WO2020054159A1 - X-ray phase imaging system - Google Patents

Abstract

This X-ray phase imaging system is provided with: an X-ray source (1); a detector (2); multiple grids including a first grid (3) and a second grid (4); an image processing unit (5) which generates a phase contrast image (10); and a control unit (6) which, by means of a cubic function represented using position coordinates of a pixel (P) in the generated phase contrast image, approximates an artifact (21) generated in the phase contrast image and corrects the phase contrast image.

Description

X-ray phase imaging system

The present invention relates to an X-ray phase imaging system, and more particularly to an X-ray phase imaging system including a plurality of gratings.

Conventionally, an X-ray phase imaging system including a plurality of gratings is known. Such an X-ray phase imaging system is disclosed in, for example, Japanese Patent No. 5833114.

The X-ray phase imaging system disclosed in Japanese Patent No. 5831614 includes an X-ray source, a detector, a G0 grating for increasing the coherence of X-rays, a G1 grating for diffracting X-rays, and a G1 grating. A G2 grating for causing interference with the grating image. The X-ray phase imaging system disclosed in Japanese Patent No. 5831614 is configured to acquire a phase contrast image by a fringe scanning method in which one of a plurality of gratings is imaged while being moved in the direction of the pitch of the grating. . The fringe scanning method is a method of imaging the inside of a subject based on the phase difference of X-rays passing through the subject and small-angle scattering of X-rays.

Here, in the case where the inside of the subject is imaged by the fringe scanning method, if the relative positions between the plurality of grids are misaligned, artifacts occur in the generated phase contrast image. Therefore, the image quality of the obtained phase contrast image deteriorates. Thus, Japanese Patent No. 5831614 discloses a configuration for correcting an artifact generated in a phase contrast image.

Specifically, the X-ray phase imaging system disclosed in Japanese Patent No. 5833114 is configured to approximate an artifact generated in a phase contrast image by a linear function or a quadratic function. The X-ray phase imaging system disclosed in Japanese Patent No. 5831614 is configured to correct a phase contrast image by subtracting an approximate artifact from the phase contrast image.

Japanese Patent No. 5833114

However, the configuration disclosed in Japanese Patent No. 5831614 is a configuration in which an artifact is approximated by a linear function or a quadratic function. For this reason, when an artifact such as a relatively complicated gradation (shading continuously changes) that cannot be approximated by a linear function or a quadratic function occurs in a phase contrast image, it is necessary to accurately approximate the artifact. And it is difficult to suppress the deterioration of the image quality of the phase contrast image.

The present invention has been made in order to solve the above-described problems, and suppresses the deterioration of the image quality of the obtained phase contrast image even when relatively complicated artifacts have occurred in the phase contrast image. To provide an X-ray phase imaging system capable of performing such operations.

In order to achieve the above object, an X-ray phase imaging system according to one aspect of the present invention includes an X-ray source that irradiates a subject with X-rays, a detector that detects X-rays emitted from the X-ray source, X-rays from the X-ray source are arranged between the X-ray source and the detector, and moire fringes are generated by interference between the first grating for forming a grating image and the grating image of the first grating. A plurality of gratings including a second grating for causing a phase contrast image to be generated based on a signal detected by the detector, and a position coordinate of a pixel in the generated phase contrast image. And a control unit that approximates an artifact generated in the phase contrast image by a third-order or higher-order function and corrects the phase contrast image based on the approximated artifact. Note that, in this specification, an artifact refers to a light and shade pattern (gradation) caused by non-uniform pixel values of pixels in a background portion of a phase contrast image.

In the X-ray phase imaging system according to one aspect of the present invention, as described above, a third-order or higher-order function expressed using the position coordinates of the pixel in the generated phase contrast image causes the phase contrast image to be generated in the phase contrast image. A control unit that approximates the artifact and corrects the phase contrast image based on the approximated artifact. As a result, even if an artifact generated in the phase contrast image has a complicated shape (distribution) that cannot be approximated by a linear function or a quadratic function, it may be approximated by a cubic or higher-order function. As a result, even when relatively complicated artifacts occur in the phase contrast image, it is possible to suppress the image quality of the obtained phase contrast image from deteriorating.

In the X-ray phase imaging system according to the one aspect, preferably, the control unit acquires the intensity distribution of the artifact as a three-dimensional approximated surface based on a third-order or higher-order function, and acquires the acquired three-dimensional approximation. The phase contrast image is configured to be corrected based on the curved surface. With this configuration, it is possible to obtain a three-dimensional approximated surface using a third-order or higher order function, so that the three-dimensional approximated surface can more accurately approximate the intensity distribution of the artifact. . As a result, it is possible to further suppress the deterioration of the image quality of the phase contrast image due to the artifact.

In this case, preferably, the control unit is configured to correct an artifact caused by a three-dimensional displacement of a relative position between the plurality of grids caused by heat fluctuation by using a three-dimensional approximated surface. I have. According to this configuration, even when a complicated positional shift due to thermal fluctuation occurs in the lattice, the artifact can be corrected based on the three-dimensional approximated surface. As a result, it is possible to suppress the image quality of the phase contrast image from deteriorating due to an artifact due to the thermal fluctuation.

In the configuration in which the phase contrast image is corrected based on the acquired three-dimensional approximated surface, the control unit preferably occurs when a relative position between the plurality of gratings is shifted from a predetermined positional relationship. It is configured to correct artifacts caused by moire fringes by using a three-dimensional approximated surface. Here, the moiré stripe is a stripe pattern in which a bright portion and a dark portion are repeated at a predetermined cycle. The artifact caused by the moiré fringe has a dark part and a light part corresponding to the bright part and the dark part of the moiré fringe, respectively. Therefore, the dark part and the light part of the artifact caused by the moire fringes are also repeated at a predetermined cycle. It is considered that artifacts caused by such moiré fringes are difficult to approximate by a linear function or a quadratic function. Therefore, with the above configuration, unlike the case of approximation using a linear function or a quadratic function, an artifact due to moiré fringes can be accurately approximated by a three-dimensional approximated surface. As a result, it is possible to suppress deterioration in image quality of the phase contrast image due to artifacts caused by the moire fringes.

In the configuration in which the phase contrast image is corrected based on the acquired three-dimensional approximated surface, preferably, the control unit acquires a plurality of pixels from the phase contrast image, plots the acquired pixels, and plots the acquired pixels. It is configured to obtain a three-dimensional approximated surface by fitting a third-order or higher-order multi-dimensional function to the plurality of pixels. With this configuration, it is possible to obtain a three-dimensional approximated surface that approximates the intensity distribution of the artifact by plotting the pixels obtained from the phase contrast image. As a result, it is possible to suppress an increase in calculation cost (calculation load) when approximating the artifact as compared with a case where the intensity distribution of the artifact is obtained from all pixels of the phase contrast image.

In the configuration in which the phase contrast image is corrected based on the obtained three-dimensional approximated surface, preferably, the control unit obtains the three-dimensional approximated surface by performing multidimensional function fitting by least squares fitting. It is configured as follows. With this configuration, a three-dimensional approximated surface can be easily obtained by the least squares fitting. As a result, artifacts generated in the phase contrast image can be easily corrected.

In the configuration in which the phase contrast image is corrected based on the obtained three-dimensional approximated surface, preferably, the control unit obtains the three-dimensional approximated surface based on a pixel in which the subject is not reflected in the phase contrast image. Then, the phase contrast image is corrected by subtracting a three-dimensional approximate curved surface from the phase contrast image. With this configuration, it is possible to accurately approximate the artifact in the background portion, as compared with a case where a three-dimensional approximated surface including not only pixels in the background portion but also pixels in which the subject is reflected is acquired. As a result, the artifact can be corrected by a three-dimensional approximation surface that accurately approximates the artifact, so that the image quality of the phase contrast image can be further suppressed from deteriorating.

In the X-ray phase imaging system according to the above aspect, preferably, the control unit is configured to correct an artifact in the phase differential image as a phase contrast image. With this configuration, it is possible to correct artifacts in a phase differential image formed by using the lattice image of the first lattice, and therefore, when suppressing deterioration in image quality of the phase differential image, Especially effective.

In the X-ray phase imaging system according to the above aspect, preferably, the plurality of gratings are arranged between the X-ray source and the first grating, and the X-ray coherence of X-rays irradiated with X-rays from the X-ray source is provided. A third grating to enhance the With this configuration, even when the focal size of the X-ray source is large, the third grating can improve the coherence of the X-rays, thereby generating a grating image of the first grating. As a result, the degree of freedom in selecting the X-ray source can be improved.

In the X-ray phase imaging system according to the above aspect, preferably, the first grating is an absorption grating that forms a stripe pattern generated by shielding a part of the X-rays as a grating image. According to this structure, like the interferometer that generates a phase contrast image based on a self-image generated by interference of X-rays diffracted by the first grating, a part of the X-rays is shielded by the first grating. Even in a non-interferometer that images a subject based on the first lattice stripe pattern generated by this, it is possible to correct an artifact that occurs in a phase contrast image. Further, the striped pattern of the first lattice is generated by blocking a part of the X-rays. Therefore, unlike the Talbot interferometer that generates a self-image of the first grating, the first grating does not have to be arranged at a predetermined distance (Talbot distance) from the X-ray source. As a result, the degree of freedom of the arrangement position of the first grating can be improved.

Advantageous Effects of Invention According to the present invention, as described above, even when relatively complicated artifacts occur in a phase contrast image, X-ray phase imaging capable of suppressing deterioration of the quality of the obtained phase contrast image A system can be provided.

FIG. 2 is a schematic diagram of the X-ray phase imaging system according to the first embodiment as viewed from a Y direction. FIG. 2 is a perspective view of a grating moving mechanism included in the X-ray phase imaging system according to the first embodiment. FIG. 3 is a schematic diagram for explaining a lattice image of a first lattice and a second lattice in the X-ray phase imaging system according to the first embodiment. It is a schematic diagram (A) of an absorption image generated by the X-ray phase imaging system according to the first embodiment, a schematic diagram of a phase differential image (B), and a schematic diagram of a dark field image (C). FIGS. 7A to 7D are schematic diagrams (A) to (D) for explaining a change in a phase differential image when a positional shift occurs between a lattice image of a first grating and a second grating. FIG. 3 is a schematic diagram for explaining an artifact that occurs in a phase contrast image. FIGS. 7A and 7B are schematic diagrams for explaining correction of an artifact according to a first comparative example. FIGS. FIG. 4 is a schematic diagram for explaining a three-dimensional approximate curved surface acquired by a control unit according to the first embodiment. FIGS. 3A and 3B are schematic diagrams for explaining correction of an artifact according to the first embodiment. FIGS. 5 is a flowchart illustrating an artifact correction process according to the first embodiment. FIG. 3 is a schematic diagram for explaining moire fringes generated in an X-ray image. 3A is a schematic diagram of an absorption image in which an artifact caused by moiré fringes has occurred, FIG. 3B is a schematic diagram of a phase differential image, and FIG. FIGS. 7A and 7B are schematic diagrams for explaining correction of an artifact according to a second comparative example. FIGS. FIGS. 11A and 11B are schematic diagrams for explaining correction of an artifact according to a third comparative example. FIGS. FIGS. 7A and 7B are schematic diagrams for explaining correction of an artifact according to the second embodiment. FIGS. 9 is a flowchart illustrating an artifact correction process according to the second embodiment. It is the schematic diagram which looked at the X-ray phase imaging system by the modification from Y direction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
The configuration of the X-ray phase imaging system 100 according to the first embodiment will be described with reference to FIGS.

(Configuration of X-ray phase imaging system)
First, the configuration of the X-ray phase imaging system 100 according to the present embodiment of the present invention will be described with reference to FIG.

Ｘ As shown in FIG. 1, the X-ray phase imaging system 100 is an apparatus for imaging the inside of the subject Q using the Talbot effect. The X-ray phase imaging system 100 is configured to image the subject Q while translating any one of the plurality of gratings in the periodic direction of the grating (X direction).

As shown in FIG. 1, the X-ray phase imaging system 100 includes an X-ray source 1, a detector 2, a plurality of gratings including a first grating 3 and a second grating 4, an image processing unit 5, The storage unit includes a unit 6, a storage unit 7, and a grid moving mechanism 8. In this specification, a direction from the X-ray source 1 toward the first grating 3 is defined as a Z2 direction, and a direction opposite thereto is defined as a Z1 direction. The left and right directions in a plane orthogonal to the Z direction are defined as X directions, the upper direction of the paper of FIG. 1 is defined as X1 direction, and the lower direction of the paper of FIG. 1 is defined as X2 direction. The vertical direction in the plane of the paper perpendicular to the Z direction is defined as the Y direction, the direction toward the near side of the paper of FIG. 1 is defined as the Y1 direction, and the direction toward the back of the paper of FIG. 1 is defined as the Y2 direction.

The X-ray source 1 is configured to generate X-rays when a high voltage is applied, and to irradiate the generated X-rays to the subject Q.

The detector 2 is configured to detect X-rays, convert the detected X-rays into an electric signal, and read the converted electric signal as an image signal. The detector 2 is, for example, an FPD (Flat @ Panel @ Detector). The detector 2 includes a plurality of conversion elements (not shown) and pixel electrodes (not shown) arranged on the plurality of conversion elements. The plurality of conversion elements and pixel electrodes are arranged in an array in the X direction and the Y direction at a predetermined cycle. The detector 2 is configured to output the acquired image signal to the image processing unit 5.

The first grating 3 is disposed between the X-ray source 1 and the second grating 4, and is irradiated with X-rays from the X-ray source 1. The first grating 3 is provided to form a grating image (self-image 30 (see FIG. 3)) of the first grating 3 by the Talbot effect. When the coherent X-rays pass through the grid in which the slit is formed, a grid image (self image 30) is formed at a position separated from the grid by a predetermined distance (Talbot distance). This is called the Talbot effect.

The first grating 3, a plurality of X-ray transmitting portion 3a arranged at a predetermined period (pitch) p ₁ in the X direction and has an X-ray phase change portion 3b. Each of the X-ray transmitting portions 3a and the X-ray phase changing portions 3b is formed so as to extend linearly along the Y direction. The X-ray transmitting portions 3a and the X-ray phase changing portions 3b are formed so as to extend in parallel with each other. The first grating 3 is a so-called phase grating.

The second grating 4 has a plurality of slits 4a and X-ray absorbing portion 4b which is arranged at a predetermined period (pitch) p ₂ in the X direction. Each of the slits 4a and the X-ray absorbing portions 4b are formed so as to extend linearly along the Y direction. The slit 4a and the X-ray absorbing portion 4b are formed so as to extend in parallel with each other. The second grating 4 is a so-called absorption grating. The first grating 3 and the second grating 4 are gratings having different roles, respectively, but the X-ray transmitting portion 3a and the slit 4a respectively transmit X-rays. Further, the X-ray phase changing section 3b has a role of changing the phase of X-rays by a difference in refractive index from the X-ray transmitting section 3a, and the X-ray absorbing section 4b has a role of shielding X-rays. ing.

The second grating 4 is disposed between the first grating 3 and the detector 2 and is irradiated with X-rays passing through the first grating 3. The second grating 4 is arranged at a position away from the first grating 3 by the Talbot distance. The second grating 4 interferes with the grating image (self-image 30) of the first grating 3 to form Moire fringes M (see FIG. 11) on the detection surface of the detector 2.

The image processing unit 5 is configured to generate the phase contrast image 10 (see FIG. 4) based on the image signal output from the detector 2. The image processing unit 5 includes, for example, a processor such as a GPU (Graphics Processing Unit) or an FPGA (Field-Programmable Gate Array) configured for image processing.

The control unit 6 is configured to control the lattice moving mechanism 8 to translate the first lattice 3 in translation. Control unit 6 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

The storage unit 7 is configured to store the phase contrast image 10 generated by the image processing unit 5 and the like. The storage unit 7 includes, for example, an HDD (Hard Disk Drive), a nonvolatile memory, and the like.

The lattice moving mechanism 8 is configured to translate one of the plurality of lattices in the periodic direction of the lattice (X direction) under the control of the control unit 6. In the first embodiment, the grid moving mechanism 8 holds the first grid 3 and is configured to translate the first grid 3.

(Lattice moving mechanism)
As shown in FIG. 2, the grid moving mechanism 8 includes an X direction, a Y direction, a Z direction, a rotation direction Rz around an axis in the Z direction, a rotation direction Rx around an axis in the X direction, and a rotation direction Rx around the axis in the Y direction. The first grating 3 is configured to be movable in the rotation direction Ry. Specifically, the lattice moving mechanism 8 includes an X-direction linear movement mechanism 80, a Y-direction linear movement mechanism 81, a Z-direction linear movement mechanism 82, a linear movement mechanism connection unit 83, a stage support unit driving unit 84, , A stage support unit 85, a stage driving unit 86, and a stage 87. The X direction translation mechanism 80 is configured to be movable in the X direction. X-direction linear motion mechanism 80 includes, for example, a motor. The Y direction translation mechanism 81 is configured to be movable in the Y direction. The Y-direction linear motion mechanism 81 includes, for example, a motor. The Z-direction translation mechanism 82 is configured to be movable in the Z direction. The Z-direction linear motion mechanism 82 includes, for example, a motor.

The lattice moving mechanism 8 is configured to move the first lattice 3 in the X direction by the operation of the X-direction linear moving mechanism 80. The grating moving mechanism 8 is configured to move the first grating 3 in the Y direction by the operation of the Y-direction linear moving mechanism 81. The lattice moving mechanism 8 is configured to move the first lattice 3 in the Z direction by the operation of the Z-direction linear moving mechanism 82.

The stage support 85 supports the stage 87 from below (Y1 direction). The stage drive unit 86 is configured to reciprocate the stage 87 in the X direction. The stage 87 has a bottom formed in a convex curved shape toward the stage support portion 85, and is configured to rotate around the optical axis of the X-ray (Rz direction) by being reciprocated in the X direction. ing. Further, the stage support drive unit 84 is configured to reciprocate the stage support 85 in the Z direction. The bottom of the stage support portion 85 is formed in a convex curved shape toward the direct-acting mechanism connection portion 83, and reciprocates in the Z direction to rotate around the axis in the X direction (Rx direction). It is configured as follows. The linear motion mechanism connecting portion 83 is provided in the X direction linear motion mechanism 80 so as to be rotatable around an axis in the Y direction (Ry direction). Therefore, the grid moving mechanism 8 can rotate the grid about the central axis in the Y direction.

(Self image of the first lattice)
In the first embodiment, the second grating 4 is arranged at a position away from the first grating 3 by the Talbot distance. Specifically, as shown in FIG. 3, a self-image 30 of the first grating 3 is formed at a position away from the first grating 3 by the Talbot distance. The self-image 30 has a bright part 30a and a dark part 30b. A bright portion 30a is formed at a position where X-rays diffracted by the first grating 3 reinforce each other. Further, a dark portion 30b is formed at a position where X-rays diffracted by the first grating 3 weaken. The bright part 30a and a dark 30b of self-image 30, respectively, are formed at predetermined intervals _{p 3.} The second grating 4, the period p ₂ is designed to substantially coincident with the period p ₃ of the self-image 30. Therefore, the bright portion 30a of the self-image 30 is located at a position substantially equal to the arrangement of the slits 4a of the second grating 4. Further, the dark part 30b of the self-image 30 is located at a position substantially equal to the X-ray absorbing part 4b of the second grating 4.

In the first embodiment, the X-ray phase imaging system 100 generates the phase contrast image 10 by a fringe scanning method in which the first grating 3 is imaged while being translated in the X direction. Specifically, the image processing unit 5 generates a first intermediate image (not shown) generated based on a plurality of images captured while translating the first lattice 3 in a state where the subject Q is not arranged. . Further, the image processing unit 5 generates a second intermediate image (not shown) generated based on a plurality of images captured while translating the first lattice 3 in a state where the subject Q is arranged. The image processing unit 5 generates a phase contrast image 10 based on the first intermediate image and the second intermediate image. The image processing unit 5 generates an absorption image 11, a phase differential image 12, and a dark field image 13 shown in FIGS. 4A to 4C as the phase contrast image 10. In the following description, the imaging of a plurality of images for acquiring the first intermediate image is described as “imaging without a subject”. In addition, imaging of a plurality of images for acquiring the second intermediate image is referred to as “imaging with subject”.

吸収 The absorption image 11 is an image formed based on attenuation of X-rays generated when X-rays pass through the subject Q. The phase differential image 12 is an image formed based on a phase shift of the X-ray generated when the X-ray passes through the subject Q. The dark field image 13 is a Visibility image obtained by a change in Visibility based on small-angle scattering of X-rays. The dark-field image 13 is also called a small-angle scattering image. “Visibility” refers to sharpness.

Here, if the relative position between the first grating 3 and the second grating 4 is displaced between the imaging without the subject and the imaging with the subject, the positional relationship between the self-image 30 and the second grating 4 is also increased. Misalignment occurs. Hereinafter, with reference to FIG. 5, a description will be given of a change in the phase differential image 12 when the relative position between the self-image 30 and the second grating 4 is displaced.

FIG. 5A shows an example in which the relative position between the first grating 3 and the second grating 4 does not deviate between the imaging without the subject and the imaging with the subject. The example shown in FIG. 5A is an example in which the relative position between the first grating 3 and the second grating 4 has no positional shift. For this reason, no displacement occurs even in the relative position between the self-image 30 and the second grating 4. It should be noted that the state in which the relative position between the self-image 30 and the second grating 4 is not displaced means that the bright portion 30a (or dark portion 30b) of the self-image 30 and the slit 4a (or X-ray This is a state in which the absorber 4b) and the absorber 4b) are arranged at substantially equal positions.

The example shown in FIG. 5B is an example in which the first grid 3 is moved in parallel with respect to the second grid 4 between the imaging without the subject and the imaging with the subject. In the example shown in FIG. 5B, the first grating 3 moves in parallel in the plus direction (X2 direction). When the first grating 3 moves in the plus direction, the average value of the luminance values of the X-rays detected by the detector 2 becomes higher than in the example shown in FIG. Therefore, the phase differential image 12b shown in FIG. 5B is an image brighter than the phase differential image 12a shown in FIG.

The example shown in FIG. 5C is an example in which the first grating 3 is moved in parallel with the second grating 4 in the minus direction (X1 direction) between the imaging without the subject and the imaging with the subject. When the first grating 3 moves in the minus direction, the average value of the luminance values of the X-rays detected by the detector 2 becomes lower than in the example shown in FIG. Therefore, the phase differential image 12c shown in FIG. 5C is an image darker than the phase differential image 12a shown in FIG.

In the example illustrated in FIG. 5D, the first grating 3 moves in the rotation direction Rz about the X-ray optical axis with respect to the second grating 4 between the imaging without the subject and the imaging with the subject. This is an example of the case. In the example shown in FIG. 5D, the first lattice 3 on the Y1 direction side is in a state of being translated in the plus direction (X2 direction). On the Y2 direction side of the first grating 3, the first grating 3 is in a state of parallel movement in the minus direction (X1 direction). Therefore, the phase differential image 12d shown in FIG. 5D is brighter on the Y1 side of the image than the phase differential image 12a shown in FIG. 5A, and darker on the Y2 direction side of the image than the phase differential image 12a. It becomes an image. In FIG. 5, the brightness of the phase differential image 12 refers to the phase value in the phase differential image 12. That is, as shown in the legend 20 of the brightness with respect to the displacement amount in FIG. 5, the phase differential image 12 becomes a brighter image as the phase value approaches “π”. Further, the phase differential image 12 becomes a darker image as the phase value approaches “−π”.

場合 When the misregistration as shown in FIGS. 5B to 5D occurs in a complex manner, an artifact 21 occurs in the phase differential image 12 as shown in FIG. The artifact 21 has a dark part 21a and a light part 21b. Further, in the example shown in FIG. 6, in the phase differential image 12, a change in the phase value along the horizontal arrow HA is illustrated as a graph G1. Further, in the example shown in FIG. 6, a change in the phase value along the vertical arrow VA in the phase differential image 12 is illustrated as a graph G2. In the graph G1, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the phase change. In the graph G2, the horizontal axis represents the position in the Y direction, and the vertical axis represents the phase change.

In the example shown in FIG. 6, since the artifact 21 is generated along the X direction, the graph G1 has a low phase value at a position corresponding to the dark portion 21a of the artifact 21, and the light beam 21b of the artifact 21 has a low phase value. The phase value is higher at the corresponding position. On the other hand, since the graph G2 shows a change in the phase value in a direction intersecting with the artifact 21, the graph G2 has a shape in which the phase value does not substantially change. As shown in FIG. 6, when an artifact 21 occurs in the phase differential image 12, shading occurs in the phase differential image 12, so that the image quality of the phase differential image 12 deteriorates. Therefore, it is conceivable to perform correction for removing the artifact 21 generated in the phase differential image 12.

As a configuration for performing the correction for removing the artifact 21, a configuration is known in which the intensity distribution of the artifact 21 is approximated by a linear function (or a quadratic function) to correct the phase differential image 12. Hereinafter, a configuration for correcting the phase differential image 12 according to the related art will be described with reference to FIG.

In the first comparative example according to the related art, an artifact 21 generated in the phase differential image 12 as shown in FIG. 7A is approximated by a plane using a linear function. Then, by subtracting the approximated artifact 21 from the phase differential image 12, a corrected phase differential image 14 as shown in FIG. 7B is obtained. Note that the example illustrated in FIG. 7A is the same as that in FIG. 6, and thus detailed description is omitted.

In the example shown in FIG. 7B, a change in the phase value along the horizontal arrow HA in the corrected phase differential image 14 is shown as a graph G3. In the example shown in FIG. 7B, a change in the phase value along the vertical arrow VA in the corrected phase differential image 14 is shown as a graph G4. In the graph G3, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the phase change. In the graph G4, the horizontal axis indicates the position in the Y direction, and the vertical axis indicates the phase change.

In the example shown in FIG. 7B, the width d2 of the change in the phase value in the graph G3 is smaller than the width d1 of the change in the phase value in the graph G1. However, at a position corresponding to the dark portion 21a of the artifact 21 and at a position corresponding to the light portion 21b of the artifact 21, the phase value decreases and increases. This is because the intensity distribution of the artifact 21 is approximated by a linear function, so that the artifact 21 cannot be accurately approximated, and the artifact 21 remains in the corrected phase differential image 14. it is conceivable that.

Therefore, in the first embodiment, the control unit 6 controls the third-order or higher-order multidimensional function represented by using the position coordinates of the pixel P (see FIG. 6) in the generated phase contrast image 10 (phase differential image 12). Thus, an artifact 21 generated in the phase contrast image 10 is approximated, and the phase contrast image 10 is corrected based on the approximated artifact 21. Specifically, the control unit 6 acquires the intensity distribution of the artifact 21 as a three-dimensional approximated surface CS based on a third-order or higher-order function, and calculates a phase based on the acquired three-dimensional approximated surface CS. The contrast image 10 is configured to be corrected. In the first embodiment, the control unit 6 corrects an artifact 21 caused by a three-dimensional displacement of a relative position between a plurality of lattices caused by heat fluctuation by using a three-dimensional approximate curved surface CS. It is configured as follows. Further, the control unit 6 is configured to correct an artifact 21 in the phase differential image 12 as the phase contrast image 10.

The example shown in FIG. 8 is an example of a three-dimensional approximated surface CS in which each pixel P is plotted by taking the x coordinate of the pixel P on the x axis, the y coordinate of the pixel P on the y axis, and the pixel value of the pixel P on the z axis. It is. In the three-dimensional first embodiment shown in FIG. 8, the control unit 6 acquires a plurality of pixels P from the phase contrast image 10, plots the acquired pixels P, and It is configured to obtain a three-dimensional approximated surface CS by fitting a third-order or higher-order multi-order function. The control unit 6 is configured to acquire a three-dimensional approximate curved surface CS based on the pixels P on which the subject Q is not reflected in the phase contrast image 10. In the first embodiment, since the cubic function is used as the tertiary or higher order function, the control unit 6 acquires at least ten or more pixels P from the phase contrast image 10. In the example illustrated in FIG. 8, ten or more pixels P are illustrated for convenience, but in the first embodiment, ten pixels P are obtained from the phase contrast image 10. The pixel P may be selected from a background portion of the phase contrast image 10 by a user such as a doctor, or may be selected from a background portion of the phase contrast image 10 by image recognition by the control unit 6.

In the first embodiment, the control unit 6 uses Equation (1) defined below as a third-order or higher-order function.

Here, z is a curved surface on which the pixels P are distributed. A ₀ to a ₉ are coefficients for determining a multi-order function (cubic function). Further, x and y are position coordinates (x coordinate and y coordinate) of each pixel P.

In the first embodiment, the control unit 6 is configured to obtain a three-dimensional approximation surface CS by performing fitting of a multi-dimensional function by least-squares fitting. Specifically, the control unit 6 defines the deviation E _k of the plurality of pixels P by the following equation (2) and obtains the sum of squares E of the deviation E _k shown in the following equation (3). To obtain a three-dimensional approximated surface CS.

Here, k is an integer from 1 to N. N is the number of pixels P to be obtained. In the first embodiment, N is 10 because ten pixels P are used.

Note that in order to obtain the sum of squares E of the deviation E _k , it is only necessary to consider a case where partial differentiation is performed on each coefficient (a ₀ to a ₉ ) of the above equation (3) and they become 0 (zero). . That is, the control unit 6 acquires the coefficients (a ₀ to a ₉ ) that satisfy the following equations (4) to (13).

If the above equations (4) to (13) are simultaneous equations, they can be expressed as the following equation (14).

Further, A, x (→) and b (→) in the above equation (14) can be expressed as the following equations (15), (16) and (17).

解 As a solution of the above equation (14), any solution may be used. In the first embodiment, the control unit 6 is configured to calculate Expression (14) by, for example, the LU decomposition method. Here, the LU decomposition method is a method of calculating a determinant by decomposing a square matrix into a product of a lower triangular matrix and an upper triangular matrix.

The control unit 6 performs correction to remove the artifact 21 from the phase differential image 12 using each coefficient (a ₀ to a ₉ ) obtained by the LU decomposition method and the following equation (18).

Here, z _k is the distribution of pixel values in the background portion of the phase differential image 12 before correction. Z _1k is the distribution of pixel values in the background portion of the corrected phase differential image 12.

As shown in the above equation (18), the control unit 6 approximates the artifact 21 with a three-dimensional three-dimensional approximation surface CS and subtracts the three-dimensional approximation surface CS from the phase differential image 12 to obtain a phase The differential image 12 is configured to be corrected.

The example shown in FIG. 9A is a schematic diagram of the phase differential image 12 before correction. The example illustrated in FIG. 9A is the same as the example illustrated in FIG. 6, and thus a detailed description is omitted. The example illustrated in FIG. 9B is a schematic diagram of the phase differential image 12e after the correction processing has been performed by the control unit 6. In the example shown in FIG. 9B, a change in phase value along the horizontal arrow HA in the corrected phase differential image 12e is shown as a graph G5. In the example shown in FIG. 9B, a change in the phase value along the vertical arrow VA in the corrected phase differential image 12e is illustrated as a graph G6. In the graph G5, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the phase change. In the graph G6, the horizontal axis indicates the position in the Y direction, and the vertical axis indicates the phase change.

で は In the example shown in FIG. 9B, the width d3 of the change in the phase value in the graph G5 is smaller than the width d1 of the change in the phase value in the graph G1. As shown in FIG. 9B, the corrected phase differential image 12 e is corrected by the control unit 6 by subtracting the three-dimensional approximate curved surface CS from the phase differential image 12, and the artifact 21 has been removed. . Therefore, unlike the phase value of the graph G3 according to the first comparative example, the shape is such that the phase value of the graph G5 does not substantially change. Further, since the graph G6 shows a change in the phase value in a direction intersecting the artifact 21, the graph G6 has a shape in which the phase value does not substantially change, like the graph G2 and the graph G4 according to the first comparative example.

Next, with reference to FIG. 10, a process of correcting the artifact 21 by the X-ray phase imaging system 100 according to the first embodiment will be described. Note that the correction processing of the artifact 21 is started when a signal for starting the processing of correcting the artifact 21 is input to the control unit 6 by an input operation by a user or the like.

In step S1, the X-ray phase imaging system 100 acquires the pixel values and the position coordinates of the plurality of pixels P in the phase contrast image 10 (phase differential image 12). Next, in step S2, the control unit 6 approximates the intensity distribution of the artifact 21 using a cubic function (Equation (1)). That is, the control unit 6 acquires a three-dimensional approximate curved surface CS that approximates the intensity distribution of the artifact 21. Thereafter, the processing proceeds to step S3.

In step S3, the control unit 6 corrects the phase contrast image 10 (phase differential image 12) based on the approximated artifact 21 (three-dimensional approximated curved surface CS), and ends the process.

(Effect of First Embodiment)
In the first embodiment, the following effects can be obtained.

In the first embodiment, as described above, the X-ray phase imaging system 100 includes the X-ray source 1 that irradiates the subject Q with X-rays, and the detector 2 that detects the X-rays emitted from the X-ray source 1. , An X-ray source 1 and a detector 2, which are irradiated with X-rays from the X-ray source 1 to form a grid image (self-image 30); A plurality of gratings including a second grating 4 for generating moiré fringes M by interference with a grating image (self-image 30) and a phase contrast image 10 (phase differential image) based on a signal detected by the detector 2 The image processing unit 5 that generates the image 12) and a cubic function expressed using the position coordinates of the pixel P in the generated phase contrast image 10 (the phase differential image 12) cause an artifact generated in the phase contrast image 10. Approximate 21 and approximated Arte Based on the facts 21 includes a control unit 6 for correcting a phase contrast image 10 (differential phase image 12), the. Thereby, even if the artifact 21 generated in the phase contrast image 10 (the phase differential image 12) has a complicated shape (distribution) that cannot be approximated by a linear function or a quadratic function, a multi-dimensional function of a third or higher order May be approximated by As a result, even when an artifact 21 that cannot be approximated by a linear function or a quadratic function occurs in the phase contrast image 10 (phase differential image 12), the obtained phase contrast image 10 (phase differential image 12) Deterioration of image quality can be suppressed.

Further, in the first embodiment, as described above, the control unit 6 acquires the intensity distribution of the artifact 21 as a three-dimensional approximate surface CS based on the cubic function, and assigns the acquired three-dimensional approximate surface CS to the acquired three-dimensional approximate surface CS. On the basis of the correction, the phase contrast image 10 (phase differential image 12) is corrected. This makes it possible to obtain a three-dimensional approximated surface CS by using a cubic function, so that the three-dimensional approximated surface CS can more accurately approximate the intensity distribution of the artifact 21. As a result, the deterioration of the image quality of the phase contrast image 10 (the phase differential image 12) due to the artifact 21 can be further suppressed.

Further, in the first embodiment, as described above, the control unit 6 removes an artifact 21 caused by a three-dimensional displacement of a relative position between a plurality of lattices caused by heat fluctuation, and a three-dimensional approximated surface. It is configured to perform correction by CS. Accordingly, even when a complicated positional shift due to thermal fluctuation occurs in the lattice, the artifact 21 can be corrected based on the three-dimensional approximated curved surface CS. As a result, it is possible to prevent the image quality of the phase contrast image 10 (the phase differential image 12) from deteriorating due to the artifact 21 caused by the thermal fluctuation.

In the first embodiment, as described above, the control unit 6 acquires a plurality of pixels P from the phase contrast image 10 (the phase differential image 12), and plots and plots the acquired pixels P. By fitting a cubic function to a plurality of pixels P, a three-dimensional approximated surface CS is obtained. This makes it possible to obtain a three-dimensional approximated surface CS that approximates the intensity distribution of the artifact 21 by plotting the pixels P obtained from the phase contrast image 10 (phase differential image 12). As a result, the calculation cost (calculation load) for approximating the artifact 21 increases as compared with the case where the intensity distribution of the artifact 21 is obtained from all the pixels P of the phase contrast image 10 (the phase differential image 12). Can be suppressed.

In the first embodiment, as described above, the control unit 6 is configured to obtain a three-dimensional approximated surface CS by performing cubic function fitting by least-squares fitting. This makes it possible to easily obtain a three-dimensional approximate curved surface CS by the least squares fitting method. As a result, the artifact 21 generated in the phase contrast image 10 (phase differential image 12) can be easily corrected.

Further, in the first embodiment, as described above, the control unit 6 acquires the three-dimensional approximate curved surface CS based on the pixel P on which the subject Q is not reflected in the phase contrast image 10 (phase differential image 12). The phase contrast image 10 (the phase differential image 12) is corrected by subtracting the three-dimensional approximate curved surface CS from the phase differential image 12. Thereby, the artifact 21 in the background portion can be accurately approximated as compared with the case where the three-dimensional approximated curved surface CS including not only the pixel P in the background portion but also the pixel P in which the subject Q appears is obtained. As a result, it is possible to correct the artifact 21 by using a three-dimensional approximated curved surface CS that accurately approximates the artifact 21. Therefore, it is possible to further suppress the deterioration of the image quality of the phase contrast image 10 (the phase differential image 12). .

In the first embodiment, as described above, the control unit 6 is configured to correct the artifact 21 in the phase differential image 12 as the phase contrast image 10. This makes it possible to correct the artifact 21 in the phase differential image 12 that is imaged using the lattice image (the self image 30) of the first grating 3, and it is possible to prevent the image quality of the phase differential image 12 from deteriorating. It is particularly effective when suppressing.

[Second embodiment]
Next, a configuration of an X-ray phase imaging system 200 (see FIG. 1) according to the second embodiment will be described with reference to FIGS. Unlike the first embodiment in which the artifact 21 generated in the phase contrast image 10 (the phase differential image 12) due to the thermal fluctuation is corrected by the three-dimensional approximated surface CS, the control provided in the X-ray phase imaging system 200 according to the second embodiment The unit 60 (see FIG. 1) is configured to correct the artifact 40 caused by the moire fringes M (see FIG. 11) by using a three-dimensional approximated surface CS. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 1, the X-ray phase imaging system 200 includes an X-ray source 1, a detector 2, a first grating 3, a second grating 4, an image processing unit 5, a control unit 60, and a storage unit. A section 7 and a grid moving mechanism 8 are provided. The X-ray phase imaging system 200 has the same configuration as the X-ray phase imaging system 100 according to the first embodiment, except that the X-ray phase imaging system 200 includes a control unit 60.

In the second embodiment, the control unit 60 uses the three-dimensional approximation surface CS to extract the artifact 40 caused by the moiré fringes M generated when the relative positions of the plurality of lattices deviate from a predetermined positional relationship. It is configured to correct.

FIG. 11 is a schematic diagram of the X-ray image 41 when the relative positions of a plurality of grids are shifted from a predetermined positional relationship. When the relative positions of the plurality of grids are shifted from a predetermined positional relationship, moire fringes M are generated in the X-ray image 41. The moire fringe M has a bright part M1 and a dark part M2. The light portion M1 and the dark portion M2 are formed at predetermined intervals.

When the moire fringes M are formed on the X-ray image 41, as shown in FIG. 12, in the phase contrast image 42 (the absorption image 43, the phase differential image 44, and the dark field image 45) generated by the image processing unit 5, Artifacts 40 due to moire fringes M may be formed. The artifact 40 has a dark part 40a and a light part 40b. As shown in FIG. 12, when the artifact 40 due to the moire fringes M occurs in the phase contrast image 42, the image quality of the phase contrast image 42 deteriorates. Therefore, it is conceivable to perform correction for removing the artifact 40 generated in the phase contrast image 42.

As a configuration for performing the correction for removing the artifact 40, a configuration in which the intensity distribution of the artifact 40 is approximated by a linear function or a quadratic function to correct the phase contrast image 42 is considered. Hereinafter, a configuration for correcting the phase differential image 44 according to the related art will be described with reference to FIGS.

In the second comparative example according to the prior art, the artifact 40 is approximated using a linear function in the phase differential image 44 in which the artifact 40 as shown in FIG. Then, by correcting the phase differential image 44 using the approximated artifact 40, a corrected phase differential image 44a as shown in FIG. 13B is obtained.

In the example shown in FIG. 13A, a change in the phase value along the horizontal arrow HA in the phase differential image 44 is shown as a graph G7. In the graph G7, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the phase change. In the example shown in FIG. 13B, a change in the phase value along the horizontal arrow HA in the corrected phase differential image 44a is illustrated as a graph G8. In the graph G8, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the phase change.

In the example shown in FIG. 13A, since the artifact 40 is generated along the X direction in the phase differential image 44, the graph G7 has a low phase value at a position corresponding to the dark portion 40a of the artifact 40. At the position corresponding to the light portion 40b of the artifact 40, the phase value is high.

In the example shown in FIG. 13B, the width d5 of the phase value change in the graph G8 is smaller than the width d4 of the phase value change in the graph G7. However, the phase value changes at a position corresponding to the dark portion 40a of the artifact 40 and at a position corresponding to the light portion 40b of the artifact 40. This is because the intensity distribution of the artifact 40 is approximated by a linear function, so that the artifact 40 cannot be accurately approximated, and the artifact 40 remains even in the corrected phase differential image 44a. it is conceivable that.

例 The example shown in FIG. 14 is a schematic diagram of a third comparative example according to the related art. The example illustrated in FIG. 14A is the same as that in FIG. 13A, and thus a detailed description is omitted. In the example shown in FIG. 14B, a change in the phase value along the horizontal arrow HA in the corrected phase differential image 44b is shown as a graph G9. In the graph G9, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the phase change.

示 す As shown in FIG. 14B, the width d6 of the phase value change in the graph G9 in the third comparative example is smaller than the width d4 of the phase value change in the graph G7. However, the phase value changes at a position corresponding to the dark portion 40a of the artifact 40 and at a position corresponding to the light portion 40b of the artifact 40. This change in the phase value is considered to be because the artifact 40 cannot be accurately approximated as in the second comparative example, and the artifact 40 remains in the corrected phase differential image 44b.

Therefore, in the second embodiment, the control unit 60 is configured to acquire the artifact 40 generated in the phase differential image 44 as a three-dimensional approximated surface CS based on a cubic function (the above equation (1)). ing. The configuration in which the control unit 60 acquires the three-dimensional approximate curved surface CS is the same as the configuration in which the control unit 6 according to the first embodiment acquires the three-dimensional approximate curved surface CS. Omitted.

例 The example shown in FIG. 15A is the same as the example shown in FIG. The example illustrated in FIG. 15B is a schematic diagram of the phase differential image 44c after the correction processing has been performed by the control unit 60. In the example shown in FIG. 15B, a change in the phase value along the horizontal arrow HA in the corrected phase differential image 44c is illustrated as a graph G10. In the graph G10, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the phase change.

In the example shown in FIG. 15B, the width d7 of the change in the phase value in the graph G10 is smaller than the width d4 of the change in the phase value in the graph G7. The phase value of the graph G10 has a shape that does not substantially change. As shown in FIG. 15B, the corrected phase differential image 44c has been corrected by the control unit 60 by subtracting the three-dimensional approximate curved surface CS from the phase differential image 44, Artifact 40 has been removed. Therefore, the graph G10 has a shape in which the phase value does not substantially change.

Next, the correction processing of the artifact 40 performed by the control unit 60 according to the second embodiment will be described with reference to FIG. Steps for performing the same processes as those performed by the control unit 6 according to the first embodiment will not be described in detail.

In step S4, the control unit 60 acquires the pixel values and the position coordinates of the plurality of pixels P in the X-ray image 41. Thereafter, the processing proceeds to step S5.

In step S5, the control unit 60 approximates the intensity distribution of the artifact 40 caused by the moiré fringes M by a cubic function (Equation (1)). That is, the control unit 60 obtains a three-dimensional approximated surface CS that approximates the intensity distribution of the artifact 40 caused by the moire fringes M. Thereafter, the processing proceeds to step S6.

In step S6, the control unit 60 corrects the phase contrast image 42 (phase differential image 44) based on the approximated artifact 40 (three-dimensional approximated curved surface CS), and ends the process.

The other configurations of the second embodiment are the same as those of the first embodiment.

(Effect of Second Embodiment)
In the second embodiment, the following effects can be obtained.

In the second embodiment, as described above, the control unit 60 converts the artifact 40 caused by the moiré fringes M generated when the relative positions of the plurality of grids deviate from the predetermined positional relationship into a three-dimensional shape. Is corrected by the approximate curved surface CS. Here, the moiré stripe M is a stripe pattern in which a bright portion M1 and a dark portion M2 are repeated at a predetermined cycle. The artifact 40 caused by the moire fringe M has a dark part 40a and a light part 40b corresponding to the bright part M1 and the dark part M2 of the moiré fringe M, respectively. Therefore, the dark portion 40a and the light portion 40b of the artifact 40 caused by the moire fringes M are also repeated at a predetermined cycle. It is considered that the artifact 40 caused by such moiré fringes M is difficult to approximate by a linear function or a quadratic function. Therefore, with the above-described configuration, the artifact 40 caused by the moiré fringes M can be accurately approximated by the three-dimensional approximated surface CS, unlike the case of approximation using a linear function or a quadratic function. As a result, it is possible to suppress the image quality of the phase contrast image 42 (the phase differential image 44) from deteriorating due to the artifact 40 caused by the moiré fringes M.

The other effects of the second embodiment are the same as those of the first embodiment.

(Modification)
It should be understood that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description of the embodiments, and includes all modifications (modifications) within the scope and meaning equivalent to the terms of the claims.

For example, in the first and second embodiments, the first grating 3 is an example of the phase grating as the plurality of gratings, but the present invention is not limited to this. For example, the first grating 3 may be an absorption grating that forms a stripe pattern generated by blocking a part of X-rays as a grating image. With this configuration, the first grating 3 generates X-rays similarly to the interferometer that generates the phase contrast image 10 based on the self-image 30 generated by the interference of the X-rays diffracted by the first grating 3. Even in a non-interferometer that images the subject Q based on the striped pattern of the first grating 3 that is generated by being partially shielded, the artifact 21 (artifact 40) that occurs in the phase contrast image 10 (the phase contrast image 42) is generated. Can be corrected. Further, the striped pattern of the first grating 3 is generated by blocking a part of the X-rays. Therefore, unlike the Talbot interferometer that generates the self-image 30 of the first grating 3, the first grating 3 does not have to be arranged at a predetermined distance (Talbot distance) from the X-ray source 1. As a result, the degree of freedom in the arrangement position of the first grating 3 can be improved.

Further, in the first and second embodiments, the X-ray phase imaging system 100 (200) has been described as an example of the configuration including the first grating 3 and the second grating 4 as a plurality of gratings. Not limited to this. For example, as in an X-ray phase imaging system 300 shown in FIG. 17, a plurality of gratings are arranged between the X-ray source 1 and the first grating 3, and X-rays irradiated with X-rays from the X-ray source 1 are used. May include a third grating 50 for increasing the coherence of the light.

Third grating 50 has a plurality of slits 50a arranged at a predetermined period (pitch) _{p 4} in the X direction and has an X-ray absorbing portion 50b. Each of the slits 50a and the X-ray absorbing portions 50b are formed so as to extend linearly along the Y direction. The slits 50a and the X-ray absorbing portions 50b are formed so as to extend in parallel with each other. The third grating 50 is a so-called absorption grating. The third grating 50 is irradiated with X-rays from the X-ray source 1. The third grating 50 is configured so that the X-rays passing through each slit 50a are used as a line light source corresponding to the position of each slit 50a. That is, the third grating 50 is a grating for increasing the coherence of the X-ray emitted from the X-ray source 1. With the configuration described above, even when the focal size of the X-ray source 1 is large, the third grating 50 improves the coherence of the X-rays, so that the grid image (self-image 30) of the first grating 3 can be formed. Can be caused. As a result, the degree of freedom in selecting the X-ray source 1 can be improved.

In the first and second embodiments, the example in which the grid moving mechanism 8 moves the first grid 3 has been described, but the present invention is not limited to this. For example, the second grid 4 may be configured to be moved in the X direction and imaged by the grid moving mechanism 8. In the case where the third grating 50 is provided as a plurality of gratings as in the X-ray phase imaging system 300 shown in FIG. 17, the third grating 50 is moved in the X direction by the grating moving mechanism 8 for imaging. It may be configured.

Also, in the first and second embodiments, an example of the configuration in which the control unit 6 (60) acquires the three-dimensional approximate curved surface CS by the least squares fitting has been described, but the present invention is not limited to this. The control unit 6 (60) may acquire the three-dimensional approximate surface CS by any method as long as the three-dimensional approximate surface CS can be acquired. For example, the control unit 6 (60) may be configured to obtain a three-dimensional approximated surface CS by an iterative method.

In the first embodiment, the control unit 6 has been described as an example of the configuration in which the phase contrast image 10 corrects the artifact 21 generated in the phase differential image 12, but the present invention is not limited to this. For example, the control unit 6 may be configured to perform a process of correcting an artifact 21 occurring in the dark field image 13 as the phase contrast image 10.

In the second embodiment, the control unit 60 has been described as an example of the configuration in which the artifact 40 generated in the phase differential image 44 is corrected as the phase contrast image 42, but the present invention is not limited to this. For example, the control unit 60 may be configured to correct the artifact 40 occurring in the absorption image 43 or the dark field image 45 as the phase contrast image 42.

In the first and second embodiments, the control unit 6 (60) obtains a three-dimensional approximate surface CS using a cubic function (the above equation (1)) as a cubic or higher-order function. Although an example of the configuration is shown, the present invention is not limited to this. The control unit 6 (60) may obtain the three-dimensional approximate curved surface CS using any function as long as it is a multi-dimensional function of third order or higher. For example, the control unit 6 (60) may be configured to obtain a three-dimensional approximate curved surface CS using a quartic function as a tertiary or higher order function.

Further, in the first embodiment, an example of the configuration in which the control unit 6 corrects the artifact 21 due to the three-dimensional displacement of the relative position between the plurality of lattices caused by heat fluctuation has been described. However, the present invention is not limited to this. For example, the control unit 6 may be configured to correct an artifact caused by a three-dimensional displacement of a relative position between a plurality of grids caused by the subject Q or the like contacting the grid.

Further, in the first and second embodiments, for convenience of explanation, the control process of the control unit 6 (60) is described with reference to an example described using a flow-driven flowchart in which processes are sequentially performed along a process flow. However, the present invention is not limited to this. In the present invention, the control process of the control unit 6 (60) may be performed by an event-driven (event-driven) process of executing a process in event units. In this case, it may be performed in a completely event-driven manner, or may be performed in a combination of event-driven and flow-driven.

Reference Signs List 1 X-ray source 2 Detector 3 First grating 4 Second grating 5 Image processing unit 6, 60 Control unit 10, 44 Phase contrast image 12, 42b Phase differential image 21, 40 Artifact 30 Self image (grating image)
100, 200, 300 X-ray phase imaging system CS Approximate three-dimensional curved surface M Moiré fringe P pixel Q subject

Claims (10)

1. An X-ray source for irradiating the subject with X-rays,
   A detector for detecting X-rays emitted from the X-ray source;
   An X-ray from the X-ray source, which is arranged between the X-ray source and the detector, and which is irradiated with X-rays from the X-ray source, and which interferes with the first grating for forming a grating image and the grating image of the first grating; A plurality of gratings, including a second grating for generating moiré fringes,
   An image processing unit that generates a phase contrast image based on the signal detected by the detector,
   An artifact generated in the phase contrast image is approximated by a third-order or higher-order function represented by using a position coordinate of a pixel in the generated phase contrast image, and the phase is determined based on the approximated artifact. An X-ray phase imaging system, comprising: a control unit that performs a contrast image.
2. The control unit acquires the intensity distribution of the artifact as a three-dimensional approximated surface based on the third-order or higher order function, and performs the phase contrast image based on the acquired three-dimensional approximated surface. The X-ray phase imaging system according to claim 1, wherein the system is configured as follows.
3. The control unit is configured to correct the artifact caused by a three-dimensional displacement of a relative position between the plurality of lattices caused by heat fluctuation by the three-dimensional approximated surface, The X-ray phase imaging system according to claim 2.
4. The control unit is configured to correct, by the three-dimensional approximation surface, the artifact caused by the moiré fringe generated when the relative positions of the plurality of lattices deviate from a predetermined positional relationship. The X-ray phase imaging system according to claim 2, wherein:
5. The control unit acquires the plurality of pixels from the phase contrast image, plots the acquired plurality of pixels, and fits the third-order or higher-order function to the plotted plurality of pixels. 3. The X-ray phase imaging system according to claim 2, wherein the X-ray phase imaging system is configured to acquire the three-dimensional approximate curved surface.
6. 3. The X-ray phase imaging system according to claim 2, wherein the control unit is configured to obtain the three-dimensional approximated surface by performing fitting of the multidimensional function by least-squares fitting. 4.
7. The control unit obtains the three-dimensional approximate surface based on the pixels in which the subject is not reflected in the phase contrast image, and subtracts the three-dimensional approximate surface from the phase contrast image, 3. The X-ray phase imaging system according to claim 2, wherein the system is configured to perform correction of a phase contrast image.
8. The X-ray phase imaging system according to claim 1, wherein the control unit is configured to correct the artifact in a phase differential image as the phase contrast image.
9. The plurality of gratings may include a third grating disposed between the X-ray source and the first grating to increase coherence of X-rays irradiated with X-rays from the X-ray source. Item 2. The X-ray phase imaging system according to Item 1.
10. 2. The X-ray phase imaging system according to claim 1, wherein the first grating is an absorption grating that forms a stripe pattern generated by blocking a part of X-rays as the grating image. 3.

Images