JP7031371B2 - X-ray phase difference imaging system - Google Patents

Description

The present invention relates to an X-ray phase difference imaging system.

Conventionally, an X-ray phase difference imaging system is known (see, for example, Patent Document 1).

Patent Document 1 discloses an X-ray phase difference imaging system that captures a phase contrast image by detecting moire fringes generated by translating a source grid. The X-ray phase difference imaging system disclosed in Patent Document 1 includes an X-ray phase difference imaging device including an X-ray source, a source grid, a phase grid, an absorption grid, and a detector. This X-ray phase difference imager is a so-called Talbot low interferometer. Further, the X-ray phase difference imaging system disclosed in Patent Document 1 calculates a translation signal for translating the source grid so that the moire fringes have a predetermined period, and the source grid is based on the calculated translation signal. Is configured to image a phase contrast image by translating.

Here, in the Talbot low interferometer, the phase grid is irradiated with X-rays that have passed through the source grid. The irradiated X-rays are diffracted as they pass through the phase grid, forming a self-image of the phase grid at a position separated by a predetermined distance (Talbot distance). The period of the self-image of the formed phase grid is so small that it cannot be detected by a general-purpose detector. Therefore, in the Talbot low interferometer, the absorption grid is arranged at the position where the self-image of the phase grid is formed, and the moire fringes that can be detected by a general-purpose detector are formed. In addition, the Talbot low interferometer detects a slight change in the self-image by performing multiple imaging (striped scanning imaging) while translating any one of the grids in the periodic direction of the grid, and detects a phase contrast image. Can be obtained.

International Publication No. 2014/030115

However, in the Talbot low interferometer described in Patent Document 1, when the relative positions of the phase grid and the absorption grid deviate from the design position, unintended moire fringes occur. In this case, since the unintended moire fringes are detected by the detector, there is an inconvenience that an artifact (virtual image) is generated in the captured image due to the unintended moire fringes. The "unintended moire fringe" is a moire fringe caused by a deviation in the relative position between the phase grid and the absorption grid, which occurs when the subject is not placed. Further, the "artifact (virtual image)" is a distortion of the phase contrast image or a deterioration of the image quality of the phase contrast image caused by unintended moire fringes.

Therefore, the Talbot-Lago interferometer adjusts the relative position between the phase grid and the absorption grid before imaging. However, in order to adjust the misalignment of the grid, the measurer must visually determine the misalignment in multiple directions such as the translational direction and the rotational direction from the shape of the complicated moire fringes. Therefore, there is a problem that knowledge and experience are required for the measurer and it takes time to adjust the grid position.

The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to be able to adjust the displacement of the lattice position without depending on the knowledge and experience of the measurer. At the same time, it is an object of the present invention to provide an X-ray phase difference imaging system capable of shortening the adjustment time.

In order to achieve the above object, the X-ray phase difference imaging system in the first aspect of the present invention includes an X-ray source, a detector for detecting X-rays emitted from the X-ray source, and an X-ray source and detection. Interference fringes with the self-image of the first lattice, which is placed between the vessel and is irradiated with X-rays from the X-ray source to form a self-image and the X-rays that have passed through the first lattice. A grid misalignment acquisition unit that acquires grid misalignment based on a plurality of grids including a second grid for forming the X-ray and a Fourier transform image obtained by Fourier transform on the interference fringe image detected by the detector. And prepare.

Here, if the relative positions of the first grid and the second grid deviate from the design positions, unintended moire fringes occur. Therefore, in the Fourier transform image, in addition to the peak caused by the self-image of the first lattice, a peak caused by an unintended moire fringe is generated. According to the present invention, since the grid position shift acquisition unit acquires the grid position shift based on the Fourier transform image, the grid position can be adjusted based on the obtained grid position shift. Therefore, it is possible to adjust the deviation of the grid position without depending on the knowledge and experience of the measurer, and it is possible to shorten the adjustment time.

The X-ray phase difference imaging system in the first aspect is preferably further provided with an adjusting mechanism for adjusting the misalignment of at least one of the first grid and the second grid, and the adjusting mechanism is the grid misalignment. It is configured to correct the misalignment of the grid based on the misalignment of the grid acquired by the acquisition unit. With this configuration, the adjustment mechanism can automatically correct the grid misalignment based on the grid misalignment acquired by the grid misalignment acquisition unit, so it depends on the knowledge and experience of the measurer. It is possible to adjust the deviation of the position of the grid more easily without doing so. Further, since the adjustment mechanism can automatically correct the misalignment of the grid, the adjustment time can be further shortened.

In the X-ray phase difference imaging system in the first aspect, preferably, the grid misalignment acquisition unit acquires the grid misalignment based on at least one of the distance between the peaks of the Fourier transformed image and the magnitude of the peak. It is configured to do. Here, the distance between the peaks of the Fourier transformed image is a quantity representing the position shift of the grid in the irradiation direction of X-rays or the position shift of the grid in the rotation direction around the optical axis direction of X-rays, which will be described later. Further, the peak size of the Fourier transformed image is not the intensity of the detected frequency component, but the peak size in the Fourier image. The size of the peak of the Fourier transformed image is the rotation direction around the central axis in the vertical direction orthogonal to the optical axis direction of the X-ray of the lattice, which will be described later, or the horizontal central axis perpendicular to the optical axis direction of the X-ray of the lattice, which will be described later. It is a quantity representing the positional deviation of the lattice in the rotation direction of. With this configuration, the position shift of the grid can be obtained by performing image processing on the Fourier transformed image. As a result, the position shift of the grid can be automatically acquired without the measurer visually confirming the moire fringes.

In the X-ray phase difference imaging system in the first aspect, preferably, the grid position shift acquisition unit is the optical axis of X-rays based on the distance between the 0th-order peak and the 1st-order peak in the Fourier transform image. It is configured to acquire the misalignment of the first grid or the second grid in the direction, or the misalignment of the first grid or the second grid in the rotation direction around the optical axis direction of the X-ray. With this configuration, the positional deviation of the first grid or the second grid in the optical axis direction of X-rays is replaced with the magnitude of the distance between the 0th-order peak and the 1st-order peak of the Fourier transformed image. be able to. As a result, by adjusting the position of the grid so that the distance between the 0th-order peak and the 1st-order peak of the Fourier transformed image becomes small, the position shift of the first grid or the second grid in the optical axis direction of the X-ray is performed. Can be easily adjusted. Alternatively, the misalignment of the first grid or the second grid in the rotation direction around the optical axis of the X-ray is replaced with the magnitude of the distance between the 0th-order peak and the 1st-order peak of the Fourier transformed image. Can be done. As a result, by adjusting the position of the grid so that the distance between the 0th-order peak and the 1st-order peak of the Fourier-transformed image becomes smaller, the first grid or the second grid in the rotation direction around the optical axis of the X-ray can be obtained. The misalignment of the grid can be easily adjusted.

In the X-ray phase difference imaging system in the first aspect, preferably, the grid misalignment acquisition unit has a large amount of grid misalignment based on the distance between the 0th-order peak and the 1st-order peak in the Fourier transformed image. It is configured to get the image. With this configuration, the magnitude of the misalignment of the grid can be obtained. As a result, the positional deviation of the first grid or the second grid can be adjusted more easily and accurately by adjusting the position of the grid using the acquired magnitude of the positional deviation as the correction amount.

In the X-ray phase difference imaging system in the first aspect, preferably, the lattice position shift acquisition unit is the X-ray of the first lattice or the second lattice based on the size of the first-order peak in the Fourier transformed image. It is configured to acquire the positional deviation of the first grid or the second grid in the rotation direction around the central axis in the vertical direction or the horizontal direction orthogonal to the optical axis direction. With this configuration, the displacement of the first grid or the second grid in the rotation direction around the central axis in the vertical direction orthogonal to the optical axis direction of the X-rays of the first grid or the second grid can be detected in the Fourier transform image. It can be grasped by replacing it with the size of the primary peak. As a result, by adjusting the grid so that the size of the primary peak of the Fourier transformed image becomes smaller, the rotation around the central axis in the vertical direction orthogonal to the optical axis direction of the X-ray of the first grid or the second grid. The misalignment of the first grid or the second grid in the direction can be easily adjusted. Alternatively, the displacement of the first grid or the second grid in the rotation direction around the central axis in the horizontal direction orthogonal to the optical axis direction of the X-ray of the first grid or the second grid is the size of the first-order peak of the Fourier transformed image. It can be replaced with a grid and grasped. As a result, by adjusting the grid so that the size of the primary peak of the Fourier transformed image becomes smaller, the rotation around the central axis in the horizontal direction orthogonal to the optical axis direction of the X-ray of the first grid or the second grid. The misalignment of the first grid or the second grid in the direction can be easily adjusted.

In the X-ray phase difference imaging system in the first aspect, preferably, the grid misalignment acquisition unit is configured to acquire the presence or absence of grid misalignment based on the size of the first-order peak in the Fourier transformed image. Has been done. With this configuration, it is possible to automatically determine whether or not the position of the first grid or the second grid is displaced by the image processing of the Fourier transformed image.

In this case, preferably, the grid position shift acquisition unit has the size of the first-order peak in the Fourier transform image based on a plurality of Fourier transform images captured by rotating either the first grid or the second grid. Is configured to acquire the amount of rotation at or near the minimum value as the amount of misalignment. With this configuration, it is possible to acquire the relative position of the lattice in which the displacement of the lattice is minimized based on a plurality of Fourier transform images. As a result, the misalignment of the first grid or the second grid can be easily and accurately adjusted.

The X-ray phase difference imaging system in the first aspect is preferably further provided with a noise removal processing unit that removes frequency noise from the image detected by the detector before performing the Fourier transform. With this configuration, it is possible to remove the artifacts (virtual images) obtained by analyzing the finite space when performing the Fourier transform and the artifacts (virtual images) derived from the detector before performing the Fourier transform. As a result, the peak caused by the misalignment of the lattice obtained by the Fourier transform can be detected more accurately.

Further, the X-ray phase difference imaging system according to the second aspect of the present invention is arranged between the X-ray source, the detector that detects the X-rays emitted from the X-ray source, and the X-ray source and the detector. Then, X-rays are irradiated from the X-ray source to form a self-image, and X-rays that have passed through the first lattice are irradiated to form an interference fringe between the self-image of the first lattice. It is provided with a plurality of grids including a second grid and a grid misalignment acquisition unit that acquires the misalignment of the grid based on the Fourier transform image obtained by the Fourier transform on the interference fringe image detected by the detector. The misalignment acquisition unit is configured to acquire the misalignment of the lattice in the optical axis direction of the X-ray based on the following equation (1) or equation (2).

Here, R is the distance between the X-ray source and the first lattice, p2 is the period of the second lattice, and dx is between the 0th-order peak and the 1st-order peak in the Fourier transformed image. It is the distance, L is the distance between the X-ray source and the second lattice, Nx is the number of pixels of the Fourier transformed image in the left-right direction in the plane orthogonal to the optical axis direction of the X-ray, and also. , Sx are the pixel sizes of the detector in the left-right direction.

The X-ray phase difference imaging system according to the third aspect of the present invention is arranged between the X-ray source, the detector that detects the X-rays emitted from the X-ray source, and the X-ray source and the detector. A second lattice for forming a self-image by irradiating X-rays from an X-ray source and a second lattice for forming an interference fringe between the X-rays passing through the first lattice and irradiating with the self-image of the first lattice. A grid misalignment acquisition unit that acquires grid misalignment based on a plurality of grids including a grid, a Fourier transform image obtained by Fourier transform on the interference fringe image detected by the detector, and Fourier on the interference fringe image. It is provided with an image processing unit that removes noise generated in the Fourier transform image by using the Fourier transform reference image obtained in advance by the conversion. With this configuration, it is possible to remove noise generated in the Fourier transformed image, so that the position and magnitude of the primary peak can be accurately acquired. As a result, the peak caused by the misalignment of the lattice obtained by the Fourier transform can be detected more accurately, so that the accuracy of adjusting the misalignment of the lattice can be improved. The noise generated in the Fourier transformed image is the noise generated in the Fourier transformed image due to the pixel defect of the detector, the sensitivity unevenness caused by the X-ray irradiation direction, the lattice defect, and the like.

In the X-ray phase difference imaging system in the third aspect, the image processing unit is preferably configured to remove noise by subtracting the Fourier transform reference image from the Fourier transform image. With this configuration, unlike random noise, noise in the Fourier transform image, which does not change easily over time, can be easily removed.

In the X-ray phase difference imaging system in the third aspect, preferably, the Fourier transform reference image is an image in which the position of the first-order peak is different from that of the Fourier-transformed image, or the first-order peak of the Fourier-transformed image is deleted. It is the obtained image. By using such a Fourier transform reference image, when the noise of the Fourier transform image is removed, it is possible to suppress the removal of the first-order peak in the Fourier transform image together with the noise by the first-order peak of the Fourier transform reference image. Can be done. As a result, noise in the Fourier transformed image can be removed regardless of the position of the first-order peak in the Fourier transformed image.

According to the present invention, as described above, it is possible to adjust the deviation of the grid position without depending on the knowledge and experience of the measurer, and it is possible to shorten the adjustment time. A phase difference imaging system can be provided.

It is a figure which shows the whole structure of the X-ray phase difference imaging system by 1st Embodiment of this invention. It is a block diagram which shows the structure of the X-ray phase difference imaging system by 1st Embodiment of this invention. It is a perspective view for demonstrating the misalignment of the grid of the X-ray phase difference imaging system by 1st Embodiment of this invention. It is a figure for demonstrating the structure of the adjustment mechanism of the X-ray phase difference imaging system by 1st Embodiment of this invention. It is a flowchart at the time of adjusting the position shift of the grid of the X-ray phase difference imaging system by 1st Embodiment of this invention. It is a figure which shows the image (A) before the position shift adjustment of a grid, and the image (B) after the position shift adjustment of a grid. It is an enlarged view when the 1st grid is misaligned in the Z direction. It is an enlarged view when the 2nd grid is misaligned in the Z direction. It is a figure for demonstrating an unintended moire fringe and a Fourier transform image which occur when the 1st grid is misaligned in the Z direction. It is an enlarged view of the Fourier transform image when the 1st lattice causes the position shift in the Z direction. It is a figure for demonstrating the unintended moire fringe and the Fourier transform image which occur when the 1st lattice causes the position shift in the rotation direction about the Z direction axis. It is an enlarged view of the Fourier transform image when the position shift in the rotation direction about the Z direction axis occurs in the 1st lattice. It is a figure for demonstrating the unintended moire fringe and the Fourier transform image which occur when the 1st lattice causes the positional displacement in the rotation direction around the central axis of X direction. It is an enlarged view of the Fourier transform image when the 1st lattice is displaced in the rotation direction around the central axis in the X direction. It is a figure for demonstrating an unintended moire fringe and a Fourier transform image which occur when the 1st lattice causes the position shift in the rotation direction around the central axis of Y direction. It is an enlarged view of the Fourier transform image when the 1st lattice is displaced in the rotation direction around the central axis in the Y direction. It is a schematic diagram of the interference fringe image in which noise was generated. It is a schematic diagram of a Fourier transform image in which noise is generated. It is a schematic diagram of a Fourier transform reference image. It is a schematic diagram of the Fourier transform image from which noise was removed. It is a flowchart at the time of adjusting the position shift of the grid of the X-ray phase difference imaging system by 2nd Embodiment of this invention. It is a schematic diagram of the Fourier transform reference image generated by the image processing unit 10 by the modification of 2nd Embodiment.

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

[First Embodiment]
The configuration of the X-ray phase difference imaging system 100 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 16.

(Configuration of X-ray phase difference imaging system)
As shown in FIG. 1, the X-ray phase difference imaging system 100 is a device that uses the phase difference of X-rays that have passed through the subject T to image the inside of the subject T. Further, the X-ray phase difference imaging system 100 is a device that images the inside of the subject T by utilizing the Talbot effect. The X-ray phase difference imaging system 100 can be used for imaging the inside of a subject T as an object, for example, in a non-destructive inspection application. Further, the X-ray phase difference imaging system 100 can be used for imaging the inside of the subject T as a living body, for example, in medical applications.

FIG. 1 is a top view of the X-ray phase difference imaging system 100. As shown in FIG. 1, the X-ray phase difference imaging system 100 includes an X-ray source 1, a third grid 2, a first grid 3, a second grid 4, a detector 5, and a grid misalignment acquisition unit. 6. The adjustment mechanism control unit 7 and the adjustment mechanism 8 are provided. In the present specification, the direction from the X-ray source 1 toward the third lattice 2 is the Z direction. Further, the left-right direction in the plane orthogonal to the Z direction is defined as the X direction. Further, the vertical direction in the plane orthogonal to the Z direction is defined as the Y direction. The X direction is an example of the "horizontal direction perpendicular to the optical axis direction of X-rays" in the claims. Further, the Y direction is an example of the "vertical direction orthogonal to the optical axis direction of X-rays" in the claims. Further, the Z direction is an example of the "optical axis direction of X-rays" in the claims.

The X-ray source 1 is configured to generate X-rays by applying a high voltage and to irradiate the generated X-rays in the Z direction.

The third lattice 2 has a plurality of X-ray transmitting portions 2a and X-ray absorbing portions 2b arranged in the X direction at a predetermined period (pitch) p0. Each X-ray transmitting portion 2a and X-ray absorbing portion 2b are configured to extend in the Y direction.

The third grid 2 is installed between the X-ray source 1 and the first grid 3, and X-rays are emitted from the X-ray source 1. The third grid 2 is configured to use the X-rays that have passed through each X-ray transmitting portion 2a as a line light source corresponding to the position of each X-ray transmitting portion 2a. As a result, the third lattice 2 can increase the coherence of X-rays emitted from the X-ray source 1.

The first grid 3 has a plurality of slits 3a arranged in the X direction with a predetermined period (pitch) p1 and an X-ray phase changing portion 3b. Each of the slits 3a and the X-ray phase changing portion 3b is formed so as to extend in the Y direction.

The first grid 3 is installed between the third grid 2 and the second grid 4, and is irradiated with X-rays that have passed through the third grid 2. The first grid 3 is provided to form a self-image 30 by the Talbot effect. When X-rays having coherence pass through the lattice in which the slit is formed, an image of the lattice (self-image 30) is formed at a position separated from the lattice by a predetermined distance (Talbot distance). This is called the Talbot effect.

The second lattice 4 has a plurality of X-ray transmitting portions 4a and X-ray absorbing portions 4b arranged in the X direction with a predetermined period (pitch) p2. The third grid 2, the first grid 3, and the second grid 4 have different roles, but the X-ray transmitting portion 2a, the slit 3a, and the X-ray transmitting portion 4a each transmit X-rays. Further, the X-ray absorbing unit 2b and the X-ray absorbing unit 4b each play a role of shielding X-rays, and the X-ray phase changing unit 3b changes the phase of X-rays depending on the difference in the refractive index from the slit 3a.

The second grid 4 is arranged between the first grid 3 and the detector 5, and is irradiated with X-rays that have passed through the first grid 3. Further, the second grid 4 is arranged at a position separated from the first grid 3 by a Talbot distance. The second grid 4 interferes with the self-image 30 of the first grid 3 to form moire fringes 12 (see FIG. 6A) on the detection surface of the detector 5.

The detector 5 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 5 is, for example, an FPD (Flat Panel Detector). The detector 5 is composed of a plurality of conversion elements (not shown) and pixel electrodes (not shown) arranged on the plurality of conversion elements. The plurality of conversion elements and pixel electrodes are arranged in an array in the X direction and the Y direction at a predetermined period (pixel pitch). Further, the detector 5 is configured to output the acquired image signal to the grid position deviation acquisition unit 6.

As shown in FIG. 2, the grid position shift acquisition unit 6 includes a control unit 9, an image processing unit 10, and a noise reduction processing unit 11. The control unit 9 is configured to Fourier transform the image signal output from the detector 5 to generate a Fourier transform image 14 (see FIG. 9). Further, the control unit 9 is configured to acquire the positional deviation of the first grid 3 or the second grid 4 and output it to the adjustment mechanism control unit 7.

The image processing unit 10 is configured to acquire the distance between peaks and the magnitude of peaks in the Fourier transform image 14 generated by the control unit 9. The peak size is the size of the peak in the Fourier transformed image 14, and is determined by the degree of dispersion of the frequency peak after the Fourier transform. Further, the size of the peak is determined by the width of the frequency peak from the maximum amplitude of the frequency peak after the Fourier transform to a predetermined amplitude. In the first embodiment, the predetermined amplitude has the width (so-called half width) of the frequency peak up to 50% of the maximum amplitude as the peak size. Further, the noise reduction processing unit 11 is configured to remove frequency noise from the image detected by the detector 5 before performing the Fourier transform. Specifically, the noise reduction processing unit 11 is configured to perform any one or a plurality of filtering by a window function, dark correction, gain correction, and defect correction. In the first embodiment, the noise reduction processing unit 11 is configured to perform all filtering and correction.

The filtering by the window function is a process of applying a specific window function to the actual data of the acquired image to remove the discontinuity of the boundary. This makes it possible to remove artifacts (virtual images) from the image after the Fourier transform by analyzing the finite space. The specific window function is, for example, a Hanning function or a Humming function.

Further, the dark correction is a process of subtracting an image (dark image) taken without irradiating X-rays from an image taken with X-rays. As a result, the artifact (virtual image) derived from the detector 5 can be removed from the image after the Fourier transform.

Further, the gain correction is a process of dividing an image (air image) taken by irradiating X-rays without placing a grid from an image taken with a grid. As a result, the artifact (virtual image) derived from the detector 5 can be removed from the image after the Fourier transform.

Further, the defect correction is a process of correcting a defective portion where the sensitivity of the detector 5 is significantly reduced by an averaging process with surrounding pixels or the like. As a result, the artifact (virtual image) derived from the detector 5 can be removed from the image after the Fourier transform.

The control unit 9 and the noise reduction processing unit 11 include, for example, a CPU (Central Processing Unit), respectively. Further, the image processing unit 10 includes, for example, a GPU (Graphics Processing Unit).

The adjustment mechanism control unit 7 outputs a signal for correcting the misalignment of the first grid 3 or the second grid 4 based on the misalignment of the first grid 3 or the second grid 4 output from the grid misalignment acquisition unit 6. It is configured to output to the adjustment mechanism 8. The adjustment mechanism control unit 7 includes, for example, a CPU.

The adjusting mechanism 8 is configured to correct the positional deviation of the first grid 3 or the second grid 4 based on the signal for correcting the positional deviation output from the adjusting mechanism control unit 7.

Next, with reference to FIGS. 3 and 4, a configuration in which the adjusting mechanism 8 adjusts the positional deviation of the first grid 3 or the second grid 4 will be described. Here, as shown in FIG. 3, the misalignment of the first grid 3 or the second grid 4 mainly includes the misalignment in the Z direction, the misalignment in the rotation direction Rz around the Z direction axis, and the center in the X direction. There is a misalignment in the rotation direction Rx around the axis and a misalignment in the rotation direction Ry around the central axis in the Y direction.

As shown in FIG. 4, the adjusting mechanism 8 includes a base unit 80, a stage support unit 81, a stage 82 on which a grid is placed, a first drive unit 83, a second drive unit 84, and a third drive unit 85. And a fourth drive unit 86 and a fifth drive unit 87. The first to fifth drive units include, for example, motors and the like, respectively. Further, the stage 82 is composed of a connecting portion 82a, a rotating portion 82b around the Z-axis direction, and a rotating portion 82c around the X-axis direction.

The first drive unit 83, the second drive unit 84, and the third drive unit 85 are each provided on the upper surface of the base unit 80. The first drive unit 83 is configured to reciprocate the stage support unit 81 in the Z direction. Further, the second drive unit 84 is configured to rotate the stage support unit 81 around the Y-axis direction. Further, the third drive unit 85 is configured to reciprocate the stage support unit 81 in the X direction. The stage support portion 81 is connected to the connecting portion 82a of the stage 82, and the stage 82 also moves as the stage support portion 81 moves.

Further, the fourth drive unit 86 is configured to reciprocate the rotation unit 82b around the axis in the Z direction in the X direction. The bottom surface of the Z-direction axis rotating portion 82b is formed in a convex curved surface shape toward the connecting portion 82a, and the stage 82 is rotated around the central axis in the Z direction by being reciprocated in the X direction. It is configured as follows. Further, the fifth drive unit 87 is configured to reciprocate the rotating unit 82c around the X-axis direction in the Z direction. The bottom surface of the rotation portion 82c around the X-axis direction is formed in a convex curved surface shape toward the rotation portion 82b around the Z-direction axis, and the stage 82 is reciprocated in the Z-direction to move the stage 82 to the central axis in the X-direction. It is configured to rotate around.

Therefore, the adjusting mechanism 8 is configured so that the grid can be adjusted in the Z direction by the first driving unit 83. Further, the adjusting mechanism 8 is configured so that the lattice can be adjusted in the rotation direction (Ry direction) around the Y-axis direction by the second drive unit 84. Further, the adjusting mechanism 8 is configured so that the grid can be adjusted in the X direction by the third drive unit 85. Further, the adjusting mechanism 8 is configured so that the lattice can be adjusted in the rotation direction (Rz direction) around the Z direction axis by the fourth drive unit 86. Further, the adjusting mechanism 8 is configured so that the grid can be adjusted in the rotation direction (Rx direction) around the X-axis direction by the fifth drive unit 87. The reciprocating motion in each axial direction is, for example, several mm. Further, the rotatable angles of the rotation direction Rx around the X-axis direction, the rotation direction Ry around the Y-axis direction, and the rotation direction Rz around the Z-direction axis are, for example, several degrees, respectively.

(Adjustment method of grid position deviation)
Next, with reference to FIGS. 5 to 16, the configuration in which the X-ray phase difference imaging system 100 in the first embodiment adjusts the positional deviation of the first grid 3 or the second grid 4 will be described.

First, with reference to FIGS. 5 and 6, the overall flow of the method in which the X-ray phase difference imaging system 100 according to the first embodiment adjusts the grid will be described.

In step S1, the detector 5 acquires an image of the self-image 30 of the first grid 3 and the second grid 4. In step S1, the image is acquired without arranging the subject T. Here, if the relative positions of the first grid 3 and the second grid 4 are different from the designed positions, unintended moire fringes 12 (see FIG. 6A) occur.

Next, in step S2, the noise reduction processing unit 11 removes frequency component noise from the image acquired in step S1. That is, the noise reduction processing unit 11 performs filtering, dark correction, gain correction, and defect correction by the window function.

Next, in step S3, the control unit 9 performs a two-dimensional Fourier transform on the image subjected to the noise removal processing in step S2 to generate a Fourier transform image 14 (see FIG. 10).

Next, in step S4, the image processing unit 10 determines the distance between the 0th-order peak 15 (see FIG. 10) and the 1st-order peak 16 (see FIG. 10) and the 1st-order peak 16 in the Fourier transformed image 14. Get the size. Here, the 0th-order peak 15 is a peak derived from a low frequency component in the image. The primary peak 16 is a peak derived from the frequency component of the unintended moire fringes 12 generated by the positional deviation between the self-image 30 of the first grid 3 and the second grid 4.

Next, in step S5, the control unit 9 acquires the position shift of the grid based on the size of the primary peak 16. If there is no misalignment of the grid, the process proceeds to step S6. If there is a misalignment of the grid, the process proceeds to step S7.

In step S6, the control unit 9 acquires the misalignment of the grid based on the distance between the 0th-order peak 15 and the 1st-order peak 16. If there is no misalignment of the grid, the process ends here. If there is a misalignment of the grid, the process proceeds to step S7.

In step S7, the control unit 9 outputs a signal for correcting the misalignment of the grid to the adjustment mechanism control unit 7. Then, the adjustment mechanism control unit 7 adjusts the position shift of the first grid 3 or the second grid 4 via the adjustment mechanism 8 based on the signal for correcting the position shift of the grid. After that, the process proceeds to step S1.

In the first embodiment, the X-ray phase difference imaging system 100 has a position shift in the rotation direction Rx around the central axis in the X direction and a Y direction based on the position shift of the grid acquired by the grid position shift acquisition unit 6. It is configured to adjust the positional deviation in the rotation direction Ry around the central axis of. After that, it is configured to adjust the positional deviation in the rotation direction Rz around the Z direction axis and the positional deviation in the Z direction.

In the first embodiment, the X-ray phase difference imaging system 100 steps until the amount of misalignment (σx, σy and dx, dy) of the first grid 3 or the second grid 4 becomes equal to or less than the threshold value (th1 and th2). It is configured to repeat S1 to step S7.

FIG. 6A is a diagram showing an example of an image in the case where a grid misalignment is present. Further, FIG. 6B is a diagram showing an example after adjusting the positional deviation of the grid. Before adjusting the misalignment of the grid, as shown in FIG. 6A, the self-image 30 of the first grid 3 and the second grid 4 cause unintended moire fringes 12 in the acquired image. In this case, by adjusting the misalignment of the grid, unintended moire fringes 12 are removed from the acquired image as shown in FIG. 6 (B).

(Acquisition of misalignment of the first grid or the second grid)
Next, with reference to FIGS. 1, 3 and 7 to 16, a configuration for acquiring the positional deviation of the first grid 3 or the second grid 4 will be described.

<Acquisition of misalignment in the Z direction>
First, with reference to FIGS. 1 and 7 to 10, a configuration will be described in which the grid misalignment acquisition unit 6 in the first embodiment acquires the misalignment of the first grid 3 or the second grid 4 in the Z direction.

In the first embodiment, the grid misalignment acquisition unit 6 determines the first grid 3 or the second grid 4 in the Z direction based on the distance between the 0th-order peak 15 and the 1st-order peak 16 in the Fourier transform image 14. It is configured to get the misalignment of.

Here, as shown in FIG. 1, when the first grid 3 and the second grid 4 are arranged so that the distance between the first grid 3 and the second grid 4 in the Z direction is the Talbot distance (ZT). The period p3 of the self-image 30 of the first grid 3 and the period p2 of the second grid 4 are equal to each other. Therefore, unintended moire fringes do not occur.

However, as shown in FIGS. 7 and 8, when the distance between the first grid 3 and the second grid 4 in the Z direction deviates from the Talbot distance (ZT), the period p3 of the self-image 30 of the first grid 3 becomes. Change. Therefore, the moire fringes 12a (see FIG. 9) are observed due to the periodic difference between the period p3 of the self-image 30 of the first lattice 3 and the period p2 of the second lattice 4.

As shown in FIG. 9, when there is no positional deviation in the first grid 3 (ΔZ1 is 0), the period p3 of the self-image 30a of the first lattice 3 and the period p2 of the second lattice 4 are equal to each other. Moire fringes 12a are not formed in the acquired image. Further, when there is no positional deviation in the first lattice 3 (ΔZ1 is 0), only the 0th-order peak 15a is detected in the Fourier transform image 14a. Further, in the moire fringe image 13a, the moire fringes as the first grid 3 moves away from the normal position (the position where the distance between the first grid 3 and the second grid 4 is the Talbot distance ZT) (the absolute value of ΔZ1 increases). The cycle of 12a becomes finer. Further, in the Fourier transform image 14a, as the first grid 3 moves away from the normal position (the position where the distance between the first grid 3 and the second grid 4 is the Talbot distance ZT) (the absolute value of ΔZ1 increases), the 0th order is obtained. The distance dx between the peak 15a and the primary peak 16a increases. The unit of the misalignment amount ΔZ1 of the first grid 3 in FIGS. 9 and 10 is “mm (millimeter)”.

FIG. 10 is an example of an enlarged view of the Fourier transform image 14a when the displacement amount ΔZ1 in the Z direction of the first grid 3 is 0.50 mm. dx is the distance in the X direction between the 0th-order peak 15a and the 1st-order peak 16a. In the first embodiment, the grid misalignment acquisition unit 6 acquires the misalignment of the first grid 3 or the second grid 4 in the Z direction based on the distance dx between the 0th-order peak 15a and the 1st-order peak 16a. It is configured to do. Hereinafter, a detailed configuration in which the grid misalignment acquisition unit 6 acquires the misalignment of the first grid 3 or the second grid 4 will be described.

As shown in FIG. 6, when the first grid 3 is displaced by ΔZ1 in the Z direction, the period p3 of the self-image 30a of the first grid 3 is expressed by the following equation (1).

At this time, on the detection surface of the detector 5, moire fringes 12a vibrating in the X direction are observed due to the periodic difference between the self-image 30a and the second grid 4. The period pmx of the moire fringes 12a is expressed by the following equation (2).

ここで、Ｎｘは取得画像のＸ方向の画素数である。また、ｓｘは、検出器５のＸ方向の画素サイズである。 On the other hand, assuming that the position of the primary peak 16a in the X direction (distance between the 0th-order peak 15a) when the moire fringe image 13a is Fourier transformed is dx, the period pmx of the moire fringe 12a is the following equation ( There is a relationship shown in 3).

Here, Nx is the number of pixels in the X direction of the acquired image. Further, sx is the pixel size of the detector 5 in the X direction.

ここで、第２格子４の周期ｐ２は、位置ずれがない（ΔＺ１＝０である）場合の自己像３０ａの周期ｐ３と等しくなるため、以下の式（５）により表される。

By eliminating pmx from the above equations (2) and (3), the following equation (4) is obtained.

Here, since the period p2 of the second lattice 4 is equal to the period p3 of the self-image 30a when there is no positional deviation (ΔZ1 = 0), it is expressed by the following equation (5).

By substituting the above equations (1) and (5) into the above equation (4), the following equation (6) is obtained.

By modifying the above equation (6), the following equation (7) can be obtained.

As can be seen from the above equation (7), the amount of misalignment ΔZ1 in the Z direction of the first grid 3 can be calculated by measuring dx.

On the other hand, as shown in FIG. 8, when the second grid 4 is deviated by ΔZ2 in the Z direction, the period p3 of the self-image 30a of the first grid 3 is expressed by the following equation (8).

Since the period p2 of the second lattice 4 is the above equation (5), the following equation (9) can be obtained by substituting the above equations (5) and (8) into the above equation (4).

By modifying the above equation (9), the following equation (10) is obtained.

As can be seen from the above equation (10), the misalignment amount ΔZ2 in the Z direction of the second grid 4 can also be calculated by measuring dx in the same manner as the misalignment amount ΔZ1 in the Z direction of the first grid 3. can. Then, the control unit 9 outputs the position shift amount ΔZ1 in the Z direction of the first grid 3 or the position shift amount ΔZ2 in the Z direction of the second grid 4 to the adjustment mechanism control unit 7 as a signal for correcting the position shift.

<Acquisition of positional deviation in the rotation direction around the Z direction axis>
Next, with reference to FIGS. 3, 11 and 12, the grid position shift acquisition unit 6 in the first embodiment acquires the position shift in the rotation direction Rz around the Z direction axis of the first grid 3. explain. The unit of the misalignment amount ΔRz1 in the rotation direction Rz around the Z direction axis of the first grid 3 of FIGS. 11 and 12 is “degree”.

In the first embodiment, the grid misalignment acquisition unit 6 is configured to acquire the misalignment of the first grid 3 or the second grid 4 in the rotation direction Rz around the Z direction axis based on the Fourier transform image 14b. ing. The rotation direction Rz around the Z-direction axis is an example of the "rotational direction around the optical axis direction of X-rays" in the claims.

As shown in FIG. 3, when the first grid 3 and the second grid 4 are not displaced in the rotation direction Rz around the Z direction axis, the periodic direction of the self-image 30 of the first grid 3 and the second grid 4 Since it coincides with the periodic direction, unintended moire fringes 12 are not observed. However, when the first grid 3 is displaced by ΔRz1, the self-image 30b is also formed at an angle as shown in the example of FIG. 11, so that the observed moire fringes 12b are formed in the Y direction. Further, as the absolute value of ΔRz1 increases, the period of the moire fringes 12b becomes finer, and the distance dy in the Y direction between the 0th-order peak 15b and the 1st-order peak 16b of the obtained Fourier transformed image 14b becomes larger. Note that FIG. 11 is an example in which the displacement amount ΔRz1 in the rotation direction Rz around the Z direction axis of the first grid 3 is 1.2 degrees. Further, in FIG. 11, the primary peak 16b is displaced in the X direction because the first grid 3 and the second grid 4 are displaced in the Z direction before the positional deviation of the first grid 3 and the second grid 4 in the Z direction is adjusted. This is because it is configured to adjust the positional deviation in the rotation direction Rz around the Z direction axis.

一方、フーリエ変換画像１４ｂの１次ピーク１６ｂのＹ方向の位置（０次ピーク１５ｂとの距離）ｄｙと、モアレ縞１２ｂの周期ｐｍｙとには、以下の式（１２）に示す関係がある。

ここで、Ｎｙは、取得画像のＹ方向の画素である。また、ｓｙは、検出器５のＹ方向の画素サイズである。 The period pmy of the moire fringes 12b generated when the position of the first grid 3 is displaced by ΔRz1 in the rotation direction Rz around the Z direction axis is expressed by the following equation (11) when ΔRz1 is close to 0.

On the other hand, the position (distance from the 0th-order peak 15b) dy of the first-order peak 16b of the Fourier-transformed image 14b and the period pmy of the moire fringes 12b have a relationship shown in the following equation (12).

Here, Ny is a pixel in the Y direction of the acquired image. Further, sy is the pixel size of the detector 5 in the Y direction.

By eliminating pmy from the above equations (11) and (12), the following equation (13) is obtained.

By modifying the above equation (13), the following equation (14) is obtained.

From the above equation (14), it can be seen that the misalignment amount ΔRz1 in the rotation direction Rz around the Z direction axis of the first grid 3 is proportional to dy. The unit of ΔRz1 is radians.

Further, since the position shift amount ΔRz2 when the second grid 4 causes a position shift in the rotation direction Rz around the Z direction axis is a relative rotation shift between the first grid 3 and the second grid 4. It is equal to ΔRz1 and is expressed by the following equation (15). The unit of ΔRz2 is radians.

As can be seen from the above equation (15), the misalignment amount ΔRz2 in the rotation direction Rz around the Z direction axis of the second grid 4 is also proportional to dy. Therefore, the positional deviation of the first grid 3 and the second grid 4 in the rotation direction Rz around the Z direction axis can be calculated by measuring dy. Then, the control unit 9 corrects the misalignment amount ΔRz1 in the rotation direction Rz around the Z direction axis of the first grid 3 or the misalignment amount ΔRz2 in the rotation direction Rz around the Z direction axis of the second grid 4. It is output to the adjustment mechanism control unit 7 as a signal to be performed.

<Acquisition of positional deviation in the rotation direction Rx around the central axis in the X direction>
Next, with reference to FIGS. 3, 13 and 14, a configuration will be described in which the grid position shift acquisition unit 6 in the first embodiment acquires the position shift in the rotation direction Rx around the central axis in the X direction. The unit of the misalignment amount ΔRx1 in the rotation direction Rx around the central axis in the X direction of the first grid 3 in FIGS. 13 and 14 is “degree”.

In the first embodiment, the grid misalignment acquisition unit 6 rotates around the central axis of the first grid 3 or the second grid 4 in the X direction based on the size of the primary peak 16c in the Fourier transform image 14c. It is configured to acquire the positional deviation of the first grid 3 or the second grid 4 in Rx.

As shown in FIG. 3, when the first grid 3 and the second grid 4 are not displaced in the rotation direction Rx around the central axis in the X direction, the frequency of the self-image 30 of the first grid 3 on the detection surface and the second grid. Since the frequencies of the two grids 4 match, unintended moire fringes 12 are not observed. However, when the first grid 3 is displaced in the rotation direction Rx around the central axis in the X direction, the enlargement ratio of the first grid 3 changes, and self-images 30c having different frequencies are formed above and below the detection surface. To. At this time, moire fringes 12c as shown in the example of FIG. 13 are generated. As the displacement amount ΔRx1 in the rotation direction Rx around the central axis in the X direction of the first grid 3 increases, the distortion of the moire fringes 12c generated also increases.

When the first grid 3 is displaced in the rotation direction Rx around the central axis in the X direction, the observed moire fringes 12c have a shape distorted vertically and horizontally, and have a plurality of frequency components in the X and Y directions. The intensity distribution includes it. Therefore, as shown in the example of FIG. 14, the primary peak 16c of the Fourier transformed image 14c spreads in the X direction and the Y direction. Further, as the absolute value of ΔRx1 increases, the spread of the primary peak 16c in the X direction and the Y direction increases. Therefore, the amount of misalignment ΔRx1 in the rotation direction Rx around the central axis of the first grid 3 in the X direction, the magnitude σx in the X direction of the primary peak 16c, and the magnitude σy in the Y direction of the primary peak 16c are different. There is a correlation.

In this way, acquiring the misalignment based on the magnitude of the primary peak 16 is paraphrased as acquiring the misalignment of the grid based on the magnitude of the dispersion of the frequency components constituting the primary peak 16. May be good.

Further, even when the position of the second grid 4 in the rotation direction Rx around the central axis in the X direction is deviated, the relative rotation deviation between the first grid 3 and the second grid 4 is deviated from the first grid 3. Since it is the same as the case where there is, the deviation amount ΔRx2 when the second grid 4 is displaced in the rotation direction Rx around the central axis in the X direction is also the magnitude σx and the primary order of the primary peak 16c in the X direction as in the case of ΔRx1. There is a correlation with the magnitude σy of the peak 16c in the Y direction. Note that FIG. 14 is an example in which the displacement amount ΔRx1 in the rotation direction Rx around the central axis in the X direction of the first grid 3 is 1.4 degrees. Further, in FIG. 13, the primary peak 16c is shifted in the X direction because the first grid 3 and the second grid 4 are shifted in the Z direction before the positional shift of the first grid 3 and the second grid 4 in the Z direction is adjusted. This is because it is configured to adjust the positional deviation in the rotation direction Rx around the central axis in the X direction.

<Acquisition of positional deviation in the rotation direction Ry around the central axis in the Y direction>
Next, with reference to FIGS. 3, 15 and 16, a configuration will be described in which the grid position shift acquisition unit 6 acquires the position shift in the rotation direction Ry around the central axis in the Y direction in the first embodiment. In FIGS. 15 and 16, the unit of the misalignment amount ΔRy1 in the rotation direction Ry around the central axis in the Y direction of the first grid 3 is “degree”.

In the first embodiment, the grid misalignment acquisition unit 6 rotates around the central axis of the first grid 3 or the second grid 4 in the Y direction based on the size of the primary peak 16d in the Fourier transform image 14d. It is configured to acquire the position shift of the first grid 3 or the second grid 4 in Ry.

As shown in FIG. 3, when the first grid 3 and the second grid 4 are not displaced in the rotation direction Ry around the central axis in the Y direction, the frequency of the self-image 30 of the first grid 3 on the detection surface and the second grid. Since the frequencies of the two grids 4 match, unintended moire fringes 12 are not observed. However, when the position of the first grid 3 in the rotation direction Ry around the central axis in the Y direction is deviated, the enlargement ratio of the first grid 3 changes, and a self-image 30d having different frequencies on the left and right of the detection surface is formed. Will be done. The moire fringes 12d generated by the interference between the self-image 30d and the second grid 4 have a shape distorted to the left and right, and have an intensity distribution including a plurality of frequency components in the X direction. Therefore, when the position of the first grid 3 in the rotation direction Ry around the central axis in the Y direction is deviated, the primary peak 16d of the Fourier transformed image 14d spreads in the X direction as shown in FIG. As the absolute value of ΔRy1 increases, the spread of the primary peak 16d in the X direction increases. That is, the displacement amount ΔRy1 in the rotation direction Ry around the central axis in the Y direction of the first grid 3 correlates with the magnitude σx in the X direction of the primary peak 16d of the Fourier transformed image 14d.

Further, even when the second lattice 4 has a positional deviation in the rotation direction Ry around the central axis in the Y direction, the relative rotational deviation between the first lattice 3 and the second lattice 4 is such that the first lattice 3 is displaced. Since it is the same as the case, the deviation amount ΔRy2 when the second grid 4 is displaced in the rotation direction Ry around the central axis in the Y direction also has a correlation with the magnitude σx of the primary peak 16d in the X direction as in the case of ΔRy1. be. Note that FIG. 16 is an example in which the misalignment amount ΔRy1 in the rotation direction Ry around the central axis in the Y direction of the first grid 3 is 1.0 degree. Further, in FIGS. 15 and 16, the primary peak 16d is displaced in the X direction because the first grid 3 and the second grid 4 are displaced in the Z direction before the positional deviation of the first grid 3 and the second grid 4 is adjusted. This is because it is configured to adjust the positional deviation in the rotation direction Ry around the central axis in the Y direction of the two grids 4.

The above-mentioned position shift in the Z direction, the position shift in the rotation direction Rz around the Z direction axis, the position shift in the rotation direction Rx around the center axis in the X direction, and the position shift in the rotation direction Ry around the center axis in the Y direction, and Fourier. The distance (dx, dy) between the 0th-order peak 15 and the 1st-order peak 16 in the converted image 14 and the magnitude (σx, σy) of the 1st-order peak 16 in the Fourier-converted image 14 are expressed by the following equations (σx, σy). It can be seen that there is a relationship between 16) and equation (19).

In the first embodiment, as described above, the grid position shift acquisition unit 6 positions the grid based on the distance (dx, dy) between the 0th-order peak 15 and the 1st-order peak 16 in the Fourier transformed image 14. It is configured to get the magnitude of the deviation. Further, the grid misalignment acquisition unit 6 is configured to acquire the presence or absence of grid misalignment based on the magnitude (σx, σy) of the primary peak 16 in the Fourier transformed image 14.

Here, in the first embodiment, the grid misalignment acquisition unit 6 has a grid misalignment amount ΔZ in the Z direction and around the Z direction axis based on the distance (dx, dy) between the peaks of the Fourier transformed image 14. The amount of misalignment ΔRz in the rotation direction Rz can be acquired. However, in the first embodiment, the grid misalignment acquisition unit 6 directly calculates the misalignment amount in the rotation direction Rx around the central axis in the X direction and the misalignment amount in the rotation direction Ry around the center axis in the Y direction. Can't. Therefore, in the first embodiment, the grid position shift acquisition unit 6 Fouriers based on a plurality of Fourier transform images 14 captured by rotating either the first grid 3 or the second grid 4 in one direction. It is configured to acquire the rotation amount at which the magnitude (σx, σy) of the primary peak 16 in the transformed image 14 is the minimum value or the vicinity of the minimum value as the displacement amount. The amount of rotation in which the magnitude (σx, σy) of the primary peak 16 is close to the minimum value means that either the first grid 3 or the second grid 4 is rotated in one direction and photographed a plurality of times. The amount of rotation in the range in which the magnitude (σx, σy) of the primary peak 16 in the Fourier transform image 14 is equal to or less than the predetermined threshold value th1.

The grid misalignment acquisition unit 6 outputs the grid misalignment amount ΔZ in the Z direction to the adjustment mechanism control unit 7 as the grid misalignment amount. Further, the grid misalignment acquisition unit 6 outputs the misalignment amount ΔRz in the rotation direction Rz around the Z direction axis as the grid misalignment amount to the adjustment mechanism control unit 7. Further, the grid misalignment acquisition unit 6 sets the grid misalignment amount as the misalignment amount in the rotation direction Rx around the central axis in the X direction (the size of the primary peak 16 in the Fourier transformed image 14 (σx, σy)). Outputs to the adjustment mechanism control unit 7 the amount of rotation of the first grid 3 or the second grid 4 in which is near the minimum value or the minimum value equal to or less than the predetermined threshold th1. Further, the grid misalignment acquisition unit 6 has the minimum misalignment amount (the size (σx) of the primary peak 16 in the Fourier transformed image 14) in the rotation direction Ry around the central axis in the Y direction as the grid misalignment amount. The rotation amount of the first grid 3 or the second grid 4 which is near the minimum value of the value or the predetermined threshold th1 or less is output to the adjustment mechanism control unit 7.

In the first embodiment, the X-ray phase difference imaging system 100 is configured to adjust the misalignment of the grid until the misalignment of the first grid 3 or the second grid 4 becomes equal to or less than a predetermined threshold value (th1, th2). Has been done. That is, in the X-ray phase difference imaging system 100, the amount of positional deviation (the size of the primary peak 16 in the Fourier transformed image 14 (σx, σy)) in the rotation direction Rx around the central axis in the X direction is equal to or less than a predetermined threshold value th1. It is configured to adjust the grid until it becomes. Further, in the X-ray phase difference imaging system 100, the amount of positional deviation (the magnitude (σx) of the primary peak 16 in the Fourier transformed image 14) in the rotation direction Ry around the central axis in the Y direction becomes a predetermined threshold value th1 or less. It is configured to adjust the grid up to. Further, the X-ray phase difference imaging system 100 is configured to adjust the grid so that the amount of misalignment ΔZ of the grid in the Z direction is equal to or less than a predetermined threshold value th2. Further, the grid is adjusted so that the misalignment amount ΔRz in the rotation direction Rz around the Z direction axis is equal to or less than a predetermined threshold value th2. In the first embodiment, the misalignment amount ΔZ of the grid in the Z direction and the misalignment amount ΔRz in the rotation direction Rz around the Z direction axis can be directly calculated. Therefore, the X-ray phase difference imaging system 100 is configured to adjust the grid to a position where the predetermined threshold value th2 becomes almost 0.

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

In the first embodiment, as described above, the X-ray phase difference imaging system 100 detects the X-ray source 1, the detector 5 for detecting the X-rays emitted from the X-ray source 1, and the X-ray source 1. Arranged between the vessel 5 and the X-ray source 1, X-rays are irradiated to form a self-image 30, and X-rays that have passed through the first lattice 3 and the first lattice 3 are irradiated to the first lattice 3. Based on a plurality of grids including a second grid 4 for forming the interference fringes 12 with the self-image 30, and a Fourier transformed image 14 obtained by a Fourier transform on the interference fringes image 13 detected by the detector 5. A grid position shift acquisition unit 6 for acquiring a grid position shift is provided. Here, if the relative positions of the first grid 3 and the second grid 4 deviate from the design positions, unintended moire fringes 12 occur. Therefore, in the Fourier transform image 14, in addition to the peak (0th-order peak 15) caused by the self-image 30 of the first lattice 3, a peak (first-order peak 16) caused by the unintended moire fringes 12 is generated. As a result, the grid position shift acquisition unit 6 acquires the grid position shift based on the Fourier transform image 14, so that the grid position adjustment can be performed based on the obtained grid position shift. Therefore, it is possible to adjust the deviation of the grid position without depending on the knowledge and experience of the measurer, and it is possible to shorten the adjustment time.

Further, in the first embodiment, as described above, the X-ray phase difference imaging system 100 further includes an adjustment mechanism 8 for adjusting the positional deviation of at least one of the first grid 3 and the second grid 4. The adjusting mechanism 8 is configured to correct the misalignment of the grid based on the misalignment of the grid acquired by the grid misalignment acquisition unit 6. As a result, the adjustment mechanism 8 can automatically correct the grid misalignment based on the grid misalignment acquired by the grid misalignment acquisition unit 6, and thus depends on the knowledge and experience of the measurer. It is possible to adjust the deviation of the position of the grid more easily. Further, since the adjustment mechanism 8 can automatically correct the positional deviation of the grid, the adjustment time can be further shortened.

Further, in the first embodiment, as described above, the grid position shift acquisition unit 6 is based on at least one of the distance between the peaks (dx, dy) and the peak size (σx, σy) of the Fourier transformed image 14. It is configured to acquire the misalignment of the grid. As a result, the position shift of the lattice can be acquired by performing image processing on the Fourier transformed image 14. As a result, the position shift of the grid can be automatically acquired without the measurer visually confirming the moire fringes 12.

Further, in the first embodiment, as described above, the grid position shift acquisition unit 6 in the Fourier transform image 14 is in the Z direction based on the distance (dx) between the 0th-order peak 15 and the 1st-order peak 16. It is configured to acquire the positional deviation of the first grid 3 or the second grid 4 in. As a result, the positional deviation of the first grid 3 or the second grid 4 in the Z direction is replaced with the magnitude of the distance (dx) between the 0th-order peak 15 and the 1st-order peak 16 of the Fourier transformed image 14 and grasped. be able to. As a result, the first grid 3 or the second grid in the Z direction is adjusted by adjusting the position of the grid so that the distance (dx) between the 0th-order peak 15 and the first-order peak 16 of the Fourier transformed image 14 becomes smaller. The misalignment of 4 can be easily adjusted.

Further, in the first embodiment, as described above, the grid position shift acquisition unit 6 in the Fourier transform image 14 is in the Z direction based on the distance (dy) between the 0th-order peak 15 and the 1st-order peak 16. It is configured to acquire the positional deviation of the first grid 3 or the second grid 4 in the rotation direction Rz around the axis. As a result, the positional deviation of the first grid 3 or the second grid 4 in the rotation direction Rz around the Z direction axis is the large distance (dy) between the 0th-order peak 15 and the 1st-order peak 16 of the Fourier transformed image 14. It can be replaced with a grid and grasped. As a result, by adjusting the position of the grid so that the distance (dy) between the 0th-order peak 15 and the 1st-order peak 16 of the Fourier transform image 14 becomes smaller, the first in the rotation direction Rz around the Z-direction axis. The misalignment of the grid 3 or the second grid 4 can be easily adjusted.

Further, in the first embodiment, as described above, the grid position shift acquisition unit 6 has a grid based on the distance (dx, dy) between the 0th-order peak 15 and the 1st-order peak 16 in the Fourier transformed image 14. It is configured to acquire the magnitude of the misalignment of. This makes it possible to obtain the magnitude of the misalignment of the grid. As a result, the positional deviation of the first grid 3 or the second grid 4 can be adjusted more easily and accurately by adjusting the position of the grid using the acquired magnitude of the positional deviation as the correction amount.

Further, in the first embodiment, as described above, the grid position shift acquisition unit 6 has the first grid 3 or the second grid 4 based on the size (σx) of the primary peak 16 in the Fourier transform image 14. It is configured to acquire the positional deviation of the first grid 3 or the second grid 4 in the rotation direction Ry around the central axis in the Y direction. As a result, the displacement of the first grid 3 or the second grid 4 in the rotation direction Ry around the central axis in the Y direction of the first grid 3 or the second grid 4 is determined by the magnitude of the primary peak 16 of the Fourier transformed image 14. It can be grasped by replacing it with (σx). As a result, by adjusting the grid so that the size (σx) of the primary peak 16 of the Fourier transformed image 14 becomes small, the rotation direction Ry around the central axis in the Y direction of the first grid 3 or the second grid 4. The misalignment of the first grid 3 or the second grid 4 in the above can be easily adjusted.

Further, in the first embodiment, as described above, the grid position shift acquisition unit 6 has the first grid 3 or the second grid 3 or the second grid based on the size (σx, σy) of the primary peak 16 in the Fourier transform image 14. It is configured to acquire the positional deviation of the first grid 3 or the second grid 4 in the rotation direction Rx around the central axis in the X direction of the grid 4. As a result, the displacement of the first grid 3 or the second grid 4 in the rotation direction Rx around the center axis in the X direction of the first grid 3 or the second grid 4 is determined by the magnitude of the primary peak 16 of the Fourier transformed image 14. It can be grasped by replacing it with (σx, σy). As a result, by adjusting the grid so that the size (σx, σy) of the primary peak 16 of the Fourier transformed image 14 becomes small, the rotation of the first grid 3 or the second grid 4 around the central axis in the X direction. The misalignment of the first grid 3 or the second grid 4 in the direction Rx can be easily adjusted.

Further, in the first embodiment, as described above, the grid misalignment acquisition unit 6 acquires the presence or absence of the grid misalignment based on the size (σx, σy) of the primary peak 16 in the Fourier transform image 14. It is configured to do. Thereby, the presence or absence of the positional deviation of the first grid 3 or the second grid 4 can be automatically determined by the image processing of the Fourier transformed image 14.

Further, in the first embodiment, as described above, the grid position shift acquisition unit 6 is based on a plurality of Fourier transform images 14 captured by rotating either the first grid 3 or the second grid 4. , The amount of rotation in which the magnitude (σx, σy) of the primary peak 16 in the Fourier transform image 14 is the minimum value or the vicinity of the minimum value is acquired as the displacement amount. Thereby, based on the plurality of Fourier transform images 14, it is possible to acquire the relative position of the lattice in which the positional deviation of the lattice is minimized. As a result, the positional deviation of the first grid 3 or the second grid 4 can be easily and accurately adjusted.

Further, in the first embodiment, as described above, the plurality of grids further include a third grid 2 arranged between the X-ray source 1 and the first grid 3. Thereby, the coherence of the X-ray source 1 can be improved by using the third lattice 2. As a result, it becomes possible to perform X-ray phase difference imaging using the X-ray source 1 whose focal length is not minute, so that the degree of freedom in selecting the X-ray source 1 can be improved.

Further, in the first embodiment, as described above, the X-ray phase difference imaging system 100 further includes a noise reduction processing unit 11 that removes frequency noise from the image detected by the detector 5 before performing the Fourier transform. .. As a result, the artifact (virtual image) obtained by analyzing the finite space when performing the Fourier transform and the artifact (virtual image) derived from the detector 5 can be removed before performing the Fourier transform. As a result, the peak (primary peak 16) caused by the positional deviation of the lattice obtained by the Fourier transform can be detected more accurately.

[Second Embodiment]
Next, the X-ray phase difference imaging system 200 (see FIG. 1) according to the second embodiment of the present invention will be described with reference to FIGS. 1, 2 and 17 to 20. Unlike the first embodiment in which the frequency noise is removed before performing the Fourier transform on the interference fringe image 13, in the second embodiment, the image processing unit 10 (see FIG. 2) performs the Fourier transform on the interference fringe image 13. The Fourier transform reference image 23 (see FIG. 19) obtained in advance by the above is used to remove the noise 22 (see FIG. 18) generated in the Fourier transform image 14. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

Here, when a pixel defect occurs in the detector 5 or a defect occurs in the first grid 3 and / or the second grid 4, as shown in FIG. 17, in the interference fringe image 13, the pixel defect of the detector 5 occurs. Noise 19 due to the above, noise 20 due to the lack of the grid, and the like are observed. Further, when X-rays are incident on the grid in an oblique direction and the detector 5 has sensitivity unevenness according to the incident angle, the sensitivity unevenness 21 is observed in the interference fringe image 13. When the interference fringe image 13 as shown in FIG. 17 is Fourier transformed, as shown in FIG. 18, peaks other than the 0th-order peak 15 and the 1st-order peak 16 are generated as noise 22 in the Fourier-transformed image 14. The noise 22 generated in the Fourier transformed image 14 is generated by the direction in which the X-ray source 1 is installed and the defects of the plurality of grids and the detector 5 itself. Therefore, unlike the random noise, the positions where the noise 22 occurs in the Fourier transform image 14 and the Fourier transform reference image 23 are substantially the same.

Therefore, in the second embodiment, as shown in FIG. 19, the image processing unit 10 uses the Fourier transform reference image 23 previously obtained by the Fourier transform on the interference fringe image 13, and the noise 22 generated in the Fourier transform image 14. Is configured to remove.

Specifically, the image processing unit 10 is configured to remove the noise 22 by subtracting the Fourier transform reference image 23 from the Fourier transform image 14. Unlike the random noise, the noise 22 does not substantially change its position in the Fourier transform image 14 and the Fourier transform reference image 23. Therefore, the noise 22 can be removed by subtracting the Fourier transform reference image 23 from the Fourier transform image 14. As shown in FIG. 20, only the first-order peak 16 is observed in the Fourier transform image 14 after the noise 22 is removed.

When the position of the first-order peak 16 in the Fourier transform image 14 and the position of the first-order peak 16 in the Fourier transform reference image 23 overlap, the first-order peak 16 is removed together with the noise 22 by subtraction, and Fourier is used. The first-order peak 16 cannot be observed in the transformed image 14. Therefore, as shown in FIG. 19, the Fourier transform reference image 23 is an image in which the positions of the first-order peak 16 are different from those of the Fourier transform image 14. Specifically, in the example shown in FIG. 19, the first-order peak 16 of the Fourier transform reference image 23 is an image in which the distance dy from the 0th-order peak 15 is larger than that of the first-order peak 16 in the Fourier transform image 14. This is an example.

The positions of the primary peaks 16 observed in the Fourier transform image 14 and the Fourier transform reference image 23 are based on the period of the moire fringes 12. Therefore, by moving at least one of the plurality of lattices to change the period of the moire fringes 12, the position of the primary peak 16 observed in the Fourier transform image 14 (Fourier transform reference image 23) is changed. Can be done.

Further, the Fourier transform reference image 23 may be acquired at any time before the position adjustment of the grid is performed. For example, the image acquired in advance may be stored in a storage unit (not shown) and used by reading it out from the storage unit when the Fourier transform image 14 is acquired, or every time the position of the grid is adjusted. You may get it. However, after a long period of time after the Fourier transform reference image 23 is acquired, pixel defects and lattice defects of the detector 5 may increase, and the noise 22 generated in the Fourier transform image 14 and the Fourier transform reference image 23 may increase. It may be different from the noise 22 generated in. Therefore, it is preferable that the Fourier transform reference image 23 is acquired before the Fourier transform image 14 is acquired each time the position of the grid is adjusted.

Next, with reference to FIG. 21, the overall flow of the method in which the X-ray phase difference imaging system 200 in the second embodiment adjusts the grid will be described. Since the processes of steps S1 to S7 are the same as those of the first embodiment, detailed description thereof will be omitted.

In steps S1 to S3, the X-ray phase difference imaging system 200 acquires the Fourier transformed image 14. After that, in step S8, the image processing unit 10 removes the noise 22 generated in the Fourier transform image 14 by subtracting the Fourier transform reference image 23 from the Fourier transform image 14.

After that, the process proceeds to step S4 to step S5. If there is no misalignment of the grid, the process proceeds to step S6 and ends the process. If there is a misalignment of the grid, the process proceeds to step S7, the control unit 9 adjusts the position of the grid, and then the process proceeds to step S1.

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

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

In the second embodiment, as described above, the image processing unit 10 for removing the noise 22 generated in the Fourier transform image 14 is further provided by using the Fourier transform reference image 23 previously obtained by the Fourier transform on the interference fringe image 13. .. This makes it possible to remove the noise 22 generated in the Fourier transform image 14, so that the position and size of the primary peak 16 can be accurately acquired. As a result, it becomes possible to more accurately detect the peak caused by the misalignment of the lattice obtained by the Fourier transform, and it is possible to improve the accuracy of adjusting the misalignment of the grid.

Further, in the second embodiment, as described above, the image processing unit 10 is configured to remove the noise 22 by subtracting the Fourier transform reference image 23 from the Fourier transform image 14. Thereby, unlike the random noise, the noise 22 of the Fourier transformed image 14 which is hard to change with time can be easily removed.

Further, in the second embodiment, as described above, the Fourier transform reference image 23 is an image in which the positions of the first-order peak 16 are different from those of the Fourier transform image 14. By using such an image, when the noise 22 of the Fourier transform image 14 is removed, the primary peak 16 of the Fourier transform image 14 is removed together with the noise 22 by the primary peak 16 of the Fourier transform reference image 23. Can be suppressed. As a result, the noise 22 of the Fourier transformed image 14 can be removed regardless of the position of the primary peak 16 in the Fourier transformed image 14.

The other effects of the second embodiment are the same as those of the first embodiment.
(Modification example)
It should be noted that the embodiments disclosed this time are exemplary in all respects and are not considered to be restrictive. The scope of the present invention is shown by the scope of claims, not the description of the above-described embodiment, and further includes all modifications (modifications) within the meaning and scope equivalent to the scope of claims.

For example, in the first and second embodiments, a phase grid is used as the first grid 3, but the present invention is not limited to this. For example, an absorption grid may be used as the first grid 3. As a result, it is possible to perform X-ray phase difference imaging in both the interferometer and non-interferometer configurations, and it is possible to improve the degree of freedom in selecting the first grid 3.

Further, in the first and second embodiments, the example in which the third lattice 2 is provided is shown, but the present invention is not limited to this. For example, if the coherence of the X-ray source 1 is sufficiently high, the third lattice 2 may not be provided.

Further, in the first and second embodiments, the control unit 9 has shown an example of generating the Fourier transform image 14, but the present invention is not limited to this. For example, the image processing unit 10 may be configured to generate the Fourier transform image 14.

Further, in the first and second embodiments, an example is shown in which the size of the 0th-order peak 15 and the size of the 1st-order peak 16 are determined by the half-value width of the frequency peak after the Fourier transform. Not limited to this. For example, a size other than the half width of the frequency peak after the Fourier transform may be used. As the size other than the full width at half maximum, for example, the size of the width of the frequency peak that is 40% from the maximum amplitude of the frequency peak after the Fourier transform may be the size of the 0th-order peak 15 and the 1st-order peak 16. Further, the areas of the 0th-order peak 15 and the 1st-order peak 16 of the Fourier transformed image 14 may be used as the magnitude of each peak.

Further, in the second embodiment, an example is shown in which the Fourier transform reference image 23 having the primary peak 16 at a position different from the position of the primary peak 16 in the Fourier transform image 14 is used, but the present invention is limited to this. do not have. For example, even if the position of the first-order peak 16 in the Fourier transform image 14 and the position of the first-order peak 16 in the Fourier transform reference image 23 overlap, as shown in FIG. 22, the image processing unit 10 uses the Fourier transform image. The Fourier transform reference image 23 obtained by deleting the primary peak 16 of 14 may be used to remove the noise 22 of the Fourier transform image 14. In the example shown in FIG. 22, the primary peak 16 deleted for convenience is shown by a broken line.

1 X-ray source 2 3rd grid 3 1st grid 4 2nd grid 5 Detector 6 Grid position shift acquisition unit 7 Adjustment mechanism control unit 8 Adjustment mechanism 10 Image processing unit 11 Noise removal processing unit 12 Interference fringes (moire fringes)
13 Interference fringe image (moire fringe image)
14 Fourier transform image 15 0th order peak 16 1st order peak 22 Noise 23 Fourier transform reference image dx Distance between 0th order peak and 1st order peak (X direction)
dy Distance between 0th-order peak and 1st-order peak (Y direction)
σx First-order peak magnitude (X direction)
σy First-order peak magnitude (Y direction)

Claims (3)

X-ray source and
A detector that detects X-rays emitted from the X-ray source, and
A first grid, which is arranged between the X-ray source and the detector and for irradiating the X-rays from the X-ray source to form a self-image, and the X-rays that have passed through the first grid A plurality of grids including a second grid to be irradiated to form an interference fringe with the self-image of the first grid, and
A grid misalignment acquisition unit that acquires the misalignment of the grid based on the Fourier transform image obtained by the Fourier transform on the interference fringe image detected by the detector.
An X-ray phase difference imaging system comprising an image processing unit that removes noise generated in the Fourier transform image using a Fourier transform reference image obtained in advance by Fourier transform on an interference fringe image. The X-ray phase difference imaging system according to claim 1 , wherein the image processing unit is configured to remove the noise by subtracting the Fourier transform reference image from the Fourier transform image. The invention according to claim 1 or 2 , wherein the Fourier transform reference image is an image in which the position of the primary peak is different from that of the Fourier transform image, or an image obtained by deleting the primary peak of the Fourier transform image. X-ray phase difference imaging system.

Images