X-ray phase imaging apparatus, X-ray image processing apparatus, X-ray image processing method, and correction curve generation method

Abstract

This X-ray phase imaging device (100) comprises: an x-ray source (1); an x-ray detector (2); a plurality of lattices; an image processing unit (7a) that generates a first dark field image (35a); a storage unit (8) that stores a plurality of correction curves (20a) that are respectively generated at positions in a direction orthogonal to a lattice direction; and a control unit (7b) that uses the plurality of correction curves corresponding respectively to the positions to correct the first dark field image. Each of the plurality of correction curves indicates, at such positions, a correspondence relationship between a value relating to the x-ray absorption of a subject (90) and a value relating to x-ray dispersion.

Description

Technical Field

[0001] The present invention relates to an X-ray phase imaging apparatus, an X-ray image processing apparatus, an X-ray image processing method, and a correction curve generation method, and particularly relates to an X-ray phase imaging apparatus, an X-ray image processing apparatus, an X-ray image processing method, and a correction curve generation method for imaging an image using a plurality of gratings.

Background Art

[0002] Conventionally, an X-ray phase imaging apparatus that images an image using a plurality of gratings has been known. Such X-ray phase imaging measures are disclosed, for example, in Japanese Patent Application Laid-Open No. 2021-194389.

[0003] Japanese Patent Application Laid-Open No. 2021-194389 discloses a radiation imaging system including a radiation generator, a radiation detector, a plurality of gratings disposed between the radiation generator and the radiation detector, and an image processing apparatus that generates a small-angle scattering image based on a signal detected by the radiation detector.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, although not disclosed in Japanese Patent Application Laid-Open No. 2021-194389, it is known that when radiation (X-rays) passes through an object, the spectrum of the X-rays changes. The degree of hardening of the X-ray spectrum also changes depending on the thickness of the object through which the X-rays pass (the path length of the X-rays). The change in the X-ray spectrum also occurs when the X-rays pass through the grating.

[0006] In addition, in a radiation imaging system (X-ray phase imaging apparatus) as disclosed in Japanese Patent Application Laid-Open No. 2021-194389, X-rays irradiated from a radiation generation apparatus (X-ray source) are irradiated in a so-called cone beam shape. In this case, in the peripheral region of the grating, the incident angle of the X-rays with respect to the grating is larger than that in the central region of the grating. When the incident angle of the X-rays with respect to the grating is different, the path length of the X-rays when passing through the grating also changes, so the degree of change in the spectrum of the X-rays is different. Therefore, due to the difference in the degree of change in the spectrum of the X-rays, there is a disadvantage that non-uniform noise occurs in the small-angle scattering image (dark field image). In this case, there is a problem that the image quality of the dark field image deteriorates due to the noise caused by the X-rays incident on the grating from an oblique direction.

[0007] The present invention has been made to solve the above problems, and one object of the present invention is to provide an X-ray phase imaging apparatus capable of suppressing a decrease in the image quality of a dark field image even when X-rays are incident on a grating from an oblique direction.

Means for Solving the Problems

[0008] As a result of intensive studies by the inventors of the present application to achieve the above object, due to the interaction between the change in the spectrum of X-rays that occurs when passing through the subject and the change in the spectrum of X-rays due to the difference in the incident angle of the X-rays with respect to the grating, it was found that the degree of scattering of the X-rays changes, and thus non-uniform noise occurs in the dark field image. That is, the X-ray phase imaging apparatus according to the first aspect of the present invention includes an X-ray source, an X-ray detector that detects X-rays irradiated from the X-ray source, and is disposed between the X-ray source and the X-ray detector Each has a lattice pattern forming part that functions as a lattice a plurality of gratings, an image processing unit that generates an X-ray phase contrast image including a first dark field image that is a dark field image of the subject based on the intensity distribution of the X-rays detected by the X-ray detector, and a plurality of gratings Each of the lattice pattern forming parts in a direction orthogonal to the grating direction, which is the direction in which the A predetermined area of the dark field image each of the plurality of correction curves generated for each is stored in a storage unit, and the above A predetermined area A control unit that corrects the first dark-field image using a corresponding correction curve for each, and each of the plurality of correction curves shows the correspondence between the value related to X-ray absorption of the subject and the value related to X-ray scattering in the above A predetermined area is shown.

[0009] An X-ray image processing apparatus according to a second aspect of the present invention includes an image acquisition unit that acquires an X-ray phase contrast image including a first dark-field image that is a dark-field image of a subject, Each has a lattice pattern forming part that functions as a lattice a plurality of gratings Each of the lattice pattern forming parts in a direction orthogonal to the grating direction that is the direction in which the A predetermined area of the dark field image extends, a storage unit that stores a plurality of correction curves generated for each, and the above A predetermined area A control unit that corrects the first dark-field image using a corresponding correction curve for each, and each of the plurality of correction curves shows the correspondence between the value related to X-ray absorption of the subject and the value related to X-ray scattering in the above A predetermined area is shown.

[0010] An X-ray image processing method according to a third aspect of the present invention includes a step of acquiring an X-ray phase contrast image including a first dark-field image that is a dark-field image of a subject, Each has a lattice pattern forming part that functions as a lattice a plurality of gratings Each of the lattice pattern forming parts in a direction orthogonal to the grating direction that is the direction in which the A predetermined area of the dark field image extends, a step of storing a plurality of correction curves generated for each, and the above A predetermined area a step of correcting the first dark-field image using a corresponding correction curve for each, and each of the plurality of correction curves shows the correspondence between the value related to X-ray absorption of the subject and the value related to X-ray scattering in the above A predetermined area is shown.

[0011] A correction curve generation method according to a fourth aspect of the present invention includes a step of imaging a correction phantom using an X-ray phase imaging apparatus having a plurality of gratings and acquiring a second dark-field image that is a dark-field image of the correction phantom, a step of acquiring a second absorption image that is an absorption image of the correction phantom, and a plurality of gratings Each of the lattice pattern forming parts in a direction orthogonal to the grating direction that is the direction in which the A predetermined area Including a step of generating a plurality of correction curves using the second dark-field image and the second absorption image each time.

Advantages of the Invention

[0012] In the X-ray phase imaging apparatus according to the first aspect, the X-ray image processing apparatus according to the second aspect, and the X-ray image processing method according to the third aspect, The above In the direction orthogonal to the grating direction A predetermined area of the dark field image A plurality of correction curves corresponding to each are stored. These plurality of correction curves show the correspondence relationship between the value related to the X-ray absorption of the subject in the above A predetermined area and the value related to the X-ray scattering. Therefore, the degree of change in the spectrum of the X-ray due to the incident angle of the X-ray in the above A predetermined area is also taken into account. Then, by correcting the first dark-field image, which is the dark-field image of the subject, using the correction curve corresponding to each, compared with the case of correcting the first dark-field image using one common correction curve, an accurate correction of the first dark-field image can be performed. As a result, even when the X-ray is incident on the grating from an oblique direction, it is possible to suppress a decrease in the image quality of the first dark-field image. A predetermined area In the correction curve generation method according to the fourth aspect of the present invention, since the plurality of correction curves are generated using the second dark-field image and the second absorption image actually obtained by imaging the correction phantom, in a state where the degree of change in the spectrum of the X-ray due to the incident angle of the X-ray in the above

[0013] is extremely accurately reflected, a plurality of correction curves can be generated. A predetermined area is extremely accurately reflected, a plurality of correction curves can be generated.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram showing the overall configuration of an X-ray phase imaging apparatus including an X-ray image processing apparatus according to an embodiment. [Figure 2] It is a diagram for explaining the configuration of a grating position adjustment mechanism included in the X-ray phase imaging apparatus according to an embodiment. [Figure 3] It is a schematic diagram for explaining the configuration in which an X-ray image processing apparatus according to an embodiment generates an X-ray phase contrast image. [Figure 4] It is a schematic diagram for explaining the non-uniform noise generated in the dark field image. [Figure 5] It is a graph for explaining the change in the pixel value of the dark field image along the broken line in FIG. 4. [Figure 6] It is a schematic diagram for explaining the difference in the incident angle of X-rays with respect to the grating. [Figure 7] It is a graph for explaining the change in the spectrum of X-rays due to the difference in the incident angle of X-rays with respect to the grating. [Figure 8] It is a schematic diagram for explaining the shape and arrangement of the correction phantom. [Figure 9] It is a schematic diagram for explaining the difference in the thickness of the correction phantom. [Figure 10] It is schematic diagram (A) and schematic diagram (B) for explaining the configuration for generating a correction curve. [Figure 11] It is a graph for explaining a set of correction curves including a plurality of correction curves. [Figure 12] It is a schematic diagram for explaining the configuration for generating a plurality of types of correction curve sets depending on correction phantoms of different materials and different imaging conditions. [Figure 13] It is schematic diagram (A), schematic diagram (B), and graph (C) for explaining the configuration in which a control unit according to an embodiment corrects a subject image. [Figure 14] It is schematic diagram (A), graph (B), schematic diagram (C), graph (D), schematic diagram (E), and graph (F) for explaining the difference in correction accuracy between the corrected dark field image according to a comparative example and the corrected dark field image according to an embodiment. [Figure 15] It is a flowchart for explaining the process in which an X-ray image processing apparatus according to an embodiment generates a correction curve. [Figure 16] It is a flowchart for explaining the process in which an X-ray image processing apparatus according to an embodiment corrects a subject image. [Figure 17] It is a schematic diagram for explaining a correction phantom according to the first modification example. [Figure 18] It is a schematic diagram for explaining a correction phantom according to the second modification example. [Figure 19] It is schematic diagram (A) and schematic diagram (B) for explaining the difference in the energy distribution of X-rays in the arrangement direction of the lattice.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments embodying the present invention will be described with reference to the drawings.

[0016] First, referring to FIG. 1, the overall configuration of an X-ray phase imaging apparatus 100 including an X-ray image processing apparatus 6 according to an embodiment of the present invention will be described.

[0017] As shown in FIG. 1, the X-ray phase imaging apparatus 100 is an apparatus that images the inside of a subject 90 using the Talbot effect. The X-ray phase imaging apparatus 100 includes an X-ray source 1, an X-ray detector 2, a plurality of gratings, and an X-ray image processing apparatus 6. Further, the X-ray phase imaging apparatus 100 includes an input reception unit 10, a display unit 11, and a grating position adjustment mechanism 12.

[0018] In this specification, the vertical direction is defined as the Z direction, the upward direction is the Z1 direction, and the downward direction is the Z2 direction. Further, the direction from the X-ray source 1 toward the X-ray detector 2 is defined as the X direction, one side is the X1 direction, and the other side is the X2 direction. In the example shown in FIG. 1, the X direction is a direction orthogonal to the Z direction. Further, the direction orthogonal to the Z direction and the X direction is defined as the Y direction, one side is the Y1 direction, and the other side is the Y2 direction. The example shown in FIG. 1 is an X-ray phase imaging apparatus 100 viewed from above.

[0019] The X-ray source 1 is configured to irradiate the subject 90 with X-rays. Specifically, the X-ray source 1 is configured to generate X-rays when a high voltage is applied.

[0020] The X-ray detector 2 is configured to detect the X-rays irradiated from the X-ray source 1. Further, the X-ray detector 2 is configured to convert the detected X-rays into an electrical signal. The X-ray detector 2 is, for example, an FPD (Flat Panel Detector). The X-ray 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 side by side in the Y direction and the Z direction at a predetermined period (pixel pitch). The detection signal (image signal) of the X-ray detector 2 is sent to the X-ray image processing device 6.

[0021] A plurality of gratings are arranged between the X-ray source 1 and the X-ray detector 2. In the present embodiment, the plurality of gratings includes a first grating 3, a second grating 4, and a third grating 5.

[0022] The first grating 3 is arranged between the X-ray source 1 and the second grating 4. The first grating 3 is irradiated with X-rays from the X-ray source 1. The first grating 3 has a plurality of slits 3a and X-ray absorption portions 3b arranged at a predetermined period (pitch) 3c in the Z direction. Each slit 3a and X-ray absorption portion 3b is formed to extend linearly in the Y direction. Further, each slit 3a and X-ray absorption portion 3b is formed to extend in parallel. The first grating 3 is configured to use the X-rays passing through each slit 3a as line light sources corresponding to the positions of the respective slits 3a.

[0023] The second grating 4 is disposed between the first grating 3 and the third grating 5. The second grating 4 is irradiated with X-rays from the first grating 3. The second grating 4 has slits 4a and an X-ray phase change portion 4b arranged at a predetermined period (grating pitch) 4c in the Y direction. Each slit 4a and the X-ray phase change portion 4b are formed to linearly extend in the Z direction. The second grating 4 is a so-called phase grating. The second grating 4 is provided to form a self-image by the X-rays irradiated from the X-ray source 1 (by the Talbot effect). Note that the Talbot effect means that when X-rays having coherence pass through a grating in which slits are formed, an image (self-image) of the grating is formed at a position separated from the grating by a predetermined distance (Talbot distance).

[0024] The third grating 5 is irradiated with X-rays from the second grating 4. The third grating 5 has a plurality of X-ray transmission portions 5a and X-ray absorption portions 5b arranged at a predetermined period (grating pitch) 5c in the Y direction. Each X-ray transmission portion 5a and the X-ray absorption portion 5b are formed to linearly extend in the Z direction. The third grating 5 is a so-called absorption grating. The third grating 5 is disposed between the second grating 4 and the X-ray detector 2 and is configured to interfere with the self-image formed by the second grating 4. The third grating 5 is disposed at a position separated from the second grating 4 by the Talbot distance in order to interfere the self-image with the third grating 5.

[0025] In this embodiment, each of the first grating 3, the second grating 4, and the third grating 5 is arranged such that the grating direction is the Z direction. Note that the grating direction is the direction in which the grating pattern forming portion extends. The grating pattern forming portion is a portion that is formed by the slit 3a and the X-ray absorption portion 3b and functions as a grating in the first grating 3. In the second grating 4, the grating pattern forming portion is formed by the slit 4a and the X-ray phase change portion 4b. In the third grating 5, the grating pattern forming portion is formed by the X-ray transmission portion 5a and the X-ray absorption portion 5b.

[0026] The X-ray image processing apparatus 6 includes, for example, a processor 7 such as a CPU (Central Processing Unit), and a GPU (Graphics Processing Unit) or an FPGA (Field-Programmable Gate Array) configured for image processing, a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory), a storage unit 8, and an image acquisition unit 9. Note that the X-ray image processing apparatus 6 may include circuitry instead of the processor 7.

[0027] The processor 7 includes an image processing unit 7a and a control unit 7b. The image processing unit 7a is configured to generate an X-ray phase contrast image 30 based on the intensity distribution of X-rays detected by the X-ray detector 2. The image processing unit 7a is configured software-wise as a functional block realized by the processor 7 executing various programs. The image processing unit 7a may be configured by hardware as a dedicated processing circuit. In the present embodiment, the X-ray phase contrast image 30 includes a first dark field image 35a (see FIG. 13(A)). Also, in the present embodiment, the X-ray phase contrast image 30 includes a first absorption image 35b (see FIG. 13(B)). Details of the configuration in which the image processing unit 7a generates the X-ray phase contrast image 30 will be described later.

[0028] The control unit 7b is configured to control the X-ray source 1 and the grating position adjustment mechanism 12, etc. The control unit 7b is configured software-wise as a functional block realized by the processor 7 executing various programs. The control unit 7b may be configured by hardware as a dedicated processing circuit.

[0029] The storage unit 8 is configured to store a plurality of types of correction curve sets 20, which will be described later. The correction curve set 20 includes a plurality of correction curves 20a, which will be described later. The storage unit 8 is also configured to store the X-ray phase contrast image 30 generated by the image processing unit 7a and various programs executed by the processor 7. The storage unit 8 includes a non-volatile storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0030] The image acquisition unit 9 is configured to acquire the X-ray phase contrast image 30 including the first dark field image 35a. The image acquisition unit 9 is, for example, an input / output interface.

[0031] The input reception unit 10 is configured to receive the operation input 21 of the operator. The input reception unit 10 includes, for example, an input device such as a keyboard or a mouse.

[0032] The display unit 11 displays the X-ray phase contrast image 30 generated by the image processing unit 7a. The display unit 11 includes, for example, a display device such as a liquid crystal monitor or an organic EL (Electro-Luminescence) monitor.

[0033] The grating position adjustment mechanism 12 is configured to move the second grating 4 in the X direction, Y direction, Z direction, the rotational direction Rz around the axis in the Z direction, the rotational direction Rx around the axis in the X direction, and the rotational direction Ry around the axis in the Y direction. The detailed configuration of the grating position adjustment mechanism 12 will be described later.

[0034] (Grating position adjustment mechanism) As shown in FIG. 2, the grating position adjustment mechanism 12 includes a Y-direction linear motion mechanism 12a, a Z-direction linear motion mechanism 12b, an X-direction linear motion mechanism 12c, a linear motion mechanism connection part 12d, a stage support part drive part 12e, a stage support part 12f, a stage drive part 12g, and a stage 12h.

[0035] The Y-direction linear motion mechanism 12a, the Z-direction linear motion mechanism 12b, and the X-direction linear motion mechanism 12c are each configured to be movable in the Y direction, the Z direction, and the X direction. The Y-direction linear motion mechanism 12a, the Z-direction linear motion mechanism 12b, and the X-direction linear motion mechanism 12c include, for example, a drive unit such as a stepping motor, a driving force transmission member that transmits the driving force from the drive unit, and a moving unit that moves by the driving force transmitted by the driving force transmission member. The grating position adjustment mechanism 12 is configured to move the second grating 4 in the Y direction, the Z direction, and the X direction by the operations of the Y-direction linear motion mechanism 12a, the Z-direction linear motion mechanism 12b, and the X-direction linear motion mechanism 12c.

[0036] The stage support portion 12f supports the stage 12h for placing the second grating 4 from below (in the Z2 direction) in FIG. 2. The stage drive unit 12g is configured to reciprocally move the stage 12h in the Y direction. The bottom of the stage 12h is formed in a convex curved surface shape toward the stage support portion 12f, and is configured to rotate around the axis in the X direction (Rx direction) when moved in the Y direction. Further, the stage support portion drive unit 12e is configured to reciprocally move the stage support portion 12f in the X direction. Also, the bottom of the stage support portion 12f is formed in a convex curved surface shape toward the linear motion mechanism connection portion 12d, and is configured to rotate around the axis in the Y direction (Ry direction) when moved in the X direction. Further, the linear motion mechanism connection portion 12d is provided on the X-direction linear motion mechanism 12c so as to be rotatable around the axis in the Z direction (Rz direction). With the above configuration, in the grating position adjustment mechanism 12, the second grating 4 can be step-moved (translated) in the X direction, the Y direction, and the Z direction.

[0037] (Configuration for generating X-ray phase contrast images) Next, with reference to FIG. 3, the configuration in which the image processing unit 7a (see FIG. 1) generates an X-ray phase contrast image 30 (see FIG. 1) will be described. The image processing unit 7a uses the intensity signal curve 23 and the intensity signal curve 24 obtained based on the intensity distribution of the X-rays detected by the X-ray detector 2 (see FIG. 1) by photographing while translating the second grating 4 by the grating position adjustment mechanism 12 (see FIG. 1) to generate the X-ray phase contrast image 30. The X-ray phase contrast image 30 includes a first absorption image 35b (see FIG. 13(B)), a second absorption image 32 (see FIG. 10(B)), a phase differential image, a first dark field image 35a (see FIG. 13(A)), and a second dark field image 31 (see FIG. 10(A)). The intensity signal curve 23 is a curve showing the distribution of the intensity of the X-rays obtained by photographing with the subject 90 (see FIG. 1) placed. Further, the intensity signal curve 24 is a curve showing the distribution of the intensity of the X-rays obtained by photographing with the subject 90 not placed. In this embodiment, a detailed description of the phase differential image is omitted. Note that the first dark field image 35a and the first absorption image 35b are a dark field image of the subject 90 and an absorption image of the subject 90, respectively. Also, the second dark field image 31 and the second absorption image 32 are a dark field image of the correction phantom 13 (see FIG. 8) described later and an absorption image of the correction phantom 13, respectively.

[0038] As shown in FIG. 3, the second absorption image 32 can be generated by the ratio of the average intensity Cs of the X-rays when imaging with the subject 90 placed and the average intensity Cr of the X-rays when imaging without the subject 90 placed. Also, the second dark field image 31 can be generated by the ratio of the Visibility (Vr) when imaging without the subject 90 placed and the Visibility (Vs) when imaging with the subject 90 placed. Vr can be obtained by the ratio of the amplitude Ar of the intensity signal curve 24 and the average intensity Cr. Also, Vs can be obtained by the ratio of the amplitude As of the intensity signal curve 23 and the average intensity Cs.

[0039] (Noise generated in the dark field image) Next, referring to FIGS. 4 to 7, the non-uniform noise generated in the second dark-field image 31 (see FIG. 4) will be described. Note that the second dark-field image 31 shown in FIG. 4 represents the difference in pixel values by applying different hatchings. Specifically, the thinner the hatching (the wider the interval between the hatchings), the larger the pixel value. The examples shown in FIGS. 4 to 7 are non-uniform noises generated in the second dark-field image 31 generated by the X-ray phase imaging apparatus 100 according to the present embodiment, and are reduced by the correction process described later.

[0040] The example shown in FIG. 4 is the second dark-field image 31 when imaging a flat aluminum material as the subject 90. Usually, since a flat aluminum material does not induce X-ray scattering, it is not imaged in the second dark-field image 31. However, as shown in FIG. 4, when imaging a flat aluminum material, a subject 90 having a different pixel value from the background 91 is imaged in the second dark-field image 31. This is considered to be because the X-ray spectrum changes (hardens) when the X-ray passes through the subject 90. Note that the hardening of the X-ray spectrum means that the central energy of the X-ray spectrum shifts to the high-energy side.

[0041] Also, as shown in FIG. 4, in the Y direction, the pixel value of the central portion region 90a of the subject 90 shown in the second dark-field image 31 is larger than those of the regions 90b and 90c on both sides.

[0042] The graph 50 shown in FIG. 5 is a graph in which the pixel values in the direction along the straight line 40 extending in the Y direction in the second dark-field image 31 shown in FIG. 4 are plotted. In the graph 50, the vertical axis represents the pixel value and the horizontal axis represents the position (pixel).

[0043] As shown by the curve 50a of the graph 50, it is confirmed that the pixel value of the central portion region 90a (see FIG. 4) of the second dark-field image 31 (see FIG. 4) is higher than the pixel values of the regions 90b (see FIG. 4) and 90c (see FIG. 4) on both sides.

[0044] Here, the X-rays irradiated from the X-ray source 1 (see FIG. 6) are so-called cone-beam X-rays. Therefore, they are incident on the plurality of gratings from an oblique direction. Due to the difference in the incident angles on the plurality of gratings, the degree of hardening of the X-ray spectrum changes, so that the pixel value of the region 90a in the central portion of the second dark-field image 31 becomes larger than the pixel values of the regions 90b and 90c on both sides.

[0045] The arrow 41 shown in FIG. 6 indicates the X-rays irradiated on the second grating 4 along the optical axis of the X-rays. Also, the dashed arrow 42 indicates the X-rays incident on the grating from an oblique direction. In the example shown in FIG. 6, for the sake of convenience, only the second grating 4 among the plurality of gratings is illustrated. When the X-rays indicated by the arrow 41 pass through the second grating 4 and are detected by the X-ray detector 2, and when the X-rays indicated by the arrow 42 pass through the second grating 4 and are detected by the X-ray detector 2, the path lengths when the X-rays pass through the second grating 4 are different according to the difference in the incident angles on the second grating 4, resulting in different spectra from each other.

[0046] The graph 51 shown in FIG. 7 is a graph showing the spectrum of the X-rays that have passed through the second grating 4 (see FIG. 6). In the graph 51, the vertical axis represents the X-ray intensity and the horizontal axis represents the energy of the X-rays.

[0047] The curve 51a shown in the graph 51 is the spectrum of the X-rays indicated by the arrow 41 in FIG. 6. Also, the dashed curve 51b shown in the graph 51 is the spectrum of the X-rays indicated by the dashed arrow 42 in FIG. 6.

[0048] When X-rays are incident on the second lattice 4 from an oblique direction, the X-rays indicated by arrow 42 have a longer path length when passing through the second lattice 4 than the X-rays indicated by arrow 41. Due to this difference in path length, as shown by curve 51b, the spectrum of the X-rays when passing through the second lattice 4 is hardened compared to the spectrum of the X-rays shown by curve 51a. Since the degree of hardening of the X-ray spectrum varies according to the incident angle of the X-rays on the second lattice 4, non-uniform noise occurs in the direction (Y direction) orthogonal to the lattice direction (Z direction) in the second dark-field image 31. When non-uniform noise occurs in the second dark-field image 31, a pixel value profile with a convex shape on the upper side in the central portion is obtained, as shown by curve 50a in the graph 50 shown in FIG. 5.

[0049] When imaging a subject 90 using X-rays with an imaging device having a plurality of lattices, such as the X-ray phase imaging device 100 according to the present embodiment, both a change in the X-ray spectrum due to the subject 90 and a change in the X-ray spectrum due to the difference in the incident angle of the X-rays on the second lattice 4 occur. Therefore, as shown in FIG. 4, non-uniform noise occurs in the second dark-field image 31, and the image quality of the second dark-field image 31 deteriorates. The non-uniform noise occurring in the second dark-field image 31 is caused by the combined occurrence of a change in the X-ray spectrum due to the subject 90 and a change in the X-ray spectrum due to the difference in the incident angle of the X-rays on the second lattice 4.

[0050] Therefore, in the present embodiment, the control unit 7b is configured to correct the first dark-field image 35a by a plurality of correction curves 20a generated for each position in the direction (Y direction) orthogonal to the lattice direction (Z direction) in which the plurality of lattices extend, the plurality of correction curves 20a showing the correspondence between the value related to the X-ray absorption of the subject 90 at the above position and the value related to the scattering (degree of diffusion) of the X-rays. Each of the plurality of correction curves 20a is generated based on the correction image 33. The correction image 33 is an image obtained by imaging the correction phantom 13.

[0051] (Correction phantom) First, referring to FIGS. 8 and 9, the correction phantom 13 used when generating a plurality of correction curves 20a will be described. Since the plurality of grids are arranged in a direction where the grid directions are equal to each other, in the example shown in FIG. 8, for convenience, only the second grid 4 is illustrated.

[0052] As shown in FIG. 8, the correction phantom 13 has a structure in which the degree of X-ray absorption varies (changes) in the direction in which the grid extends (Z direction). The correction phantom 13 is formed such that the thickness in the X-ray irradiation direction (X direction) changes in the Z direction. Specifically, the correction phantom 13 has a stepped shape in which the thickness in the X-ray irradiation direction changes stepwise in the Z direction. The correction phantom 13 is integrally formed of a homogeneous material.

[0053] The correction phantom 13 has a plurality of stepped portions. Specifically, the correction phantom 13 has a first stepped portion 13a to a fourth stepped portion 13d.

[0054] As shown in FIG. 9, the thickness of each stepped portion is such that the thickness 60a of the first stepped portion 13a is the largest and the thickness 60d of the fourth stepped portion 13d is the smallest.

[0055] Note that the thickness per step of the correction phantom 13 is constant. That is, when the thickness 60d of the fourth stepped portion 13d is used as a reference, the thickness 60c of the third stepped portion 13c is twice the thickness 60d. Similarly, the thickness 60b of the second stepped portion 13b is three times the thickness 60d. Also, the thickness 60a of the first stepped portion 13a is four times the thickness 60d. Note that the thickness per step of the correction phantom 13 does not have to be constant.

[0056] (Correction image) By imaging the correction phantom 13, correction images 33 as shown in FIGS. 10(A) and 10(B) are obtained.

[0057] FIG. 10(A) is a schematic diagram showing a second dark-field image 31, which is a dark-field image of the correction phantom 13 among the correction images 33. FIG. 10(B) is a schematic diagram showing a second absorption image 32, which is an absorption image of the correction phantom 13 among the correction images 33. In FIGS. 10(A) and 10(B), different hatchings are used to represent the difference in pixel values. Specifically, in FIGS. 10(A) and 10(B), as the hatching becomes darker (the interval between the hatchings becomes narrower), the pixel value increases.

[0058] In the second dark-field image 31 shown in FIG. 10(A), regions with different pixel values appear for each thickness of the correction phantom 13. Specifically, the first region 70a is a region where the first stepped portion 13a of the correction phantom 13 appears. The second region 70b is a region where the second stepped portion 13b of the correction phantom 13 appears. The third region 70c is a region where the third stepped portion 13c of the correction phantom 13 appears. The fourth region 70d is a region where the fourth stepped portion 13d of the correction phantom 13 appears. The fifth region 70e is a region of the portion (background) where the correction phantom 13 does not appear.

[0059] In the second absorption image 32 shown in FIG. 10(B), regions with different pixel values appear for each thickness of the correction phantom 13. Specifically, the first region 71a is a region where the first stepped portion 13a of the correction phantom 13 appears. The second region 71b is a region where the second stepped portion 13b of the correction phantom 13 appears. The third region 71c is a region where the third stepped portion 13c of the correction phantom 13 appears. The fourth region 71d is a region where the fourth stepped portion 13d of the correction phantom 13 appears. The fifth region 71e is a region of the portion (background) where the correction phantom 13 does not appear.

[0060] As shown in FIGS. 10(A) and 10(B), non-uniform noise due to hardening of the X-ray spectrum when passing through the subject 90 and hardening of the X-ray spectrum due to differences in the incident angles of X-rays on the plurality of gratings occurs only in the second dark-field image 31.

[0061] (Correction curve) Next, with reference to FIGS. 10 to 13, a configuration in which the control unit 7b generates a plurality of correction curves 20a will be described.

[0062] In the present embodiment, each of the plurality of correction curves 20a is based on the pixel values of the second absorption image 32 and the pixel values of the second dark field image 31 in regions of different thicknesses among the correction phantoms 13 shown in the correction image 33 obtained by imaging the correction phantom 13 with the thickness varying along the lattice direction (Z direction).

[0063] In other words, the control unit 7b acquires the correspondence between the pixel values of the second dark field image 31 (values related to X-ray scattering specified from the second dark field image 31) and the pixel values of the second absorption image 32 (values related to X-ray absorption specified from the second absorption image 32), and generates a plurality of correction curves 20a. Since the correction phantom 13 is formed of a homogeneous material, when the thicknesses of the correction phantoms 13 are equal, the change in the pixel values of the second dark field image 31 with respect to the pixel values of the second absorption image 32 becomes constant. That is, the factor causing the change in the pixel values of the second dark field image 31 with respect to the pixel values of the second absorption image 32 is limited to the difference in the thickness of the correction phantom 13. Therefore, by generating the correction curve 20a based on the pixel values of the second absorption image 32 and the pixel values of the second dark field image 31 in regions of different thicknesses of the correction phantom 13 according to the position in the direction orthogonal to the lattice direction, the correction curve 20a corresponding to the difference in the thickness of the subject 90 can be easily generated.

[0064] The graph 52 shown in FIG. 11 is a graph showing a plurality of correction curves 20a. The graph 52 is a graph in which graphs with the vertical axis being the absorption value (an example of a value related to X-ray absorption) and the horizontal axis being the dark field value (an example of a value related to X-ray scattering) are arranged for each position in the Y direction of the correction image 33. The dark field value and the absorption value are obtained by the following formulas (1) and (2).

Equation

[0065] The configuration in which the control unit 7b generates the curve 52a shown in the graph 52 will be described as a representative, and the configuration in which the control unit 7b generates a plurality of correction curves 20a will be described.

[0066] In the present embodiment, the control unit 7b determines the position of the first plot 14a in the graph 52 based on the dark field value obtained from the pixel value of the first pixel 31a (see FIG. 10(A)) of the second dark field image 31 and the absorption value obtained from the pixel value of the first pixel 32a (see FIG. 10(B)) of the second absorption image 32. Also, the control unit 7b determines the position of the second plot 14b in the graph 52 based on the dark field value obtained from the pixel value of the second pixel 31b (see FIG. 10(A)) of the second dark field image 31 and the absorption value obtained from the pixel value of the second pixel 32b (see FIG. 10(B)) of the second absorption image 32.

[0067] Also, the control unit 7b determines the position of the third plot 14c in the graph 52 based on the dark field value obtained from the pixel value of the third pixel 31c (see FIG. 10(A)) of the second dark field image 31 and the absorption value obtained from the pixel value of the third pixel 32c (see FIG. 10(B)) of the second absorption image 32. Also, the control unit 7b determines the position of the fourth plot 14d in the graph 52 based on the dark field value obtained from the pixel value of the fourth pixel 31d (see FIG. 10(A)) of the second dark field image 31 and the absorption value obtained from the pixel value of the fourth pixel 32d (see FIG. 10(B)) of the second absorption image 32.

[0068] Note that random noise or the like may be captured in the correction image 33. In such a case, if the correction curve 20a is generated based on the pixel value of one pixel within a region where the thickness of the correction phantom 13 is equal, the accuracy (approximation system) of the correction curve 20a may decrease due to the random noise. Therefore, in the present embodiment, each of the plurality of correction curves 20a is generated based on the pixel values of a plurality of locations of the second absorption images 32 and the pixel values of the second dark field images 31 within a region where the thickness in the lattice direction is equal among the correction phantoms 13 captured in the correction image 33. In other words, each of the plurality of correction curves 20a is generated based on the representative value of the pixel values of the second dark field image 31 and the representative value of the pixel values of the second absorption image 32. The representative value is, for example, the average value of the pixel values within the same region in the Y direction with equal thickness. That is, when obtaining the average value of the first pixels 31a, the position in the Y direction is Ya, and the average value of the pixel values within the first region 70a is obtained. Thereby, for example, the correction curve 20a can be generated using the representative value of the pixel values of the second absorption images 32 at a plurality of locations within a region where the thickness in the lattice direction is equal, and the representative value of the pixel values of the second dark field images 31 at a plurality of locations within a region where the thickness in the lattice direction is equal. As a result, compared with the configuration in which the correction curve 20a is generated based on the pixel value of one location of the second absorption image 32 and the pixel value of the second dark field image 31 within a region where the thickness of the correction phantom 13 is equal, it is possible to suppress a decrease in the accuracy of the correction curve 20a due to the random noise generated in the correction image 33.

[0069] The control unit 7b generates a correction curve 20a as shown by the curve 52a by curve approximating the first plot 14a to the fourth plot 14d.

[0070] The control unit 7b performs the same process while varying the position in the Y direction of the correction image 33, thereby generating a correction curve 20a as shown by the curve 52b and a correction curve 20a as shown by the curve 52c for each position in the Y direction of the correction image 33. That is, the control unit 7b generates a correction curve 20a at the position Ya in the Y direction, a correction curve 20a at the position Yb in the Y direction, and a correction curve 20a at the position Yc in the Y direction.

[0071] Note that since the change in the pixel value of the second dark field image 31 in the Y direction is a gentle change, it is not necessary to generate the correction curve 20a for each pixel in the Y direction. Therefore, the control unit 7b generates a preset number of correction curves 20a based on the size of the correction image 33 in the Y direction. In the examples shown in FIGS. 10 and 11, the control unit 7b generates three correction curves 20a. Note that the number of correction curves 20a generated may be other than three. Also, for example, the number of correction curves 20a to be obtained may be determined based on the pixel value profile (graph 50 shown in FIG. 5) of the second dark field image 31 in the Y direction, or the correction curves 20a may be generated for each predetermined distance in the Y direction.

[0072] Here, the transmittance of X-rays changes due to the X-ray absorption rate and thickness of the subject 90. Therefore, even if the thickness of the subject 90 and the thickness of the correction phantom 13 are equal to each other, when the X-ray absorption rates are different, the accuracy of correcting the first dark field image 35a by the correction curve 20a may decrease due to the difference in the transmittance of X-rays. Therefore, it is preferable to change the correction phantom 13 imaged when generating the correction curve 20a according to the material of the subject 90. Specifically, the correction phantom 13 is preferably changed according to the elemental composition of the subject 90. For example, when the subject 90 is CFRP (Carbon Fiber Reinforced Plastics), it is preferable to use the correction phantom 13 formed of an acrylic material in view of the proximity of the X-ray absorption rate and the ease of obtaining a homogeneous phantom with few defects and density variations. Also, for example, when the subject 90 is GFRP (Glass Fiber Reinforced Plastics), it is preferable to use the correction phantom 13 formed of an aluminum material in view of the proximity of the X-ray absorption rate and the ease of obtaining a homogeneous phantom with few defects and density variations.

[0073] Therefore, in the present embodiment, the plurality of correction curves 20a include a plurality of types of correction curve sets 20 generated based on a plurality of correction image sets 34 (see FIG. 12) of a correction phantom 13 that has different X-ray absorption rates for different materials of the subject 90.

[0074] In addition, when the setting of the imaging condition 22 of the X-ray phase contrast image 30 is changed, a difference occurs in the degree of change in the X-ray spectrum before and after the change of the imaging condition 22. Therefore, in the present embodiment, the plurality of correction curves 20a include a plurality of correction curve sets 20 for each imaging condition 22 generated based on the correction images 33 captured under different imaging conditions 22. Note that the imaging condition 22 includes the value of the tube voltage applied to the X-ray source 1 and the rotation angles of the plurality of gratings.

[0075] Referring to FIG. 12, a configuration in which the control unit 7b generates a plurality of types of correction curve sets 20 will be described.

[0076] In the example shown in FIG. 12, a plurality of types of correction curve sets 20 are generated using a first correction phantom 13e and a second correction phantom 13f. The first correction phantom 13e is, for example, a phantom formed of an acrylic material. The second correction phantom 13f is, for example, a phantom formed of an aluminum material.

[0077] The first imaging condition and the second imaging condition are imaging conditions 22 in which the tube voltages applied to the X-ray source 1 are different from each other.

[0078] In the example shown in FIG. 12, the plurality of correction image sets 34 include a total of four types of correction images 33 including the correction images 33 obtained by imaging the first correction phantom 13e under the first imaging condition and the second imaging condition, and the correction images 33 obtained by imaging the second correction phantom 13f under the first imaging condition and the second imaging condition. Each of the four types of correction images 33 includes a dark field image 33a and an absorption image 33b.

[0079] The control unit 7b generates a plurality of correction curve sets 20 using each of the four types of correction images 33. Then, the control unit 7b stores the plurality of correction curve sets 20 in the storage unit 8.

[0080] In the present embodiment, the storage unit 8 stores a plurality of correction curves 20a in association with the imaging conditions 22. The storage unit 8 also stores a plurality of correction curves 20a in association with the material of the subject 90. That is, in the present embodiment, the storage unit 8 stores a plurality of types of correction curve sets 20 according to the imaging conditions 22 and the X-ray absorption rate. Specifically, the storage unit 8 stores a correction curve set 20 generated based on a correction image set 34 obtained by imaging the first correction phantom 13e under the first imaging condition, a correction curve set 20 generated based on a correction image set 34 obtained by imaging the second correction phantom 13f under the first imaging condition, a correction curve set 20 generated based on a correction image set 34 obtained by imaging the first correction phantom 13e under the second imaging condition, and a correction curve set 20 generated based on a correction image set 34 obtained by imaging the second correction phantom 13f under the second imaging condition.

[0081] Note that the correction curve 20a is a curve that associates the dark field value with the absorption value. Therefore, based on the absorption value obtained based on the pixel value of the second absorption image 32 and the correction curve 20a, the dark field value of the corresponding pixel can be obtained.

[0082] (Correction of dark field image) Next, with reference to FIGS. 13(A) to 13(C), a configuration in which the control unit 7b corrects the subject image 35 will be described. The subject image 35 includes a first dark field image 35a shown in FIG. 13(A) and a first absorption image 35b shown in FIG. 13(B). The control unit 7b corrects the first dark field image 35a among the subject images 35. Further, the graph 53 shown in FIG. 13(C) is a correction curve 20a corresponding to the first region 72a (see FIG. 13(A)) among the plurality of correction curves 20a. In the graph 53, the vertical axis represents the absorption value and the horizontal axis represents the dark field value. In the examples shown in FIGS. 13(A) and 13(B), in order to make the effect of correction easy to understand, an image in which regions with different pixel values in the Z direction are shown is illustrated.

[0083] The control unit 7b is configured to correct the first dark field image 35a using the corresponding correction curve 20a for each position.

[0084] The control unit 7b is configured to correct the first dark field image 35a based on the first absorption image 35b and the plurality of correction curves 20a. Since the non-uniform noise causes a gentle change in pixel values in the Y direction, the control unit 7b performs correction in the Z direction of the subject image 35 using the corresponding correction curve 20a for every predetermined number of pixels in the Y direction. In the example shown in FIG. 13(A), the control unit 7b performs correction in the Z direction of the subject image 35 using the corresponding correction curve 20a for each of the first region 72a, the second region 72b, and the third region 72c.

[0085] As a configuration in which the control unit 7b corrects the first dark field image 35a, the correction in the first region 72a of the subject image 35 (first dark field image 35a) will be representatively described. Using the pixel value of the first pixel 37a in the first region 73a of the first absorption image 35b corresponding to the first region 72a of the first dark field image 35a and the above formula (2), the first absorption value 80a at the first pixel 37a is obtained. Then, the control unit 7b obtains the first dark field value 81a based on the first absorption value 80a and the correction curve 20a.

[0086] Similarly, the control unit 7b obtains the second absorption value 80b, the third absorption value 80c, and the fourth absorption value 80d based on the pixel values of the second pixel 37b, the third pixel 37c, and the fourth pixel 37d of the first absorption image 35b and the above formula (2). Then, the control unit 7b obtains the second dark field value 81b, the third dark field value 81c, and the fourth dark field value 81d based on the second absorption value 80b, the third absorption value 80c, and the fourth absorption value 80d and the correction curve 20a. That is, the control unit 7b refers to the corresponding correction curve 20a for each position of the first absorption image 35b and specifies the value related to X-ray scattering associated with the value related to X-ray absorption of the first absorption image 35b.

[0087] The control unit 7b uses the obtained first dark field values 81a to 81d and the following formula (3) to obtain the pseudo-signal components of each pixel from the dark field values of the first pixel 36a to the fourth pixel 36d of the first dark field image 35a. Note that the pseudo-signal component is the signal component of the first dark field image 35a including non-uniform noise.

Equation

[0088] Then, the control unit 7b obtains the pixel values of each pixel of the corrected dark field image 35d (see FIG. 14(E)) using the pixel value of the pseudo-signal component of each pixel and the pixel value of each pixel as shown in the following formula (4).

Equation

[0089] The control unit 7b also performs the same process on the second region 72b and the third region 72c of the first dark field image 35a using the correction curve 20a corresponding to each region and the pixel values of the pixels in the second region 73b and the third region 73c of the first absorption image 35b, and corrects the first dark field image 35a. That is, the control unit 7b is configured to correct the first dark field image 35a using the value related to the specified X-ray scattering.

[0090] In addition, in the present embodiment, the control unit 7b is configured to select a plurality of corresponding correction curves 20a (see FIG. 1) from among a plurality of types of correction curve sets 20 (see FIG. 1) according to the material of the subject 90. Further, the control unit 7b is configured to correct the first dark field image 35a (see FIG. 14(A)) using the selected plurality of correction curves 20a. Specifically, the control unit 7b is configured to select the correction curve 20a used for correcting the first dark field image 35a based on the operation input 21 received by the input reception unit 10. For example, the control unit 7b causes the display unit 11 to display a combo box for selecting the type of the subject 90. Then, the control unit 7b acquires the correction curve 20a used for correcting the first dark field image 35a according to the material of the subject 90 input by the operator selecting the combo box. Thereby, the first dark field image 35a is corrected by the correction curve 20a corresponding to the operation input 21 of the operator. Therefore, since it is possible to correct the first dark field image 35a by the correction curve 20a selected by the operator, the convenience (usability) of the user can be improved.

[0091] The control unit 7b is configured to select a plurality of corresponding correction curves 20a according to the imaging conditions 22. Further, the control unit 7b is configured to correct the first dark field image 35a (see FIG. 14(A)) using the selected plurality of correction curves 20a. Specifically, the control unit 7b acquires the value of the tube voltage applied to the X-ray source 1 as the imaging conditions 22. Then, the control unit 7b acquires the plurality of correction curves 20a used for correcting the first dark field image 35a from among the plurality of types of correction curve sets 20 according to the acquired value of the tube voltage.

[0092] That is, the control unit 7b acquires a plurality of correction curves 20a used for correcting the first dark field image 35a (see FIG. 14(A)) from among the plurality of types of correction curve sets 20 according to the material of the subject 90 and the imaging conditions 22.

[0093] (Effect of dark field image correction) Next, with reference to FIGS. 14(A) to 14(F), the subject image before correction (first dark field image 35a) will be described with respect to the dark field image 35c after correction by the comparative example and the dark field image 35d after correction according to the present embodiment corrected using the correction curve set 20 corresponding to each position in the Y direction. Note that the dark field image 35c after correction by the comparative example is an image corrected using one type of correction curve set 20 regardless of the position in the Y direction.

[0094] The first dark field image 35a shown in FIG. 14(A) is the dark field image before correction. The graph 54 shown in FIG. 14(B) is a graph showing the change in pixel values along the first straight line 41a to the fifth straight line 41e in each of the first region 74a to the fifth region 74e of the first dark field image 35a before correction.

[0095] Further, FIG. 14(C) is the dark field image 35c after correction by the comparative example, in which the first dark field image 35a before correction is corrected using one type of correction curve set 20 regardless of the position in the Y direction. Also, the graph 55 shown in FIG. 14(D) is a graph showing the change in pixel values along the first straight line 42a to the fifth straight line 42e in each of the first region 74a to the fifth region 74e of the dark field image 35c after correction by the comparative example.

[0096] Further, FIG. 14(E) is the dark field image 35d after correction according to the present embodiment, in which the first dark field image 35a before correction is corrected using the correction curve set 20 corresponding to each position in the Y direction. Also, the graph 56 shown in FIG. 14(F) is a graph showing the change in pixel values along the first straight line 43a to the fifth straight line 43e in each of the first region 74a to the fifth region 74e of the dark field image 35d after correction according to the present embodiment.

[0097] For each of Graphs 54 to 56, the vertical axis represents pixel values, and the horizontal axis represents position (pixels). The first curve 54a, the second curve 54b, the third curve 54c, the fourth curve 54d, and the fifth curve 54e shown in Graph 54 respectively show the changes in pixel values along the first straight line 41a, the second straight line 41b, the third straight line 41c, the fourth straight line 41d, and the fifth straight line 41e in each region of the dark field image 35d before correction.

[0098] Also, the first curve 55a, the second curve 55b, the third curve 5c, the fourth curve 55d, and the fifth curve 55e shown in Graph 55 respectively show the changes in pixel values along the first straight line 42a, the second straight line 42b, the third straight line 42c, the fourth straight line 42d, and the fifth straight line 42e in each region of the dark field image 35c after correction according to the comparative example.

[0099] Also, the first curve 56a, the second curve 56b, the third curve 56c, the fourth curve 56d, and the fifth curve 56e shown in Graph 56 respectively show the changes in pixel values along the first straight line 43a, the second straight line 43b, the third straight line 43c, the fourth straight line 43d, and the fifth straight line 43e in each region of the dark field image 35d after correction according to this embodiment.

[0100] In the first dark field image 35a before correction, as shown in Graph 54, the pixel values are different from each other in each of the first region 74a to the fifth region 74e. Also, in the second region 74b to the fifth region 74e, as shown in Graph 54, in the Y direction, the pixel values in the central part of the image are high, and the pixel values on both sides are low.

[0101] As shown in graph 55, for the dark-field image 35c after correction according to the comparative example, the difference in pixel values of each region from the first region 74a to the fifth region 74e is smaller than the difference in pixel values of each region of the first dark-field image 35a before correction. Also, in the central portion of the image, non-uniform noise has been removed. However, since the dark-field image 35c after correction according to the comparative example was corrected using one type of correction curve set 20 regardless of the position in the Y direction, as shown in graph 55, in the second region 74b to the fifth region 74e, the pixel values in the central portion of the image are still high and the pixel values on both sides are low.

[0102] As shown in graph 56, for the dark-field image 35d after correction according to the present embodiment, the difference in pixel values of the first region 74a to the fifth region 74e is substantially eliminated. Also, in the dark-field image 35d after correction according to the present embodiment, in each of the second region 74b to the fifth region 74e, the difference between the pixel values in the central portion of the image and the pixel values on both sides is also substantially eliminated. That is, in the dark-field image 35d after correction according to the present embodiment, non-uniform noise generated by the interaction of both the change in the X-ray spectrum due to the subject 90 (see FIG. 1) and the change in the spectrum caused by the X-ray incident on the grating from an oblique direction is reduced.

[0103] (Generation process of correction curve and correction process of dark-field image) Next, with reference to FIGS. 15 and 16, an X-ray image processing method by the X-ray image processing apparatus 6 according to the present embodiment will be described. In the present embodiment, the X-ray image processing method is roughly divided into a process of generating a correction curve 20a and a process of correcting the first dark-field image 35a.

[0104] First, with reference to FIG. 15, a process in which the X-ray image processing apparatus 6 generates a correction curve 20a will be described.

[0105] In step 101, the control unit 7b controls the X-ray source 1 to capture a correction image 33 including a second dark-field image 31 (see FIG. 10(A)) and a second absorption image 32 (see FIG. 10(B)) of the correction phantom 13.

[0106] The control unit 7b captures the correction image 33 in a state where the correction phantom 13 is arranged such that the direction in which the thickness of the correction phantom 13 changes is along the direction along the lattice direction (Z direction).

[0107] In step 102, the control unit 7b generates the correction curve 20a based on the correction image 33.

[0108] In step 102, the control unit 7b generates the correction curve 20a based on the pixel values of the second absorption image 32 and the pixel values of the second dark field image 31 in regions of the correction phantom 13 shown in the correction image 33 that have different thicknesses from each other. Specifically, the control unit 7b generates a plurality of correction curves 20a based on the pixel values of the second absorption image 32 and the pixel values of the second dark field image 31 at different positions in the direction (Y direction) orthogonal to the lattice direction (Z direction). More specifically, the control unit 7b generates a plurality of correction curves 20a based on the pixel values of the second absorption image 32 and the pixel values of the second dark field image 31 at a plurality of locations within a region of the correction phantom 13 shown in the correction image 33 that has the same thickness in the lattice direction. Further, the control unit 7b stores the plurality of generated correction curves 20a in the storage unit 8.

[0109] In step 103, the control unit 7b determines whether a plurality of correction curves 20a have been generated under all of a plurality of preset imaging conditions 22. If a plurality of correction curves 20a have not been generated under all of the plurality of imaging conditions 22, the process proceeds to step 104. If a plurality of correction curves 20a have been generated under all of the plurality of imaging conditions 22, the process proceeds to step 105.

[0110] In step 104, the control unit 7b changes the imaging condition 22. Thereafter, the process proceeds to step 101.

[0111] When the process proceeds from step 103 to step 105, in step 105, the control unit 7b determines whether a plurality of correction curves 20a have been generated for all of the plurality of correction phantoms 13 (see FIG. 8). If the plurality of correction curves 20a have not been generated for all of the plurality of correction phantoms 13, the process proceeds to step 106. If the plurality of correction curves 20a have been generated for all of the plurality of correction phantoms 13, the process ends.

[0112] In step 106, the control unit 7b changes the correction phantom 13. For example, the control unit 7b prompts the operator to change the correction phantom 13 by displaying a message for changing the correction phantom 13 on the display unit 11. When the correction phantom 13 is changed, the process proceeds to step 101.

[0113] As described above, by repeating steps 101 to 104, in the step of imaging the correction phantom 13 under different imaging conditions 22 and generating a plurality of correction curves 20a, a plurality of correction curve sets 20 are generated for each imaging condition 22.

[0114] Also, by repeating steps 101 to 106, in the step of imaging a plurality of types of correction phantoms 13 having different X-ray absorption rates according to the materials of different subjects 90 and generating a plurality of correction curves 20a, a plurality of correction curve sets 20 are generated for each type of correction phantom 13.

[0115] Next, with reference to FIG. 16, the process of the X-ray image processing apparatus 6 for correcting the subject image 35 will be described.

[0116] In step 200, the image acquisition unit 9 acquires a subject image 35 including a first dark field image 35a (see FIG. 13(A)) and a first absorption image 35b (see FIG. 13(B)) obtained by imaging the subject 90.

[0117] In step 201, the control unit 7b acquires the imaging condition 22. In the present embodiment, the control unit 7b acquires the value of the tube voltage applied to the X-ray source 1 as the imaging condition 22.

[0118] In step 202, the control unit 7b acquires the material of the subject 90. Specifically, the control unit 7b receives an input of the material of the subject 90. The control unit 7b receives an input of the material of the subject 90 by receiving the operation input 21 from the input receiving unit 10.

[0119] In step 203, the control unit 7b acquires the correction curve set 20 used for correcting the first dark field image 35a from among the plurality of types of correction curve sets 20 based on the imaging condition 22 and the material of the subject 90.

[0120] In step 204, the control unit 7b corrects the subject image 35 (the first dark field image 35a) based on the plurality of correction curves 20a. Specifically, the control unit 7b corrects the first dark field image 35a based on the first absorption image 35b (see FIG. 13(B)) and the plurality of correction curves 20a. More specifically, the control unit 7b corrects the subject image 35 (the first dark field image 35a) based on the plurality of correction curves 20a of the type corresponding to the material of the subject 90 for which the input has been received among the plurality of correction curve sets 20. The control unit 7b corrects the subject image 35 (the first dark field image 35a) based on the plurality of correction curves 20a of the type corresponding to the acquired imaging condition 22 among the plurality of correction curve sets 20. That is, the control unit 7b determines the correction curve set 20 used for correcting the subject image 35 from among the plurality of types of correction curve sets 20 based on the material of the subject 90 and the imaging condition 22, and corrects the subject image 35. Thereafter, the process ends.

[0121] (Effect of the present embodiment) In the present embodiment, the following effects can be obtained.

[0122] In the above embodiment, the X-ray phase imaging apparatus 100 includes an X-ray source 1, an X-ray detector 2 that detects X-rays irradiated from the X-ray source 1, a plurality of gratings disposed between the X-ray source 1 and the X-ray detector 2, and an image processing unit 7a that generates an X-ray phase contrast image 30 including a first dark-field image 35a that is a dark-field image of the subject 90 based on the intensity distribution of the X-rays detected by the X-ray detector 2, a storage unit 8 that stores a plurality of correction curves 20a generated for each position in a direction orthogonal to the grating direction (the direction in which the plurality of gratings extend), and a control unit 7b that corrects the first dark-field image 35a using the plurality of correction curves 20a corresponding to each of the above positions. Each of the plurality of correction curves 20a shows the correspondence between the value related to the X-ray absorption of the subject 90 and the value related to the X-ray scattering at the above position.

[0123] From this, the storage unit 8 stores a plurality of correction curves 20a corresponding to each position in the direction (Y direction) orthogonal to the grating direction (Z direction). Since these plurality of correction curves 20a show the correspondence between the value related to the X-ray absorption of the subject 90 and the value related to the X-ray scattering at the above position, the degree of change in the spectrum of the X-rays due to the incident angle of the X-rays at the above position is also taken into account. And by correcting the first dark-field image 35a, which is the dark-field image of the subject 90, using the correction curve 20a corresponding to each of the above positions, compared with the case of correcting the first dark-field image 35a using one common correction curve 20a, an accurate correction of the first dark-field image 35a can be performed. As a result, even when the X-rays are incident on the grating from an oblique direction, it is possible to suppress a decrease in the image quality of the first dark-field image 35a. Regarding the X-ray image processing apparatus 6 and the X-ray image processing method according to the above embodiment, similar to the X-ray phase imaging apparatus 100 according to the above embodiment, even when the X-rays are incident on the grating from an oblique direction, it is possible to suppress a decrease in the image quality of the first dark-field image 35a.

[0124] Also, in the above-described embodiment, the correction curve generation method uses the X-ray phase imaging apparatus 100 having a plurality of gratings to image the correction phantom 13, and obtains the second dark-field image 31 which is the dark-field image of the correction phantom 13, and obtains the second absorption image 32 which is the absorption image of the correction phantom 13, and generates a plurality of correction curves 20a using the second dark-field image 31 and the second absorption image 32 for each position in the direction (Y direction) orthogonal to the grating direction (Z direction) in which the plurality of gratings extend. Thereby, since the plurality of correction curves 20a are generated using the second dark-field image 31 and the second absorption image 32 actually obtained by imaging the correction phantom 13, the plurality of correction curves 20a can be generated in a state where the degree of change in the spectrum of the X-rays due to the incident angle of the X-rays at the above position is extremely accurately reflected.

[0125] Also, in the above-described embodiment, by configuring as follows, the following further effects can be obtained.

[0126] That is, in the present embodiment, as described above, the image processing unit 7a further generates the first absorption image 35b which is the absorption image of the subject 90 in addition to the first dark-field image 35a for the subject 90, and the control unit 7b refers to the corresponding correction curve 20a for each of the above positions, specifies the value related to X-ray scattering associated with the value related to X-ray absorption of the first absorption image 35b, and corrects the first dark-field image 35a using the specified value related to X-ray scattering. Further, the control unit 7b obtains the value related to X-ray absorption at the above position in the first absorption image 35b. The control unit 7b refers to the correction curve 20a for each of the above positions and obtains the value related to X-ray scattering corresponding to the value related to X-ray absorption. Then, the control unit 7b corrects the first dark-field image 35a using the obtained value related to X-ray scattering. By performing these processes, as described above, the first dark-field image 35a can be accurately corrected.

[0127] Also, in the present embodiment, as described above, the storage unit 8 is configured to store a plurality of correction curves 20a in association with the material of the subject 90, and the control unit 7b selects the corresponding correction curve 20a according to the material of the subject 90, and corrects the first dark field image 35a using the selected correction curve 20a. Thereby, by selecting the correction curve 20a according to the material of the subject 90, the first dark field image 35a can be corrected by the correction curve 20a according to the X-ray absorption rate of the subject 90. As a result, for example, compared with a configuration in which the first dark field image 35a is corrected by one type of correction curve 20a regardless of the material of the subject 90, it is possible to suppress a decrease in the accuracy of correcting the first dark field image 35a. Therefore, it is possible to further suppress a decrease in the image quality of the first dark field image 35a.

[0128] Also, in the present embodiment, as described above, the storage unit 8 is configured to store a plurality of correction curves 20a in association with the imaging conditions 22, and the control unit 7b selects the corresponding plurality of correction curves 20a according to the imaging conditions 22, and corrects the first dark field image 35a using the selected correction curve 20a. Here, when the setting of the imaging conditions 22 is changed, the spectrum of the X-rays detected by the X-ray detector 2 is also changed. Therefore, in the case of a configuration in which the first dark field image 35a is corrected using one type of correction curve 20a regardless of the imaging conditions 22, the accuracy of correction may decrease. By configuring as described above, it is possible to correct the first dark field image 35a with a plurality of correction curves 20a according to the set imaging conditions 22, so that it is possible to suppress a decrease in the correction accuracy of the first dark field image 35a.

[0129] [Modification Example] It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and further includes all changes (modification examples) within the meaning and scope equivalent to the claims.

[0130] For example, in the above embodiment, an example of the configuration in which the correction phantom 13 has a stepped shape in which the thickness in the X-ray irradiation direction (X direction) changes stepwise in the Z direction was shown, but the present invention is not limited to this. For example, as in the first modification shown in FIG. 17, the thickness of the correction phantom 130 in the X-ray irradiation direction (X direction) may change continuously. Specifically, as shown in FIG. 17, the correction phantom 130 according to the first modification may have an inclined surface 130a.

[0131] Also, in the above embodiment, an example of the configuration in which the correction phantom 13 is integrally formed of a homogeneous material was shown, but the present invention is not limited to this. For example, the correction phantom 13 may not be integrally configured. For example, as in the second modification shown in FIG. 18, the correction phantom 131 may be configured by combining a plurality of plate-like members. Specifically, the correction phantom 131 according to the second modification may be formed by combining a first plate-like member 131a, a second plate-like member 131b, a third plate-like member 131c, and a fourth plate-like member 131d.

[0132] Also, in the above embodiment, an example of the configuration in which the X-ray phase imaging apparatus 100 performs imaging with the orientation of the grating fixed was shown, but the present invention is not limited to this. For example, the X-ray phase imaging apparatus may include a grating rotation mechanism that rotates a plurality of gratings around the axis of the X-ray optical axis, and may be configured to perform imaging by changing the angles of the plurality of gratings.

[0133] When a plurality of gratings are rotated, the energy distribution of the X-rays detected by the X-ray detector 2 changes. The change in the energy distribution of the X-rays due to the difference in the rotation angles of the plurality of gratings will be described with reference to FIGS. 19(A) and 19(B). In the examples shown in FIGS. 19(A) and 19(B), the difference in the energy of the X-rays is illustrated by the difference in hatching as shown in the legend 60. Specifically, as the hatching becomes darker (the interval of the hatching becomes narrower), the energy of the X-rays becomes smaller. Also, for the sake of convenience, a boundary line is illustrated between regions with different X-ray energies, but the actual change in the X-ray energy is a smooth change.

[0134] The example shown in FIG. 19(A) is an image 38a showing the energy distribution of X-rays in the X-ray detector 2 when a plurality of gratings are arranged such that the grating directions of the plurality of gratings are in the Z direction. In the example shown in FIG. 19(A), since the grating direction is oriented in the Z direction, a change occurs in the energy distribution of the X-rays in the Y direction, which is a direction orthogonal to the grating direction. Specifically, in the Y direction, the energy of the X-rays in the central portion of the image 38a is low, and as it goes towards the end of the image 38a, the energy of the X-rays becomes high.

[0135] The example shown in FIG. 19(B) is an image 38b showing the energy distribution of X-rays when a plurality of gratings are rotated around the axis in the X-ray irradiation axis direction (X direction). The image 38b shown in FIG. 19(B) is an image showing the energy distribution of X-rays when a plurality of gratings are rotated by 45 degrees. When a plurality of gratings are rotated, the energy distribution of the X-rays rotates according to the direction of the X-rays. That is, in the image 38b, the energy distribution of the image 38a is in a state rotated by 45 degrees.

[0136] Therefore, when a plurality of gratings are rotated around the axis of the X-ray irradiation axis, without using a correction image obtained by rotating the correction phantom 13 (see FIG. 8) in the same manner as the gratings for imaging, coordinate transformation is performed on the correction curve 20a stored in the storage unit 8 (see FIG. 1) in advance, whereby the first dark field image 35a (see FIG. 14(A)) can be corrected. Therefore, the control unit 7b corrects the first dark field image 35a by transforming the coordinates of a plurality of correction curves 20a.

[0137] In the above-described embodiment, an example of the configuration is shown in which the control unit 7b corrects the first dark-field image 35a using the correction curve 20a corresponding to the material of the subject 90 among the plurality of types of correction curve sets 20 generated according to the material of the subject 90. However, the present invention is not limited to this. For example, the control unit may be configured to correct the first dark-field image 35a using a plurality of correction curves 20a included in one type of correction curve set regardless of the material of the subject 90. However, when the control unit corrects the first dark-field image 35a using a plurality of correction curves 20a included in one type of correction curve set regardless of the material of the subject 90, the accuracy of the correction decreases. Therefore, it is preferable that the control unit is configured to correct the first dark-field image 35a using a plurality of correction curves 20a included in one type of correction curve set.

[0138] In the above-described embodiment, the X-ray phase imaging apparatus 100 may not include the input reception unit 10. That is, the control unit 7b may automatically select a plurality of correction curves 20a using the first dark-field image 35a and the first absorption image 35b. For example, it is conceivable to apply techniques such as machine learning and pixel processing for selection.

[0139] In the above-described embodiment, an example of the configuration is shown in which the storage unit 8 stores a plurality of correction curve sets 20 for each imaging condition 22 generated based on the correction images 33 imaged under different imaging conditions 22, and the control unit 7b corrects the first dark-field image 35a based on the plurality of correction curves 20a corresponding to the imaging condition 22. However, the present invention is not limited to this. For example, the storage unit 8 may not store a plurality of correction curve sets 20 for each imaging condition 22. In this case, the control unit 7b may correct the first dark-field image 35a using one type of correction curve set 20 regardless of the imaging condition 22. However, when the storage unit 8 does not store a plurality of correction curve sets 20 for each imaging condition 22, the accuracy of the correction of the first dark-field image 35a may decrease when the imaging condition 22 is changed. Therefore, it is preferable that the storage unit 8 stores a plurality of correction curve sets 20 for each imaging condition 22.

[0140] In the above-described embodiment, an example of the configuration in which the X-ray image processing apparatus 6 generates the correction curve 20a has been shown, but the present invention is not limited to this. For example, the X-ray image processing apparatus 6 may be configured to store a plurality of correction curves 20a generated by different image processing apparatuses.

[0141] In the above-described embodiment, an example of the configuration in which the X-ray image processing apparatus 6 generates a plurality of correction curves 20a using the correction image 33 captured in a state where the correction phantom 13 is arranged such that the direction in which the thickness of the correction phantom 13 changes is along the lattice direction (Z direction) has been shown, but the present invention is not limited to this. When arranging the correction phantom 13, the direction in which the thickness of the correction phantom 13 changes may not be along the lattice direction. However, when the direction in which the thickness of the correction phantom 13 changes is not along the lattice direction, it becomes difficult to correct the non-uniform noise generated by the X-ray incident from an oblique direction with respect to the lattice. Therefore, when capturing the correction image 33, it is preferable to arrange the direction in which the thickness of the correction phantom 13 changes to be along the lattice direction.

[0142] In the above-described embodiment, an example of the configuration in which the control unit 7b uses one type of correction curve set 20 when correcting the first dark field image 35a has been shown, but the present invention is not limited to this. For example, when correcting a dark field image obtained by imaging a subject in which different materials are laminated in the X-ray irradiation direction, the dark field image may be configured to be corrected using a plurality of types of correction curve sets 20. Specifically, when correcting a dark field image obtained by imaging a subject in which an acrylic material and an aluminum material are laminated in the X-ray irradiation axis direction, the correction curve 20a suitable for the acrylic material and the correction curve 20a suitable for the aluminum material may be used in combination for correction. When using the correction curve 20a suitable for the acrylic material and the correction curve 20a suitable for the aluminum material in combination, for example, the dark field image may be corrected using a correction curve obtained by averaging each correction curve 20a.

[0143] In the above-described embodiment, an example of the configuration in which the X-ray phase imaging apparatus 100 includes the X-ray image processing apparatus 6 has been shown. However, the present invention is not limited to this. For example, the X-ray phase imaging apparatus 100 may not include the X-ray image processing apparatus 6. The X-ray image processing apparatus 6 may be provided independently of the X-ray phase imaging apparatus 100. In this case, the first dark field image 35a may be corrected by processing the X-ray phase contrast image 30 captured by the X-ray phase imaging apparatus 100 with the X-ray image processing apparatus 6.

[0144] In the above-described embodiment, an example of the configuration in which the grating position adjustment mechanism 12 adjusts the position of the second grating 4 has been shown. However, the present invention is not limited to this. The grating position adjustment mechanism 12 may be configured to adjust the positions of gratings other than the second grating 4. The grating position adjustment mechanism 12 may adjust the position of any one of the plurality of gratings.

[0145] [Aspect] It is understood by those skilled in the art that the above-described exemplary embodiments are specific examples of the following aspects.

[0146] (Item 1) An X-ray source, An X-ray detector that detects X-rays irradiated from the X-ray source, A plurality of gratings disposed between the X-ray source and the X-ray detector, An image processing unit that generates an X-ray phase contrast image including a first dark field image that is a dark field image of a subject based on the intensity distribution of the X-rays detected by the X-ray detector, A storage unit that stores a plurality of correction curves generated for each position in a direction orthogonal to the grating direction, which is the direction in which the plurality of gratings extend, A control unit that corrects the first dark field image using the correction curve corresponding to each position, and Each of the plurality of correction curves shows a correspondence relationship between a value related to X-ray absorption of a subject and a value related to X-ray scattering at the position, an X-ray phase imaging apparatus.

[0147] (Item 2) The image processing unit further generates, for the subject, a first absorption image that is an absorption image of the subject, in addition to the first dark field image. The control unit is configured to, for each position, refer to the corresponding correction curve, specify a value related to X-ray scattering associated with a value related to X-ray absorption of the first absorption image, and correct the first dark field image using the specified value related to X-ray scattering. The X-ray phase imaging apparatus according to item 1.

[0148] (Item 3) The storage unit is configured to store the plurality of correction curves in association with the material of the subject. The control unit is configured to select the corresponding plurality of correction curves according to the material of the subject and correct the first dark field image using the selected plurality of correction curves. The X-ray phase imaging apparatus according to item 1 or 2.

[0149] (Item 4) The storage unit is configured to store the plurality of correction curves in association with the imaging conditions. The control unit is configured to select the corresponding plurality of correction curves according to the imaging conditions and correct the first dark field image using the selected correction curve. The X-ray phase imaging apparatus according to item 1 or 2.

[0150] (Item 5) An image acquisition unit that acquires an X-ray phase contrast image including a first dark field image that is a dark field image of the subject. A storage unit that stores a plurality of correction curves generated for each position in a direction orthogonal to the grating direction in which the plurality of gratings extend. A control unit that corrects the first dark field image using the correction curve corresponding to each position, and is provided with: Each of the plurality of correction curves shows a correspondence relationship between a value related to X-ray absorption of the subject and a value related to X-ray scattering at the position. An X-ray image processing apparatus.

[0151] (Item 6) A step of obtaining an X-ray phase contrast image including a first dark field image which is a dark field image of a subject; A step of storing a plurality of correction curves generated for each position in a direction orthogonal to a grating direction which is a direction in which a plurality of gratings extend; A step of correcting the first dark field image by using the correction curve corresponding to each position, and comprising: An X-ray image processing method, wherein each of the plurality of correction curves shows a correspondence relationship between a value related to X-ray absorption of a subject and a value related to X-ray scattering at the position.

[0152] (Item 7) A method for generating the plurality of correction curves used in the X-ray image processing method according to Item 6, comprising: A step of imaging a correction phantom using an X-ray phase imaging apparatus having a plurality of gratings, and obtaining a second dark field image which is a dark field image of the correction phantom; A step of obtaining a second absorption image which is an absorption image of the correction phantom; A correction curve generation method including a step of generating the plurality of correction curves for each position in a direction orthogonal to a grating direction which is a direction in which the plurality of gratings extend, by using the second dark field image and the second absorption image.

[0153] (Item 8) The correction phantom has a structure in which an X-ray absorption degree changes in a grating direction of the plurality of gratings, In the step of generating the plurality of correction curves, for each position, a correspondence relationship between a value related to X-ray absorption specified from the second absorption image and a value related to X-ray scattering specified from the second dark field image is obtained, and the plurality of correction curves are generated. The correction curve generation method according to Item 7.

[0154] (Item 9) The correction phantom has a structure in which a thickness in an X-ray irradiation direction changes in a grating direction of the plurality of gratings, In the step of generating the plurality of correction curves, for each position, a correspondence relationship between a value related to X-ray absorption specified from the second absorption image and a value related to X-ray scattering specified from the second dark field image is obtained, and the plurality of correction curves are generated. The correction curve generation method according to item 7.

Explanation of symbols

[0155] 1 X-ray source 2 X-ray detector 3 First grating (plural gratings) 4 Second grating (plural gratings) 5 Third grating (plural gratings) 6 X-ray image processing apparatus 7a Image processing unit 7b Control unit 8 Storage unit 9 Image acquisition unit 13, 13e, 13f, 130, 131 Phantom for correction 22 Imaging condition 30 X-ray phase contrast image 31 Second dark field image (dark field image of the phantom for correction) 32 Second absorption image (absorption image of the phantom for correction) 35a First dark field image (dark field image of the subject) 35b First absorption image (absorption image of the subject) 90 Subject 100 X-ray phase imaging apparatus

Claims

1. an X-ray source, an X-ray detector that detects X-rays irradiated from the X-ray source, a plurality of gratings each having a grating pattern forming portion that is disposed between the X-ray source and the X-ray detector and functions as a grating, an image processing unit that generates an X-ray phase contrast image including a first dark field image that is a dark field image of a subject based on an intensity distribution of the X-rays detected by the X-ray detector, a storage unit that stores a plurality of correction curves generated for each predetermined region of the dark field image in a direction orthogonal to the grating direction that is the direction in which the grating pattern forming portion of each of the plurality of gratings extends, a control unit that corrects the first dark field image using the correction curve corresponding to each predetermined region, and each of the plurality of correction curves shows a correspondence relationship between a value related to X-ray absorption of a subject and a value related to X-ray scattering in the predetermined region, an X-ray phase imaging apparatus.

2. the image processing unit further generates, for the subject, in addition to the first dark field image, a first absorption image that is an absorption image of the subject, the control unit refers to the corresponding correction curve for each predetermined region, identifies a value related to X-ray scattering associated with a value related to X-ray absorption of the first absorption image, and corrects the first dark field image using the identified value related to X-ray scattering, the X-ray phase imaging apparatus according to claim 1.

3. the storage unit is configured to store the plurality of correction curves in association with the material of the subject, the control unit is configured to select the plurality of corresponding correction curves according to the material of the subject and correct the first dark field image using the selected plurality of correction curves, the X-ray phase imaging apparatus according to claim 1 or 2.

4. the storage unit is configured to store the plurality of correction curves in association with imaging conditions, the control unit is configured to select the plurality of corresponding correction curves according to the imaging conditions and correct the first dark field image using the selected plurality of correction curves, the X-ray phase imaging apparatus according to claim 1 or 2.

5. an image acquisition unit that acquires an X-ray phase contrast image including a first dark field image that is a dark field image of a subject, A storage unit that stores a plurality of correction curves generated for each predetermined region of the dark-field image in a direction orthogonal to the grating direction, which is the direction in which the grating pattern forming unit, which is a part that functions as a grating, extends, for each of the plurality of gratings each having the grating pattern forming unit; A control unit that corrects the first dark-field image using the correction curve corresponding to each of the predetermined regions; An X-ray image processing apparatus, wherein each of the plurality of correction curves shows a correspondence relationship between a value related to X-ray absorption of a subject and a value related to X-ray scattering in the predetermined region. **Claim 6** A step of acquiring an X-ray phase contrast image including a first dark-field image that is a dark-field image of a subject; A step of storing a plurality of correction curves generated for each predetermined region of the dark-field image in a direction orthogonal to the grating direction, which is the direction in which the grating pattern forming unit, which is a part that functions as a grating, extends, for each of the plurality of gratings each having the grating pattern forming unit; A step of correcting the first dark-field image using the correction curve corresponding to each of the predetermined regions; An X-ray image processing method, wherein each of the plurality of correction curves shows a correspondence relationship between a value related to X-ray absorption of a subject and a value related to X-ray scattering in the predetermined region. **Claim 7** A method for generating the plurality of correction curves used in the X-ray image processing method according to Claim 6, comprising: A step of imaging a correction phantom using an X-ray phase imaging apparatus having a plurality of gratings and acquiring a second dark-field image that is a dark-field image of the correction phantom; A step of acquiring a second absorption image that is an absorption image of the correction phantom; A step of generating the plurality of correction curves using the second dark-field image and the second absorption image for each of the predetermined regions in a direction orthogonal to the grating direction, which is the direction in which the grating pattern forming unit of each of the plurality of gratings extends. **Claim 8** The correction phantom has a structure in which the degree of X-ray absorption changes in the grating direction of the plurality of gratings; The correction curve generation method according to Claim 7, wherein in the step of generating the plurality of correction curves, for each of the predetermined regions, a correspondence relationship between a value related to X-ray absorption specified from the second absorption image and a value related to X-ray scattering specified from the second dark-field image is acquired to generate the plurality of correction curves. **Claim 9** The correction phantom has a structure in which the thickness in the irradiation direction of X-rays changes in the grating direction of the plurality of gratings. The correction curve generation method according to claim 7, wherein, in the step of generating the plurality of correction curves, for each of the predetermined regions, a correspondence relationship between a value related to X-ray absorption specified from the second absorption image and a value related to X-ray scattering specified from the second dark field image is obtained to generate the plurality of correction curves.

Images