron emission unit 12. The change in focal position 14 alters the magnification ratio of the subject 90 in each of the multiple projection image data 50. Furthermore, the change in focal position 14 alters the position of the projected image of the subject 90 in each of the multiple projection image data 50. Therefore, the image processing unit 5 performs correction processing to correct the change in the magnification ratio of the subject 90 in each of the multiple projection image data 50, and to correct the position of the projected image of the subject 90 in each of the multiple projection image data 50. In addition, in this embodiment, the image processing unit 5 performs reconstruction processing using the FDK method (Feldkamp method), a type of analytical reconstruction method.

[0065] (Correction for changes in the subject's magnification) This section describes the correction of the magnification change of the subject 90 in each of the multiple projection image data 50. The correction of the magnification change of the subject 90 is a correction process to compensate for the change in the magnification of the subject 90 caused by the movement of the focal position in the X direction (see Figure 11) due to the switching of the electron emission unit 12 (switching of the focal position 14). In Figures 10 to 12, the direction perpendicular to the rotation axis 11b of the rotating target 11 and the direction in which X-rays are irradiated is described as the X direction. The direction of the rotation axis of the rotating target 11 is described as the Z direction. The direction perpendicular to the X direction and the Z direction is described as the Y direction.

[0066] In Figure 10, on the inclined surface 11a of the rotating target 11, three focal positions 14a, 14b, and 14c are positioned in the X direction as the respective focal positions 14 of the three electron emission units 12 (see Figure 3). Of the three focal positions 14a, 14b, and 14c, the electron beam 36 is irradiated onto the central focal position 14b in the X direction, and X-rays 10 are emitted from the central focal position 14b. At this time, the object 90 having dimension R0 in the YZ plane is magnified and projected onto the detection surface of the detector 2, forming a projected image with dimension R1 on the detection surface. The magnification ratio R1 / R0 is given by the following equation (1).

number

[0067] Here, as shown in Figures 10 and 11, when the focal position 14 is switched from the central focal position 14b in the X direction to the right (outer edge) focal position 14c, SRD1 and SDD1 before the switch in focal position 14 change to SRD2 and SDD2 after the switch in focal position 14. As a result, the magnification ratio R1 / R0 before the switch in focal position 14 also changes to the magnification ratio R2 / R0 after the switch in focal position 14. In other words, the magnification ratio of the subject 90 projected on the detection surface changes before and after the switch in focal position 14.

[0068] Therefore, before performing the reconstruction process, the image processing unit 5 corrects the magnification of the subject 90 on the detection surface so that the magnification of the subject 90 on the detection surface, which changes with the switching of the focal position 14, is equal at all focal positions 14. In this embodiment, the magnification of the subject 90 in the projected image data 50 is corrected so that the magnification of the subject 90 projected on the detection surface at focal position 14b in the projected image data 50 matches the magnification of the subject 90 projected on the detection surface at focal position 14c in the projected image data 50.

[0069] The image processing unit 5 acquires SRD1 and SDD1 associated with the projection image data 50 captured at the central focal position 14b, which is stored in the storage unit 22. The image processing unit 5 also acquires the dimension R1 of the subject 90 based on the projection image data 50, SRD1, and SDD1 captured at the central focal position 14b. The image processing unit 5 acquires the magnification ratio R1 / R0 based on the acquired SRD1, SDD1, and the dimension R1 of the subject 90. The magnification ratio R1 / R0 is given by the above formula (1).

[0070] Next, the image processing unit 5 acquires SRD2 and SDD2 associated with the projection image data 50 captured at the right focal position 14c, which is stored in the memory unit 22. The image processing unit 5 also acquires the dimension R2 of the subject 90 based on the projection image data 50 captured at the right focal position 14c. The image processing unit 5 acquires the magnification ratio R2 / R0 based on the acquired SRD2, SDD2, and the dimension R2 of the subject 90. The magnification ratio R2 / R0 is given by the following equation (2).

number

[0071] The magnification of the subject 90 in the projected image data 50 can be corrected by multiplying the dimension R2 of the subject 90 by the value obtained by dividing the magnification R1 / R0 by the magnification R2 / R0. The value obtained by dividing the magnification R1 / R0 by the magnification R2 / R0 is given by the following formula (3).

number

[0072] The image processing unit 5 performs magnification correction based on the above equation (3) to equalize the magnification of each image included in the projected image data 50. Through this correction process, the change in magnification of the subject 90 due to the movement of the focal point in the X direction can be corrected.

[0073] (Correction of the position of the projected image of the subject) Next, the correction of the position of the projected image of the subject 90 in each of the multiple projection image data 50 will be described. The correction of the position of the projected image of the subject 90 is a correction process to correct the position of the projected image of the subject 90 due to the movement of the focal position in the Z direction (see Figure 12) caused by the switching of the electron emission unit 12 (switching of the focal position 14). The correction process for the position of the projected image of the subject 90 is performed on the projection image data 50 in which the correction process for the change in the magnification of the subject 90 has been performed.

[0074] In Figure 12, the inclined surface 11a of the rotating target 11 has three focal positions 14a, 14b, and 14c aligned in the X direction, representing the respective focal positions 14 of the three electron emission units 12 (see Figure 3). Of the three focal positions 14a, 14b, and 14c, the electron beam 36 is irradiated onto the central focal position 14b in the X direction, and X-rays 10 are emitted from the central focal position 14b. Here, if the focal position 14 is switched from the central focal position 14b in the X direction to the right (outer edge) focal position 14c, the position of the projected image of the subject 90 projected onto the detection surface of the detector 2 moves in the Z direction. Therefore, the image processing unit 5 corrects the position of the projected image of the subject 90 due to the movement of the focal position in the Z direction for the projected image data 50, which has been corrected for the change in the magnification of the subject 90.

[0075] When the focal point position 14b in the X direction is switched to the right (outer edge) focal point position 14c, the right focal point position 14c moves by an amount z0 in the Z direction compared to the central focal point position 14b. Also, the position of the projected image of the subject 90 at the right focal point position 14c moves by an amount z1 in the Z direction on the detection surface of the detector 2 compared to the position of the projected image of the subject 90 at the central focal point position 14b. The amount z0 of movement of the focal point position 14 in the Z direction is stored in advance in the storage unit 22.

[0076] Furthermore, the position correction process for the projected image is performed on the projected image data 50 from which the correction process for the change in the magnification of the subject 90 has been performed. Due to the correction process for the change in the magnification of the subject 90, the magnification of the subject 90 in the projected image data 50 at the right focal position 14c matches the magnification of the subject 90 in the projected image data 50 at the central focal position 14b. Also, SRD2 and SDD2 of the projected image data 50 at the right focal position 14c match SRD1 and SDD1 of the projected image data 50 at the central focal position 14b. Therefore, in these projected image data 50, the starting point of X-ray irradiation in the X direction is at the same position. As a result, in these projected image data 50, it can be considered that the starting point of X-ray irradiation in the X direction has moved only in the Z direction.

[0077] At this time, the amount of displacement z1 of the projected image of the subject 90 is calculated by the following equation (4). Here, SRD and SDD are SRD1 and SDD1 at the reference central focal position 14b.

number

[0078] Based on equation (4) above, the image processing unit 5 performs a correction on the projected image data 50 at the right focal position 14c, where the correction process for the change in the magnification of the subject 90 has been performed, by moving the position of the projected image of the subject 90 by a movement amount z1. Through this correction process, the position of the projected image of the subject 90 can be corrected in accordance with the movement of the focal position in the Z direction.

[0079] Next, the image processing unit 5 is configured to generate a CT image 56 by performing a reconstruction process, including filtering and back projection, using a plurality of projection image data 50 that have undergone correction processing to correct the magnification of the subject 90 and the position of the projected image of the subject 90.

[0080] The image processing unit 5 is configured to perform a filter process on multiple projection image data 50 that have undergone correction processing in the reconstruction process to correct the magnification of the subject 90 and the position of the projected image of the subject 90. The filter process can be performed using known methods.

[0081] The image processing unit 5 is configured to perform back projection processing on each of the multiple projected image data 50 during the reconstruction process. Back projection processing can be performed using known methods. In this embodiment, the image processing unit 5 performs reconstruction processing using the FDK method (Feldkamp method).

[0082] As a result of the reconstruction process, the image processing unit 5 generates a CT image 56 of the subject 90.

[0083] (Operation of X-ray imaging device 100) Next, the imaging operation of the X-ray imaging apparatus 100 of this embodiment will be described with reference to Figure 14. The X-ray imaging apparatus 100 implements the X-ray imaging method according to this embodiment. The imaging control unit 6 controls the imaging operation in the X-ray imaging apparatus 100. The image processing unit 5 acquires the projection image data 50 and generates the CT image 56. In the following description of the operation, the device configuration of the X-ray imaging apparatus 100 will be referred to in Figures 1 and 6-8, and various data will be referred to in Figure 9.

[0084] The shooting operation is initiated when the control device 20 receives an operation input via the input device 25. After the subject is placed in the subject placement unit 3, when the control device 20 receives an operation input to start shooting via the input device 25, the main control unit 21 sends a signal to the shooting control unit 6 instructing it to start the shooting operation. Upon receiving the signal from the main control unit 21, the shooting control unit 6 controls the X-ray source 1 and the rotation mechanism 4 to start the shooting operation of the subject.

[0085] In step 101, the imaging control unit 6 selects from among multiple electron emission units 12 which electron emission unit 12 to be used for X-ray irradiation at the current imaging angle 40. For the first imaging in CT scanning, the first electron emission unit 12a used for X-ray irradiation at the preset initial first imaging angle 40a (β=0 degrees) is selected. The switching order (selection order) of the electron emission units 12 is preset in the setting information.

[0086] In step 102, the imaging control unit 6 controls the X-ray source 1 to emit the electron beam 36 using the first electron emitter 12a selected in step 101. The imaging control unit 6 controls the switching unit 17 (see Figure 3) to irradiate the rotating target 11 with the electron beam 36 from the selected first electron emitter 12a among the multiple electron emitters 12. As a result, X-rays are emitted from the focal position 14a corresponding to the selected first electron emitter 12a.

[0087] X-rays emitted from the focal point 14a of the X-ray source 1 pass through the subject 90 and are detected on the detection surface of the detector 2. In step 103, the image processing unit 5 acquires (generates) projection image data 50 based on the detection signal output from the detector 2. The acquired projection image data 50 is stored in the storage unit 22, associated with the shooting angle 40, the emission unit identification information of the electron emission unit 12 used, SRD, and SDD.

[0088] In step 104, the shooting control unit 6 determines whether or not shooting (acquisition of projected image data 50) has been performed for a predetermined angle range (360 degrees). If shooting has not been performed for the predetermined angle range, the shooting control unit 6 proceeds to step 105.

[0089] In step 105, the shooting control unit 6 controls the rotation mechanism 4 to move to the second shooting angle 40b for the next shooting. The shooting control unit 6 controls the rotation mechanism 4 to rotate the subject mounting unit 3 and the shooting unit 7 relative to each other by a unit angle obtained by dividing a predetermined angle range (360 degrees) by the number of shooting angles. In this embodiment, the rotation mechanism 4 rotates the subject mounting unit 3 as described above.

[0090] In step 106, the imaging control unit 6 determines whether the remaining time for irradiation of the electron beam 36 to the focal position 14a of the first electron emission unit 12a, which irradiated the electron beam 36 at the first imaging angle 40a, is shorter than the irradiation time of the electron beam 36 at the second imaging angle 40b.

[0091] Subsequently, the imaging control unit 6 returns the process to step 101. In step 101, if the result of the determination in step 106 is that the remaining irradiation time of the electron beam 36 of the first electron emission unit 12a is shorter than the irradiation time of the electron beam 36 at the second imaging angle 40b, the imaging control unit 6 switches the electron emission unit 12 that irradiates with the electron beam 36 from the first electron emission unit 12a to the second electron emission unit 12b. That is, the imaging control unit 6 selects the second electron emission unit 12b as the electron emission unit 12 to be used for X-ray irradiation at the second imaging angle 40b.

[0092] In response to this, in step 101, if the determination result in step 106 is that the remaining irradiation time of the electron beam 36 of the first electron emission unit 12a is not shorter than the irradiation time of the electron beam 36 at the second imaging angle 40b, the imaging control unit 6 does not switch the electron emission unit 12 that irradiates the electron beam 36, but selects the first electron emission unit 12a as the electron emission unit 12 to be used for X-ray irradiation at the second imaging angle 40b. Then, in steps 102 and 103, the projection image data 50 at the current imaging angle 40 is acquired.

[0093] The shooting control unit 66 repeats steps 101 to 106 a number of times corresponding to the number of shooting angles, thereby capturing each projection image data 50 within a predetermined angle range (360 degrees). As a result, a projection dataset consisting of each projection image data 50 within the predetermined angle range (360 degrees) is stored in the storage unit 22. Once the shooting for the predetermined angle range has been completed, the shooting control unit 6 proceeds to steps 104 to 107.

[0094] In step 107, the image processing unit 5 performs a reconstruction process, including the correction process described above, based on each projection image data 50 included in the projection dataset.

[0095] In step 108, the image processing unit 5 outputs the CT image 56 generated as a result of step 107. The image processing unit 5 stores the CT image 56 in the storage unit 22 and displays it on the display device 24. In this way, the X-ray imaging device 100 performs its imaging operation.

[0096] (Control of the reconstruction process) Next, we will explain the operation flow of the reconstruction process in step 107 of Figure 13.

[0097] In step 111 of Figure 14, the image processing unit 5 obtains from the storage unit 22 one of the projection image data 50 included in the projection dataset, along with the shooting angle 40, emission unit identification information, SRD information 57, and SDD information 58 associated with that projection image data 50. The image processing unit 5 also obtains from the storage unit 22 information 52 of the focal position 14 corresponding to the electron emission unit 12 identified by the emission unit identification information.

[0098] In step 112, the image processing unit 5 performs correction processing to correct the magnification of the subject 90 and the position of the projected image of the subject 90 in the projected image data 50, based on reconstruction information including information 52 about the focal position 14 of the electron emission unit 12 used to acquire the projected image data 50, SRD information 57, and SDD information 58.

[0099] In step 113, the image processing unit 5 performs a filter process on the corrected projection image data 50.

[0100] In step 114, the image processing unit 5 determines whether or not correction and filtering processing has been completed for all of the multiple projection image data 50 included in the projection dataset. If correction and filtering processing has not been completed for all of the projection image data 50, the image processing unit 5 returns to step 111.

[0101] As steps 111 to 114 are repeated, the image processing unit 5 performs correction and filtering on all of the projection image data 50 for each shooting angle 40 included in the projection dataset. In this case, the image processing unit 5 proceeds to step 115.

[0102] In step 115, the image processing unit 5 performs back projection processing on the projected image data 50 for each shooting angle 40 that has undergone correction processing and filtering processing.

[0103] As a result, in step 116, the image processing unit 5 generates a CT image 56.

[0104] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0105] In this embodiment, as described above, the X-ray imaging apparatus 100 includes a rotating target 11 supported so as to be rotatable around a rotation axis 11b, and a plurality of electron emission units 12 that irradiate a plurality of focal positions 14 on the rotating target 11 at different distances from the rotation axis 11b with electron beams 36 each. The X-ray source 1 is adjusted so that the incident angle θ of the electron beams 36 irradiated from each of the plurality of electron emission units 12 and incident on each of the focal positions 14 of the plurality of electron emission units 12 on the rotating target 11 is constant. The detector 2 detects the X-rays emitted from the X-ray source 1, an image processing unit 5 generates an image based on the detection signal output from the detector, and an imaging control unit 6 controls the X-ray source 1 to sequentially switch the plurality of electron emission units 12 to irradiate with electron beams 36. By sequentially switching the plurality of electron emission units 12 to irradiate with electron beams 36, the electron beams 36 are irradiated onto a plurality of focal positions 14 on the rotating target 11 at different distances from the rotation axis 11b. By changing the focal point position 14 on the rotating target 11, the heat-generating areas on the rotating target 11 can be dispersed. Therefore, compared to the case where the same focal point position 14 on the rotating target 11 continuously generates heat, the localized temperature rise on the rotating target 11 can be reduced, thereby suppressing damage to the rotating target 11 caused by heat generation due to collisions with the electron beam 36. Furthermore, by adjusting the incident angle θ of the electron beam 36 irradiated from each of the multiple electron emission units 12 and incident on each of the different focal point positions 14 of the multiple electron emission units 12 on the rotating target 11 to be constant, changes in focal size at each of the focal point positions 14 of the multiple electron emission units 12 can be suppressed. Therefore, the effects of aberrations caused by switching the electron emission units 12 can be suppressed. As a result, while suppressing damage to the rotating target 11 caused by heat generation due to collisions with the electron beam 36, it is possible to suppress blurring of the acquired X-ray image due to fluctuations in the distance between the cathode and anode.

[0106] Furthermore, in this embodiment, as described above, the focal positions 14 of each of the multiple electron emission units 12 are positioned so as to be aligned radially on the rotating target 11. As a result, multiple circular focal trajectories 37 with different radii are formed on the rotating target 11, each composed of the focal positions 14 of the multiple electron emission units 12. Therefore, compared to the case where the same focal trajectory 37 on the rotating target 11 continuously generates heat, the localized temperature rise on the rotating target 11 can be easily reduced.

[0107] Furthermore, in this embodiment, as described above, the X-ray source 1 further includes a substrate 31 on which a plurality of electron emission units 12 are provided, and the surface portion where a plurality of focal positions 14 arranged radially on the rotating target 11 are located and the surface of the substrate 31 are adjusted to be parallel to each other. This makes it possible to adjust the incident angle θ of the electron beam 36 irradiated from each of the plurality of electron emission units 12 and incident on each of the different focal positions 14 of the plurality of electron emission units 12 on the rotating target 11 to be constant, with a simple configuration.

[0108] Furthermore, in this embodiment, as described above, adjacent focal ranges 14d on the rotating target 11 are positioned apart and do not overlap. This suppresses the effect of heat generated by an electron collision at one focal position 14 from extending to the other adjacent focal range 14d. Therefore, even when the focal positions 14 are switched in a sequence of adjacent positions in a certain direction, it is possible to suppress the effect of heat from one adjacent focal range 14d that was irradiated immediately before from extending to the other adjacent focal range 14d that is irradiated next.

[0109] Furthermore, in this embodiment, as described above, the imaging control unit 6 controls the X-ray source 1 to sequentially switch between multiple electron emission units 12 to irradiate the rotating target 11 with the electron beam 36, based on the irradiation time of the electron beam 36, which is the longest time for which the rotating target 11 can be continuously irradiated with the electron beam 36 from the electron emission unit 12 at the focal position 14 without being damaged by heat, as acquired in advance. This makes it possible to appropriately suppress damage to the rotating target 11 caused by heat generated by the collision of the electron beam 36 with the rotating target 11, based on the irradiation time of the electron beam 36.

[0110] Furthermore, in this embodiment, as described above, the system further includes a subject mounting section 3 positioned between the X-ray source 1 and the detector 2 to support the subject, and a rotation mechanism 4 that rotates the imaging section 7, which includes the X-ray source 1 and the detector 2, and the subject mounting section 3 relative to each other so as to change the imaging angle 40 of the subject. The plurality of electron emission sections 12 include a first electron emission section 12a and a second electron emission section 12b different from the first electron emission section 12a. The image processing section 5 generates a plurality of projection image data 50 based on the detection signals at each of the plurality of imaging angles 40, and generates a CT image 56, which is an image, based on the generated plurality of projection image data 50. The rotation mechanism 4 further rotates the image data 56. When the X-ray source 1 is rotated from the first shooting angle 40a to the second shooting angle 40b at a given shooting angle 40, the shooting control unit 6 determines whether the remaining time available for the electron beam 36 to irradiate the focal position 14a of the first electron emission unit 12a, which irradiated the electron beam 36 at the first shooting angle 40a, is shorter than the irradiation time available for the electron beam 36 to irradiate the focal position 14 at the second shooting angle 40b. If the shooting control unit 6 determines that the remaining time available for the electron beam 36 to irradiate the electron beam 36 of the first electron emission unit 12a is shorter than the irradiation time available for the electron beam 36 at the second shooting angle 40b, it controls the X-ray source 1 to switch from the first electron emission unit 12a to the second electron emission unit 12b and irradiate the electron beam 36. This prevents switching from the first electron emission unit 12a to the second electron emission unit 12b and irradiating the electron beam 36 while shooting (acquisition of projection image data 50) is being performed at a given shooting angle 40. Therefore, the magnification of the subject 90 and the position of the projected image of the subject 90 can be appropriately corrected for the acquired projection image data 50.

[0111] Furthermore, in this embodiment, as described above, the irradiation time of the electron beam 36 is set to decrease as the distance between the focal point 14 and the rotation axis 11b decreases. When the irradiation time of the electron beam 36 is the same, a shorter focal trajectory (circumference) increases the number of electron beam collisions with the same focal point on the rotating target 11 compared to a longer focal trajectory (circumference). Therefore, a shorter focal trajectory (circumference) is more prone to temperature rise than a longer focal trajectory (circumference). Thus, by setting the irradiation time of the electron beam 36 according to the distance between the focal point 14, which determines the length of the focal trajectory 37, and the rotation axis 11b, damage to the rotating target 11 caused by heat generation due to collisions of the electron beam 36 can be more effectively suppressed.

[0112] Furthermore, in this embodiment, as described above, the system further includes a storage unit 22 that stores information on the focal position 14 of each of the multiple electron emission units 12. The image processing unit 5 is configured to generate a CT image 56 by performing reconstruction processing on the multiple projection image data 50 based on reconstruction information including information 52 on the focal position 14 of the multiple electron emission units 12 used to acquire each of the multiple projection image data 50, SRD information 57 on the distance between the focal position 14 and the subject placement unit 3, and SDD information 58 on the distance between the focal position 14 and the detector 2. This makes it possible to generate an appropriate CT image 56 even when the electron emission units 12 are switched.

[0113] Furthermore, in this embodiment, as described above, the image processing unit 5 is configured to correct the magnification ratio of the subject 90 and the position of the projected image of the subject 90 in each of the multiple projection image data 50 based on the reconstruction information during the reconstruction process. This makes it possible to correct the change in the magnification ratio of the subject due to the movement of the focal position in the X direction and the position of the projected image of the subject 90 due to the movement of the focal position in the Z direction, which are caused by the switching of the electron emission unit 12. Therefore, a more appropriate CT image 56 can be generated compared to when the reconstruction process is performed without these correction processes.

[0114] [Differentiation] It should be noted that the embodiments 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 description of the embodiments above, and further includes all modifications (exceptions) within the meaning and scope equivalent to the claims.

[0115] For example, in the above embodiment, when the camera is rotated from a first shooting angle 40a to a second shooting angle 40b, the shooting control unit 6 determines whether the remaining time that the electron beam 36 can be irradiated to the focal position 14a of the first electron emission unit 12a, which irradiated the electron beam 36 at the first shooting angle 40a, is shorter than the irradiation time of the electron beam 36 at the second shooting angle 40b. If it is determined that the remaining time that the electron beam 36 can be irradiated to the first electron emission unit 12a is shorter than the irradiation time of the electron beam 36 at the second shooting angle 40b, the camera switches from the first electron emission unit 12a to the second electron emission unit 12b and irradiates the electron beam 36. However, the present invention is not limited to this.

[0116] In this invention, the maximum number of shooting angles (maximum number of views) to which the electron beam 36 can be irradiated for each electron emission unit may be obtained in advance by subtracting the irradiation time of the electron beam 36 at a plurality of shooting angles 40 obtained in advance from the irradiation time of the electron beam 36 at the focal position 14 of each electron emission unit obtained in advance. If the shooting angle 40 is changed and the number of shooting angles (number of views) exceeds the maximum number of shooting angles (maximum number of views) of the selected first electron emission unit 12a, the shooting control unit 6 may switch from the first electron emission unit 12a to the second electron emission unit 12b and irradiate with the electron beam 36. The number of shooting angles (number of views) that serves as the basis for switching from the first electron emission unit 12a to the second electron emission unit 12b is not particularly limited as long as it is within the maximum number of shooting angles (maximum number of views) to which the electron beam 36 can be irradiated. Furthermore, the number of shooting angles (views) for each electron emission unit may be set in advance based on the maximum number of shooting angles (maximum number of views) of the electron emission unit 12 and the irradiation time of the electron beam 36 at each shooting angle 40, which have been acquired in advance. In this case, the shooting control unit 6 may switch the electron emission unit 12 based on the number of shooting angles (views) for each electron emission unit that has been set in advance.

[0117] Furthermore, in the above embodiment, an example was shown in which the imaging control unit 6 selects different electron emission units 12 in a sequence adjacent in a certain direction, corresponding to a plurality of focal positions 14 arranged radially on the rotating target 11. However, the present invention is not limited to this. In the present invention, the imaging control unit 6 may be configured to randomly select a second electron emission unit 12b different from the first electron emission unit 12a. The switching order of the electron emission units 12 by the imaging control unit 6 is not particularly limited.

[0118] Furthermore, although the above embodiment shows an example of generating a CT image 56 based on multiple projection image data 50, the present invention is not limited thereto. In the present invention, a simple X-ray image may be generated based on multiple projection image data 50, or a simple X-ray image may be generated based on a single projection image data 50.

[0119] Furthermore, in the above embodiment, the image processing unit 5 is shown to perform a correction process in the reconstruction process to correct the magnification ratio of the subject 90 and the position of the projected image of the subject 90 in each of the projected image data 50, but the present invention is not limited to this. In the present invention, a reconstruction process that does not include the above correction process may be performed. However, in order to improve the image quality of the CT image 56, it is preferable to perform a reconstruction process that includes the above correction process.

[0120] Furthermore, in the above embodiment, a calculation method applying the FDK method, a type of analytical method, was shown as an example of reconstruction processing, but the present invention is not limited thereto. In the present invention, the reconstruction processing of the CT image 56 by the image processing unit 5 may be performed using an analytical method other than the FDK method. Alternatively, a reconstruction processing method other than an analytical method, such as a successive approximation method, may be performed.

[0121] Furthermore, in the above embodiment, an example was shown in which the portion of the inclined surface 11a on the rotating target 11 where the multiple focal positions 14 aligned radially are located and the surface of the substrate 31 are adjusted to be parallel to each other, but the present invention is not limited to this. In the present invention, the portion of the inclined surface 11a on the rotating target 11 where the multiple focal positions 14 aligned radially are located and the surface of the substrate 31 do not have to be parallel to each other.

[0122] Furthermore, in the above embodiment, an example was shown in which the electron beam 36 irradiated from the electron emission unit 12 is incident perpendicularly to the focal position 14 on the inclined surface 11a of the rotating target 11, but the present invention is not limited thereto. In the present invention, the electron beam 36 irradiated from the electron emission unit 12 may be incident obliquely to the focal position 14 on the inclined surface 11a of the rotating target 11.

[0123] Furthermore, while the above embodiment shows an example in which the rotating mechanism 4 rotates the subject mounting section 3 to change the imaging angle 40 of the subject, the present invention is not limited to this. In the present invention, the rotating mechanism 4 may also rotate the imaging section 7 (X-ray source 1 and detector 2) to change the imaging angle 40 of the subject.

[0124] Furthermore, in the above embodiment, the plurality of electron emission units 12 are composed of cold cathode electron sources 30, and the cold cathode electron sources 30 are shown to be spint-type electron sources, but the present invention is not limited to this. In the present invention, the plurality of electron emission units 12 may be composed of hot cathode electron sources.

[0125] [Pattern] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0126] (Item 1) An X-ray source comprising a rotating target supported so as to be rotatable around a rotation axis, and a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, wherein the incident angle of the electron beams irradiated from each of the plurality of electron emission units and incident at each of the focal positions of the plurality of electron emission units on the rotating target is adjusted to be constant, A detector for detecting X-rays emitted from the X-ray source, An image processing unit that generates an image based on the detection signal output from the detection unit, An X-ray imaging apparatus comprising: an imaging control unit that controls the X-ray source to sequentially switch the plurality of electron emission units to irradiate with an electron beam.

[0127] (Item 2) The X-ray imaging apparatus according to item 1, wherein the focal positions of each of the plurality of electron-emitting units are positioned so as to be aligned radially on the rotating target.

[0128] (Item 3) The X-ray source further includes a substrate on which the plurality of electron emission sections are provided, The X-ray imaging apparatus according to item 2, wherein the rotating target is adjusted so that the surface portion on which the multiple focal positions arranged radially are located and the surface of the substrate are parallel to each other.

[0129] (Item 4) An X-ray imaging apparatus according to any one of items 1 to 3, wherein adjacent focal ranges on the rotating target are positioned apart and do not overlap.

[0130] (Item 5) The X-ray imaging apparatus according to any one of items 1 to 4, wherein the imaging control unit controls the X-ray source to sequentially switch the plurality of electron emission units to irradiate the X-ray source based on the electron beam irradiation time, which is the longest time for which the electron beam irradiated from the electron emission unit can be continuously irradiated to the focal position without the rotating target being damaged by heat, and which has been acquired in advance.

[0131] (Item 6) A subject support unit is positioned between the X-ray source and the detector and supports the subject, The system further includes a rotation mechanism that rotates the imaging unit, which includes the X-ray source and the detector, and the subject placement unit relative to each other so as to change the imaging angle of the subject, The plurality of electron emission units include a first electron emission unit and a second electron emission unit different from the first electron emission unit. The image processing unit generates a plurality of projection image data based on the detection signals at each of the plurality of shooting angles, and generates a CT image based on the plurality of projection image data generated. When the rotation mechanism rotates the first shooting angle to the second shooting angle in a plurality of shooting angles, the shooting control unit determines whether the remaining time that the electron beam can be irradiated to the focal position of the first electron emitter, which irradiated the focal position with the electron beam at the first shooting angle, is shorter than the time that the electron beam can be irradiated to the focal position at the second shooting angle. The X-ray imaging apparatus according to item 5, wherein the imaging control unit controls the X-ray source to switch from the first electron emission unit to the second electron emission unit and irradiate with an electron beam when it determines that the remaining time available for irradiation of the electron beam in the first electron emission unit is shorter than the irradiation time of the electron beam at the second imaging angle.

[0132] (Item 7) The X-ray imaging apparatus according to item 6, wherein the irradiation time of the electron beam is shortened as the distance between the focal point and the axis of rotation decreases.

[0133] (Item 8) The system further includes a storage unit that stores information about the focal position of each of the plurality of electron emission units. The X-ray imaging apparatus according to item 6 or 7, wherein the image processing unit is configured to generate the CT image by performing a reconstruction process on the plurality of projection image data, based on reconstruction information including information on the focal positions of the plurality of electron emission units used to acquire each of the plurality of projection image data, information on the distance between the focal positions and the subject placement unit, and information on the distance between the focal positions and the detector.

[0134] (Item 9) The X-ray imaging apparatus according to item 8, wherein the image processing unit is configured to correct, in the reconstruction process, the magnification of the subject and the position of the projected image of the subject in each of the plurality of projection image data based on the reconstruction information. [Explanation of symbols]

[0135] 1 X-ray source 2 detectors 3 Subject installation section 4 Rotation mechanism 5 Image Processing Unit 6. Image capture control unit 7. Photography Department 10 X-ray 11 Rotating Targets 11b Rotation axis 12(12a, 12b, 12c) Electron emission part 14(14a, 14b, 14c) Focus position 14d focal range 22 Memory section 31 circuit boards 36 Electron beam 40 (40a, 40b, 40c) Shooting angle 50 Projected image data 52. Focal Position Information 57 Information on the distance between the focal point and the subject mounting area. 58 Information on the distance between the focal point and the detector 56 CT characters 90 Subjects 100 X-ray imaging equipment θ incident angle

Claims

1. An X-ray source comprising a rotating target supported so as to be rotatable around a rotation axis, and a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, wherein the incident angle of the electron beams irradiated from each of the plurality of electron emission units and incident at each of the focal positions of the plurality of electron emission units on the rotating target is adjusted to be constant, A detector for detecting X-rays emitted from the X-ray source to the subject, An image processing unit that generates multiple images based on detection signals output from the detector at each of multiple shooting angles, The system includes an imaging control unit that controls the X-ray source to sequentially switch between the plurality of electron emission units to irradiate with an electron beam, An X-ray imaging apparatus, wherein the image processing unit is configured to correct the position of the projected image of the subject in the plurality of images for each of the plurality of imaging angles based on electron beams irradiated from each of the plurality of electron emission units.

2. The X-ray imaging apparatus according to claim 1, wherein the imaging control unit controls the X-ray source to sequentially switch the plurality of electron emission units and irradiate with electron beams based on the electron beam irradiation time, which is the longest time for which the electron beam irradiated from the electron emission unit can be continuously irradiated to the focal position without the rotating target being damaged by heat, and which has been acquired in advance.

3. An X-ray source comprising a rotating target supported so as to be rotatable around a rotation axis, and a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, wherein the incident angle of the electron beams irradiated from each of the plurality of electron emission units and incident at each of the focal positions of the plurality of electron emission units on the rotating target is adjusted to be constant, A detector for detecting X-rays emitted from the aforementioned X-ray source, An image processing unit that generates an image based on the detection signal output from the aforementioned detector, The system includes an imaging control unit that controls the X-ray source to sequentially switch between the plurality of electron emission units to irradiate with an electron beam, An X-ray imaging apparatus, wherein the imaging control unit controls the X-ray source to sequentially switch between the plurality of electron emission units and irradiate with electron beams, based on the remaining amount of electron beam irradiation time, which is the maximum amount of time for which the rotating target can be continuously irradiated at the focal position without being damaged by heat, and which has been acquired in advance.

4. The X-ray imaging apparatus according to any one of claims 1 to 3, wherein the focal positions of each of the plurality of electron-emitting units are positioned to be aligned radially on the rotating target.

5. The X-ray source further includes a substrate on which the plurality of electron emission sections are provided, The X-ray imaging apparatus according to claim 4, wherein the rotating target is adjusted so that the surface portion on which the plurality of focal positions arranged radially are located and the surface of the substrate are parallel to each other.

6. The X-ray imaging apparatus according to any one of claims 1 to 5, wherein adjacent focal ranges on the rotating target are positioned apart and do not overlap.

7. An X-ray source comprising a rotating target supported so as to be rotatable about a rotation axis, and a plurality of electron emission units that irradiate electron beams at a plurality of focal positions on the rotating target at different distances from the rotation axis, wherein the incident angle of the electron beams irradiated from each of the plurality of electron emission units and incident at each of the focal positions of the plurality of electron emission units on the rotating target is adjusted to be constant, A detector for detecting X-rays emitted from the aforementioned X-ray source, An image processing unit that generates an image based on the detection signal output from the aforementioned detector, A photography control unit controls the X-ray source to sequentially switch between the plurality of electron emission units to irradiate with an electron beam, A subject support unit is positioned between the X-ray source and the detector and supports the subject, The system includes a rotation mechanism that rotates the imaging unit, which includes the X-ray source and the detector, and the subject placement unit relative to each other so as to change the imaging angle of the subject, The plurality of electron emission units include a first electron emission unit and a second electron emission unit different from the first electron emission unit. The imaging control unit controls the X-ray source to sequentially switch between the plurality of electron emission units and irradiate with electron beams, based on a previously acquired electron beam irradiation time which is the longest time for which the rotating target can be continuously irradiated to the focal position without being damaged by heat. The image processing unit generates a plurality of projection image data based on the detection signals at each of the plurality of shooting angles, and generates a CT image, which is the image, based on the plurality of projection image data generated. When the rotation mechanism rotates the first shooting angle to the second shooting angle in a plurality of shooting angles, the shooting control unit determines whether the remaining time that the electron beam can be irradiated to the focal position of the first electron emitter, which irradiated the focal position with the electron beam at the first shooting angle, is shorter than the time that the electron beam can be irradiated to the focal position at the second shooting angle. X-ray imaging apparatus, wherein the imaging control unit controls the X-ray source to switch from the first electron emission unit to the second electron emission unit and irradiate with an electron beam when it determines that the remaining time available for irradiation of the electron beam in the first electron emission unit is shorter than the irradiation time of the electron beam at the second imaging angle.

8. The X-ray imaging apparatus according to claim 7, wherein the irradiation time of the electron beam is shortened as the distance between the focal point and the axis of rotation decreases.

9. The system further includes a storage unit that stores information about the focal position of each of the plurality of electron emission units. The X-ray imaging apparatus according to claim 7 or 8, wherein the image processing unit is configured to generate the CT image by performing a reconstruction process on the plurality of projection image data, based on reconstruction information including information on the focal positions of the plurality of electron emission units used to acquire each of the plurality of projection image data, information on the distance between the focal position and the subject placement unit, and information on the distance between the focal position and the detector.

10. The X-ray imaging apparatus according to claim 9, wherein the image processing unit is configured to correct, in the reconstruction process, the magnification of the subject and the position of the projected image of the subject in each of the plurality of projection image data based on the reconstruction information.

Images