JP5708652B2 - X-ray imaging system - Google Patents

Description

  The present invention relates to an X-ray imaging system using a Talbot-Lau interferometer.

  Most of medical X-ray images used for diagnosis are images by an absorption contrast method. In the absorption contrast method, contrast is formed by a difference in attenuation of X-ray intensity when X-rays pass through a subject. On the other hand, a phase contrast method has been proposed in which contrast is obtained not by X-ray absorption but by X-ray phase change. For example, phase contrast imaging is performed in which X-ray images with high visibility are obtained by edge enhancement using X-ray refraction during magnified imaging (see, for example, Patent Documents 1 and 2).

  The absorption contrast method is effective for photographing a subject having a large X-ray absorption such as bone. On the other hand, the phase contrast method has a small X-ray absorption difference and can image breast tissue, articular cartilage, and soft tissue around the joint, which are difficult to appear as an image by the absorption contrast method. Application to diagnosis is expected.

  As one of phase contrast imaging, a Talbot interferometer using the Talbot effect has been studied (for example, Patent Documents 3 to 5). The Talbot effect is a phenomenon in which, when coherent light is transmitted through a first grating provided with slits at a certain period, the grating image is formed at a certain period in the light traveling direction. This lattice image is called a self-image, and the Talbot interferometer arranges the second lattice at a position connecting the self-images, and measures interference fringes generated by slightly shifting the second lattice. If an object is placed in front of the second grating, the moire is disturbed. Therefore, if X-ray imaging is performed with a Talbot interferometer, the object is placed in front of the first grating and irradiated with coherent X-rays. It is possible to obtain a reconstructed image of the subject by calculating a moire image.

  There has also been proposed a Talbot-Lau interferometer in which a multi-slit is installed between the X-ray source and the first grating to increase the X-ray irradiation dose (see, for example, Patent Document 6). A conventional Talbot-Lau interferometer takes a plurality of moire images at a constant interval while moving the first grating or the second grating (relatively moving both gratings). Is provided for the increase of

  The inventors of the present application have also found that an image equivalent to the reconstructed image obtained by the conventional method can be obtained by moving the multi slit with respect to the first grating and the second grating in the Talbot-Lau interferometer. The application was filed in Japanese Patent Application 2009-214483 (PCT / JP2010 / 53978).

  As a method for creating a reconstructed image from a moire image, as described above, a reconstructed image is created by a fringe scanning method from a plurality of moire images with a constant periodic interval obtained by a Talbot interferometer and a Talbot-low interferometer. In addition, a method of creating a reconstructed image from a single moire image using a Fourier transform method is also known (see, for example, Non-Patent Document 1). The reconstructed image obtained by the Fourier transform method has a lower spatial resolution than the fringe scanning method, but does not require a plurality of moire images unlike the fringe scanning method. Therefore, it is possible to shorten the shooting time and to suppress the influence of the body movement of the subject during a plurality of shootings. Further, since the mechanism operation at the time of photographing is eliminated, there is no false image due to an error of the grating or multi-slit feeding mechanism.

  In order for the reconstructed image created by the fringe scanning method to be clear, the interference fringes of the individual moire images used to create the reconstructed image are not only clear but also the number of interference fringes is small. It is known that it is necessary (see, for example, Non-Patent Document 2 (page 15)). On the other hand, it is known that in order to create a reconstructed image by the Fourier transform method, it is necessary that the interference fringes of the moire image be sufficiently fine.

JP 2007-268033 A JP 2008-18060 A JP 58-16216 A International Publication No. 2004/058070 Pamphlet Japanese Patent Application Laid-Open No. 2007-203063 International Publication No. 2008/102898 Pamphlet

M. Takeda, H. Ina, and S. Kobayashi, “Fourier-Transform Methode of Fringe-Pattern Analysis for Computer-Based Topography and Interferometry” J.Opt.Soc.Am.72,156 (1982) Asahi Yamada, edited by Shunsuke Yokoseki, “Moire fringe and interference fringe applied measurement method”, Corona, December 10, 1996

As described above, since the fringe scanning method and the Fourier transform method have different merits, it is preferable that the photographing apparatus can photograph the moire image for the fringe scanning method and the moire image for the Fourier transform method according to the purpose. . For that purpose, the relative positional relationship between the first grating and the second grating, and the slit longitudinal direction of the first grating and the second grating (slit direction) so that the number of interference fringes of the moire image is optimized respectively. It is necessary to adjust the slit direction of the multi slit.
However, it is not easy to perform adjustment to optimize the number of interference fringes in the moire image every time the two imaging methods are switched, and it takes a considerable amount of time for adjustment.

  An object of the present invention is to make it possible to easily switch between a shooting mode for the fringe scanning method and a shooting mode for the Fourier transform method as necessary.

In order to solve the above problems, according to a first aspect of the present invention,
An X-ray source that emits X-rays;
A multi-slit composed of a plurality of slits arranged in a direction orthogonal to the X-ray irradiation axis direction;
A driving unit for moving the multi-slit in the slit arrangement direction;
A first grating and a second grating configured by arranging a plurality of slits in a direction orthogonal to the X-ray irradiation axis direction;
Subject table,
A conversion element that generates an electrical signal in accordance with the irradiated X-rays is arranged in a two-dimensional manner, and includes an X-ray detector that reads the electrical signal generated by the conversion element as an image signal,
The multi-slit is moved in the slit arrangement direction by the driving unit, and the X-ray detector detects the image signal in accordance with the X-rays emitted from the X-ray source every time the multi-slit moves at a constant cycle interval. An X-ray imaging system capable of repeating a reading process and obtaining a plurality of moire images at a constant cycle interval,
A setting unit for setting one of the first shooting mode and the second shooting mode;
A relative angle adjusting unit that adjusts a relative angle between the first grating and the second grating in accordance with the photographing mode set by the setting unit;
In accordance with the shooting mode set by the setting unit, a control unit that controls activation or stop of the drive unit,
An image processing unit that creates a reconstructed image from a moire image obtained by the X-ray detector according to the imaging mode set by the setting unit;
Is provided.

The X-ray imaging system includes:
The first lattice and the second lattice adjusted to a relative angle according to the set photographing mode by the relative angle adjustment unit with respect to the subject placed on the subject table while maintaining the relative angle. A grating rotating unit that rotates around an X-ray irradiation axis to adjust the slit direction of the first grating and the second grating;
A multi-slit rotating unit that rotates the multi-slit around the X-ray irradiation axis in order to adjust the slit direction of the multi-slit;
With
The control unit is configured such that the slit direction of the multi-slit is predetermined with respect to the first grating and the second grating in which the slit direction with respect to the subject placed on the subject table is adjusted by the grating rotating unit. It is preferable to control the multi-slit rotator so that

  The multi-slit rotating unit preferably rotates the multi-slit and the driving unit integrally.

  The grating rotating unit preferably rotates the first grating, the second grating, and the relative angle adjusting unit integrally.

  The grating rotating unit preferably rotates the first grating, the second grating, and the X-ray detector integrally.

According to the present invention, it is possible to easily switch between the shooting mode for the fringe scanning method and the shooting mode for the Fourier transform method as necessary.
In the fringe scanning method, the multi-slit is moved with respect to the first grating and the second grating, the switching between the fringe scanning method and the Fourier transform method is performed, and the relative phase angle between the first grating and the second grating is variable. Therefore, the accuracy required in both shooting modes can be maintained.
Furthermore, using the imaging apparatus according to the present invention, a primary diagnosis is performed based on an image obtained by a Fourier transform method that can be performed in a relatively short time. The secondary diagnosis (precise diagnosis) can be performed based on the obtained image, and the diagnosis flow in the hospital can be made more efficient.
Further, when performing the fringe scanning method of the secondary diagnosis (precise diagnosis), the multi-slit, the first grating, and the second grating are applied to the subject based on the diagnosis result in the primary diagnosis based on the image by the Fourier transform method. By adjusting the phase direction, it is possible to obtain a precise image (reproduced the lesion part faithfully) of the subject site, and it is possible to lead to early detection and early treatment of the lesion site.

1 is a diagram illustrating an X-ray imaging system (including a side view of an X-ray imaging apparatus) according to the present embodiment. It is a top view of a multi slit. It is the top view and side view of the state which hold | maintained the multi slit in the holder. It is the top view and side view of a multi slit rotation part. It is a top view of a subject holder. It is a side view of a subject holder. It is a top view of a lattice rotation part. It is the top view and side view of a grating | lattice rotation part of the state which mounted | wore the 1st grating | lattice and the 2nd grating | lattice. It is the top view which expanded and showed the holding | maintenance part of the lattice rotation part in the holding | maintenance part of FIG. It is EE 'sectional drawing in FIG. 7A. It is a figure which shows the state which hold | maintained the lattice rotation part in the holding | maintenance part. It is sectional drawing which shows the rotation tray which can rotate 1st grating | lattice and 2nd grating | lattice, and an X-ray detector integrally. It is a block diagram which shows the functional structure of a main-body part. It is a block diagram which shows the functional structure of a controller. It is a figure explaining the principle of a Talbot interferometer. It is a flowchart which shows the imaging | photography control processing by the control part of an X-ray imaging apparatus. It is a flowchart which shows the 1st imaging | photography mode process performed by step S2 of FIG. It is a flowchart which shows the 1st imaging | photography mode process performed by step S2 of FIG. It is a flowchart which shows the 2nd imaging | photography mode process performed by step S3 of FIG. It is a flowchart which shows the 2nd imaging | photography mode process performed by step S3 of FIG. It is a flowchart which shows the reconstruction image creation process by the fringe scanning method performed by the control part of a controller. It is a flowchart which shows the reconstruction image creation process by the fringe scanning method performed by the control part of a controller. It is a figure for demonstrating the X-ray intensity fluctuation | variation correction | amendment between several moire images. It is a figure which shows the moire image obtained by imaging | photography of 5 steps. It is a graph which shows the X-ray relative intensity of the attention pixel of the moire image of each step. It is a flowchart which shows the reconstruction image preparation process by the Fourier-transform method performed by the control part of a controller. It is a figure which shows an example of the moire image with a subject image | photographed in 2nd imaging | photography mode. It is a figure which shows the result of having performed the two-dimensional Fourier transform of the moire image of FIG. 19A. It is a figure which shows an example of the moiré image without a subject image | photographed in 2nd imaging | photography mode. It is a figure which shows the result of having performed the two-dimensional Fourier transform of the moire image of FIG. 20A. The grating direction when the slit direction of the grating is arranged vertically, the interference fringes photographed in the first photographing mode, the interference fringes photographed in the second photographing mode, and the interference fringes photographed in the second photographing mode. It is a figure which shows the result of Fourier-transform. The grating direction when the slit direction of the grating is horizontally arranged, the interference fringes photographed in the first photographing mode, the interference fringes photographed in the second photographing mode, and the interference fringes photographed in the second photographing mode. It is a figure which shows the result of Fourier-transform. The grating direction when the slit direction of the grating is arranged obliquely, the interference fringes photographed in the first photographing mode, the interference fringes photographed in the second photographing mode, and the interference fringes photographed in the second photographing mode. It is a figure which shows the result of Fourier-transform. It is a figure which shows the example which extracted the 0th-order component obtained by Fourier-transforming with the Hanning window. It is a figure which shows the example which shifted by the carrier frequency and cut out with the Hanning window the primary component obtained by Fourier-transform. It is a figure which shows an example of the window in an improved Fourier-transform method. It is a figure which shows an example of the reconstruction image of the to-be-photographed object obtained by the fringe scanning method. It is a figure which shows an example of the reconstruction image obtained by the improved Fourier-transform method. It is a figure which shows an example of the reconstruction image obtained by the conventional Fourier-transform method. It is a figure which shows schematic structure of an X-ray imaging apparatus at the time of hold | maintaining a to-be-photographed object stand in the holding part different from the holding part of a 1st grating | lattice and a 2nd grating | lattice. It is a top view of the X-ray imaging apparatus shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an X-ray imaging system according to this embodiment. The X-ray imaging system includes an X-ray imaging apparatus 1 and a controller 5. The X-ray imaging apparatus 1 performs X-ray imaging using a Talbot-Lau interferometer, and the controller 5 creates a reconstructed image of the subject using the moire image obtained by the X-ray imaging. In the present embodiment, the X-ray imaging apparatus 1 will be described as an apparatus that images a finger as a subject, but is not limited to this.

  As shown in FIG. 1, the X-ray imaging apparatus 1 includes an X-ray source 11, a multi-slit 12, a subject table 13, a first grating 14, a second grating 15, an X-ray detector 16, a holding part 17, and a body part 18. Etc. The X-ray imaging apparatus 1 is a vertical type, and an X-ray source 11, a multi slit 12, a subject table 13, a first grating 14, a second grating 15, and an X-ray detector 16 are arranged in this order in the z direction, which is the gravitational direction. Placed in. The distance between the focal point of the X-ray source 11 and the multi-slit 12 is d 1 (mm), the distance between the focal point of the X-ray source 11 and the X-ray detector 16 is d 2 (mm), and the distance between the multi-slit 12 and the first grating 14. The distance is represented by d3 (mm), and the distance between the first grating 14 and the second grating 15 is represented by d4 (mm).

The distance d1 is preferably 5 to 500 (mm), more preferably 5 to 300 (mm).
The distance d2 is preferably at least 3000 (mm) or less since the height of the radiology room is generally about 3 (m) or less. Especially, the distance d2 is preferably 400 to 2500 (mm), and more preferably 500 to 2000 (mm).
The distance (d1 + d3) between the focal point of the X-ray source 11 and the first grating 14 is preferably 300 to 5000 (mm), and more preferably 400 to 1800 (mm).
The distance (d1 + d3 + d4) between the focal point of the X-ray source 11 and the second grating 15 is preferably 400 to 5000 (mm), more preferably 500 to 2000 (mm).
Each distance may be set by calculating an optimum distance at which the lattice image (self-image) by the first lattice 14 overlaps the second lattice 15 from the wavelength of the X-rays emitted from the X-ray source 11.

The X-ray source 11, the multi slit 12, the subject table 13, the first grating 14, the second grating 15, and the X-ray detector 16 are integrally held by the same holding unit 17 and the positional relationship in the z direction is fixed. ing. The holding portion 17 is formed in a C-shaped arm shape, and is attached to the main body portion 18 so as to be movable (up and down) in the z direction by a driving portion 18 a provided in the main body portion 18.
The X-ray source 11 is held via a buffer member 17a. Any material may be used for the buffer member 17a as long as it can absorb shocks and vibrations, and examples thereof include an elastomer. Since the X-ray source 11 generates heat upon irradiation with X-rays, it is preferable that the buffer member 17a on the X-ray source 11 side is additionally a heat insulating material.

The X-ray source 11 includes an X-ray tube, generates X-rays from the X-ray tube, and irradiates the X-rays in the z direction (gravity direction). As the X-ray tube, for example, a Coolidge X-ray tube or a rotary anode X-ray tube widely used in the medical field can be used. As the anode, tungsten or molybdenum can be used.
The focal diameter of the X-ray is preferably 0.03 to 3 (mm), more preferably 0.1 to 1 (mm).

  The multi slit 12 is a diffraction grating, and a plurality of slits are arranged at predetermined intervals as shown in FIG. 2A. The plurality of slits are arranged in a direction (indicated by white arrows in FIG. 2A) orthogonal to the X-ray irradiation axis direction (z direction in FIG. 1). The multi-slit 12 is formed on a substrate having a low X-ray absorption rate such as silicon or glass by using a material having a high X-ray shielding power such as tungsten, lead, or gold, that is, a high X-ray absorption rate. For example, the resist layer is masked in a slit shape by photolithography, and UV is irradiated to transfer the slit pattern to the resist layer. A slit structure having the same shape as the pattern is obtained by exposure, and a metal is embedded between the slit structures by electroforming to form a multi-slit 12.

The slit period of the multi slit 12 is 1 to 60 (μm). As shown in FIG. 2A, the slit period is defined as a period between adjacent slits. The width of the slit (the length of each slit in the slit arrangement direction) is 1 to 60 (%) of the slit period, and more preferably 10 to 40 (%). The height of the slit (the height in the z direction) is 1 to 500 (μm), preferably 1 to 150 (μm).
When the slit period of the multi slit 12 is w ₀ (μm) and the slit period of the first grating 14 is w ₁ (μm), the slit period w ₀ can be obtained by the following equation.
w ₀ = w ₁ · (d3 + d4) / d4
By determining the period w ₀ so as to satisfy the equation, the self-images formed by the X-rays that have passed through the slits of the multi-slit 12 and the first grating 14 overlap each other on the second grating 15. Can be in a suitable state.

  As shown in FIG. 2B, the multi slit 12 is held by a holder 12b having a rack 12a. The rack 12 a is provided in the slit arrangement direction of the multi slit 12. The rack 12a is engaged with a pinion 122c of the driving unit 122 described later, and moves the multi slit 12 held by the holder 12b in the slit arrangement direction according to the rotation (phase angle) of the pinion 122c.

  In the present embodiment, the X-ray imaging apparatus 1 is provided with a multi-slit rotating unit 121 and a driving unit 122. The multi-slit rotator 121 is a mechanism for rotating the multi-slit 12 around the X-ray irradiation axis according to the rotation of the first grating 14 and the second grating 15 around the X-ray irradiation axis. The drive unit 122 is a mechanism for moving the multi-slit 12 in the slit arrangement direction for photographing a plurality of moire images.

  In FIG. 3, the top view and AA 'cross section figure of the multi slit rotation part 121 and the drive part 122 are shown.

As shown in FIG. 3, the multi-slit rotating unit 121 includes a motor unit 121a, a gear unit 121b, a gear unit 121c, a support unit 121d, and the like. The motor part 121a, the gear part 121b, and the gear part 121c are held by the holding part 17 via the support part 121d.
The motor unit 121a is a pulse motor that can be switched to microstep driving, is driven in accordance with control from the control unit 181 (see FIG. 8), and drives the gear unit 121c to the X-ray irradiation axis (see FIG. 8) via the gear unit 121b. 3) (represented by a dashed line R in FIG. 3). The gear part 121c has an opening part 121e for mounting the multi slit 12 held by the holder 12b. By rotating the gear part 121c, the multi slit 12 mounted on the opening 121e can be rotated around the X-ray irradiation axis, and the slit arrangement direction of the multi slit 12 can be varied. In photographing, the multi slit 12 only needs to be able to rotate about 0 ° to 90 °. Therefore, the gear portion 121c does not have to be on the entire circumference, and the range indicated by the two-dot chain line in FIG. ).
The opening 121e has a shape and size that allows the multi slit 12 held by the holder 12b to be fitted from above. Here, the size w4 of the opening 121e in the slit arrangement direction is slightly larger than the size W2 of the holder 12b in the slit arrangement direction, and the multi-slit 12 can be slid in the slit arrangement direction. The size w3 in the direction orthogonal to the slit arrangement direction in the opening 121e is a dimension that allows precise fitting with the size W1 in the direction orthogonal to the slit arrangement direction in the holder 12b, and the holder 12b is attached to the opening 121e. Then, the rack 12a provided in the holder 12b is disposed outside the opening 121e so as to be engageable with a pinion 122c described later.

The drive unit 122 includes a precision reducer that moves the multi slit 12 in the slit arrangement direction in units of 0.1 μm to several tens of μm according to the multi slit period. For example, as shown in FIG. 3, the drive unit 122 includes a motor unit 122a, a gear unit 122b, a pinion 122c, and the like, and is fixed to the gear unit 121c of the multi-slit rotating unit 121 by an L-shaped sheet metal (not shown). Has been. Thereby, the multi slit 12 and the drive part 122 are rotated integrally.
For example, the motor unit 122a is driven in accordance with control from the control unit 181 and rotates the pinion 122c via the gear unit 122b. The pinion 122c engages with the rack 12a of the multi slit 12 and rotates to move the multi slit 12 in the slit arrangement direction.

  Returning to FIG. 1, the subject table 13 is a table for placing a finger as a subject. The subject table 13 is preferably provided at a height at which the patient's elbow can be placed. In this way, by being configured to be placed up to the patient's elbow, the patient can have a comfortable posture, and the movement of the imaging part of the fingertip can be reduced during imaging for a relatively long time.

  The subject table 13 is provided with a subject holder 130 for fixing the subject. As shown in FIG. 4A, the subject holder 130 is a plate-like member having an elliptical shape 131 such as a mouse that can be easily grasped by the palm. When the cross section of the elliptical shape 131 is observed from the side, as shown in FIG. 4B, it is a gentle convex curved surface of the palm size, and the subject is less likely to get tired by grasping the elliptical shape 131 with the palm. Thus, the downward movement of the subject can be suppressed.

When the subject holder 130 has a nonuniform X-ray complex refractive index shape or thickness depending on the location, the X-ray complex refractive index of the subject holder 130 is not uniform for the X-ray dose reaching the X-ray detector 16. Cause unevenness.
An inter-finger spacer 133 is preferably provided on the subject holder 130 in order to further stabilize the subject posture. In addition, since the size between the hands and fingers differs for each patient, the subject holder 130 is created according to the shape of the palm for each patient, and the subject holder 130 for the patient is magnetized on the subject table 13 at the time of photographing. It is preferable to attach by etc. Since the load from the arm to the wrist is supported by the subject table 13, the subject holder 130 only needs to be able to withstand the weight of the fingertip and the force pressed by the patient from above, and can be made of plastic that can be mass-produced at low cost. It is.

  Returning to FIG. 1, the first grating 14 is a diffraction grating provided with a plurality of slits arranged in a direction orthogonal to the z direction, which is the X-ray irradiation axis direction, like the multi-slit 12. The first lattice 14 can be formed by photolithography using UV as in the case of the multi-slit 12, or a silicon substrate is deeply digged with a fine fine line by a so-called ICP method to form a lattice structure only with silicon. It is good as well. The slit period of the first grating 14 is 1 to 20 (μm). The width of the slit is 20 to 70 (%) of the slit period, and preferably 35 to 60 (%). The height of the slit is 1 to 100 (μm).

  When a phase type is used as the first grating 14, the slit height (z-direction height) is a phase difference of π between the two materials forming the slit period, that is, the materials of the X-ray transmitting portion and the X-ray shielding portion. / 8 to 15 × π / 8. The height is preferably π / 4 to 3 × π / 4. When an absorption type is used as the first grating 14, the height of the slit is set to a height at which X-rays are sufficiently absorbed by the X-ray shielding part.

When the first grating 14 is a phase type, the distance d4 between the first grating 14 and the second grating 15 needs to substantially satisfy the following condition.
d4 = (m + 1/2) · w ₁ ² / λ
Note that m is an integer, and λ is the wavelength of X-rays.

  The above-mentioned condition is that the first grating 14 is a π / 2 type grating, that is, the case where the phase difference due to the materials of the X-ray shielding part and the X-ray transmitting part of the first grating is in the vicinity of π / 2. However, the first lattice 14 may be a π-type, and a condition corresponding to the type of the lattice to be used may be calculated.

  Similar to the multi-slit 12, the second grating 15 is a diffraction grating in which a plurality of slits are arranged in a direction orthogonal to the z-direction that is the X-ray irradiation axis direction. The second grating 15 can also be formed by photolithography. The slit period of the second grating 15 is 1 to 20 (μm). The width of the slit is 30 to 70 (%) of the slit cycle, and preferably 35 to 60 (%). The height of the slit is 1 to 100 (μm).

  In the present embodiment, each of the first grating 14 and the second grating 15 has a lattice plane perpendicular to the z direction (parallel in the xy plane), and the slit arrangement direction of the first grating 14 and the second grating 15. The slit arrangement direction is inclined at a predetermined angle in the xy plane, but both may be arranged in parallel. Moreover, in this embodiment, the 1st grating | lattice 14 and the 2nd grating | lattice 15 are disk shape.

The multi-slit 12, the first grating 14, and the second grating 15 can be configured as follows, for example.
Focal diameter of X-ray tube of X-ray source 11: 300 (μm), tube voltage: 40 (kVp), additional filter: aluminum 1.6 (mm)
Distance d1 from the focal point of the X-ray source 11 to the multi slit 12: 240 (mm)
Distance d3 from the multi slit 12 to the first grating 14: 1110 (mm)
Distance d3 + d4: 1370 (mm) from the multi slit 12 to the second grating 15
Multi slit 12 size: 10 (mm square), slit period: 22.8 (μm)
Size of the first grating 14: 50 (mm square), slit period: 4.3 (μm)
Size of the second grating 15: 50 (mm square), slit period: 5.3 (μm)

  In the present embodiment, the first grating 14 and the second grating 15 are attached to the grating rotating unit 210. FIG. 5 shows a plan view of the lattice rotation unit 210. FIG. 6 shows a plan view and a DD ′ sectional view of the grating rotating unit 210 in a state where the first grating 14 and the second grating 15 are mounted.

  As shown in FIG. 5, the lattice rotating unit 210 includes a handle 211, a relative angle adjusting unit 213, a stopper 214, and the like on a rotating tray 212.

The rotating tray 212 has an opening 212 a for holding the first lattice 14 and the second lattice 15.
Here, in the present embodiment, the first lattice 14 includes a circular lattice portion 140 in which a plurality of slits are arranged, and a first holder portion 141 and a second holder for attaching the lattice portion 140 to the opening 212a. And a holder part 142 (see FIG. 6). The first holder portion 141 is a member attached to the outer periphery of the lattice portion 140 and having the same radius (peripheral radius) as the opening portion 212a. The first holder portion 141 is fitted to the opening portion 212a when the first lattice 14 is attached. The second holder part 142 is a member that is attached to the outer side of the first holder part 141 and has a slightly larger radius (periphery radius) than the opening 212a. The second holder portion 142 has a part of the outer periphery that is gear processed. In addition, a protrusion 142 a is provided at a predetermined position on the outer periphery of the second holder portion 142.
The second grid 15 includes a circular grid section 150 in which a plurality of slits are arranged, and a holder section 151 for attaching the grid section 150 to the opening 212a. The holder portion 151 is a disk-shaped member having a radius substantially the same as the radius of the opening 212a. The lattice part 150 is held on the upper surface of the central part of the holder part 151 (see FIG. 6).

  When mounting the first grid 14 and the second grid 15 on the rotating tray 212, first, the second grid 15 is fitted into the bottom surface of the opening 212a. Next, the first grid 14 is fitted into the opening 212 a from above the second grid 15. Accordingly, the first grating 14 and the second grating 15 are held on the rotating tray 212 in the state shown in FIG.

The relative angle in the slit direction of the first grating 14 and the second grating 15 held in the opening 212a is adjusted by the relative angle adjusting unit 213 according to the imaging mode.
Here, the X-ray imaging apparatus 1 performs imaging in one or two directions for a first imaging mode in which imaging is performed in a plurality of steps for a reconstructed image by a fringe scanning method, and for a reconstructed image by a Fourier transform method. 2 shooting modes. The relative angle between the slit direction of the first grating 14 and the slit direction of the second grating 15 required in photographing for the fringe scanning method depends on the period of the second grating, the image size, and the number of fringes. In the fringe scanning method, it is known that the smaller the number of interference fringes in a moire image and the clearer the interference fringes, the clearer the reconstructed image created based on this moire image (non-non-uniformity). Patent Document 2). Therefore, assuming that the period of the second grating is 5.3 μm and that there are about 0 to 3 interference fringes in a 60 mm square image, the relative angle needs to be 0 ° to ± 0.015 °. On the other hand, the relative angle between the slit direction of the first grating 14 and the slit direction of the second grating 15 required in imaging for the Fourier transform method depends on the pixel pitch of the X-ray detector 16 and the spatial resolution. In the case of a commonly used detector (spatial resolution 30 μm to 200 μm), the relative angle needs to be 0.4 degrees to 3 degrees. Therefore, in order to switch between the first shooting mode and the second shooting mode, it is necessary to adjust the relative angle between the first grating and the second grating in accordance with the shooting mode. However, for example, in the above configuration, a deviation of 0.005 degrees in the fringe scanning method angle corresponds to one fringe period. In order to maintain the state where the fringes are always spread by the fringe scanning method, adjustment with milli-degree accuracy is required. Therefore, the relative angles in the slit direction of the first grating 14 and the second grating 15 are manually adjusted. It is difficult.
Therefore, in the X-ray imaging apparatus 1, the relative angle adjustment unit 213 can automatically adjust the relative angle between the first grating 14 and the second grating 15 according to the imaging mode set by the operation unit 182. It has become.

  As shown in FIGS. 5 and 6, the relative angle adjustment unit 213 includes a motor unit 213a, a first gear 213b, a second gear 213c, and a lever 213d. The motor unit 213a engages with the second gear 213c, and rotates the second gear 213c according to control from the control unit 181. The center of the second gear 213c is connected to the center of the first gear 213b via the lever 213d, and the circumference thereof is engaged with the first gear 213b. When the second gear 213c rotates according to the driving of the motor unit 213a, the first gear 213b rotates around the second gear 213c with the center of the second gear 213c as the rotation axis, and the first gear 14 The first grating 14 can be rotated around the X-ray irradiation axis without engaging the gear portion of the two holder 142 and rotating the second grating 15.

In the present embodiment, the first grating 14 and the second grating 15 are formed when the protrusion 142a of the second holder 142 abuts against a stopper (convex protrusion) 214 provided on the rotating tray 212 at the time of factory shipment. The position of the stopper 214 and the relative angle between the first grating 14 and the second grating 15 are set so that the relative angle in the slit direction becomes an optimum relative angle in the first imaging mode (imaging mode for the fringe scanning method). It is adjusted in advance and attached to the opening 212a. When the second shooting mode (Fourier transform shooting mode) is set, the relative angle adjustment unit is controlled by the control unit 181 so that the relative angle between the first grating 14 and the second grating is optimal for the second shooting mode. The motor unit 213a employing the pulse motor 213 is driven (energization control). Accordingly, the first gear 213b rotates through the second gear 213c and engages with the gear portion of the second holder part 142, and the relative angle in the slit direction between the first grating 14 and the second grating 15 is the second angle. The second holder 142 is rotated so as to be optimal for the shooting mode. After that, by changing the energization state of the pulse motor, the energization state (less than 50% of the rated current at the time of driving, etc.) to the extent that the motor self-holding force (excitation force) that overcomes the spring force described later is exhibited. The second holder part 142 can be maintained in this phase.
Since the rotation angle at this time is as small as about 1 degree, first, the second holder part 142 is rotated counterclockwise by the pulse motor of the motor part 213a until the projection part 142a reaches the reference position 215. If it is detected by a sensor (not shown) that 142a has reached the reference position 215, it is preferable to rotate the second holder part 142 by microstep driving by switching the rotation direction of the second holder part 142 clockwise.
The second holder part 142 is biased by a spring (not shown). When the engagement of the first gear 213b and the second holder part 142 is released by driving the motor part 213a, the projecting part 142a is caused by the biasing force of the spring. Returns to the position of the stopper 214. That is, the first grating 14 and the second grating 15 return to the optimum relative angle for the first imaging mode.

As described above, the relative angle between the first grating 14 and the second grating 15 is adjusted to an angle corresponding to the photographing mode.
The grid rotating unit 210 can also integrally rotate the first grid 14 and the second grid 15 whose relative angles are adjusted around the X-ray irradiation axis (indicated by a dotted line R in FIG. 6) with respect to the subject. it can.
Here, in the Talbot interferometer and the Talbot-Lau interferometer using a one-dimensional grating (slit), the structure extending linearly in parallel with the slit direction of the first grating 14 and the second grating 15 can be clearly photographed. There is a characteristic that it cannot. Therefore, it is necessary to adjust the angle of the slit direction of the first grating 14 and the second grating 15 in accordance with the arrangement direction of the structure to be noticed by the subject. The grating rotating unit 210 rotates the first grating 14 and the second grating 15 integrally around the X-ray irradiation axis while maintaining the relative angle by the following mechanism, so that the object is focused on the arrangement direction of the structure to be noted. The angle in the slit direction of the first grating 14 and the second grating 15 can be adjusted.

The rotary tray 212 is provided with the handle 211 as described above. The handle 211 is a protrusion for an operator such as a radiographer to manually rotate the rotating tray 212 around the X-ray irradiation axis (indicated by a dotted line R in FIG. 6). Further, the rotation tray 212 has recesses 212b to 212e for fixing the rotation angle of the rotation tray 212. The recesses 212b to 212e are positioned at a predetermined rotation angle (here, the position where the recess 212b faces the ball of the tray fixing member 171b is a 0 ° position) (here, the position where the recess 212b faces the ball of the tray fixing member 171b). (0 °, 30 °, 60 °, 90 °). Angle detection sensors SE1 to SE4 are provided in the recesses 212b to 212e, respectively, and detect that they are engaged with the tray fixing member 171b and output the detection signals to the control unit 181.
As described above, since the rotation tray 212 is manually rotated, it is not necessary to provide an electric cord or the like for integrally rotating the first grid 14 and the second grid 15 in a range touched by the patient, thereby ensuring safety. be able to.

  In the present embodiment, the position (angle) of the first grating 14 and the second grating 15 when the rotation tray 212 is set to 0 ° is set as the home position. The position (angle) at which the slit direction of the first grating 14 and the slit direction of the multi-slit 12 are parallel when the first grating 14 and the second grating 15 are at the home position is defined as the home position of the multi-slit 12.

7A is an enlarged plan view showing the holding portion 171 of the lattice rotating unit 210 in the holding unit 17, and FIG. 7B is a cross-sectional view taken along line EE ′ in FIG. 7A. FIG. 7C is a diagram illustrating a state in which the lattice rotation unit 210 is held by the holding unit 17.
As shown in FIGS. 7A and 7B, the holding portion 171 has a size that fits precisely with the rotating tray 212 of the lattice rotating unit 210, and has an opening 171a that rotatably holds the rotating tray 212, and the rotating tray 212. And a tray fixing member 171b for fixing the rotation angle. The space between the bottom of the opening 171a and the mounting portion of the X-ray detector 16 is preferably hollow or made of aluminum or carbon having a high X-ray transmittance so as not to prevent the transmission of X-rays. When the tray fixing member 171b is positioned so that any of the recesses 212b to 212e faces the tray fixing member 171b, the tray fixing member 171b guides the ball in the direction of the arrow in FIGS. 7A and 7B. For this purpose, a slide guide (a guide of a pressing spring) (not shown) is used. When rotation of the rotary tray 212 stops at a position where any of the recesses 212b to 212e faces the tray fixing member 171b, the slide guide of the tray fixing member 171b causes the ball to engage with the facing recess and The engagement of the ball is detected by the provided angle detection sensor (any one of SE1 to SE4), and a detection signal is output to the control unit 181. Thereby, the control unit 181 can detect the rotation angle of the rotating tray 212, that is, the rotation angles of the first grating 14 and the second grating 15.

  Further, as shown in FIG. 7D, a mounting portion 212f of the X-ray detector 16 is provided below the opening 212a of the rotating tray 212, and the first grating 14, the second grating 15, and the X-ray detector 16 are integrated. It may be possible to rotate as follows. In this way, since the vertical and horizontal sharpness anisotropy of the X-ray detector 16 is not affected, the vertical and horizontal sharpnesses of the reconstructed image are rotated by the first and second gratings 14 and 15. It can be generally constant regardless of the angle.

  Returning to FIG. 1, the X-ray detector 16 has two-dimensionally arranged conversion elements that generate electric signals according to the irradiated X-rays, and reads the electric signals generated by the conversion elements as image signals. The pixel size of the X-ray detector 16 is 10 to 300 (μm), more preferably 50 to 200 (μm).

It is preferable that the position of the X-ray detector 16 is fixed to the holding unit 17 so as to contact the second grating 15. This is because the moire image obtained by the X-ray detector 16 becomes blurred as the distance between the second grating 15 and the X-ray detector 16 increases.
As the X-ray detector 16, an FPD (Flat Panel Detector) can be used. The FPD includes an indirect conversion type in which X-rays are converted into electric signals by a photoelectric conversion element via a scintillator, and a direct conversion type in which X-rays are directly converted into electric signals. Any of these may be used.

In the indirect conversion type, photoelectric conversion elements are two-dimensionally arranged with TFTs (thin film transistors) under a scintillator plate such as CsI or Gd ₂ O ₂ to constitute each pixel. When the X-rays incident on the X-ray detector 16 are absorbed by the scintillator plate, the scintillator plate emits light. Charges are accumulated in each photoelectric conversion element by the emitted light, and the accumulated charges are read as an image signal.

In the direct conversion type, an amorphous selenium film having a film pressure of 100 to 1000 (μm) is formed on glass by thermal vapor deposition of amorphous selenium, and the amorphous selenium film and the electrode are arranged on a two-dimensionally arranged TFT array. Vapor deposited. When the amorphous selenium film absorbs X-rays, a voltage is released in the material in the form of electron-hole pairs, and a voltage signal between the electrodes is read by the TFT.
Note that imaging means such as a CCD (Charge Coupled Device) or an X-ray camera may be used as the X-ray detector 16.

A series of processing by the FPD at the time of X-ray imaging will be described.
First, the FPD is reset to remove unnecessary charges remaining after the previous photographing (reading). Thereafter, charges are accumulated at the timing when the X-ray irradiation starts, and the charges accumulated at the timing when the X-ray irradiation ends are read as an image signal. Note that dark reading for offset correction is performed immediately after resetting or after reading an image signal.

As shown in FIG. 8, the main body 18 includes a control unit 181, an operation unit 182, a display unit 183, a communication unit 184, and a storage unit 185.
The control unit 181 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like, and controls each unit of the X-ray imaging apparatus 1 in cooperation with a program stored in the storage unit 185 and various types. Execute the process. For example, the control unit 181 executes various processes including an imaging control process described later.

The operation unit 182 includes a touch panel configured integrally with the display of the display unit 183 in addition to a key group used for input operations such as an exposure switch and an imaging condition, and generates an operation signal corresponding to these operations to generate a control unit. It outputs to 181.
The display unit 183 displays the operation screen, the operation status of the X-ray imaging apparatus 1 and the like on the display according to the display control of the control unit 181.

The communication unit 184 includes a communication interface and communicates with the controller 5 on the network. For example, the communication unit 184 transmits the moire image read by the X-ray detector 16 and stored in the storage unit 185 to the controller 5.
The storage unit 185 stores a program executed by the control unit 181 and data necessary for executing the program. The storage unit 185 stores the moire image obtained by the X-ray detector 16.

  The controller 5 controls the imaging operation of the X-ray imaging apparatus 1 according to the operation by the operator. The controller 5 functions as an image processing unit that creates a diagnostic subject reconstructed image using the moire image obtained by the X-ray imaging apparatus 1.

As illustrated in FIG. 9, the controller 5 includes a control unit 51, an operation unit 52, a display unit 53, a communication unit 54, and a storage unit 55.
The control unit 51 is configured by a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like, and in cooperation with a program stored in the storage unit 55, a reconstructed image creation process by a fringe scanning method described later, Various processes including a reconstructed image creation process by a Fourier transform method are executed.

  The operation unit 52 includes a keyboard having cursor keys, numeric input keys, various function keys, and the like, and a pointing device such as a mouse, and includes a key pressing signal pressed by the keyboard and an operation signal by the mouse. Is output to the control unit 51 as an input signal. It is good also as a structure provided with the touchscreen comprised integrally with the display of the display part 53, and producing | generating the operation signal according to these operation to the control part 51. FIG.

  The display unit 53 includes, for example, a monitor such as a CRT (Cathode Ray Tube) or an LCD (Liquid Crystal Display). According to the display control of the control unit 51, the operation screen and the operation status of the X-ray imaging apparatus 1 are included. The created subject reconstructed image or the like is displayed.

  The communication unit 54 includes a communication interface and communicates with the X-ray imaging apparatus 1 and the X-ray detector 16 on the network by wire or wirelessly. For example, the communication unit 54 transmits imaging conditions and control signals to the X-ray imaging apparatus 1 and receives a moire image from the X-ray imaging apparatus 1 or the X-ray detector 16.

The storage unit 55 stores a program executed by the control unit 51 and data necessary for executing the program. For example, the storage unit 55 stores imaging order information indicating an order reserved by a RIS, HIS or the like or a reservation device (not shown). The imaging order information is information such as a patient name, an imaging region, and an imaging mode. The storage unit 55 stores the moire image obtained by the X-ray detector 16 and the diagnostic subject reconstructed image created based on the moire image in association with the imaging order information.
The storage unit 55 stores in advance gain correction data corresponding to the X-ray detector 16, a defective pixel map, and the like.

In the controller 5, when a list display of imaging order information is instructed by operating the operation unit 52, the imaging unit information is read from the storage unit 55 by the control unit 51 and displayed on the display unit 53. When radiographing order information is designated by the operation unit 52, setting information of radiographing conditions (including radiographing mode) according to the designated radiographing order information, an instruction for warming up the X-ray source 11, and the like are transmitted by the communication unit 54. It is transmitted to the line imaging apparatus 1. Thereby, an imaging mode is set in the X-ray imaging apparatus 1. That is, the controller 5 functions as a setting unit that sets the shooting mode. Further, when the X-ray detector 16 is a cableless cassette type FPD device, the control unit 51 starts from the sleep state for preventing the internal battery consumption to the imaging ready state.
In the X-ray imaging apparatus 1, when the communication unit 184 receives imaging condition setting information from the controller 5, preparation for X-ray imaging is executed.

An X-ray imaging method (imaging method in the first imaging mode) using the Talbot-Lau interferometer of the X-ray imaging apparatus 1 will be described.
As shown in FIG. 10, when the X-rays irradiated from the X-ray source 11 pass through the first grating 14, the transmitted X-rays form an image at a constant interval in the z direction. This image is called a self-image, and the phenomenon in which a self-image is formed is called the Talbot effect. The second grating 15 is arranged in parallel at a position connecting the self-images, and the second grating 15 is slightly tilted from a position parallel to the grating direction of the first grating 14, and therefore the second grating 15. A moire image M is obtained by the X-rays transmitted through. When the subject H is present between the X-ray source 11 and the first grating 14, the phase of the X-ray is shifted by the subject H, so that the interference fringes on the moire image M are bordered on the edge of the subject H as shown in FIG. 10. Disturbed. The disturbance of the interference fringes can be detected by processing the moire image M, and the subject image can be imaged. This is the principle of the Talbot interferometer and Talbot low interferometer.

  In the X-ray imaging apparatus 1, a multi-slit 12 is disposed near the X-ray source 11 between the X-ray source 11 and the first grating 14, and X-ray imaging using a Talbot-Lau interferometer is performed. The Talbot interferometer is based on the premise that the X-ray source 11 is an ideal point source. However, since a focal point having a large focal diameter is used for actual imaging, it is as if a plurality of point sources are connected by the multi slit 12. Multiple light sources are used as if they were irradiated with X-rays. This is an X-ray imaging method using a Talbot-Lau interferometer, and a Talbot effect similar to that of a Talbot interferometer can be obtained even when the focal diameter is somewhat large.

In the conventional Talbot-Lau interferometer, the multi-slit 12 is used for the purpose of increasing the number of light sources and increasing the irradiation dose as described above, and in order to obtain a plurality of moire images, the first grating 14 or the second grating 15 is used. It was moved relative. However, in the present embodiment, the first grating 14 or the second grating 15 is not moved relatively, but the positions of the first grating 14 and the second grating 15 are fixed and the first grating 14 and the second grating 15 are fixed. On the other hand, by moving the multi-slit 12, a plurality of moire images having a constant cycle interval are obtained.
Note that when a moire image is obtained in the second shooting mode, the multi-slit 12 is not moved, and shooting is performed once or twice while rotating the subject and the slit direction by 90 degrees.

  FIG. 11 is a flowchart showing an imaging control process executed by the control unit 181 of the X-ray imaging apparatus 1. The imaging control process is executed by the cooperation of programs stored in the control unit 181 and the storage unit 185.

  First, based on the setting information received from the controller 5, it is determined which of the first imaging mode (for fringe scanning method) or the second imaging mode (for Fourier transform method) is set. (Step S1). If it is determined that the first shooting mode is set (step S1; first shooting mode), the first shooting mode process is executed (step S2). On the other hand, if it is determined that the second shooting mode is set (step S1; second shooting mode), the second shooting mode process is executed (step S3).

  12A to 12B are flowcharts showing the first imaging mode process executed by the control unit 181 of the X-ray imaging apparatus 1 in step S2 of FIG. The first shooting mode process is executed in cooperation with a program stored in the control unit 181 and the storage unit 185.

  Here, the X-ray imaging method using the Talbot-Lau interferometer is used for X-ray imaging in the first imaging mode, and the fringe scanning method is used for reconstruction of the subject image. In the X-ray imaging apparatus 1, the drive unit 122 is driven and stopped by the control of the control unit 181, so that the multi-slit 12 is moved by a plurality of steps at regular intervals, and imaging is performed for each step. An image is obtained.

  The number of steps is 2 to 20, more preferably 3 to 10. From the viewpoint of obtaining a reconstructed image with high visibility in a short time, 5 steps are preferable (Reference (1) K. Hibino, BFOreb and DIFarrant, Phase shifting for nonsinusoidal wave forms with phase-shift errors, J.Opt.Soc.Am.A, Vol.12, 761-768 (1995), Reference (2) A.Momose, W.Yashiro, Y. Takeda, Y.Suzuki and T.Hattori, Phase Tomography by X -ray Talbot Interferometetry for biological imaging, Jpn. J. Appl. Phys., Vol. 45, 5254-5262 (2006)).

As shown in FIGS. 12A to 12B, first, the control unit 181 switches the X-ray source 11 to the warm-up state (step S101).
Next, the relative angle adjusting unit 213 of the grating rotating unit 210 is controlled so that the relative angle between the first grating 14 and the second grating 15 is optimal for the first imaging mode (the protrusion 142a contacts the stopper 214). The first grid 14 is rotated (so that it is in position). Thereby, the relative angle of the 1st grating | lattice 14 and the 2nd grating | lattice 15 is adjusted (step S102).

  Next, the first grid 14 and the second grid 15 are integrally rotated according to the operation of the operator, and the slit directions of the first grid 14 and the second grid 15 with respect to the subject are set (step S103). That is, an operator such as a photographic engineer rotates the handle 211 of the grid rotation unit 210, and the first grid 14 and the second grid 15 according to the arrangement direction of the structure to be noted of the subject placed on the subject table 13. Set the slit direction. When the rotation of the handle 211 is stopped and the position is fixed by the engagement of the spring-biased ball of the tray fixing member 171b, a detection signal is output from any of the angle detection sensors SE1 to SE4 to the control unit 181 and the control is performed. In the unit 181, the rotation angle from the home position of the rotation tray 212 (that is, the first grating 14 and the second grating 15) of the grating rotating unit 210 corresponding to the set slit direction is acquired.

  Next, the motor unit 121a of the multi-slit rotating unit 121 is controlled by a pulse according to the rotation angle of the first grating 14 and the second grating 15, and the multi-slit according to the rotation angle of the first grating 14 and the second grating 15. 12 is rotated (step S104). For example, the pulse motor of the motor unit 121a is controlled, and the rotation angle of the multi-slit 12 from the home position is rapidly close to the rotation angle of the rotation tray 212 (for example, about 29 ° when the rotation tray 212 is set to 30 °). It is rotated.

  Next, the motor unit 121a is switched to microstep precision control, and photographing is performed at a plurality of rotation angles while rotating the multi slit 12 little by little, and a plurality of moire images for adjustment are generated (step S105). For example, when the rotation tray 212 is set to 30 °, the multi-slit 12 is set to three rotation angles of 29.5 °, 30 °, and 30.5 °, and low-dose X-rays are emitted from the X-ray source 11. Irradiated and photographed. Thereby, three moire images for adjustment are acquired. Note that in step S105, shooting is performed without placing the subject on the subject table 13.

  The plurality of adjustment moire images that have been photographed are displayed side by side in association with the rotation angle of the multi-slit 12 on the display unit 183 (step S106).

Here, as described above, since the relative angle between the first grating 14 and the second grating 15 is adjusted in step S102 so that the number of interference fringes is minimized, in step S103, the rotation tray 212 is rotated. The first grating 14 and the second grating 15 are rotated while maintaining the relative angle. However, when the rotation tray 212 on which the first grating 14 and the second grating 15 are placed rotates and the relative angle between the multi slit 12 and the first grating 14 and the second grating 15 changes, interference fringes (that is, moire) are generated. The sharpness will change. Therefore, it is necessary to adjust the relative angle between the multi slit 12 and the first and second gratings 14 and 15, that is, the rotary tray 212 on which these are placed.
In general, the smaller the relative angle between the multi-slit 12 and the first grating 14, the more moire images with the clearer fringes are obtained. However, since the multi slit 12 is disposed in the vicinity of the X-ray source 11 that is a heat generating portion, it is easily affected by heat. Therefore, in consideration of deformation of the multi-slit 12, etc., not only the multi-slit 12 is rotated by the same angle as the rotary tray 212, but also the motor unit 121a is micro-step driven to perform fine adjustment in steps S105 to S108. It is valid.

The operator observes the moire image displayed on the display unit 183 in step S106, and selects the rotation angle at which the interference fringes are clear as the rotation angle used for photographing. Here, although the sharpness of the interference fringes is observed by the operator's visual observation, the sharpness indicating the degree of the sharpness of the interference fringes is set to the maximum value in the sine curve (see FIG. 17) described later, and the minimum value. In the case of MIN, it can be expressed by the following formula. Using this interference fringe definition, a rotation angle that automatically reaches a maximum value may be set by a program instead of an operator.
Interference fringe definition = (MAX−MIN) / (MAX + MIN) = amplitude / average value

  When the rotation angle of the multi slit 12 is input by the operation unit 182 (step S107; YES), the motor unit 121a is re-driven so that the rotation angle from the home position of the multi slit 12 becomes the input rotation angle. Then, the position of the multi slit 12 is finely adjusted (step S108).

After the rotation angle of the multi-slit 12 is adjusted, when the subject is placed on the subject table 13 and the exposure switch is turned on by the operator (step S109; YES), the multi-slit 12 is arranged in the slit arrangement direction by the drive unit 122. And a plurality of steps of photographing are executed, and a plurality of moire images with a subject are generated (step S110).
First, X-ray irradiation by the X-ray source 11 is started with the multi-slit 12 stopped. After the reset, the X-ray detector 16 accumulates charges in accordance with the timing of X-ray irradiation, and reads the accumulated charges as image signals in accordance with the timing of X-ray irradiation stop. This is one step of shooting. At the timing when the photographing for one step is completed, the drive unit 122 is activated by the control of the control unit 181 and the movement of the multi-slit 12 is started. When the predetermined amount is moved, the driving unit 122 is stopped to stop the movement of the multi-slit, and the next step photographing is performed. In this manner, the movement and stop of the multi-slit 12 are repeated for a predetermined number of steps, and when the multi-slit 12 is stopped, X-ray irradiation and image signal reading are performed. The read image signal is output to the main body 18 as a moire image.

  For example, assume that the slit period of the multi-slit 12 is 22.8 (μm), and five-step imaging is performed in 10 seconds. Shooting is performed every time the multi slit 12 moves and stops 4.56 (μm) corresponding to 1/5 of the slit period.

  When the second grating 15 (or the first grating 14) is moved as in the prior art, the slit period of the second grating 15 is relatively small and the movement amount of each step is small, but the slit period of the multi slit 12 is the first. It is relatively larger than the two grids 15, and the movement amount of each step is also large. For example, the amount of movement of the second grating 15 with a slit period of 5.3 (μm) per step is 1.06 (μm), whereas the amount of movement of the multi-slit 12 with a slit period of 22.8 (μm) is It is 4.56 (μm), about four times as large. When the same drive transmission system (including a drive source and a deceleration transmission system) is used and shooting is performed by repeatedly starting and stopping the drive unit 122 at the time of shooting at each step, a moving pulse motor (drive source) The ratio of the movement amount error due to the influence of the backlash of the drive unit 122 at the start time and the stop time in the actual movement amount corresponding to the control amount (number of drive pulses) of the multi-slit 12 as in this embodiment. The method of moving is smaller. This indicates that it is easy to obtain a moire image along a sine curve, which will be described later, and that a high-definition reconstructed image can be obtained even when the activation and the stop are repeated. Alternatively, if the image based on the conventional method is sufficiently suitable for diagnosis, the accuracy of the entire drive transmission system including the motor (drive source) (especially, start characteristics and stop characteristics) is relaxed, and the components of the drive transmission system are reduced. This shows that the cost can be reduced.

  When the photographing of each step is completed, the moire image of each step is transmitted from the communication unit 184 of the main body unit 18 to the controller 5 (step S111). A moire image with a subject is transmitted from the main body 18 to the controller 5 one by one every time photographing of each step is completed.

Next, dark reading is performed in the X-ray detector 16 to obtain a dark image (offset correction data) for correcting image data with a subject (step S112). The dark reading is performed at least once. Alternatively, the average value may be acquired as a dark image by performing multiple dark readings. The dark image is transmitted from the communication unit 184 to the controller 5 (step S113). The offset correction data based on the dark reading is commonly used for correcting each moire image signal.
The acquisition of the dark image may be performed by performing dark reading of the corresponding step after generating the moire image of each step and generating offset correction data dedicated to each step.

  Next, the operator enters an ON switch waiting state for the exposure switch (step S114). Here, the operator removes the subject from the subject table 13 and retracts the patient so that a moire image without the subject can be created. When preparation for shooting without a subject is completed, the exposure switch is pressed.

  When the exposure switch is pressed (step S114; YES), the multi-slit 12 is moved in the slit arrangement direction by the driving unit 122, and a plurality of steps of photographing are executed without a subject, and a plurality of moire images without a subject are obtained. It is generated (step S115). When the photographing of each step is completed, the moire image of each step is transmitted from the communication unit 184 of the main body unit 18 to the controller 5 (step S116). A moire image without a subject is transmitted from the main body 18 to the controller 5 one by one by the communication unit 184 every time photographing of each step is completed.

Next, dark reading is performed in the X-ray detector 16, and a dark image without a subject is acquired (step S117). The dark reading is performed at least once. Alternatively, the average value may be acquired as a dark image by performing multiple dark readings. The dark image is transmitted from the communication unit 184 to the controller 5 (step S118), and a series of imaging for one imaging order is completed.
The acquisition of the dark image may be performed by performing dark reading of the corresponding step after generating the moire image of each step and generating offset correction data dedicated to each step.
In addition, it is most preferable that a plurality of moire images without a subject and dark reading be performed immediately after photographing with a subject. However, in order to shorten the time until reconstruction of a subject image, it is necessary in advance to start a work. It is also possible to use data that has already been acquired.
In the controller 5, when the moire image is received by the communication unit 54, the received moire image is stored in the storage unit 55 in association with the shooting order information specified at the start of shooting.

  13A to 13B are flowcharts showing the second imaging mode process executed by the control unit 181 of the X-ray imaging apparatus 1 in step S3 of FIG. The second shooting mode process is executed by the cooperation of the program stored in the control unit 181 and the storage unit 185.

As shown in FIGS. 13A to 13B, first, the X-ray source 11 is switched to the warm-up state by the control unit 181 (step S201).
Next, the relative angle adjustment unit 213 of the grid rotation unit 210 is controlled so that the relative angle between the first grid 14 and the second grid 15 is optimal for the second imaging mode (the projection 142a is at a predetermined angle from the home position). Adjustment is performed so that the rotation position is reached (step S202).

  Subsequently, the process of step S203-step S208 is performed. The processing in steps S203 to S208 is the same as that described in steps S103 to 108 in FIG.

  When the subject is placed on the subject table 13 and the exposure switch is turned on by the operator (step S209; YES), shooting is performed and a moire image with the subject is generated (step S210). That is, radiation is emitted from the X-ray source 11 and reading is performed by the X-ray detector 16. In the second shooting mode, only one image is shot without moving the multi slit 12 while the drive unit 122 is stopped.

  When shooting is completed, a moire image obtained by shooting is transmitted from the communication unit 184 of the main body 18 to the controller 5 (step S211).

  Next, dark reading is performed in the X-ray detector 16, and a dark image (offset correction data) for correcting image data with a subject is acquired (step S212). The dark reading is performed at least once. Alternatively, the average value may be acquired as a dark image by performing multiple dark readings. The dark image is transmitted from the communication unit 184 to the controller 5 (step S213). The offset correction data based on the dark reading is commonly used for correcting the moire image signal.

  Next, the operator enters an ON switch waiting state for the exposure switch (step S214). Here, the operator removes the subject from the subject table 13 and retracts the patient so that a moire image without the subject can be created. When preparation for shooting without a subject is completed, the exposure switch is pressed.

When the exposure switch is pressed (step S214; YES), shooting is performed without a subject, and a moire image without a subject is generated (step S215). In step S215, as in step S210, only one image is taken without moving the multi-slit 12 while the driving unit 122 is stopped.
When shooting is completed, a moire image is transmitted from the communication unit 184 of the main body unit 18 to the controller 5 (step S216).

Next, dark reading is performed in the X-ray detector 16, and a dark image without a subject is acquired (step S217). The dark reading is performed at least once. Alternatively, the average value may be acquired as a dark image by performing multiple dark readings. The dark image is transmitted from the communication unit 184 to the controller 5 (step S218), and a series of shooting for one shooting order is completed.
In addition, it is most preferable that a plurality of moire images without a subject and dark reading be performed immediately after photographing with a subject. However, in order to shorten the time until reconstruction of a subject image, it is necessary in advance to start a work. It is also possible to use data that has already been acquired.

  When the moire image is received by the communication unit 54, the controller 51 of the controller 5 performs fringe scanning when the shooting mode set in the shooting order information currently being processed is the first shooting mode. A reconstructed image creation process by the Fourier transform method is executed in the second imaging mode.

  14A to 14B are flowcharts showing a reconstructed image creation process by the fringe scanning method executed by the control unit 51. The reconstructed image creation process by the fringe scanning method is executed in cooperation with the control unit 51 and a program stored in the storage unit 55.

  First, in steps S <b> 11 to S <b> 13, correction processing for correcting variation of each pixel of the X-ray detector 16 is performed for each of a plurality of moire images with a subject and a plurality of moire images without a subject. Specifically, an offset correction process (step S11), a gain correction process (step S12), and a defective pixel correction process (step S13) are executed.

In step S11, offset correction is performed on each moire image with a subject based on the dark image for correcting the image data with a subject. Based on the dark image for correcting the image data without a subject, an offset process is performed on each moire image without the subject. In step S12, gain correction data corresponding to the X-ray detector 16 used for imaging is read from the storage unit 55, and gain correction is performed on each moire image based on the read gain correction data. The
In step S13, the defective pixel map (data indicating the defective pixel position) corresponding to the X-ray detector 16 used for imaging is read from the storage unit 55, and the position indicated by the defective pixel position map in each moire image is read. Pixel values (signal values) are interpolated and calculated by surrounding pixels.

Next, X-ray intensity fluctuation correction (trend correction) is performed between the plurality of moire images (step S14). In the fringe scanning method, one subject reconstructed image is created based on a plurality of moire images. For this reason, if there is fluctuation (variation) in the intensity of X-rays irradiated in capturing each moiré image, an elaborate subject reconstructed image cannot be obtained, and fine signal changes may be overlooked. Therefore, in step S14, processing for correcting a signal value difference due to X-ray intensity fluctuations at the time of imaging in a plurality of moire images is performed.
As specific processing, a correction method using a signal value of a predetermined pixel of each moire image, a signal value difference in a predetermined direction of the X-ray detector 16 between each moire image is corrected ( Any one of a method for correcting one-dimensionally and a method for correcting a signal value difference in a two-dimensional direction between each moire image (two-dimensional correction) may be used.

  In the correction method using the signal value of one pixel, first, as shown in FIG. 15, for each of a plurality of moire images, a direct X outside the moire image area (subject placement area) 161 of the X-ray detector 16 is used. A signal value of a pixel at a predetermined position P corresponding to the line area is acquired. Next, the first moire image (for example, the first moire image taken with a subject) is normalized by the average signal value of the pixels at the acquired position P for the second and subsequent images, and the normalized position Based on the value of P, correction coefficients for the second and subsequent moire images are calculated. Then, the X-ray intensity fluctuation is corrected by multiplying the second and subsequent moire images by a correction coefficient. With this correction method, it is possible to easily correct the variation in the overall X-ray intensity between the radiographing. In addition, detection means such as a sensor for detecting the X-ray irradiation amount is provided on the back side of the X-ray detector 16, and based on the X-ray irradiation amount at the time of capturing each moire image output from the detection means, It is also possible to correct the signal value difference caused by the X-ray intensity fluctuation at the time of imaging.

  In the one-dimensional correction, first, an average signal value of pixels in a predetermined row L1 (a row indicates a reading line direction in the X-ray detector 16) is calculated for each of a plurality of moire images. Next, the first moire image is normalized by the average signal value of the second and subsequent pixels, and two images are obtained based on the signal value of each pixel in the normalized row L1 and the second and subsequent rows L1. A correction coefficient in the row direction of each moire image after the eye is calculated. Then, the X-ray intensity fluctuation in the row direction is corrected by multiplying the second and subsequent moire images by a correction coefficient corresponding to the position in the row direction. In this correction method, the fluctuation of the X-ray intensity in the one-dimensional direction between each imaging can be easily corrected. For example, in a certain radiographing, when a deviation between the irradiation timing of the X-ray source 11 and the reading timing of the X-ray detector 16 occurs, the X-ray intensity fluctuation in the reading line direction of the X-ray detector 16 and the like caused by this difference It can be corrected.

  In the two-dimensional correction, first, for each of a plurality of moire images, an average of pixels in each of a predetermined row L1 and column L2 (the column indicates a direction orthogonal to the reading line direction in the X-ray detector 16). A signal value is calculated. Next, the first moiré image is normalized by the average signal value of the pixels in the second and subsequent rows L1, and based on the signal values of the pixels in the normalized row L1 and the second and subsequent rows L1. The correction coefficient in the row direction of each of the second and subsequent moire images is calculated. Similarly, the first moire image is normalized by the average signal value of the pixels in the second and subsequent columns L2, and is based on the signal values of the respective pixels in the normalized column L2 and the second and subsequent columns L2. Thus, the correction coefficients in the column direction of the second and subsequent moire images are calculated. Then, the correction coefficients for the pixels in the second and subsequent moire images are calculated by multiplying the correction coefficients in the row direction and the column direction. Then, by multiplying each pixel by a correction coefficient in the row direction and the column direction, fluctuations in X-ray intensity in the two-dimensional direction are corrected. In this correction method, the fluctuation of the X-ray intensity in the two-dimensional direction between each imaging can be easily corrected.

Next, the analysis of the moire image is performed (step S15), and it is determined whether or not it can be used to create a reconstructed image (step S16). When the multi-slit 12 can be moved at a constant feed amount with ideal feed accuracy, five moire images corresponding to one slit period of the multi-slit 12 can be obtained in five steps as shown in FIG. Since the moire image of each step is a result of stripe scanning at fixed intervals of 0.2 cycles, when attention is paid to any one pixel of each moire image, the X-ray relative intensity obtained by normalizing the signal value Draws a sine curve as shown in FIG. Therefore, the controller 5 obtains the X-ray relative intensity by paying attention to the pixel having the moire image obtained in each step. If the X-ray relative intensity obtained from each moiré image forms a sine curve as shown in FIG. 17, it is determined that a moiré image having a constant periodic interval is obtained and can be used to create a reconstructed image. be able to.
The sine curve shape depends on the opening width of the multi-slit 12, the period of the first grating 14 and the second grating 15, and the distance between the gratings of the first and second gratings. In the case of coherent light, it has a triangular wave shape, but the X-rays act as quasi-coherent light due to the multi-slit effect, thereby drawing a sine curve. The analysis in step S15 is performed for each of the moire image with the subject and the moire image without the subject.

If there is a moire image in which a sine curve cannot be formed in the moire image at each step, it is determined that it cannot be used to create a reconstructed image (step S16; NO), and an instruction is given to change the shooting timing and reshoot. Control information is transmitted from the controller 5 to the X-ray imaging apparatus 1 (step S17). For example, as shown in FIG. 17, if the third step is originally 0.4 cycle, and the cycle is shifted and a moiré image of 0.35 cycle is obtained, the feeding accuracy of the drive unit 122 is reduced. This is considered to be caused (for example, noise superimposition on the drive pulse of the pulse motor). Therefore, it suffices to instruct to re-shoot only the third step by advancing the shooting timing by 0.05 cycles. Alternatively, it may be instructed to re-photograph all five steps and to advance the photographing time for 0.05 cycles only at the third step. When the moire images in all five steps are deviated from the sine curve by a predetermined amount, it may be instructed to increase or decrease the number of drive pulses from the start to the stop of the drive unit 122.
In the X-ray imaging apparatus 1, the imaging timing is adjusted according to the control information, and re-imaging is executed.

On the other hand, if it is determined that a moire image can be used to create a reconstructed image (step S16; YES), a reconstructed image with a subject and no subject are used by using a plurality of moire images with and without a subject, respectively. The reconstructed image is created (steps S18 to S20).
Specifically, an absorption image is created by adding interference fringes of a plurality of moire images (step S18). Further, the phase of the interference fringe is calculated using the principle of the fringe scanning method, and a differential phase image is created (step S19). Further, the visibility of interference fringes is calculated using the principle of the fringe scanning method (Visibility = 2 × amplitude ÷ average value), and a small-angle scattered image is created (step S20).

Next, using the reconstructed image without the subject, correction processing for removing the phase of the interference fringes and removing image unevenness (artifact) is performed from the reconstructed image with the subject (step S21). In the process of step S21, the X-ray dose distribution unevenness due to the slit direction change of the multi-slit 12 and the first and second gratings 14 and 15 at the time of imaging, the dose distribution unevenness due to the manufacturing variation of the slit, In addition, processing for removing image unevenness (artifact) including mainly unevenness due to the image of the subject holder 130 in the image is included.
For example, when the reconstructed image with the subject is a differential phase image, the signal value of the corresponding differential phase image without the subject (the pixel at the same position) is calculated from the signal value of each pixel of the differential phase image with the subject. Subtraction processing is performed (public literature (A); Timm Weitkamp, Ana Diazand, Christian David, franz Pfeiffer and Marco Stampanoni, Peter Cloetens and Eric Ziegler, X-ray Phase Imaging with a grating interferometer, OPTICS EXPRESS, Vol. 13, No. 16,6296-6004 (2005), public literature (B); Atsushi Momose, Wataru Yashiro, Yoshihiro Takeda, Yoshio Suzuki and Tadashi Hattori, Phase Tomography by X-ray Talbot Interferometry for Biological Imaging, Japanese Journal of Applied Physics, Vol. 45, No. 6A, 2006, pp. 5254-5262 (2006)).
When the reconstructed image with the subject is an absorption image or a small-angle scattered image, the signal value of each pixel of the reconstructed image with the subject is reconstructed without the subject, as described in publicly known document (C). A division process is performed to divide by the signal value of the corresponding pixel of the image (public literature (C); F. Pfeiffer, M. Bech, O. Bunk, P. Kraft, EFEikenberry, CH. Broennimann, C. Grunzweig, and C. David, Hard-X-ray dark-field imaging using a grating interferometer, nature materials Vol.7, 134-137 (2008)).

In the above processing, not only the X-ray dose distribution unevenness due to the slit direction change of the multi-slit 12, the first grating 14, and the second grating 15 and the object table characteristics, but also the X-ray detector used for imaging Even if there are variations in the characteristics of the 16 individual pixels, this effect can be removed, which is preferable. Therefore, even if the slit direction is variable according to the subject, the arrangement direction of the X-ray detector 16 with respect to the subject can be fixed (without changing the position), and the subject in the subject reconstructed image displayed on the controller 5 can be fixed. Since the display orientation is always in the same direction on the controller display screen, it is not necessary to perform an operation for aligning the orientation of the subject reconstructed image in the controller 5 when performing comparative interpretation with a past image during follow-up observation or the like. More preferred.
When the process of step 21 is finished, the reconstructed image creation process by the fringe scanning method is finished.

  FIG. 18 is a flowchart showing a reconstructed image creation process by the Fourier transform method executed by the control unit 51. The reconstructed image creation process by the Fourier transform method is executed in cooperation with the control unit 51 and the program stored in the storage unit 55.

  First, in steps S31 to S33, correction processing for correcting variations in each pixel of the X-ray detector 16 is executed for each of a plurality of moire images with a subject and a plurality of moire images without a subject. Specifically, offset correction processing (step S31), gain correction processing (step S32), and defective pixel correction processing (step S33) are executed. The contents of each process are the same as those described in steps S11 to S13 in FIG.

  Next, X-ray intensity fluctuation correction (trend correction) between the moire image with the subject and the moire image without the subject is performed (step S34). The specific processing content of the X-ray intensity fluctuation correction is the same as that described in step S14 in FIG.

  Next, in the processing from step S35, a reconstructed image of the subject is created by the Fourier transform method. The creation of the reconstructed image by the Fourier transform method can be performed by a known method (see Non-Patent Document 1).

First, the corrected moire image with a subject and the moire image without a subject are each subjected to Fourier transform (two-dimensional Fourier transform) (step S35). FIG. 19A shows an example of a moiré image with a subject photographed in the second photographing mode. In FIG. 19A, H1 is a magic pen, and H2 is a USB memory. FIG. 19B shows the result of two-dimensional Fourier transform of the moire image of FIG. 19A. FIG. 20A shows an example of a moiré image without a subject shot in the second shooting mode. FIG. 20B shows the result of two-dimensional Fourier transform of the moire image of FIG. 20A. Since the calculation result after the Fourier transform is a complex number, in FIG. 19B and FIG. 20B, the norm (amplitude) of the real part and the imaginary part is displayed.
As shown in FIG. 19B and FIG. 20B, when one moiré image is Fourier transformed, a low frequency component (referred to as a zeroth order component) and a component near the interference fringe frequency (referred to as a first order component) or a zeroth order component In addition to the primary component, a high frequency component (depending on the coherence of the X-ray imaging apparatus 1) is obtained side by side. The direction in which the zero-order component and the first-order component are arranged is related to the direction of the stripes in the moire image, and is substantially perpendicular to the direction of the stripes in the moire image.

Here, a description will be given of the relationship between the orientation of the multi-slit 12, first grating 14, and second grating 15 (slit direction) and the direction in which interference fringes, zero-order components, and first-order components are arranged.
For example, as shown in A1 of FIG. 21, when the orientations of the multi slit 12, the first grating 14, and the second grating 15 are vertical, the moire image for the fringe scanning method (with respect to the first grating 14). The fringes of the image obtained by slightly tilting the second grating are horizontal as shown by A2 in FIG. As shown by A3 in FIG. 21, the fringes of the moiré image for Fourier transform (image obtained by further tilting the second grating) are fine horizontal stripes compared to A2 in FIG. An image obtained by performing Fourier transform on a moire image for Fourier transform is an image in which 0th-order components and 1st-order components are vertically arranged, as indicated by A4 in FIG.
As shown in B1 of FIG. 22, when the orientations of the multi-slit 12, the first grating 14, and the second grating 15 are horizontal, the moire image for the fringe scanning method (second with respect to the first grating 14). The stripes of the image obtained by slightly tilting the grid are vertical as shown by B2 in FIG. Stripes of a moiré image for Fourier transform (an image obtained by further tilting the second grating) are finer vertical stripes than B2 of FIG. 22, as shown by B3 of FIG. An image obtained by performing Fourier transform on a moire image for Fourier transform is an image in which a zeroth-order component and a first-order component are arranged side by side, as indicated by B4 in FIG.
As shown in C1 of FIG. 23, when the orientation of the multi slit 12, the first grating 14, and the second grating 15 is 45 °, the moire image for the fringe scanning method (slightly relative to the first grating 14). The stripes of the image obtained by slightly tilting the second grating are inclined 45 ° (oblique in the direction opposite to the slit direction) as shown by C2 in FIG. As shown in C3 of FIG. 23, the stripes of the Fourier transform moire image (an image obtained by further tilting the second grating) are finer diagonal stripes in the same direction as C2 of FIG. An image obtained by performing Fourier transform on a moiré image for Fourier transform is an image in which the zeroth-order component and the first-order component are arranged at an angle of 45 ° opposite to the stripe direction, as indicated by C4 in FIG.

Next, in the image obtained by the Fourier transform (each with and without the subject), the zero-order component is cut out by the Hanning window W shown in FIG. 24 (step S36). By cutting out with the Hanning window W, the peripheral part of the Hanning window W is dropped to 0, and the central part of the Hanning window W is passed as it is.
Next, in the image obtained by Fourier transform, the primary component is shifted by the carrier frequency (= moire frequency) as shown in FIG. 25, and cut out by the Hanning window W (step S37). The cutting window function is not limited to the Hanning window, and a Hamming window, a Gaussian window, or the like may be used depending on the application.
Next, each of the extracted 0th order component and 1st order component is subjected to inverse Fourier transform (step S38).

  When the inverse Fourier transform is completed, reconstructed images with and without the subject are created using the zeroth-order component and the first-order component subjected to the inverse Fourier transform (steps S39 to S41). Specifically, an absorption image is created from the amplitude of the zeroth-order component (step S39). A differential phase image is created from the phase of the primary component (step S40). Further, a small-angle scattered image is created from the ratio (= Visibility) of the amplitude of the zeroth-order component and the first-order component (step S41).

  Next, correction processing for removing the phase of the interference fringes from the reconstructed image with the subject and removing image unevenness (artifact) is performed using the reconstructed image without the subject (step S42). The processing in step S42 is the same as that described in step S21 in FIG. When the correction of the image unevenness is finished, the reconstructed image creation process by the Fourier transform method is finished.

  In the above-described conventional Fourier transform method, when cutting out the 0th-order component and the 1st-order component, the high-frequency components are discarded in both the vertical and horizontal directions, so that the spatial resolution is lowered and the image is totally blurred. Here, when the one-dimensional grating is used for the X-ray grating, the inventors of the present application have the information of the differential phase image and the small-angle scattered image of the Talbot interferometer and the Talbot-Lau interferometer as the grating (multi slit 12, first grating 14 and paying attention to the fact that there is only one direction orthogonal to the slit direction of the second grating 15), the window w used in steps S36 and S37 is not the conventional square but the slit direction of the grating as shown in FIG. If the rectangle extends in the orthogonal direction, the high-frequency component of the signal in the direction orthogonal to the slit direction of the grating including image information can be extracted without dropping, and blur in the direction orthogonal to the slit direction of the grating is reduced. I found that I can do it. The present invention is characterized in that the direction parallel to the slit direction of the lattice, in which a decrease in spatial resolution is unavoidable in principle, does not originally include image information. A great advantage can be obtained for the imaging of the Fourier transform method using a lattice. (FIG. 26 shows an example in which a rectangular window W is set in A4 of FIG. 21.)

FIG. 27A shows an example of a reconstructed image of a subject obtained by the fringe scanning method. FIG. 27B shows an example of a reconstructed image obtained by the improved Fourier transform method. FIG. 27C shows an example of a reconstructed image obtained by a conventional Fourier transform method. The reconstructed images in FIGS. 27A to 27C are differential phase images obtained by photographing with the slit direction of the grating being vertical. As shown in FIG. 27A, the image obtained by the fringe scanning method is less blurred in both the vertical and horizontal directions. As shown in FIG. 27B, the image obtained by the improved Fourier transform method is blurred only in the vertical direction and is not blurred in the horizontal direction. As shown in FIG. 27C, the image obtained by the conventional Fourier transform method is blurred both in the vertical direction and in the horizontal direction.
27A to 27C show differential phase images, the blur directions by the respective methods are the same in the absorption image and the small-angle scattering image.

As described above, in the improved Fourier transform method, only the signal component in the direction parallel to the slit direction of the grating is blurred, so the first photographing is performed by arranging the subject so that the longitudinal direction of the subject is perpendicular to the slit direction of the grating. Then, the relative angle between the subject and the grid is rotated by 90 °, the second shooting is performed, and the moiré images obtained by the first shooting and the second shooting are combined to remove the peripheral portion of the combined image. In the region, it is possible to acquire a two-dimensional image with little blur in both the vertical and horizontal directions of the subject (in the case of a differential phase image and a small angle scattered image).
Although it is possible to shoot by a Fourier transform method using a two-dimensional lattice, since the primary component exists in both the vertical and horizontal directions, the window w to be cut out is limited to a narrow range in both the vertical and horizontal directions. Therefore, it is inevitable that the spatial resolution is greatly reduced. On the other hand, according to the present method, it is possible to generate a two-dimensional image using a one-dimensional lattice without greatly reducing the resolution. In radiography at a medical site, since the region of interest of a subject is generally located at the center of the imaging region, the above-described loss of subject information in the peripheral portion does not cause a problem. Further, since the photographing itself only needs to be performed twice, the influence of the subject's body movement can be suppressed.
When changing the shooting direction (changing the slit direction relative to the subject), it is necessary to simultaneously rotate the multi-slit 12, the first grating 14 and the second grating 15 by 90 °, as in the fringe scanning method.

When the first and second shootings are performed by changing the relative angle of the first grid 14 and the second grid 15 by 90 °, the control unit 51 of the controller 5 determines the first shot image and the second shot image. After executing the reconstructed image creation process by the Fourier transform method shown in FIG. 18 for each, the two images are synthesized. When the same part of the subject is not drawn on the same pixel in the first image and the second image (when the subject is deformed or moved), either one of the images is moved in parallel or rotated. Then, after aligning at the position where the error between the two images becomes the smallest, the composition is performed. Various methods can be used as the synthesis method. For example, the pixel of the first captured image is f1 (x, y), the pixel of the second captured image is f2 (x, y), and the pixel of the composite image is g (x, y). Calculate and take the average power (take the square root of the sum of squares).
g (x, y) = √ (f1 (x, y) ^ 2 + f2 (x, y) ^ 2)
Further, for example, the first captured image may be displayed in red, and the second captured image may be displayed in color.

  Incidentally, as can be seen from the images of FIGS. 27A to 27C, the reconstructed image obtained by the fringe scanning method is clearer and less blurred than the reconstructed image obtained by the Fourier transform method. However, in the scanning for the fringe scanning method, multiple images are taken continuously, so the imaging time becomes longer depending on the detector capture time, processing time before and after X-ray exposure, mechanism operation time, etc. 1 minute), body movement is likely to occur. On the other hand, in the Fourier transform method, one image is obtained by one image, so the image taking time depends only on the X-ray exposure time and can be suppressed to about 5 seconds. I can expect. Furthermore, the improved Fourier transform method can suppress the degradation of spatial resolution. Therefore, for example, (1) The object that can fix the subject is the fringe scanning method, and the Fourier transform method is used to suppress body movement, and (2) The Fourier transform method is used for the simple inspection, which is a more precise inspection. By using both of them together, such as a fringe scanning method, it is possible to acquire an image according to the purpose and to perform imaging with less burden on the patient and less imaging. In the present embodiment, the relative angle between the first grating 14 and the second grating 15 can be easily adjusted to switch between the imaging for the fringe scanning method and the imaging for the Fourier transform method. Optimal shooting can be performed.

  As described above, according to the X-ray imaging system, the relative angle adjustment unit 213 automatically adjusts the relative angles of the first grating 14 and the second grating 15 in accordance with the imaging mode set by the controller 5. In accordance with the set imaging mode, the controller 181 controls the activation or stop of the driving unit 122 that moves the multi slits 12 in the slit arrangement direction, and the controller 5 detects X-rays according to the set imaging mode. A reconstructed image is created from the moire image obtained by the device 16.

  Therefore, it is possible to easily switch between the shooting mode for the fringe scanning method and the shooting mode for the Fourier transform method according to the purpose and the like.

  In addition, the X-ray imaging system rotates the first grating 14 and the second grating 15 adjusted to the relative angle according to the set imaging mode around the X-ray irradiation axis while maintaining the relative angle. Since the unit 210 is provided, the slit directions of the first grating 14 and the second grating 15 with respect to the subject placed on the subject table 13 can be easily adjusted without destroying the relative angle once adjusted. Become.

  Further, the X-ray imaging system includes a multi-slit rotating unit 121 that rotates the multi-slit 12 around the X-ray irradiation axis, and the control unit 181 performs the slit direction with respect to the subject placed on the subject table 13 by the lattice rotating unit 210. The multi-slit rotating unit 121 is controlled such that the slit direction of the multi-slit 12 is in a predetermined positional relationship with respect to the first grating 14 and the second grating 15 that are adjusted. Accordingly, the multi slit 12 can be automatically adjusted to the optimum position according to the rotation of the first grating 14 and the second grating 15.

  Further, since the multi-slit rotating unit 121 integrally rotates the multi-slit 12 and the driving unit 122, even when the multi-slit 12 is rotated, the multi-slit 12 can be stably placed in the slit arrangement direction even when the multi-slit 12 is rotated. It can be moved.

  In addition, since the grid rotating unit 210 integrally rotates the first grid 14 and the second grid 15 and the relative angle adjusting unit 213, the relative angle between the first grid 14 and the second grid 15 can be adjusted stably. can do.

  In addition, by adopting a configuration in which the first grating 14 and the second grating 15 and the X-ray detector 16 are rotated integrally, the X-ray detector 16 is affected by the anisotropy of the sharpness in the vertical and horizontal directions. Therefore, the vertical and horizontal sharpness of the reconstructed image can be made substantially constant regardless of the rotation angles of the first grid 14 and the second grid 15.

In addition, the said embodiment is a suitable example of this invention, and is not limited to this.
For example, in the first and second embodiments, the X-ray source 11, the multi slit 12, the subject table 13, the first grating 14, the second grating 15, and the X-ray detector 16 are arranged in this order (hereinafter referred to as the first However, the arrangement of the X-ray source 11, the multi slit 12, the first grating 14, the subject table 13, the second grating 15, and the X-ray detector 16 (hereinafter referred to as the second arrangement) is also possible. The reconstructed image can be obtained by moving the multi slit 12 while the first grating 14 and the second grating 15 are fixed.
In the second arrangement, the subject center and the first grid 14 are separated from each other by the thickness of the subject, which is slightly inferior in sensitivity compared to the above-described embodiment. In consideration of dose reduction, the arrangement effectively uses X-rays by the amount of X-ray absorption in the first grating 14.
The effective spatial resolution at the subject position depends on the focal diameter of the X-ray, the spatial resolution of the detector, the magnification of the subject, the thickness of the subject, and the like. When the resolution is 120 μm (Gauss half width) or less, the effective spatial resolution is smaller in the second arrangement than in the first arrangement.
It is preferable to determine the arrangement order of the first grating 14 and the object table 13 in consideration of sensitivity, spatial resolution, X-ray absorption amount in the first grating 14, and the like.

  Further, the order of shooting with a subject and shooting without a subject is not limited to the above-described embodiment, and either may be used first. The same applies to the order of creating a reconstructed image with a subject and creating a reconstructed image without a subject.

  Further, as the X-ray detector 16, a cableless cassette type FPD that incorporates a battery and outputs an image signal to the main body 18 by radio may be used. According to the cassette type FPD, cables connected to the main body 18 can be eliminated, and a further space around the X-ray detector 16 can be reduced. By reducing the space, the subject's feet can be configured wider, and the patient can be more difficult to touch.

  Further, the subject table 13 easily transmits vibrations due to contact with the patient. Therefore, the subject table 13 may be separated from the holding unit 17 including the multi slit, the first grating 14, the second grating 15, and the like that require a highly accurate positional relationship, and may be held in another holding unit. FIG. 28 is a side view when the subject table 13 is held by another holding portion 13b, and FIG. 29 is a plan view. In this way, by separating the subject table 13 from the first grating 14 and the second grating 15 and so on to have a separate structure, the influence on the positional relationship among the multi slit 12, the first grating 14 and the second grating 15 can be affected as much as possible. It is possible to reduce and maintain the positional relationship.

  When the subject table 13 has a separate configuration, as shown in FIGS. 28 and 29, a drive unit 13a for moving the subject table 13 in the z direction is provided in the holding unit 13b. Thereby, the position of the subject table 13 can be adjusted according to the height of the subject. Although a load such as the weight of the patient is applied to the subject table 13, the load applied to the holding unit 17 that moves up and down can be removed by making the subject table 13 separate from the holding unit 17. There is no need to reinforce the holding portion 17 to withstand the load, and the cost can be reduced.

  Further, in the above-described embodiment, an example in which the movement and stop of the multi-slit 12 are repeated for each step of photographing in the fringe scanning method has been described. However, depending on the configuration of the drive unit 122, if the error between the control amount and the actual movement amount is cumulatively expanded by repeating the movement and the stop, it is assumed that it is difficult to obtain a moire image at regular intervals. In particular, a continuous shooting method in which shooting is performed a plurality of times while moving the multi slit 12 is preferable. When the exposure switch is turned on, the multi-slit 12 starts to move, exceeds the unstable movement area at the time of activation, reaches the stable movement area, and further moves the multi-slit continuously to a predetermined amount. (For example, 4.56 (μm)) X-ray pulse irradiation and reading of an image signal are repeated each time it moves.

It is preferable to use an X-ray tube capable of pulse irradiation as the X-ray source 11 in the continuous imaging system.
Further, the X-ray detector 16 is preferably an FPD that can handle a large frame rate (number of times that imaging can be performed per unit time) and that can capture moving images. Assuming that shooting is performed five times or more in several hundred milliseconds to several seconds, a frame rate of at least 10 frames / second is necessary, and a frame rate of 20 frames / second or more is preferable.

In the case of the continuous shooting method, preliminary shooting may be further performed before and after each step.
When the drive unit 122 can move the multi-slit 12 at a constant feed amount, that is, a constant moving speed with an ideal feed accuracy, a sine curve can be formed by a moire image at each step as shown in FIG. . However, if the feed amount is deviated due to aging, the inertial effect at the time of starting the driving unit 122, the viscous effect of grease, or the like, a moire image with a constant periodic interval cannot be obtained. For example, as shown in FIG. 17, a three-step moire image originally corresponds to 0.4 cycles, but if the feed amount of the drive unit 122 at three steps is shifted, a moire image of around 0.4 cycles is obtained. It is done.

  As described above, when the period of the moire image at each step varies, an accurate phase cannot be calculated, and the subject image cannot be accurately reproduced in the reconstructed image. Therefore, for example, a total of 15 shootings are performed by adding a preliminary shooting in which each shooting time is ± 0.1 seconds. As a result, three moire images are obtained for each step, and the moire image closest to the sine curve of the X-ray relative intensity is selected and used. Thereby, even if an error occurs in the feed amount of the drive unit 122, the reproducibility of the reconstructed image can be improved.

  The above-described ± 0.1 second as an adjustment time for preliminary shooting is an example, and the adjustment time may be appropriately determined by test shooting. For example, when the X-ray imaging apparatus 1 is installed, test imaging is performed by changing the adjustment time at the time of preliminary imaging, such as ± 0.1 seconds, ± 0.2 seconds, etc. before and after the imaging at each step. It is good also as calculating | requiring the adjustment time which is easy to correspond. Thereby, it is possible to cope with the case where the necessary adjustment time differs depending on the device characteristics of the drive unit 122.

  In addition, only a series (5 steps) of shooting without a subject is periodically performed, and it is determined whether each of these images is well matched with the sine curve described above. In this case, if the necessity of apparatus maintenance is notified on the controller and maintenance such as a precision deceleration system is performed, a high-definition reconstructed image for diagnosis can be maintained.

  In addition, the detailed configuration and detailed operation of each apparatus constituting the X-ray imaging system can be appropriately changed without departing from the spirit of the invention.

  It should be noted that Japanese Patent Application No. 1993 filed on August 31, 2010, including the description, claims, drawings and abstract. The entire disclosure of 2010-194057 is incorporated in its entirety into this application.

  There is a possibility of taking X-ray images in the medical field.

DESCRIPTION OF SYMBOLS 1 X-ray imaging apparatus 11 X-ray source 12 Multi slit 12a Rack 12b Holder 121 Multi slit rotation part 121a Motor part 121b Gear part 121c Gear part 121d Support part 121e Opening part 122 Drive part 122a Motor part 122b Gear part 122c Pinion 13 Subject stand 130 Subject holder 131 Oval shape 133 Inter-finger spacer 14 First grating 140 Lattice part 141 First holder part 142 Second holder part 142a Projection part 15 Second grating 150 Grating part 151 Holder part 16 X-ray detector 17 Holding part 17a Buffer Member 17b Arm 171a Opening portion 171b Tray fixing member 18 Main body portion 181 Control portion 182 Operation portion 183 Display portion 184 Communication portion 185 Storage portion 18a Drive portion 210 Grid rotation portion 211 Handle 212 Rotating tray 212a Opening portion 2 2b~212e recess 213 relative angular adjustment portion 213a motor unit 213b first gear 213c second gear 213d lever 214 stopper 5 controller 51 control unit 52 operation unit 53 display unit 54 communication unit 55 storage unit 13b holding portion

Claims (5)

An X-ray source that emits X-rays;
A multi-slit composed of a plurality of slits arranged in a direction orthogonal to the X-ray irradiation axis direction;
A driving unit for moving the multi-slit in the slit arrangement direction;
A first grating and a second grating configured by arranging a plurality of slits in a direction orthogonal to the X-ray irradiation axis direction;
Subject table,
A conversion element that generates an electrical signal in accordance with the irradiated X-rays is arranged in a two-dimensional manner, and includes an X-ray detector that reads the electrical signal generated by the conversion element as an image signal,
The multi-slit is moved in the slit arrangement direction by the driving unit, and the X-ray detector detects the image signal in accordance with the X-rays emitted from the X-ray source every time the multi-slit moves at a constant cycle interval. An X-ray imaging system capable of repeating a reading process and obtaining a plurality of moire images at a constant cycle interval,
A setting unit for setting one of the first shooting mode and the second shooting mode;
A relative angle adjusting unit that adjusts a relative angle between the first grating and the second grating in accordance with the photographing mode set by the setting unit;
In accordance with the shooting mode set by the setting unit, a control unit that controls activation or stop of the drive unit,
An image processing unit that creates a reconstructed image from a moire image obtained by the X-ray detector according to the imaging mode set by the setting unit;
X-ray imaging system. The first lattice and the second lattice adjusted to a relative angle according to the set photographing mode by the relative angle adjustment unit with respect to the subject placed on the subject table while maintaining the relative angle. A grating rotating unit that rotates around an X-ray irradiation axis to adjust the slit direction of the first grating and the second grating;
A multi-slit rotating unit that rotates the multi-slit around the X-ray irradiation axis in order to adjust the slit direction of the multi-slit with respect to the subject placed on the subject table;
With
The control unit is configured such that the slit direction of the multi-slit is predetermined with respect to the first grating and the second grating in which the slit direction with respect to the subject placed on the subject table is adjusted by the grating rotating unit. The X-ray imaging system according to claim 1, wherein the multi-slit rotating unit is controlled so that   The X-ray imaging system according to claim 2, wherein the multi-slit rotating unit integrally rotates the multi-slit and the driving unit.   The X-ray imaging system according to claim 2 or 3, wherein the grating rotating unit integrally rotates the first grating and the second grating and the relative angle adjusting unit.   The X-ray imaging system according to any one of claims 2 to 4, wherein the grating rotating unit integrally rotates the first and second gratings and the X-ray detector.

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