WO2012081376A1

WO2012081376A1 - Grids for radiography and radiography system

Info

Publication number: WO2012081376A1
Application number: PCT/JP2011/077178
Authority: WO
Inventors: 金子　泰久; 伊藤　嘉広
Original assignee: 富士フイルム株式会社
Priority date: 2010-12-14
Filing date: 2011-11-25
Publication date: 2012-06-21
Also published as: JP2014039569A

Abstract

Provided are grids for radiography with which resilience to external force is improved, and the occurrence of artifacts resulting from boundary lines between adjacent small grids is avoided. First and second grids (13, 14) are positioned between an x-ray source (11) and an x-ray image detection apparatus (15). The first and second grids (13, 14) have an identical configuration aside from having different widths, array pitches, and thicknesses in the x-ray absorbing parts thereof. The first grid (13) is configured by laying, without any gaps, a plurality of small grids (13a) comprising regular hexagonal grid contours, upon a flat face (13c) of a support substrate (13b). X-ray absorption parts and x-ray transmission parts, which extend along the y-axis in the small grids (13a), are positioned alternately along the x-axis in the small grids (13a). Each edge which configures the grid contours of the small grids (13a) is non-parallel with the y-axis.

Description

Radiation imaging grid and radiation imaging system

The present invention relates to a radiographic imaging grid and a radiographic imaging system for obtaining an image based on a phase change of radiation.

When radiation, for example, X-rays enter an object, the intensity and phase change due to the interaction with the object. It is known that the phase change of X-rays at an object is larger than the intensity change. Research on X-ray phase imaging that uses this X-ray property to obtain a high-contrast image (hereinafter referred to as a phase contrast image) from a subject having a low X-ray absorption capacity based on the phase change of the X-ray is actively conducted. Has been done.

As an X-ray imaging system for performing this X-ray phase imaging, a system using two transmission diffraction gratings (grids) is known (for example, see Patent Document 1 and Non-Patent Document 1). In this X-ray imaging system, the first grid is disposed behind the subject as viewed from the X-ray source, and the second grid is disposed downstream from the first grid by the Talbot distance. An X-ray image detector is disposed behind the second grid. The first and second grids are striped grids in which X-ray absorbing portions and X-ray transmitting portions extended in one direction are alternately arranged along an arrangement direction orthogonal to the extending direction. The Talbot distance is a distance at which X-rays that have passed through the first grid form a self-image due to the Talbot effect. This self-image is modulated by the interaction between the subject and the X-ray.

In this X-ray imaging system, a plurality of fringe images generated by superposition (intensity modulation) of the self-image of the first grid and the second grid are detected based on the fringe scanning method. Specifically, the second grid is moved step by step with respect to the first grid, and an intensity modulation signal representing an intensity change of the pixel value accompanying the movement of the second grid is generated for each pixel. A phase differential image is generated by calculating the phase shift amount (phase shift amount with and without the subject) of the intensity modulation signal. A phase contrast image is obtained by integrating the phase differential image. This fringe scanning method is also used in an imaging apparatus using laser light (see, for example, Non-Patent Document 2).

This X-ray imaging system is used for medical diagnosis. In order to image a large subject such as a patient, it is necessary to increase the size of the first and second grids as well as the size of the X-ray image detector. Since the first and second grids have a fine structure in which X-ray absorption parts and X-ray transmission parts are alternately arranged at an arrangement pitch of μm order, it is impossible to manufacture a large grid at a time. Have difficulty. Thus, it has been proposed to construct a large grid by manufacturing a plurality of small rectangular grids and laying them out without gaps (see Patent Document 2).

Japanese Patent No. 4445397 JP 2007-203061 A

However, since the grid described in Patent Document 2 has a rectangular shape and its two opposing sides are parallel to the extending direction of the X-ray absorbing portion, it is easy to bend in a direction orthogonal to the extending direction and is durable against external force. There is a problem that the nature is low. In addition, when a large grid is manufactured by laying small grids having such a configuration without gaps, the boundary line between the adjacent small grids is parallel to the extending direction of the X-ray absorption unit, so the boundary line is There is a problem that artifacts are generated in the phase contrast image by acting like grid lines.

A first object of the present invention is to provide a radiographic imaging grid having high durability against external force and a radiographic imaging system using the radiographic imaging grid.

The second object of the present invention is to provide a radiographic imaging grid capable of preventing the occurrence of artifacts when a large grid is constructed by laying a plurality of small grids without gaps, and the radiographic imaging It is to provide a radiographic imaging system using a grid.

The grid for radiographic imaging of the present invention includes a plurality of radiation absorbing portions extending in one direction and a plurality of radiation absorbing portions extending in the one direction and arranged alternately with the radiation absorbing portions in a direction substantially orthogonal to the one direction. A radiation transmitting portion; and a grid contour configured by a plurality of sides non-parallel to the one direction.

The radiographic imaging grid of the present invention is a radiographic imaging grid configured by laying a plurality of small grids without gaps. Each of the small grids extends in the one direction, and includes a plurality of radiation transmitting portions arranged alternately with the radiation absorbing portion in a direction substantially orthogonal to the one direction, and a plurality of sides non-parallel to the one direction. A configured grid contour. The grid contour is preferably one of a regular hexagon, a regular square, and a regular triangle.

Further, it is preferable to include a support substrate that supports the plurality of small grids. The surface of the support substrate that supports the plurality of small grids is preferably a flat surface or a concave surface.

Furthermore, the radiographic imaging system of the present invention includes a radiation source, a first grid for generating a first periodic pattern image by passing the radiation emitted from the radiation source, and the first periodic pattern image. A second grid that partially shields and generates a second periodic pattern image, and a radiation image detector that detects the second periodic pattern image are provided. At least one of the first and second grids is configured by laying a plurality of small grids without gaps. Each of the small grids includes a plurality of radiation absorbing portions extending in one direction, and a plurality of radiation transmitting portions extending in the one direction and arranged alternately with the radiation absorbing portions in a direction substantially orthogonal to the one direction. And a grid contour constituted by a plurality of sides that are non-parallel to the one direction.

Since the grid for radiographic imaging of the present invention has a grid outline composed of a plurality of sides non-parallel to the extending direction of the radiation absorbing portion and the radiation transmitting portion, durability against external force is improved.

Further, the radiographic imaging grid of the present invention is a radiographic imaging grid configured by laying a plurality of small grids, and each side constituting the grid outline of the small grid includes a radiation absorbing unit and a radiation transmitting unit. Therefore, the generation of artifacts due to the boundary line between the small grids is reduced.

It is a schematic diagram which shows the structure of a X-ray imaging system. It is a top view which shows the structure of a 1st grid. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is explanatory drawing explaining the manufacturing process of the small grid of a 1st grid. It is a top view which shows the silicon wafer in which the small grid was formed. It is a figure which shows the 1st grid of 2nd Embodiment, (A) is a top view, (B) is sectional drawing which follows the BB line of (A), (C) is C of (A). It is sectional drawing which follows the -C line. It is a top view which shows the modification of a small grid. It is a top view which shows the other modification of a small grid.

[First Embodiment]
In FIG. 1, the X-ray imaging system 10 includes an X-ray source 11, a first grid 13, a second grid 14, and an X-ray image detector 15. As is well known, the X-ray source 11 has a rotating anode type X-ray tube (not shown) and a collimator (not shown) for limiting the X-ray irradiation field, and faces the subject H. X-rays are emitted.

The first grid 13 and the second grid 14 are absorption type grids that absorb X-rays, and are disposed opposite to the X-ray source 11 in the Z direction, which is the X-ray irradiation direction. A space is provided between the X-ray source 11 and the first grid 13 so that the subject H can be arranged. The X-ray image detector 15 is, for example, a flat panel detector (FPD: Flat Panel Detector) using a semiconductor circuit, and is arranged behind the second grid 14.

The first grid 13 is configured by laying a plurality of small grids 13a having a regular hexagonal grid outline (outer shape) on the flat surface 13c of the support substrate 13b without gaps. Similarly, the second grid 14 is configured by laying a plurality of small grids 14a having a regular hexagonal grid outline on the flat surface 14c of the support substrate 14b without gaps.

Hereinafter, the configuration of the grid will be described using the first grid 13 as an example. The second grid 14 has the same configuration as the first grid 13 except that the size is different. Therefore, detailed description of the first grid 14 is omitted.

2 and 3, the small grid 13 a includes a grid layer 22 including a plurality of X-ray absorption parts 20 and a plurality of X-ray transmission parts 21, and a conductive layer 23. The X-ray absorption unit 20 is formed of a metal having X-ray absorption such as gold (Au) or platinum (Pt). The X-ray transmission part 21 is made of single crystal silicon having X-ray transmission. The conductive layer 23 is formed of a metal having X-ray absorption such as chromium (Cr).

The X-ray absorption unit 20 and the X-ray transmission unit 21 extend in the Y direction in the XY plane orthogonal to the Z direction. Further, the X-ray absorption unit 20 and the X-ray transmission unit 21 are alternately arranged along the X direction (a direction substantially orthogonal to the Z direction and the Y direction) to form a striped pattern.

The grid outline of the small grid 13a is composed of first to sixth sides 24a to 24f having the same length. The extending directions of the X-ray absorption unit 20 and the X-ray transmission unit 21 are orthogonal to the second side 24b and the fifth 24e, and are not parallel to any of the first to sixth sides 24a to 24f.

As shown in FIG. 1, the X-ray absorption unit 20 and the X-ray transmission unit 21 are arranged so as to be continuous in a straight line across adjacent small grids 13 a when a plurality of small grids 13 a are laid without gaps. ing.

The width W _{1 in} the X direction and the arrangement pitch P ₁ of the X-ray absorber 20 are the distance between the X-ray source 11 and the first grid 13, the distance between the first grid 13 and the second grid 14, And it is determined according to the arrangement pitch of the X-ray absorption parts of the first grid 14 or the like. For example, the width W ₁ is about 2 to 20 μm, and the arrangement pitch P ₁ is about 4 to 40 μm, which is twice as large. The thickness T _{1 in} the Z direction of the X-ray absorber 20 is set to, for example, about 100 μm in consideration of the vignetting of cone-beam X-rays emitted from the X-ray source 11. The first grid 13 projects incident X-rays onto the second grid 14 almost geometrically optically.

Next, the operation of the X-ray imaging system 10 will be described. The X-ray radiated from the X-ray source 11 undergoes a phase change when passing through the subject H. The X-ray passes through the first grid 13 and becomes a first periodic pattern image reflecting the transmission phase information of the subject H determined from the refractive index of the subject H and the transmitted optical path length.

The first periodic pattern image is intensity-modulated by being partially shielded by the second grid 14 and becomes a second periodic pattern image. In the present embodiment, according to the fringe scanning method, the second grid 14 is intermittently moved with respect to the first grid 13 at a predetermined scanning pitch, and the subject H is moved from the X-ray source 11 during each stop. The X-ray image detector 15 radiates X-rays toward the center and captures a second periodic pattern image. The scanning pitch is a value obtained by equally dividing (for example, dividing into 5) the arrangement pitch in the X direction of the X-ray absorbing portion of the first grid 14.

As a result of the fringe scanning, the phase differential of the intensity modulation signal for each pixel obtained by the X-ray image detector 15 is calculated by calculating the phase shift amount (phase shift amount with and without the subject). An image is obtained. Here, the intensity modulation signal is a waveform signal representing intensity modulation of the pixel value with respect to the movement of the second grid 14. The phase differential image corresponds to the angular distribution of X-rays refracted by the subject. By integrating this phase differential image along the X direction, a phase contrast image is obtained.

Next, a method for manufacturing the first grid 13 will be described. In addition, since the 2nd grid 14 is manufactured similarly to the 1st grid 13, detailed description is abbreviate | omitted.

4A, a conductive layer 23 is bonded or deposited on the lower surface of the silicon wafer 30. In FIG. The silicon wafer 30 is a substantially circular single crystal silicon wafer used in a normal semiconductor process. The conductive layer 23 is formed of a conductive material such as chromium. As this conductive material, a material having a small difference in thermal expansion coefficient from the silicon wafer 30 is preferable, and Kovar, Invar, or the like may be used. In addition, when bonding the conductive layer 23 to the silicon wafer 30, diffusion bonding performed while applying heat and pressure, or room temperature bonding in which the surfaces are activated in a high vacuum is used.

In FIG. 4B, a resist layer 31 is formed on the upper surface of the silicon wafer 30. The resist layer 31 is formed through, for example, a coating process in which a liquid resist is applied to the silicon wafer 30 by a coating method such as spin coating, a pre-baking process in which an organic solvent is evaporated from the applied liquid resist, and the like.

In FIG. 4C, a striped exposure mask 32 having a line pattern with an arrangement pitch P ₁ in the X direction is disposed above the resist layer 31, and light such as ultraviolet rays is transmitted through the exposure mask 32 through the resist layer 31. Is irradiated. After this exposure, development processing is performed in FIG. 4D, and the exposed portion of the resist layer 31 is removed. As a result, a striped etching mask 33 having a plurality of line patterns extending in the Y direction and arranged along the X direction is formed on the silicon wafer 30. The resist layer 31 is a positive resist, but a negative resist may be used instead.

4E, dry etching is performed through the etching mask 33, and a plurality of grooves 34 extending in the Y direction and arranged along the X direction are formed in the silicon wafer 30. As this dry etching, a Bosch process, which is a deep trench dry etching capable of forming a groove 34 having a high aspect ratio, is used. Note that a cryo process may be used instead of the Bosch process.

4 (F), an X-ray absorber 35 such as gold (Au) is embedded in the groove 34 by electrolytic plating using the conductive layer 23 as a seed layer. In this electrolytic plating method, a bonding substrate formed by the silicon wafer 30 and the conductive layer 23 is immersed in a plating solution, and the other electrode (anode) is disposed at a position facing the bonding substrate. When a current is passed between the conductive layer 23 and the other electrode, metal ions in the plating solution are deposited on the patterned substrate, and the X-ray absorber 35 is embedded in the groove 34.

4G, the etching mask 33 is removed from the silicon wafer 30 by ashing or the like. Thereby, the grid structure of the small grid 13a is completed. Here, the X-ray absorber 35 corresponds to the X-ray absorber 20, and the portion of the silicon wafer 30 adjacent to the X-ray absorber 35 corresponds to the X-ray transmitter 21. Thereafter, the conductive layer 23 may be removed from the silicon wafer 30.

Through the above steps, the small grid 13a is formed on the silicon wafer 30 as shown in FIG. And the small grid 13a is cut out from the silicon wafer 30 using the dicing apparatus (not shown) used with a general semiconductor process. At this time, by cutting while rotating the silicon wafer 30 by 60 degrees so as to form regular hexagonal grid outlines of the small grid 13a one by one, the first non-parallel to the extending direction of the X-ray absorbing unit 20 is performed. To sixth sides 24a to 24f are formed.

In the cutting process of the silicon wafer 30, the X-ray absorber 20 is not cut along the extending direction when any one of the first to sixth sides 24a to 24f is formed. For this reason, defects, such as a crack, are hard to produce and the small grid 13a with high durability is manufactured. Moreover, since the grid outline of the small grid 13a is a regular hexagon, compared with the case where the conventional rectangular small grid is manufactured, there are few parts cut off from the silicon wafer 30, and productivity is high.

The manufacturing process of the small grid 13a is repeated a plurality of times or in parallel to form a plurality of small grids 13a. Then, a plurality of small grids 13a are laid without gaps on the flat surface 13c of the support substrate 13b formed of glass or the like, whereby the first grid 13 is completed.

Note that the small grid 13a and the support substrate 13b are joined by an adhesive or the like. Further, the alignment of the adjacent small grids 13a is performed with reference to the positions of the sides and the X-ray absorbing unit 20 and the X-ray transmitting unit 21. In order to perform alignment with higher accuracy, an alignment mark (not shown) for aligning the small grid 13a may be provided on the flat surface 13c of the support substrate 13b.

As described above, in the present embodiment, the first grid 13 is configured by laying the small grids 13a having the regular hexagonal grid outline without gaps, and the small grids 13b having the regular hexagonal grid outlines are laid without gaps. The second grid 14 is configured by packing. For this reason, the first and

second grids

13 and 14 have high productivity. In addition, since the boundary line between the adjacent small grids 13a and the boundary line between the adjacent small grids 14a are not arranged in a straight line, the first and

second grids

13 and 14 are not easily bent, and are resistant to external forces. High nature.

In addition, when any of the sides constituting the grid outline of the

small grids

13a and 14a is parallel to the extending direction of the X-ray absorbing unit 20, the side acts like a grid line and an artifact is generated in the phase contrast image. However, in this embodiment, since neither side of the

small grids

13a and 14a is parallel to the extending direction of the X-ray absorber 20, the occurrence of artifacts is reduced.

Hereinafter, other embodiments of the present invention will be described. In the following embodiments, the same reference numerals are used for the same configurations as those already described, and detailed description thereof is omitted. Also in each of the following embodiments, the second grid uses the same configuration and manufacturing method as the first grid, except that the arrangement pitch and thickness of the X-ray absorption part and the X-ray transmission part are different. Therefore, detailed description is omitted.

[Second Embodiment]
In the first embodiment, the first and second grids are configured by disposing a plurality of small grids on a flat support substrate, but are configured by disposing the small grids on a concave support substrate. May be.

6, the first grid 40 includes a support substrate 41 having a concave surface 41 a and a plurality of small grids 42. The plurality of small grids 42 are laid without any gaps on the concave surface 41a. The small grid 42 has the same configuration as the small grid 13a of the first embodiment and has a regular hexagonal grid outline. The shape of the concave surface 41a of the support substrate 41 is a shape along a spherical surface centered on the focal point of the X-ray source 11, and the X-rays radiated from the X-ray source 11 are incident substantially perpendicularly.

[Other Embodiments]
In each of the above embodiments, the grid outline of the small grid is a regular hexagon, but may be another regular polygon or a polygon other than a regular polygon. The angle formed between each side of the small grid and the extending direction of the X-ray absorption part is preferably at least 3 °. Below, the modification of a small grid is shown.

In FIG. 7, the grid outline of the small grid 50 is a regular square and has first to fourth sides 51a to 51d. The X-ray absorption parts 52 and the X-ray transmission parts 53 are each extended in the Y direction and alternately arranged along the X direction. The extending directions of the X-ray absorption part 52 and the X-ray transmission part 53 are not parallel to any of the first to fourth sides 51a to 51d.

In FIG. 8, the grid outline of the small grid 60 is an equilateral triangle, and has first to third sides 61a to 61c. The X-ray absorption unit 62 and the X-ray transmission unit 63 are each extended in the Y direction and alternately arranged along the X direction. The extending directions of the X-ray absorption part 62 and the X-ray transmission part 63 are not parallel to any of the first to third sides 61a to 61c.

In each of the above embodiments, a large grid is configured by laying a plurality of small grids without gaps, but either one or both of the first and second grids are configured by a single small grid. May be.

In each of the above embodiments, only the first and

second grids

13 and 14 are provided between the X-ray source 11 and the X-ray image detector 15. A well-known radiation source grid (multi-slit) described in WO 2006/131235 (US Pat. No. 7,898,838) or the like may be provided between the grid 13 and the grid 13. In this case, the present invention can be applied to the source grid.

In each of the above-described embodiments, the first grid projects geometrically optically the X-rays that have passed through the X-ray transmission part. However, Japanese Patent No. 4445397 (US Pat. No. 7,180,796) and the like As described above, the Talbot effect may be generated by diffracting X-rays at the X-ray transmission part. However, in this case, it is necessary to set the distance between the first and second grids to the Talbot distance. In this case, the first grid can be a phase grid instead of the absorption grid.

In each of the above-described embodiments, an example is shown in which the phase contrast image is generated by changing the relative positions of the first and second grids and performing imaging a plurality of times. However, the first and second grids are illustrated. It is also possible to generate a phase-contrast image by performing one-time shooting while fixing.

For example, in the X-ray imaging system described in International Publication No. WO2010 / 05083 (US Pat. No. 8,0097,979), X-ray image detection is performed by performing one imaging while the first and second grids are fixed. A spatial frequency spectrum is obtained by generating image data with a filter and Fourier transforming the intensity distribution of moire fringes in this image data, and separating the spectrum corresponding to the carrier frequency from this spatial frequency spectrum and performing an inverse Fourier transform. By doing so, a phase differential image is generated. The grid of the present invention is also suitable for such an X-ray imaging system.

Further, in each of the above embodiments, the subject H is arranged between the X-ray source and the first grid, but the subject H is arranged between the first grid and the second grid. Also good. In this case as well, a phase differential image and a phase contrast image can be similarly generated.

The above embodiments may be combined with each other within a consistent range. The present invention is applicable not only to a radiographic imaging system for medical diagnosis but also to other radiographic systems for industrial use and nondestructive inspection. The present invention is also applicable to a scattered radiation removal grid that removes scattered radiation in X-ray imaging. Furthermore, the present invention can also be applied to a radiographic imaging system that uses gamma rays or the like as X-rays as radiation.

DESCRIPTION OF SYMBOLS 10 X-ray imaging system 13 1st grid 13a Small grid 13b Support substrate 13c Plane 14 2nd grid 14a Small grid 14b Support substrate 14c Plane 20 X-ray absorption part 21 X-ray transmission part 24a-24f 1st-6th Side 30 Silicon wafer

Claims

A plurality of radiation absorbing portions extending in one direction;
A plurality of radiation transmitting portions extending in the one direction and alternately arranged with the radiation absorbing portion in a direction substantially orthogonal to the one direction;
A grid contour composed of a plurality of sides non-parallel to the one direction;
A grid for radiographic imaging, comprising:
A radiographic imaging grid configured by laying a plurality of small grids without gaps, each of the small grids,
A plurality of radiation transmitting portions extending in the one direction and alternately arranged with the radiation absorbing portion in a direction substantially orthogonal to the one direction;
A grid contour composed of a plurality of sides non-parallel to the one direction;
A grid for radiographic imaging, comprising:
3. The radiographic imaging grid according to claim 2, wherein the grid outline is one of a regular hexagon, a regular square, and a regular triangle.
The radiographic imaging grid according to claim 2, further comprising a support substrate that supports the plurality of small grids.
The radiographic imaging grid according to claim 4, wherein a surface of the support substrate that supports the plurality of small grids is a flat surface or a concave surface.
A radiation source, a first grid for generating a first periodic pattern image by passing radiation emitted from the radiation source, and a second periodic pattern by partially shielding the first periodic pattern image In a radiographic imaging system comprising a second grid for generating an image and a radiographic image detector for detecting the second periodic pattern image,
At least one of the first and second grids is configured by laying a plurality of small grids without gaps,
(A) a plurality of radiation absorbing portions extending in one direction;
(B) a plurality of radiation transmitting portions extending in the one direction and alternately arranged with the radiation absorbing portion in a direction substantially orthogonal to the one direction;
(C) a grid contour constituted by a plurality of sides non-parallel to the one direction;
A radiographic imaging system comprising: