WO2019111505A1 - Phase-contrast x-ray imaging system - Google Patents

Abstract

This phase-contrast X-ray imaging system (100) comprises an X-ray source (1), an X-ray detector (4), a grating unit, and a control unit (6). The control unit (6) acquires at least one type of positional deviation from among the positional deviation of the grating unit in the optical axis direction connecting the X-ray source (1) and X-ray detector (4), the positional deviation of the grating unit in a direction orthogonal to the slits of the grating unit, and the positional deviation of the grating unit resulting from rotation around the optical axis.

Description

X-ray phase contrast imaging system

The present invention relates to an X-ray phase-contrast imaging system, and more particularly to acquisition of misalignment of a grating of an X-ray phase-contrast imaging apparatus for imaging using a plurality of gratings and adjustment of the grating position.

Conventionally, X-ray phase contrast imaging systems are known. Such an X-ray phase contrast imaging system is disclosed, for example, in WO 2014/030115.

WO 2014/030115 discloses an X-ray phase contrast imaging system for imaging a phase contrast image by detecting interference fringes generated by translating a source grating. An X-ray phase-contrast imaging system disclosed in WO 2014/030115 comprises an X-ray phase-contrast imaging device including an X-ray source, a source grating, a phase grating, an absorption grating, and a detector. Including. This X-ray phase difference imaging apparatus is a so-called Talbot-Lau interferometer. Further, the X-ray phase difference imaging system disclosed in Patent Document 1 acquires a translation signal for translating the source grating so that the interference fringes have a predetermined period, and the source grating is obtained based on the acquired translation signal. Are configured to capture a phase contrast image by translating.

Here, in the Talbot-Lau interferometer, X-rays that have passed through the source grating are irradiated to the phase grating. The irradiated X-rays are diffracted when passing through the phase grating, and form a self-image of the phase grating at a position separated by a predetermined distance (talbot distance). The period of the self-image of the formed phase grating is so small that it can not be detected by a general purpose detector. Therefore, in the Talbot-Lau interferometer, an absorption grating is disposed at a position where a self-image of the phase grating is formed, and an interference pattern that can be detected by a general-purpose detector is formed. In the Talbot-Lau interferometer, slight changes in the self-image are detected by performing multiple imaging (fringe scanning imaging) while translating any one of the gratings in the periodic direction of the grating, and a phase contrast image is obtained. You can get

In order to obtain a phase contrast image using a Talbot-Lau interferometer, it is necessary to take an image (air data) taken without a subject and an image (sample data) taken with the subject placed. At this time, the air data is taken under the same conditions as the sample data. Therefore, if the conditions do not change, it is not necessary to acquire air data again after acquiring it once.

International Publication No. 2014/030115

In the Talbot-Lau interferometer described in WO 2014/030115, unintended interference fringes occur when the relative position between the phase grating and the absorption grating deviates from the designed position. In this case, since the unintended interference fringes are detected by the detector, there is a disadvantage that an artifact (virtual image) is generated in the captured image due to the unintended interference fringes. Note that “unintended interference fringes” refers to interference fringes that occur in a state in which a subject is not disposed and that are caused by a shift in the relative position between the phase grating and the absorption grating. Also, “artifact (virtual image)” refers to the disturbance of the phase contrast image or the deterioration of the image quality of the phase contrast image, which is caused by unintended interference fringes.

However, it is difficult to mechanically suppress the grid so as not to cause misalignment. Therefore, the user needs to periodically update the air data in order to maintain the same imaging conditions. In addition, even if a mechanism for automatically updating air data using an automatic stage is provided, if the frequency of updating is high, the measurement time is increased accordingly, and thus the user is stressed.

The present invention has been made to solve the above-described problems, and provides an X-ray phase difference imaging system capable of easily maintaining the same imaging conditions without updating air data. It is.

In order to achieve the above object, an x-ray phase contrast imaging system according to one aspect of the present invention comprises an x-ray source, an x-ray detector for detecting irradiated x-rays, an x-ray source and an x-ray detector And a plurality of lattice sections including a first lattice section for transmitting X-rays between them and a second lattice section for causing interference with the self-image of the first lattice section, and the lattice sections at a constant interval And an image processing unit that generates a contrast image based on an X-ray image acquired from an X-ray detector, and a control unit that acquires positional deviation of the lattice unit, and The unit and the second grid unit include a shooting area unit for shooting an object, and a detection area unit other than the shooting area unit, and at least one of the first grid unit and the second grid unit is a shooting unit. The slit pattern is different from the area section, and the control section Positional displacement of the grating in the direction of the optical axis connecting the X-ray source and the X-ray detector, positional deviation of the grating in the direction orthogonal to the slits of the grating, or light It is configured to acquire at least one of the positional deviations of the grid portion due to the rotation around the axis.

In the X-ray phase difference imaging system according to one aspect of the present invention, as described above, in the direction of the optical axis connecting the X-ray source and the X-ray detector based on the interference fringes of the X-ray image in the detection area. At least one of positional deviation of the lattice part, positional deviation of the lattice part in a direction orthogonal to the slits of the lattice part, or positional deviation of the lattice part due to rotation around the optical axis is obtained . With such a configuration, it is possible to obtain positional deviation based on interference fringes generated by interference between the detection area section of the first lattice section and the detection area section of the second lattice section. As a result, the user can easily acquire positional deviation of the grid (change in imaging condition) by generating interference fringes by normal imaging without reacquiring air data. That is, by analyzing the change in the phase and period of the interference fringes, it is possible to obtain the positional deviation of the grid that has occurred from the time of air data shooting to the time of sample data shooting. As a result, since it becomes possible to adjust the positional deviation of the grid based on the acquired positional deviation, the same imaging condition can be easily maintained without updating the air data.

In the X-ray phase-contrast imaging system according to the above aspect, preferably, the control unit is configured to acquire a phase shift and a cycle shift of the interference fringes based on an image after Fourier transformation of the interference fringes of the X-ray image. ing. Here, when the phase shift and the cycle shift of the interference fringes occur, the position of the primary peak appearing in the image after Fourier transform is different. That is, based on the change in the position of the primary peak of the image after Fourier transform, it is possible to acquire the phase shift and the cycle shift of the interference fringes. As a result, when configured as described above, the user can acquire positional deviation of the lattice portion from the acquired image after Fourier transform. As a result, since it is possible to adjust the positional deviation of the grid based on the acquired positional deviation, it is possible to maintain the same imaging conditions as when the air data is acquired first.

In the X-ray phase-contrast imaging system according to the above aspect, preferably, the control unit performs, based on an image after Fourier transform of interference fringes of the X-ray image, a direction perpendicular to the slit direction and a direction parallel to the slit direction. Position of the grating in the direction of the optical axis connecting the X-ray source and the X-ray detector from the distance between the zeroth peak and the first peak of It is configured to get. Here, the positional deviation of the grating portion in the optical axis direction connecting the X-ray source and the X-ray detector appears as the distance between the zero-order peak and the first-order peak in the X-axis direction. Further, the positional deviation of the grating portion due to the rotation around the optical axis appears as the distance in the Y-axis direction between the zero-order peak and the first-order peak after Fourier transform. Therefore, if configured as described above, the user can shift the position of the grating portion in the direction of the optical axis connecting the X-ray source and the X-ray detector from the image after Fourier transformation and the grating portion by rotation around the optical axis Misalignment can be easily obtained.

In this case, preferably, the X-ray image of the detection area is Fourier-transformed to cut out the area around the primary peak, the other areas are set to 0, and then moved to the center of the image to perform inverse Fourier transformation. Thus, the positional deviation of the grating portion in the direction orthogonal to the slits of the grating portion is acquired from the acquired phase distribution. Here, the positional deviation in the direction orthogonal to the slits of the grating portion appears as a phase deviation in the result after inverse Fourier transform. Therefore, according to the above configuration, the user can easily acquire positional deviation in the direction orthogonal to the slits of the lattice portion.

Preferably, the X-ray phase difference imaging system according to the above aspect further comprises a position adjustment mechanism for adjusting the position of the grating section, and the control section determines the position of the grating section based on the acquired positional deviation of the grating section. Is controlled by the position adjusting mechanism. According to this structure, since the position adjustment mechanism adjusts the position of the grid, the user does not have to perform an operation of adjusting the position of the obtained grid. As a result, since the same imaging conditions can be more easily maintained, the burden on the user can be reduced.

In the X-ray phase-contrast imaging system according to the above aspect, preferably, the position of the grating portion is adjusted based on the obtained positional deviation of the grating every time one or a plurality of X-ray images are generated. It is configured to control the alignment mechanism to do so. According to this structure, the same imaging condition can be maintained as accurately as possible by adjusting the position of the grid by the position adjustment mechanism each time the position shift of the grid is acquired. In addition, by adjusting the position of the grid by the position adjustment mechanism each time a plurality of X-ray images are generated, the frequency at which the position adjustment mechanism adjusts the position is compared to the case where the position is adjusted each time one sheet is generated. It can be reduced. As a result, it is possible to reduce the time required to adjust the position of the grid while maintaining the imaging conditions in a range that causes no practical problems.

In the X-ray phase difference imaging system according to the first aspect, the detection area portion is provided outside the imaging area portion. According to this structure, the slit pattern of the imaging area and the slit pattern of the detection area are separately designed without complicating the slit pattern such as changing a part of the slit pattern in the imaging area. It can be formed. As a result, the user can easily create the first lattice portion and the second lattice portion provided with the detection area portion.

In the X-ray phase contrast imaging system according to the above aspect, the detection area portion is provided in the grating area portion. According to this structure, by providing the detection area portion in the imaging area portion, it is not necessary to separate the slit pattern formation area into a plurality of places. As a result, an increase in size of the entire grid can be suppressed.

In the X-ray phase contrast imaging system in the above one aspect, preferably, the detection area portion is set immediately above the center point of the imaging area. Here, when provided in the lateral direction of the imaging region (in the direction orthogonal to the slit from the center point), the X-rays are obliquely incident on the slits of the grating section, and the attenuation of the X-rays is caused by hitting the slits. It occurs. However, when set just above the center point, the X-rays are incident perpendicularly to the slit, and therefore the slit does not hit and attenuation of the X-ray does not occur. Therefore, according to the above configuration, a sufficient amount of X-rays can be detected in the detection area portion, so that it is possible to generate an X-ray image in which interference fringes are clear.

In the X-ray phase contrast imaging system according to the above aspect, preferably, the detection area of the second grating has a slit pattern different from that of the imaging area, and the detection area of the first grating is the imaging area And the same slit pattern. With such a configuration, the position at which the imaging area portion of the first lattice portion forms a self-image and the position at which the detection area portion forms a self-image become the same. Therefore, it is not necessary to adjust the distance between the first lattice portion and the second lattice portion so that each of the imaging area portion and the detection area portion forms a self-image. In addition, with regard to the first grating portion, the same slit pattern may be formed in the imaging region portion and the detection region portion, so that the first grating portion can be easily formed.

According to the present invention, there is provided an X-ray phase difference imaging system capable of easily maintaining the same imaging conditions without updating air data. can do.

FIG. 1 shows the overall structure of an X-ray phase contrast imaging system according to an embodiment of the present invention. FIG. 7 shows an example of a position adjustment mechanism according to an embodiment of the present invention. It is a figure which shows an example of the detection area | region part of the X-ray phase difference imaging system by one Embodiment of this invention. (A) shows an example in the case of providing a detection area part out of an imaging area part. (B) shows the example at the time of providing a detection area part in an imaging area part. It is a figure for demonstrating the moire fringe and the image after Fourier transformation which are not intended generate | occur | produced when a 1st grating | lattice produces position shift in Z direction. It is an enlarged view of a Fourier-transformed image when the 1st grating | lattice raise | generates position shift of a Z direction. It is a figure for demonstrating the result of the unintended moire fringe and Fourier transformation which generate | occur | produce when the 1st grating | lattice produces position shift in the rotation direction around a Z direction axis. It is an enlarged view of a result of a Fourier transform when position shift in the rotation direction about the 1st lattice about a Z direction axis occurs. FIG. 5 illustrates a phase distribution after inverse Fourier transform according to an embodiment of the present invention. 5 is a flowchart illustrating the operation of an x-ray phase contrast imaging system according to an embodiment of the present invention. It is a figure which shows the modification of the detection area part of the X-ray phase difference imaging system by one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described based on the drawings.

(Configuration of X-ray phase contrast imaging system)
The configuration of an X-ray phase difference imaging system 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 10.

The X-ray phase difference imaging system 100 is an apparatus for imaging the inside of the subject T using the phase difference of the X-rays passing through the subject T. Further, the X-ray phase difference imaging system 100 is an apparatus for imaging the inside of the subject T by using a Talbot effect. The X-ray phase-contrast imaging system 100 can be used, for example, for imaging the inside of a subject T as an object in a nondestructive inspection application. In addition, for example, in medical applications, the X-ray phase difference imaging system 100 can be used for imaging the inside of a subject T as a living body.

As shown in FIG. 1, the X-ray phase difference imaging system 100 includes an X-ray source 1, a first grating unit 2, a second grating unit 3, an X-ray detector 4, an image processing unit 5, and a control unit. 6, a position adjusting mechanism 7, and a lattice part moving mechanism 8. In the present specification, the direction from the X-ray source 1 toward the first grating portion 2 is the Z2 direction, the opposite direction is the Z1 direction, and the Z1 direction and the Z2 direction are collectively the Z axis direction. The direction from the back side to the front side in the drawing is orthogonal to the Z axis, the Y1 direction and the opposite direction to the Y2 direction, and the Y1 direction and the Y2 direction are collectively referred to as the Y axis direction. Further, the upper direction in the drawing is the X1 direction, the lower direction in the drawing is the X2 direction, and the X1 direction and the X2 direction are collectively referred to as the X axis direction. In the first grating portion 2 and the second grating portion 3 of the present invention, slits are formed in the Y-axis direction. The X-axis direction is an example of the “direction orthogonal to the direction of the slits of the grating” in the claims. Furthermore, the Z-axis direction is an example of the “optical axis direction connecting the X-ray source and the X-ray detector” 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 Z1 direction.

The first grating section 2 has a plurality of slits 2a arranged in a predetermined cycle (pitch) d1 in the X-axis direction, and an X-ray phase change section 2b. Each of the slits 2a and the X-ray phase change portion 2b is formed to extend linearly. Further, each slit 2a and the X-ray phase change portion 2b are formed to extend in parallel with each other. The first grating section 2 is a so-called phase grating.

The first grating unit 2 is disposed between the X-ray source 1 and the second grating unit 3, and X-rays are emitted from the X-ray source 1. The first grating portion 2 is provided to form a self-image (not shown) of the first grating portion 2 by the Talbot effect. When the coherent X-rays pass through the slit-formed grid, an image (self-image) of the grid is formed at a predetermined distance (talbot distance) from the grid. This is called Talbot effect.

The second grating section 3 has a plurality of X-ray transmitting sections 3a and X-ray absorbing sections 3b arranged in the X axis direction at a predetermined period (pitch) d2. Each of the X-ray transmitting parts 3a and the X-ray absorbing parts 3b is formed to extend in a straight line. Further, each of the X-ray transmitting parts 3a and the X-ray absorbing parts 3b is formed to extend in parallel. The second grating section 3 is a so-called absorption grating. The first grating portion 2 and the second grating portion 3 are gratings having different roles, but the slit 2a and the X-ray transmitting portion 3a transmit X-rays. Further, the X-ray absorbing portion 3b plays a role of shielding the X-ray, and the X-ray phase change portion 2b changes the phase of the X-ray due to the difference in refractive index with the slit 2a.

The second grating unit 3 is disposed between the first grating unit 2 and the X-ray detector 4, and the X-rays that have passed through the first grating unit 2 are irradiated. In addition, the second grid portion 3 is disposed at a position separated from the first grid portion 2 by the Talbot distance. The second grating 3 interferes with the self-image of the first grating 2 to form interference fringes (not shown) on the detection surface of the X-ray detector 4. That is, in the X-ray phase difference imaging system 100, the first grating unit 2 and the second grating unit 3 are provided as a plurality of gratings, and the first grating unit 1 in the Z2 direction from the X-ray source 1 to the X-ray detector 4 The lattice portion 2 and the second lattice portion 3 are arranged in this order.

The first lattice unit 2 and the second lattice unit 3 include an imaging area unit 10 for imaging the subject T, and a detection area unit 9 other than the imaging area unit 10.

<Detection area part>
The detection area unit 9 is a place where a pixel value for acquiring positional deviation is acquired. The detection area part 9 is provided in each of the first lattice part 2 and the second lattice part 3 (see FIG. 1). FIG. 3 is a view of the first grating section 2 in the Z2 direction from the X-ray source 1 to the second grating section 3. The detection area unit 9 and the imaging area unit 10 are provided on the same substrate (see FIG. 3). The detection area unit 9 may be provided in the imaging area unit 10, but is provided separately from the imaging area unit 10. At least one detection area unit 9 of the first lattice unit 2 or the second lattice unit 3 has a lattice arrangement pattern different from that of the imaging area unit 10. The slit pattern of the detection area 9 of the first grating 2 is different from the slit pattern of the detection area 9 of the second grating 3 in order to form interference fringes. The detection area unit 9 of the second grid unit 3 has a slit pattern different from that of the imaging area unit 10, and the detection area unit 9 of the first lattice unit 2 has the same slit pattern as the imaging area unit 10. FIG. 3A shows an example in which the arrangement pitch of the slits of the grating is changed. FIG. 3B shows an example in which the slit pattern of the grating is changed. FIG. 3A shows an example in which the detection area unit 9 is provided outside the lattice area of the imaging area unit 10. FIG. 3B shows an example in which the detection area unit 9 is provided in the lattice area of the imaging area unit 10. The position shift due to the rotation becomes larger as it goes away from the center of the imaging area 10 of the lattice section, and detection becomes easier. Therefore, the detection area 9 is provided away from the center of the imaging area 10.

The detection area unit 9 is provided at one point immediately above the center point of the imaging area unit 10 of the lattice unit. That is, one point is provided in the Y1 direction from the center point of the imaging area unit 10. When X-rays are obliquely incident on the slit from the center point of the imaging region in a direction orthogonal to the slit, the attenuation of the X-ray occurs due to the aspect ratio of the depth and the width of the slit of the grating section. However, setting the position just above the center point makes X-ray incidence perpendicular to the slit, so that attenuation of the X-ray hardly occurs. When it is desired to increase the accuracy of acquisition of positional deviation, the detection area section 9 is widely provided. Alternatively, the detection area unit 9 may be provided at two places above and below the center point of the imaging area unit 10, and is provided at a total of four places in the upper, lower, left and right.

The X-ray detector 4 is configured to detect an X-ray, convert the detected X-ray into an electric signal, and read the converted electric signal as an image signal. The X-ray detector 4 is, for example, an FPD (Flat Panel Detector). The X-ray detector 4 is composed of a plurality of conversion elements (not shown) and pixel electrodes (not shown) disposed on the plurality of conversion elements. The plurality of conversion elements and the pixel electrodes are arrayed in the X direction and the Y direction at a predetermined period (pixel pitch). The X-ray detector 4 is configured to output the acquired image signal to the image processing unit 5.

The image processing unit 5 generates a contrast image based on the X-ray image acquired from the X-ray detector 4. Interference fringes are formed on the acquired X-ray image.

Based on the interference fringes of the X-ray image in the detection area unit 9, the control unit 6 shifts the position of the lattice unit in the optical axis direction (Z-axis direction) connecting the X-ray source 1 and the X-ray detector 4 At least one positional deviation of the positional deviation of the lattice part in the direction (X-axis direction) orthogonal to the slit of the part or the positional deviation of the lattice part due to rotation around the optical axis (Rz) is acquired.

The control unit 6 acquires the phase shift and the cycle shift of the interference pattern based on the image 11 after Fourier transform of the interference pattern of the X-ray image. Based on the image 11 after Fourier transform of the interference fringes of the X-ray image, the control unit 6 has zero-order peaks in a direction (X-axis direction) orthogonal to the slit direction and in a direction (Y-axis direction) parallel to the slit direction. Positional deviation of the grating portion in the optical axis direction (Z-axis direction) connecting the X-ray source 1 and the X-ray detector 4 from the distance between 12 and the primary peak 13 and around the optical axis (Rz) The positional deviation of the grid part by rotation is acquired. The control unit 6 is configured to control the position adjusting mechanism 7 to adjust the position of the grid based on the position shift of the obtained grid every time one X-ray image is generated or a plurality of X-ray images are generated. ing. The user sets the frequency of position adjustment in the control unit 6 based on the frequency of occurrence of grid misalignment or the like.

As shown in FIG. 2, the position adjustment mechanism 7 includes a base 70, a stage support 71, a stage 72 on which a grid is placed, a first drive 73, a second drive 74, and a third drive. 75, a fourth drive unit 76, and a fifth drive unit 77. The first drive unit 73 to the fifth drive unit 77 each include, for example, a motor and the like. Further, the stage 72 is configured by a connecting portion 72a, a rotating portion 72b around the Z-axis direction, and a rotating portion 72c around the X-axis direction.

The first drive unit 73, the second drive unit 74, and the third drive unit 75 are respectively provided on the upper surface of the base unit 70. The first drive unit 73 is configured to reciprocate the stage support unit 71 in the Z direction. Further, the second drive unit 74 is configured to rotate the stage support unit 71 around the Y-axis direction. Further, the third drive unit 75 is configured to reciprocate the stage support unit 71 in the X-axis direction. The stage support portion 71 is connected to the connecting portion 72 a of the stage 72, and the stage 72 also moves with the movement of the stage support portion 71.

The fourth drive unit 76 is configured to reciprocate the rotation unit 72b around the Z-axis direction in the X direction. A bottom surface of the rotation portion 72b in the Z-axis direction is formed in a convex curved shape toward the connection portion 72a, and by reciprocating in the X direction, the stage 72 is rotated about the Z-axis direction. It is configured. The fifth drive unit 77 is configured to reciprocate the rotation unit 72c around the X-axis direction in the Z-axis direction. The bottom surface of the rotation portion 72c around the X axis direction is formed in a convex curved shape toward the rotation portion 72b around the Z axis direction, and the stage 72 can be reciprocated in the Z axis direction. It is configured to pivot on the

Therefore, the position adjustment mechanism 7 is configured to be able to adjust the grating in the Z-axis direction by the first drive unit 73. Further, the position adjustment mechanism 7 is configured to be able to adjust the grating in the rotational direction (Ry direction) around the Y-axis direction by the second drive unit 74. The position adjustment mechanism 7 is configured to be able to adjust the grid in the X-axis direction by the third drive unit 75. Further, the position adjustment mechanism 7 is configured to be able to adjust the grating in the rotation direction (Rz direction) around the Z-axis direction by the fourth drive unit 76. Further, the position adjustment mechanism 7 is configured to be able to adjust the grating in the rotation direction (Rx direction) around the X-axis direction by the fifth drive unit 77. Reciprocation in each axial direction is, for example, several mm, respectively. Further, the pivotable 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 axis direction are, for example, several degrees, respectively. The position adjustment mechanism 7 is connected to at least one of the first grating unit 2 and the second grating unit 3.

The grid unit moving mechanism 8 is configured to step-move the first grid unit 2 in the grid plane (in the XY plane) in the direction (X-axis direction) orthogonal to the grid direction based on the signal from the control unit 6 It is done. Specifically, the grid unit moving mechanism 8 divides the period d2 of the second grid unit 3 into n, and moves the second grid unit 3 in steps of d2 / n. Here, n is a positive integer. Further, the lattice part moving mechanism 8 includes, for example, a stepping motor, a piezo actuator, and the like.

The control unit 6 performs fast Fourier transform (FFT) on the X-ray image generated by the image processing unit 5.

Here, in the image after Fourier transform 11 shown in FIG. 4, based on the distance between the zero-order peak 12 and the first-order peak 13, the positional deviation of the first grating section 2 or the second grating section 3 in the Z direction, The rotational deviation in the Rz direction is configured to be acquired.

The X-ray phase difference imaging system 100 arranges the first grating 2 and the second grating 3 such that the distance in the Z direction between the first grating 2 and the second grating 3 is the Talbot distance. In the embodiment, since the slit patterns of the gratings of the first grating section 2 and the second grating section 3 are different, interference fringes are observed.

However, when the distance in the Z direction between the first grating portion 2 and the second grating portion 3 deviates from the Talbot distance, the period of the self-image of the first grating portion 2 changes. In the interference fringe image, as the first grating portion 2 is separated from the normal position (a position where the distance between the first grating portion 2 and the second grating portion 3 is the Talbot distance), the period of the interference fringes becomes finer. Moreover, in the image 11 after Fourier transform, the 0th order peak 12 and the 1st order peak are separated as the first lattice portion 2 is separated from the normal position (the position where the distance between the first lattice portion 2 and the second lattice portion 3 is the Talbot distance). The distance dx between 13 and 13 increases.

FIG. 5 is an example of the enlarged view of the image 11 after Fourier transform in the case where positional deviation in the optical axis direction (Z-axis direction) of the first grating portion 2 occurs. dx is the distance in the X direction between the zero-order peak 12 and the first-order peak 13; In the present embodiment, the control unit 6 obtains positional deviation of the first grating unit 2 or the second grating unit 3 in the Z direction based on the distance dx between the zero-order peak 12 and the first-order peak 13 Is configured.

Further, as shown in FIG. 6, in the embodiment, since the slit patterns of the gratings of the first grating portion 2 and the second grating portion 3 are different, interference fringes are observed. When a shift due to rotation around the optical axis (Rz) occurs in the first grating portion 2, as shown in the example of FIG. 6, the self-image is also inclined and thus, the observed interference fringes in the Y direction It is formed. Also, as the positional deviation due to rotation increases, the period of the interference fringes becomes finer, and the distance dy in the Y direction between the zero-order peak 12 and the first-order peak 13 of the obtained Fourier-transformed image 11 increases.

In FIG. 8, the control unit 6 cuts out the peripheral region of the primary peak 13 of the image obtained by subjecting the interference fringes of the X-ray image to fast Fourier transform (FFT), and sets the other regions to 0. , And further inverse Fourier fast transform (IFFT) to show the obtained phase distribution 14. The distribution of the phases of the formed interference fringes appears in the phase distribution 14. For example, when a positional deviation of a half cycle occurs in the lattice, the phase distribution 14 has a pixel value brighter by π than the phase distribution 14 of the sample image. The control unit 6 obtains pixel values from the phase distribution 14 and obtains displacement in the X-axis direction.

(Position shift acquisition operation)
The operation of the X-ray phase difference imaging system 100 in the present embodiment for acquiring positional deviation will be described with reference to FIG. 9. In the present embodiment, a case where one detection area portion 9 is provided immediately above (in the Y1 direction) will be described as an example.

First, the user acquires air data to be photographed without arranging the subject T, and at the same time acquires a value (initial value) in a state where no deviation occurs as a reference for acquiring a positional deviation. In step S <b> 1, the X-ray phase difference imaging system 100 applies X-rays from the X-ray source 1 to the detection area unit 9 and the imaging area unit 10.

In step S <b> 2, the X-ray detector 4 acquires an X-ray image in which interference fringes are formed in the detection area portion 9. In step S3, the control unit 6 Fourier-transforms the acquired X-ray image. Then, a zero-order peak 12 and a first-order peak 13 appear in the image 11 after Fourier transform.

In step S4, the distance in the X-axis direction between the zero-order peak 12 and the primary peak 13 and the distance in the y-axis direction are acquired. The initial value of the distance in the X-axis direction between the zero-order peak 12 and the first-order peak 13 appearing in the image 11 after Fourier transform is dx ', and the y-axis direction between the zero-order peak 12 and the first-order peak 13 Let dy 'be the initial value of the distance of.

In step S5, the area around the primary peak 13 is cut out, the other areas are set to 0, and the image is moved to the center. Then, in step S6, inverse Fourier transform is performed with the primary peak 13 at the center of the image. Then, the phase distribution 14 can be acquired. As shown in FIG. 8, in the phase distribution 14, a distribution of phases of the formed interference fringes appears. Step S7 obtains pixel values from a plurality of locations of the phase distribution 14 and obtains an average φ ′ of the phase values. The average of the phase values acquired as the initial value is assumed to be φ '. Through the above steps, the initial value is obtained.

Next, the user arranges the subject T and acquires a sample image to be photographed, and at the same time acquires positional deviation. In step S8, the X-ray phase difference imaging system 100 applies X-rays from the X-ray source 1 to the detection area unit 9 and the imaging area unit 10.

In step S <b> 9, the X-ray detector 4 acquires an X-ray image in which interference fringes are formed in the detection area portion 9. In step S10, the control unit 6 Fourier-transforms the acquired X-ray image. Then, a zero-order peak 12 and a first-order peak 13 appear in the image 11 after Fourier transform.

In step S11, the distance dx in the X-axis direction between the zero-order peak 12 and the primary peak 13 and the distance dy in the y-axis direction (see FIGS. 5 and 7) are acquired.

In step S12, the area around the primary peak 13 is cut out, the other areas are set to 0, and the image is moved to the center. Then, in step S13, inverse Fourier transform is performed with the primary peak 13 at the center of the image. Then, the phase distribution 14 can be acquired. As shown in FIG. 8, in the phase distribution 14, a distribution of phases of the formed interference fringes appears. A step S14 acquires pixel values from a plurality of locations of the phase distribution 14, and acquires an average value φ.

Moving to step S15, the positional deviation is acquired. Positional displacement [Delta] X ₁ in the X-axis direction, positional displacement [Delta] Z ₁ and the optical axis (Rz) positional deviation DerutaRz ₁ by rotation about the optical axis (Z-axis) is determined by Equation (1) below. p _{1 and} p ₂ represent the period of the lattice, and the unit is m. s _x and s _y represent the image size of the detection area unit 9. Δφ = φ′−φ. R ₁ is the distance between the gratings, D is represents the distance from the center of the imaging region 10 to the detection region 9, the unit is m. _{Δd x = d x '-d x} , Δd y = d y' is -d _y.

Moving to step S16, the position adjustment mechanism 7 corrects the position of the grid based on the acquired positional deviation.

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

In the X-ray phase-contrast imaging system 100 of the present embodiment, as described above, the first grating portion 2 provided between the X-ray source 1 and the X-ray detector 4 for forming a self-image; A plurality of lattice units including the second lattice unit 3 for causing interference with the self-image of the one lattice unit 2, a lattice unit moving mechanism 8 for moving the lattice units at constant intervals, and control for acquiring positional deviation of the lattice units The first lattice unit 2 and the second lattice unit 3 include a photographing area unit 10 for photographing the subject T, and a detection area unit 9 other than the photographing area unit 10, and the first lattice unit 2 is provided. And at least one detection area section 9 of the second grid section 3 has a slit pattern different from that of the imaging area section 10, and the control section 6 determines X based on the interference fringes of the X-ray image in the detection area section 9. Misalignment of the grating in the direction of the optical axis connecting the radiation source 1 and the X-ray detector 4 Position of the grating portion in a direction perpendicular to the bets deviation, or is configured to obtain at least one of the displacement of the positional deviation of the grating portion by rotation of the optical axis. With this configuration, the detection area section 9 of the first grating section 2 and the detection area section 9 of the second grating section 3 obtain positional deviation based on interference fringes generated by interference. Can. As a result, the user can easily acquire positional deviation of the grid (change in imaging condition) by generating interference fringes by normal imaging without reacquiring air data. That is, by analyzing the change in the phase and period of the interference fringes, it is possible to obtain the positional deviation of the grid that has occurred from the time of air data shooting to the time of sample data shooting. As a result, since it becomes possible to adjust the positional deviation of the grid based on the acquired positional deviation, the same imaging condition can be easily maintained without updating the air data.

Further, the control unit 6 is configured to acquire the phase shift and the cycle shift of the interference fringes based on the image 11 after Fourier transform of the interference fringes of the X-ray image. Here, when the phase shift and the cycle shift of the interference fringes occur, the position of the primary peak 13 appearing in the image 11 after Fourier transform is different. That is, based on the position of the primary peak 13 of the image 11 after Fourier transform, it is possible to acquire the phase shift and the cycle shift of the interference fringes. As a result, according to the above configuration, the user can acquire the positional deviation of the lattice portion from the acquired image 11 after Fourier transform. As a result, since it is possible to adjust the positional deviation of the grid based on the acquired positional deviation, it is possible to maintain the same imaging conditions as when the air data is acquired first.

Further, based on the image 11 after Fourier transform of the interference fringes of the X-ray image, the control unit 6 sets the zeroth order peak 12 and the first order peak 13 in the direction orthogonal to the slit direction and in the direction parallel to the slit direction. From the distance between the X-ray source 1 and the X-ray detector 4 in the direction of the optical axis, and the positional deviation of the grating due to rotation around the optical axis. . Here, the positional deviation of the grating portion in the optical axis direction connecting the X-ray source 1 and the X-ray detector 4 is the distance between the zero-order peak 12 and the primary peak 13 in the X-axis direction as a result after Fourier transformation. Appears as In addition, positional deviation of the grating portion due to rotation around the optical axis appears as a distance between the zero-order peak 12 and the primary peak 13 after the Fourier transform in the Y-axis direction. Therefore, if configured as described above, the user is able to position the grid portion in the optical axis direction connecting the X-ray source 1 and the X-ray detector 4 from the Fourier transformed image 11 and rotate around the optical axis It is possible to easily obtain the positional deviation of the grid part due to

Also, the X-ray image of the detection area section 9 is subjected to Fourier transform to cut out the area around the primary peak 13 and the other areas are set to 0, and then moved to the center of the image to perform inverse Fourier transform. The positional deviation of the grating portion in the direction orthogonal to the slits of the grating portion is acquired from the acquired phase distribution 14. Here, the positional deviation in the direction orthogonal to the slits of the grating portion appears as a phase deviation in the result after inverse Fourier transform. Therefore, if configured as described above, the user can easily acquire positional deviation in the direction orthogonal to the slits of the lattice portion.

In addition, the X-ray phase difference imaging system 100 of the present embodiment further includes a position adjustment mechanism 7 for adjusting the position of the grating unit, and the control unit 6 determines the position of the grating unit based on the acquired positional deviation. Control is performed to adjust the position by the position adjustment mechanism 7. By doing this, since the position adjustment mechanism 7 adjusts the position of the grid, the user does not have to perform the work of adjusting the position of the obtained grid. As a result, since the same imaging conditions can be more easily maintained, the burden on the user can be reduced.

Further, in the X-ray phase difference imaging system 100 according to the present embodiment, the control unit 6 generates a single X-ray image or generates a plurality of X-ray images, based on the acquired positional deviation of the lattice. It is configured to control the position adjustment mechanism 7 so as to adjust the position. By doing this, the same imaging conditions can be maintained as accurately as possible by adjusting the position of the grid by the position adjustment mechanism 7 each time the position shift of the grid is acquired. In addition, the position adjustment mechanism 7 adjusts the position by adjusting the position of the grid by the position adjustment mechanism 7 each time a plurality of X-ray images are generated, as compared to the case where the position is adjusted each time one sheet is generated. The frequency can be reduced. As a result, it is possible to reduce the time required to adjust the position of the grid while maintaining the imaging conditions in a range that causes no practical problems.

In addition, in the X-ray phase difference imaging system 100 of the present embodiment, the detection area unit 9 is provided outside the lattice area. By doing this, the slit pattern of the imaging area unit 10 and the slit pattern of the detection area unit 9 can be obtained without changing the slit pattern of the imaging area unit 10 or making the slit pattern complicated. It can be designed and formed separately. As a result, the user can easily create the first lattice portion 2 and the second lattice portion 3 provided with the detection area portion 9.

Further, in the X-ray phase difference imaging system 100 of the present embodiment, the detection area unit 9 is provided in the imaging area unit 10. By providing the detection area section 9 in the imaging area section 10 in this way, it is not necessary to separate the slit pattern formation area into a plurality of places. As a result, an increase in size of the entire grid can be suppressed.

Further, in the X-ray phase difference imaging system 100 of the present embodiment, the detection area unit 9 is set immediately above the center point. Here, when provided in the side of the imaging region 10 (in the direction perpendicular to the slit from the center point), the X-rays are obliquely incident on the slits of the grating, and the X-rays Attenuation occurs. However, when set right above the center point, the X-rays are perpendicularly incident on the slit, and thus the slit does not collide with the X-ray attenuation. Therefore, with the above-described configuration, a sufficient amount of X-rays can be detected in the detection area unit 9, and an X-ray image with a clear interference fringe can be generated.

Further, in the X-ray phase difference imaging system 100 of the present embodiment, the detection area 9 of the second grating 3 has a slit pattern different from that of the imaging area 10, and the detection area 9 of the first grating 2 is , Has the same slit pattern as the imaging area unit 10. By doing this, the position where the imaging area unit 10 of the first grid unit 2 forms a self-image and the position where the detection area unit 9 forms a self-image become the same. Therefore, there is no need to adjust the distance between the first grating unit 2 and the second grating unit 3 so that each of the imaging region unit 10 and the detection region unit 9 forms a self-image. In addition, since the same slit pattern may be formed in the imaging area unit 10 and the detection area unit 9 for the first lattice unit 2, the first lattice unit 2 can be easily formed.

(Modification)
It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the description of the embodiment described above but by the scope of the claims, and further includes all modifications (variations) within the meaning and scope equivalent to the scope of the claims.

For example, although the example which provides the 1st lattice part 2 and the 2nd lattice part 3 as a plurality of lattices was shown in a 1st embodiment of the above, the present invention is not limited to this. For example, the third grating may be provided between the X-ray source 1 and the first grating section 2. The third grating is disposed between the X-ray source 1 and the first grating section 2, and X-rays are emitted from the X-ray source 1. The third grating is configured to set the X-rays that have passed through the slits as line light sources corresponding to the positions of the slits. Thereby, the coherence of the X-ray irradiated from the X-ray source 1 can be enhanced by the third grating. As a result, since it becomes possible to form a self-image of the first grating portion 2 without depending on the focal diameter of the X-ray source 1, the freedom of selection of the X-ray source 1 can be improved.

When the detection area unit 9 is provided in the lattice area, a threshold may be provided for the pixel value of the detection area unit 9 so that the subject T is not included in the detection area unit 9. When a threshold is provided, it may be configured to change the detection area unit 9 if it is less than the threshold.

Although the example which provides the detection area | region part 9 in one each in the 1st grating | lattice part 2 and the 2nd grating | lattice part 3 was shown, as shown in FIG. 10, you may provide the detection area | region part 9 in four places. The positional deviation ΔX ₁ in the X-axis direction, the positional deviation ΔZ _{1 in} the optical axis direction (Z-axis), and the positional deviation ΔRz ₁ due to rotation around the optical axis (Rz) in the case of providing four detection regions 9 are as follows It is obtained by the following equation (2). p ₁ p ₂ represents the period of the lattice, and the unit is m. Δφ _u = φ _u '-φ _u , Δφ _d = φ _d ' -φ _d , Δφ _w = φ _w '-φ _w , Δφ _r = φ _r ' -φ _r is the air data in each detection area portion 9 the average of the differential phase value _{(φ u ', φ d'} , φ w ', φ r') and the average of the differential phase value of the sample data _{(φ u, φ d, φ} w, φ r) represents the difference, The unit is radians. R1 represents the distance between the grids, D represents the distance from the center of the imaging area 10 to the detection area 9, and the unit is m.

DESCRIPTION OF SYMBOLS 1 X-ray source 2 1st grating | lattice part 3 2nd grating | lattice part 4 X-ray detector 5 Image processing part 6 control part 7 position adjustment mechanism 8 lattice part moving mechanism 9 detection area part 10 imaging area part 100 X-ray phase difference imaging system

Claims (10)

An x-ray source,
An X-ray detector for detecting the irradiated X-rays;
A first grating portion for transmitting X-rays provided between the X-ray source and the X-ray detector, and a second grating portion for causing interference with the self-image of the first grating portion With multiple grids,
A grid part moving mechanism for moving the grid part at a constant interval;
An image processing unit that generates a contrast image from the X-ray detector based on the X-ray image;
A control unit that acquires positional deviation of the grid unit;
Equipped with
The first grid unit and the second grid unit include a shooting area unit for shooting an object, and a detection area unit other than the shooting area unit.
At least one of the detection area units of the first lattice unit and the second lattice unit has a slit pattern different from that of the imaging area unit,
The control unit is configured to shift the position of the grid unit in the direction of the optical axis connecting the X-ray source and the X-ray detector based on the interference fringes of the X-ray image in the detection area unit; An X-ray phase difference imaging system configured to acquire at least one positional deviation of positional deviation of the lattice in a direction orthogonal to a slit or positional deviation of the lattice due to rotation around an optical axis. The X-ray phase difference imaging according to claim 1, wherein the control unit is configured to acquire a phase shift and a cycle shift of interference fringes based on an image obtained by subjecting the interference fringes of the X-ray image to Fourier transform. system. The controller determines a distance between a zero-order peak and a first-order peak in a direction orthogonal to the direction of the slit and in a direction parallel to the direction of the slit based on the image after the Fourier transform of the interference fringes of the X-ray image From the above, it is configured to acquire the positional deviation of the grating part in the optical axis direction connecting the X-ray source and the X-ray detector, and the positional deviation of the grating part due to rotation around the optical axis. The X-ray phase difference imaging system according to claim 2. The control unit Fourier-transforms the X-ray image of the detection area portion to cut out the peripheral area of the primary peak, sets the other areas to 0, moves the area to the center of the image, and performs inverse Fourier transform The X-ray phase difference imaging system according to claim 2, configured to acquire positional deviation of the grating part in a direction orthogonal to the slit of the grating part from the acquired phase distribution. It further comprises a position adjustment mechanism for adjusting the position of the grid part,
The X-ray phase difference imaging according to claim 1, wherein the control unit is configured to perform control of adjusting the position of the grating unit by the position adjusting mechanism based on the acquired positional deviation of the grating unit. system. The control unit is configured to adjust the position of the grid unit based on the acquired positional shift of the grid unit every time one or a plurality of X-ray images are generated. The X-ray phase difference imaging system according to claim 5, configured to control The X-ray phase difference imaging system according to claim 1, wherein the detection area unit is provided outside an imaging area. The X-ray phase difference imaging system according to claim 1, wherein the detection area unit is provided in an imaging area. The X-ray phase difference imaging system according to claim 1, wherein the detection area unit is set immediately above a center point of the imaging area unit. The detection area portion of the second grid portion has a slit pattern different from the imaging area portion, and the detection region portion of the first grid portion has the same slit pattern as the imaging area portion. The X-ray phase difference imaging system according to claim 1.

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