JP2011237773A - Imaging apparatus and imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus and an imaging method enabling an analysis with higher resolution to be performed in analyzing the moire period due to Talbot interference by use of the wave number space with respect to the above-described problem to be solved.SOLUTION: An imaging apparatus comprises: a first grating for forming a two-dimensional interference pattern by diffracting light from a light source; a second grating with shield parts shielding the light and transmission parts transmitting the light two-dimensionally arranged, for shielding a part of the interference pattern; a detector for detecting the light passing through the second grating; and an arithmetic part for calculating the phase image or differential phase image of a specimen based on the periodic pattern of intensity distribution of the light detected by the detector, the first and second gratings being constituted in such a manner that all the periods of the intensity distribution in a first direction are equal in whole areas on a detection face of the detector.

Description

  The present invention relates to an imaging apparatus and an imaging method, and more particularly to an imaging apparatus and an imaging method for imaging a subject using Talbot interference.

Imaging techniques using interference of light of various wavelengths including visible light and X-rays are known.
Talbot interferometry is known as one of such imaging methods.
An outline of Talbot interferometry will be described. When the subject is irradiated with light, the phase of the light changes by passing through the subject.
When this light is irradiated onto a first grating (diffraction grating) having a specific pattern, the light diffracted by the first grating interferes at a certain distance to form an interference pattern called a self-image. By analyzing this self-image, information on the phase of the subject can be obtained.

Further, in Patent Document 1, a shielding part that shields light at a position where a self-image is formed and a shielding grating having a transmission part that transmits light are arranged, and a moire is formed by shielding a part of the self-image. I am letting.
By using a method that forms moiré using a self-image as described and detects this moiré, information about the phase of the subject can be obtained using a detector with a resolution larger than the period of the self-image. Can do.
In general, when X-rays are used as light, the period of the self-image is smaller than the resolution of the detector. Therefore, the method for forming moire as described in Patent Document 1 uses X-rays as light. It is especially effective when. The imaging apparatus described in Patent Document 1 arranges a second grating (shielding grating) having a shielding part that shields light and a transmission part that transmits light at a position where a self-image is formed, and Moire is formed by shielding a part.

There are several methods for generating moire using the second grating.
For example, there is a method of using a second grating having the same shape including the self image and the period, and producing a moire with high visibility by slightly rotating the angle.
There is also a method of generating moire using a second grating having a slightly different period from the self-image.
In any case, it is the same in that the self-image is emphasized by moire.
There are also some methods for calculating the change in the wavefront shape of light by the subject from the displacement of the moire.
One of them is a method of analyzing the moiré period using a wave number space, and specifically includes Fourier transform, wavelet transform, and the like.
However, in this specification, the Fourier transform includes a Fourier transform with a window function.
Non-Patent Document 1 describes a method of performing Fourier transform of a moire using a Fourier transform method and extracting and analyzing a moire component in a wave number space. The principle of this method will be briefly described.
First, the detection result is Fourier transformed to obtain a spatial frequency spectrum. Next, the spectrum of the frequency of the fundamental period component of moire (hereinafter referred to as carrier frequency) and its periphery are cut out and moved to the origin.
The frequency spectrum is subjected to inverse Fourier transform to obtain a differential phase image of the subject, and further integrated to obtain a phase image of the subject.

US Pat. No. 5,812,629

M.M. Takeda, H .; Ina, and S.M. Kobayashi, J. et al. Opt. Soc. Am. 72, 156-160 (1982).

The technique disclosed in Non-Patent Document 1 is a one-dimensional Fourier transform method, and a differential phase image in a two-dimensional direction cannot be obtained by this transform method.
Therefore, a self-image having a two-dimensional pattern is formed by making the first grating in the Talbot interferometer into a two-dimensional structure. Then, a two-dimensional moire can be caused to appear by installing a second lattice having an appropriate shape corresponding to the self-image.
However, when analyzing the moire period using the wave number space, the phase of the light cannot be recovered with the same accuracy with any shape of moire.
That is, in phase recovery using a method of analyzing the moire period using the wave number space, a satisfactory result cannot be obtained in terms of accuracy depending on the combination of the first grating and the second grating. There is.
For this reason, it becomes an important subject to form a moire suitable for the analysis method using the wave number space by combining the first grating and the second grating.

  In view of the above problems, an object of the present invention is to provide an imaging apparatus and an imaging method capable of performing analysis with higher resolution when analyzing the period of moire due to Talbot interference using a wave number space.

The imaging device of the present invention includes a first grating that forms a two-dimensional interference pattern by diffracting light from a light source,
A shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged; and a second grating that shields a part of the interference pattern;
A detector for detecting the light having passed through the second grating;
A calculation unit that calculates a phase image or a differential phase image of the subject based on a periodic pattern of the intensity distribution of the light detected by the detector, and
The first grating and the second grating are configured so that the period of the intensity distribution in the first direction is equal in all regions on the detection surface of the detector. .
The imaging method of the present invention includes a step of forming a two-dimensional interference pattern by the first grating diffracting light,
A part of the interference pattern is shielded by a second grating in which a shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged;
A step of detecting a light intensity distribution through the second grating by a detector;
Analyzing the periodic pattern of the intensity distribution detected by the detector by the calculation unit to calculate a phase image or a differential phase image of the subject, and
The period of the intensity distribution in the first direction is constant on the detection surface of the detector,
In addition, the first grating and the second grating are configured so that the period of the intensity distribution in the second direction is constant on the detection surface of the detector, so that the subject is a phase image or A differential phase image is acquired.

  According to the present invention, it is possible to provide an imaging apparatus and an imaging method capable of performing analysis with higher resolution when analyzing the period of moire due to Talbot interference using a wave number space.

It is a figure which shows the apparatus structure of the X-ray phase imaging regarding embodiment. (A) is a figure which shows the 1st grating | lattice regarding embodiment, (b) is a figure which shows the self-image regarding embodiment. It is a figure which shows the 2nd grating | lattice regarding embodiment. (A) is a figure which shows the moire regarding embodiment, (b) is the schematic of what carried out the Fourier transform of the moire regarding embodiment, (c) is a figure which shows intensity distribution of the moire regarding embodiment. It is the figure which showed the result of the wavefront analysis by embodiment. (A) is a diagram showing a second grating related to Example 2, (b) is a diagram showing moire related to Example 2, (c) is a schematic diagram of Fourier transform of moire related to Example 2, and (d) is a schematic diagram of (4). FIG. 6 is a diagram showing a moire intensity distribution related to Example 2. 6 is a diagram illustrating a result of wavefront analysis according to Example 2. FIG. (A) is a figure which shows the 1st grating | lattice regarding Example 3, (b) is a figure which shows the self-image regarding Example 3. FIG. (A) is a diagram showing a second grating related to Example 3, (b) is a diagram showing moire related to Example 3, (c) is a schematic diagram of a Fourier transform of the moire related to Example 3, and (d) is a diagram showing FIG. 6 is a diagram illustrating a moire intensity distribution related to Example 3. FIG. 6 is a diagram illustrating a result of wavefront analysis according to Example 3. (A) is a diagram showing a second grating related to Example 4, (b) is a diagram showing moire related to Example 4, (c) is a schematic diagram of a Fourier transform of the moire related to Example 4, and (d) is a schematic diagram of (4). FIG. 6 is a diagram illustrating a moire intensity distribution related to Example 4; It is a figure showing the result of the wavefront analysis by Example 4. It is a figure which shows a subject. (A) is a figure which shows an example of the phase recovery method procedure using Fourier transform, (b) is a figure which shows an example of the phase recovery method procedure using Fourier transform, (c) is the phase recovery method using Fourier transform The figure which shows an example of a procedure, (d) is a figure which shows an example of the phase recovery method procedure using Fourier transform. (A) is a diagram showing a second lattice relating to the comparative example, (b) is a diagram showing moire relating to the comparative example, (c) is a schematic diagram of a Fourier transform of moire relating to the comparative example, and (d) is related to the comparative example. It is a figure which shows intensity distribution of a moire. It is a figure showing the result of the wavefront analysis by a comparative example.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
The imaging apparatus according to the present embodiment uses X-rays having a wavelength of 10 nm or less as light, analyzes a moiré periodic pattern due to Talbot interference by a window Fourier transform method, and obtains a phase image or a differential phase image of a subject.
FIG. 1 shows an imaging apparatus used in this embodiment.
The imaging apparatus according to the present embodiment shields an X-ray source 110 that emits spatially coherent X-rays, a first grating 130 that forms a two-dimensional interference pattern by diffracting the X-rays, and X-rays. The shielding part and the transmission part through which X-rays pass are provided with a second grating 140 in which the two-dimensional periodic array is arranged.
Moreover, the detector 150 which detects the intensity distribution of the X-rays which passed through the 2nd grating | lattice, and the arithmetic unit 160 which analyzes a detection result are provided.
The imaging apparatus of this embodiment includes an X-ray source 110 as a light source. When the X-ray emitted from the X-ray source 110 passes through the subject 120, the phase changes according to the refractive index and shape of the subject. In FIG. 1, the subject 120 is disposed between the X-ray source 110 and the first grating 130, but may be disposed between the first grating 130 and the second grating 140.
The first grating 130 is a transmission type diffraction grating called a phase grating, and is arranged so that portions having two kinds of transmission characteristics have a two-dimensional periodic structure. For this reason, the X-rays transmitted through the first grating form a self-image in which bright and dark portions are two-dimensionally arranged at regular intervals.

FIG. 2A shows the first grating used in this embodiment. However, FIG. 2A is an enlarged view of a part of the first lattice.
FIG. 2A shows a lattice characterized in that the X-ray transmitted through one region 301 is relatively shifted in phase by π from the X-ray transmitted through the other region 302 (π lattice).
FIG. 2B is a self-image formed when the phase grating shown in FIG. In the self image, the dark part 311 and the bright part 312 are arranged in a grid pattern with a period p1, and the self image has a two-dimensional period.
However, the self-image shown in FIG. 2B is a self-image when the subject is not placed between the X-ray source and the first grating. Hereinafter, unless otherwise specified, when the shape of the self-image is described in the present specification, it refers to a self-image when no subject is placed between the X-ray source and the first grating.
In the present embodiment, the self-image shown in FIG. 2B is formed by using the first grating shown in FIG. 2A, but the first grating used in the present invention is not limited to this. In addition, the self-image formed by the first grating is not limited to this.

When phase imaging using X-rays is performed, the period of the first grating is about several micrometers.
In the case of a Talbot interferometer, when the first grating period is d and the wavelength of incident light is λ, the basic distance z called the Talbot distance is

z = d ² / 2λ (1)

Because it is given by.
Actually, various coefficients are applied to the equation (1) depending on the shape of the first grating and the desired contrast.
However, on the basis of the equation (1), in order to make the distance from the first grating to the self-image about several tens of centimeters in view of the size of the apparatus, the grating period of the first grating is about several microns. You can see that it needs to be ordered.
As a result, the period of the self-image is about several micrometers. The resolution of a commonly used X-ray detector is about several tens of microns at most, which is different from the period of the self-image. Therefore, since the self-image cannot be picked up as it is, the image pickup apparatus of the present embodiment emphasizes the self-image by using moire.

In the present embodiment, moire is formed using the second grating 140. A second grating in the present embodiment is shown in FIG. However, FIG. 3 is an enlarged view of a part of the second grating.
In the second grating 140, a shielding part 802 that shields X-rays and a transmission part 801 that transmits X-rays are arranged in a checkered pattern with a period p2, and the second grating has a two-dimensional period. The period p2 of the second grating 140 is slightly different from the period p1 of the self image, and the difference in period causes light and dark waves, that is, moire.
A moire formed using the first grating shown in FIG. 2A and the second grating shown in FIG. 3 is shown in FIG. Moire and Fourier transform will be explained later. Note that the moire shown in FIG. 4A is a moire when the subject is not placed between the X-ray source and the first grating or between the first and second gratings. Unless otherwise specified, when the moire shape is described in the present specification, when the subject is not placed between the X-ray source and the first grating or between the first grating and the second grating. Of moire. Moreover, in this embodiment, the 2nd grating | lattice 140 by which the shielding part and the permeation | transmission part were arranged in the checkered grid | lattice form was used, However, The 2nd grating | lattice used for this invention is not limited to this. Further, the shielding part may not completely shield X-rays, and the transmission part may not completely transmit X-rays. However, the X-rays need to be shielded or transmitted to such an extent that the moiré can be formed by overlapping the shielding part and the transmission part on the self-image.

The detector 150 is an image sensor (for example, a CCD) that can detect the intensity of X-rays, and detects the intensity distribution of X-rays that passes through the second grating, that is, moire.
The X-ray intensity distribution detected by the detector 150 is analyzed by the calculation unit 160.
In the present embodiment, a phase image or a differential phase image of a subject is obtained using a technique based on a Fourier transform method with a window function (window Fourier transform).
The window Fourier transform is a process of determining the phase by sequentially performing Fourier transform while applying a window function having a local value to the moire. Although this processing requires a large amount of data and takes time, it is possible to perform more accurate and precise phase recovery than the Fourier transform method that does not use a window function.

Here, the concept of the phase recovery method by Fourier transform will be briefly described. FIG. 14 is a diagram showing the outline.
In the Fourier transform method, moire is decomposed into Fourier components, and analysis is performed on a specific frequency region to restore an image.
FIG. 14A shows an example of moire before analysis.
A periodic moire 202 is formed in the screen 201. This misalignment of the moire represents information related to the phase change of the X-ray by the subject.
When the moire 202 is Fourier transformed over the entire screen 201, the result is as shown in FIG.
Here, the origin of the wave number space is placed at the center of the screen 211. On the wave number space, the zero-order spectrum 212 appears at the origin, and the first-order spectra 213, 214, 215, and 216 appear around it.
The position and number of the spectrum around the origin depend on the shape of the moire before the Fourier transform. At least one of the spectra is used for wavefront analysis. In general, one of the primary spectral points is used.

In the method according to Non-Patent Document 1, one point of the primary spectrum point and its periphery are cut and moved to the origin 222 on another wave number space 221 (FIG. 14C).
By subjecting this to an inverse Fourier transform, a differential image 232 of the subject can be acquired on the real space 231 (FIG. 14D). The wavefront is recovered by integrating the differential image 232.
The above method is an example of a Fourier transform method, and the present invention is not limited to such an analysis method, and other methods can also be used.
For example, a plurality of spectral points may be used to analyze the wave number space in more detail.

An analysis method for obtaining a phase image or a differential phase image of a subject from the moire intensity distribution detected in the present embodiment will be briefly described. A schematic representation of the moire (FIG. 4A) in this embodiment, which is Fourier-transformed over the entire detection surface of the detector 150, has the form shown in FIG. 4B.
In FIG. 4B, the zero-order spectrum 812 exists in the center of the wave number space 811 and the primary spectra 813, 814, 815, and 816 exist around it.
When at least one arbitrary spectrum is analyzed from the primary spectrum as shown in FIG. 14, a differential phase image of the subject is obtained. Further, when this is integrated, a phase image of the subject is obtained.

FIG. 4C shows the X-ray intensity distribution along the moire axes A1 and B1 in FIG. 4A. The intensity distribution along the axis A1 is a solid line and the intensity distribution along the axis B1. Is indicated by a broken line. The axis B1 is parallel to the axis A1. As shown in FIG. 4C, the intensity distribution along the axis A1 and the intensity distribution along the axis B1 have the same period although the shape and amplitude are different.
Similarly to the case other than the axis B1, the moiré shown in FIG. 4A has an intensity distribution along all the axes parallel to the axis A1, and an intensity distribution having the same period as the intensity distribution along the axis A1. .
That is, assuming that the direction parallel to the axis A1 in FIG. 4A is the first direction, the moire shown in FIG. 4A has a period of intensity distribution on the moire in the first direction (detection by the detector). It is the same for all areas on the surface.
The moire has a two-dimensional period, and the intensity distribution along the axis C1 perpendicular to the axis A1 also has a period.
Similarly to the axis A1, when the direction parallel to the axis C1 is the second direction, the moire shown in FIG. 4A has a period of intensity distribution in the second direction intersecting the first direction. Equal in all areas on the moire.
However, all the regions on the moire in this specification do not include regions that are not used for analysis using wave number space (for example, Fourier transform).
In order to correctly calculate the wavefront derivative of X-rays in the Fourier transform method, it is necessary that the period of the X-ray intensity distribution of the cross section along the differential direction is equal, and the shape of this intensity distribution has a sinusoidal shape. It is more desirable.

As described above, when the direction parallel to the axis A1 in FIG. 4A is the first direction, the moire shown in FIG. 4A is the first direction, and the period of the intensity distribution is all over the moire. Equal in the region
Further, if the direction parallel to the axis C1 in FIG. 4A is the second direction, the moire shown in FIG. 4A has the period of the intensity distribution in all areas on the moire also in the second direction. equal.
Therefore, if the first direction and the second direction are differential directions, the spectrum of the period can be extracted from all regions on the moire by Fourier transform, so that the X-ray phase change by the subject is more detailed than in the past. It becomes possible to analyze. Since only one differential direction may be used, even if only the first direction or the second direction is set as the differential direction, the phase change of the X-ray caused by the subject is analyzed in detail as compared with the conventional case (one differential direction). be able to.

Specific examples and comparative examples will be described below.
In the following examples and comparative examples, differential phase images obtained when using a circular pattern with a thickness of 40 μm patterned on silicon as shown in FIG. And the comparative example was compared.
In the figure, the height of the pattern is expressed by contrast.
First, a comparative example will be described.
[Comparative example]
This comparative example will be described with reference to FIG.
The imaging device of this comparative example is different from the imaging device described in the embodiment in the second grating, and the other configuration is the same as that of the imaging device of the embodiment.
The imaging apparatus of this comparative example has an X-ray source that emits parallel X-rays of 17.5 keV as a light source, a phase grating (π grating) shown in FIG. 2A as a first grating, and a second grating Includes a grid having the structure shown in FIG. 15A, and further includes a detector and a calculation unit.
FIG. 15A is a schematic view enlarging a part of the shape of the second grating. The second grating of this comparative example includes a transmission part 601 through which incident X-rays pass and a shielding part 602 that shields incident X-rays. The second grating has a slightly different period from that of the first grating, and a moire as shown in FIG.

A schematic diagram of the Fourier transform of the moire shown in FIG. 15B is shown in FIG.
Similar to FIG. 4B, the zero-order spectrum 612 exists in the center of the wave number space 611, and the first-order spectra 613, 614, 615, and 616 exist around it. An arbitrary spectrum is analyzed from the primary spectrum, and a differential phase image of the subject is calculated.

FIG. 16 is a differential phase image of the subject obtained in this comparative example.
In this figure, the shape in FIG. 13 is differentiated in the x-axis (horizontal axis) direction. The shape is reproduced as a whole, but if you look closely, there is staircase noise (jaggy) in the shape that should be round, but the detailed shape cannot be reproduced.
This is because the shape of the moire resulting from the combination of the self-image of the first grating and the second grating is not suitable for wavefront recovery.

FIG. 15D shows the X-ray intensity distribution along the moiré axes A5 and B5 of FIG. 15A. The intensity distribution along the axis A5 is indicated by a solid line, and the intensity distribution along the axis B5 is indicated by a broken line. Indicated.
The axis B5 is parallel to the axis A5. As described above, the Fourier transform method requires that the periods of the X-ray intensity distribution along the differential direction are equal.
As shown in FIG. 15D, the X-ray intensity distribution along the axis A5 has a triangular wave shape and has a period that can be analyzed using the Fourier transform, but the X-ray intensity distribution along the axis B5. The intensity distribution of the line is constantly 0 on the axis, and information on the wavefront relating to the B5 axis cannot be obtained.
Therefore, the wavefront cannot be analyzed in detail, and an overall step-like jaggy as shown in FIG. 16 appears.

[Example 1]
Example 1 will be described with reference to FIG.
Example 1 has the same configuration as the imaging device described in the embodiment, and the second grating is different from the comparative example. That is, the light source of the image pickup apparatus of this embodiment is an X-ray source that emits parallel X-rays of 17.5 keV, the first grating is the phase grating shown in FIG. 2A, and the second grating is shown in FIG. In addition, the grid has a detector and a calculation unit. As described above, the period p2 of the second grating is slightly different from the period p1 of the first grating, and the moire as shown in FIG. 4A is formed by the difference, and this moire is Fourier transformed. FIG. 4B shows the X-ray intensity distribution along the axis A1 and the axis B1 on the moire as indicated by the solid line and the broken line in FIG.
One arbitrary spectrum is selected from the primary spectra 813, 814, 815, and 816 shown in FIG. 4B, analyzed, and a differential phase image of the subject is calculated.
FIG. 5 is a differential phase image obtained in this example.
Compared to the comparative example, since the position of the primary spectrum is in the direction of 45 degrees obliquely, the differential phase image is also inclined to 45 degrees obliquely compared to FIG. However, excluding the difference, edge jaggies are not conspicuous compared to the differential phase image of FIG. 16, and a detailed shape can be reproduced.

As described above, FIG. 4C shows the X-ray intensity distribution along the moiré axes A1 and B1 of FIG. 4A, and the intensity distribution along the axis A1 and along the axis B1. The intensity distribution has the same period although the shape and amplitude are different.
The same applies to other than the axis B1, and when the direction parallel to the axis A1 in FIG. 4A is the first direction, the moire shown in FIG. Equal in all areas above.
Therefore, if the first direction is the differential direction, the spectrum of the period can be extracted from all regions on the moire by Fourier transform, so that the wavefront can be analyzed in detail, and the detailed shape compared with the comparative example It becomes possible to do.

[Example 2]
As Example 2, an imaging apparatus using a second grating having a semi-transmissive portion will be described with reference to FIG. The imaging apparatus of the second embodiment has the same structure as that of the first embodiment except for the second grating.
The structure of the second grating in this example is shown in FIG. FIG. 6A is a schematic diagram enlarging a part of the shape of the second grating. Reference numeral 1001 denotes an incident X-ray transmission part, and reference numeral 1002 denotes a shielding part.
Further, the second grating used in this embodiment has a semi-transmissive portion 1003 that transmits 50% of incident X-rays.
When X-rays are transmitted through the semi-transmissive part of this embodiment, the intensity of the incident X-rays is halved. However, X-rays may be transmitted through the shielding part and shielded from the transmissive part.
In the second grating of this embodiment, the shielding part, the transmissive part, and the semi-transmissive part are each arranged in a checkered pattern as shown in FIG. 6A, and the shielding part, the transmissive part, and the semi-transmissive part are arranged. The transmission parts are arranged in a so-called Bayer array.
Similar to the first embodiment, the period of the second grating is slightly different from the period of the self-image, and a moire as shown in FIG. 6B is formed by the difference.
As in Example 1, the result of Fourier transform of this moire is FIG. 6C, and the X-ray intensity distribution along the axis A2 on the moire is the solid line in FIG. 6D, and the X-ray intensity along the axis B2. The distribution is a broken line in FIG.

When the moire shown in FIG. 6B is Fourier transformed, a spectrum as shown in FIG. 6C appears.
Similar to FIG. 4B, FIG. 6C also has a zero-order spectrum 1012 in the center of the wave number space 1011 and a first-order spectrum 1013, 1014, 1015, 1016 around it.
One arbitrary spectrum is selected from the primary spectra 1013, 1014, 1015, and 1016 in FIG. 6C, analyzed, and a differential phase image of the subject is calculated.
FIG. 7 is a differential phase image obtained in this example.
A primary spectrum appears at the same position as in the comparative example, and edge jaggies are not noticeable compared to the differential phase image of FIG. 16, and a detailed shape can be reproduced.

FIG. 6D shows an X-ray intensity distribution along the axes A2 and B2 of the moire in FIG. 6B. Similar to the moire in FIG. 4 (a), the moire in FIG. 6 (b) also has a period of intensity distribution equal in all areas on the moire in the first direction when the direction parallel to the axis A2 is the first direction. Like Example 1, it becomes possible to analyze a detailed shape compared with a comparative example.
Also, unlike the moiré shown in FIG. 4A, the moiré of the axis B2 shown in FIG. 6 has the same intensity distribution and amplitude and shape in the first direction, and the same pattern has the same period in all areas on the moiré. Is repeated. Therefore, the spectrum of the period can be easily extracted by Fourier transform.

[Example 3]
In the third embodiment, an imaging apparatus that forms a self-image different from the imaging apparatus of the first embodiment will be described with reference to FIGS. 8 and 9. The imaging apparatus according to the third embodiment has the same structure as that of the first embodiment except for the first grating and the second grating.
FIG. 8A shows the first grating used in this example. However, FIG. 8A is a schematic view in which a part of the first lattice is enlarged.
FIG. 8A shows a lattice characterized in that the phase of x-rays transmitted through one region 401 is relatively shifted by π / 2 from the x-rays transmitted through the other region 402 (π / 2 lattice). . FIG. 8B is a self-image formed when the phase grating of FIG. 8A is used. In the self-image, the dark portion 411 and the light portion 412 are arranged in a periodic checkered pattern (checkerboard), and the self-image has a two-dimensional period.
FIG. 9A shows the second grating used in this example. However, FIG. 9A is an enlarged schematic view of a part of the second lattice. In the second grating used in this embodiment, a transmission part 1201 that transmits X-rays and a shielding part 1202 that shields X-rays are arranged in a checkered pattern. The second grating has a slightly different period from that of the first grating, and a moire as shown in FIG. 9B is generated due to the difference. As in Example 1, the result of Fourier transform of this moire is FIG. 9C, and the X-ray intensity distribution along the axis A3 on the moire is the solid line in FIG. 9D, and the X-ray intensity along the axis B3. The distribution is a broken line in FIG.

When the moire shown in FIG. 9B is Fourier transformed, a spectrum as shown in FIG. 9C appears. Similarly to FIG. 4B, similarly, a zero-order spectrum 1204 and a first-order spectrum 1205, 1206, 1207, 1208 exist in the center of the wave number space 1203.
FIG. 10 is a differential phase image obtained in this example.
Compared to the comparative example, since the position of the primary spectrum is in the direction of 45 degrees obliquely, the differential phase image is also inclined to 45 degrees obliquely compared to FIG. However, excluding the difference, edge jaggies are not noticeable compared to the differential phase image of FIG. 16, and a detailed shape can be reproduced.
FIG. 9D shows the X-ray intensity distribution along the moiré axes A3 and B3 of FIG. 9B. Similar to the moire in FIG. 4A, the moire in FIG. 9B also assumes that the first direction is the direction parallel to the axis A3, and the period of the intensity distribution in the first direction is the same in all regions on the moire. Like Example 1, it becomes possible to analyze a detailed shape compared with a comparative example.

[Example 4]
In the fourth embodiment, an imaging apparatus using the same first grating as that of the third embodiment will be described with reference to FIG. The second embodiment is different from the third embodiment in the second lattice, and the other configurations are the same.
FIG. 11A is a schematic view enlarging a part of the second grating.
The second grating used in this embodiment has such a shape that an X-ray transmission part 1401 and a shielding part 1402 are arranged in a grid pattern and rotated by 45 ° with respect to the self-image. The second grating has a slightly different period from the first grating, and the difference causes a moire pattern as shown in FIG. As in Example 1, the result of Fourier transform of this moire is FIG. 11 (c), and the X-ray intensity distribution along the axis A4 on the moire is the solid line in FIG. 11 (d), and the X-ray intensity along the axis B4. The distribution is a broken line in FIG.

When the moire shown in FIG. 11B is Fourier transformed, a spectrum as shown in FIG. 11C appears. Similar to FIG. 4B, FIG. 11C also has a zero-order spectrum 1412 in the center of the wave number space 1411 and primary spectra 1413, 1414, 1415, and 1416 around it in the wave number space 1411.
FIG. 10 is a differential phase image obtained in this example.
Compared to the comparative example, since the position of the primary spectrum is in the direction of 45 degrees obliquely, the differential phase image is also inclined to 45 degrees obliquely compared to FIG. However, excluding the difference, edge jaggy is reduced as compared with the differential phase image of FIG. 16, and a smooth curved surface is expressed.
FIG. 11D shows the X-ray intensity distribution along the axes A4 and B4 of the moire in FIG. 11B. Similar to the moire in FIG. 4A, the moire in FIG. 11B also assumes that the period parallel to the axis A4 is the first direction, and the period of the intensity distribution in the first direction is the same in all regions on the moire. Like Example 1, it becomes possible to analyze a detailed shape compared with a comparative example.
Further, the shape of the period of the intensity distribution is closest to the sine curve in the embodiments. This indicates that a high-order spectrum that becomes noise upon Fourier transform hardly appears, and in this respect, the fourth embodiment is more suitable than the first to third embodiments in wavefront analysis.

110: X-ray source 120: Subject 130: First grating 140: Second grating 150: Detector 160: Calculation unit

Claims (12)

A first grating that forms a two-dimensional interference pattern by diffracting light from a light source;
A shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged; and a second grating that shields a part of the interference pattern;
A detector for detecting the light having passed through the second grating;
A calculation unit that calculates a phase image or a differential phase image of the subject based on a periodic pattern of the intensity distribution of the light detected by the detector, and
The first grating and the second grating are configured so that the period of the intensity distribution in the first direction is equal in all regions on the detection surface of the detector. Imaging device.   The first grating and the second grating are such that the period of the intensity distribution in a second direction intersecting the first direction is equal in all regions on the detection surface of the detector. The imaging apparatus according to claim 1, wherein the imaging apparatus is configured.   The imaging apparatus according to claim 2, wherein the first direction and the second direction intersect perpendicularly.   The imaging apparatus according to claim 2, wherein a period of the intensity distribution in the first direction is equal to a period of the intensity distribution in the second direction.   5. The imaging apparatus according to claim 1, wherein the calculation unit analyzes the intensity distribution using a Fourier transform method. 6. The calculation unit calculates the differential phase image of the subject,
The imaging apparatus according to claim 2, wherein the first direction and the second direction are differential directions of the differential phase image.   The imaging apparatus according to claim 1, wherein the light is an X-ray. A first grating that forms a two-dimensional interference pattern by diffracting light from a light source;
A shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged; a second grating that shields a part of the interference pattern;
A detector for detecting the light having passed through the second grating;
A calculation unit that calculates a phase image or a differential phase image of the subject based on a periodic pattern of the intensity distribution of the light detected by the detector, and
The interference pattern is a grid pattern.
The image pickup apparatus, wherein the second grating has the shielding part and the transmission part arranged in a checkered pattern. A first grating that forms a two-dimensional interference pattern by diffracting light from a light source;
A shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged; a second grating that shields a part of the interference pattern;
A detector for detecting the light having passed through the second grating;
A calculation unit that calculates a phase image or a differential phase image of the subject based on a periodic pattern of the intensity distribution of the light detected by the detector, and
The interference pattern is a grid pattern.
The second grating includes the shielding part, the transmission part, and a semi-transmission part that transmits light more than the shielding part and shields light from the transmission part.
An imaging apparatus, wherein the shielding part, the transmissive part, and the semi-transmissive part are arranged in a Bayer array in which the shielding part, the transmissive part, and the semi-transmissive part are arranged in a checkered pattern. A first grating that forms a two-dimensional interference pattern by diffracting light from a light source;
A shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged; a second grating that shields a part of the interference pattern;
A detector for detecting the light having passed through the second grating;
A calculation unit that calculates a phase image or a differential phase image of the subject based on a periodic pattern of the intensity distribution of the light detected by the detector, and
The interference pattern is a checkered pattern,
The image pickup apparatus, wherein the second grating has the shielding part and the transmission part arranged in a checkered pattern. A first grating that forms a two-dimensional interference pattern by diffracting light from a light source;
A shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged; a second grating that shields a part of the interference pattern;
A detector for detecting the light having passed through the second grating;
A calculation unit that calculates a phase image or a differential phase image of the subject based on a periodic pattern of the intensity distribution of the light detected by the detector, and
The interference pattern is a checkered pattern,
In the second grating, the shielding unit and the transmission unit are arranged in a grid pattern. Forming a two-dimensional interference pattern by the first grating diffracting light;
A part of the interference pattern is shielded by a second grating in which a shielding part that shields the light and a transmission part that transmits the light are two-dimensionally arranged;
A step of detecting a light intensity distribution through the second grating by a detector;
Analyzing the periodic pattern of the intensity distribution detected by the detector by the calculation unit to calculate a phase image or a differential phase image of the subject, and
The period of the intensity distribution in the first direction is constant on the detection surface of the detector,
In addition, the first grating and the second grating are configured so that the period of the intensity distribution in the second direction is constant on the detection surface of the detector, so that the subject is a phase image or An imaging method characterized by acquiring a differential phase image.

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