JP2017083411A - X-ray Talbot interferometer and Talbot interferometer system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a talbot interferometer with which it is possible to acquire a scattering force in three or more directions without having to rotate a grating or a test object around an optical axis, and in which a difference in scattering sensitivity per direction is small.SOLUTION: An X-ray talbot interferometer 10 comprises: a beam splitter grating 2 for diffracting X-rays and forming an interference pattern of hexagonal lattice shape; an X-ray detector 5 for detecting the interference pattern; and an arithmetic device 6 for calculating, using the result of detection by the X-ray detector 5, information pertaining to X-ray scattering by a test object 8 that is arranged in an X-ray optical path. The arithmetic device 6 calculates the information pertaining to X-ray scattering making use of an amplitude change of three cycle components of the interference pattern that are equal in cycle and different in cycle direction. The information pertaining to X-ray scattering includes at least one of information on degree of anisotropy of scattering and information on main direction of scattering.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an X-ray Talbot interferometer and a Talbot interferometer system.

  Imaging methods using absorption of X-rays by a subject have been widely used in the medical and industrial fields. In recent years, an imaging method using a phase shift when X-rays pass through a subject has been developed. In particular, an X-ray Talbot interferometer, which is an imaging method using an X-ray diffraction grating, has been widely studied.

  The X-ray Talbot interferometer includes a beam splitter grating that forms an X-ray interference pattern and a detector that detects the interference pattern. When an X-ray Talbot interferometer is used, three types of subject images, that is, an absorption image, a differential phase image, and a scattered image, can be acquired from changes in the interference pattern depending on the subject. The absorption image is similar to an image obtained by X-ray imaging using X-ray absorption by a conventional subject. The differential phase image is an image based on the spatial differential value of the X-ray phase shift by the subject, and is an image in which edges of various structures in the subject are particularly remarkably depicted. The scattered image is an image based on the magnitude of the X-ray scattering force caused by a fine structure exceeding the spatial resolution of the interferometer in the subject. As for the differential phase image, information corresponding to the result obtained by differentiating the phase shift distribution along the periodic direction of the periodic component used for imaging in the interference pattern is obtained. As for the scattered image, information on scattering specific to the length and direction of the period can be obtained from the periodic component used for imaging in the interference pattern. Since scattering from the fine structure in the subject has a distribution inherent to the structure in the scattering direction, for example, when multiple periodic components are used for imaging, information on the scattering power obtained by using each of the periodic components is Has independent information on the two-dimensional scattering force distribution. That is, when the periodic components in the x direction and the y direction are used, the scattered image in the x direction and the scattered image in the y direction have independent information. In Patent Document 1, a square lattice is used to acquire scattered images in a total of four directions: two directions intersecting at an angle of 45 ° with the x direction, the y direction, and the x axis (hereinafter sometimes referred to as an oblique direction). It is disclosed.

  As described above, the X-ray scattering image of the subject acquired by the Talbot interferometer generally includes information on the two-dimensional scattering force distribution at each position (for example, part of information in the x direction). Only).

  In recent years, there has been proposed a method for acquiring a scattered image that is more sophisticated than the conventional method using information on the angular distribution of scattering. For example, Non-Patent Document 2 uses a one-dimensional grating and performs scattering force measurement using a single periodic component in an interference pattern a plurality of times while rotating the subject, resulting in the subject being subject to the measurement. Discloses a method for measuring scattering power in a plurality of directions. Non-Patent Document 2 further discloses an example in which information on the anisotropy of scattering is acquired using the measurement results of scattering power in a plurality of directions. The information on the anisotropy of scattering is information on the degree of anisotropy of scattering (sometimes referred to as scattering anisotropy) and the main scattering direction (which means the direction in which the scattering power is maximized). Refers to that. In this way, by measuring the scattering force in multiple directions, it is possible to obtain more information on scattering (that is, more information on the fine structure in the subject causing the scattering). It becomes.

I. Zanette et al. “Two-Dimensional X-Ray Grafting Interferometer”, Physical Review Letters, Vol. 105, 248102 (2010) T. T. H. Jensen et al. “Directional x-ray dark-field imaging” Physics in Medicine and Biology, Vol. 55,3317-3323 (2010)

  In the method using a one-dimensional grating as in Non-Patent Document 2, the scattering force that can be measured at a time is only the scattering force in one direction. On the other hand, in order to obtain information on scattering anisotropy, information on scattering power in at least three directions is necessary. Therefore, in order to obtain information on the anisotropy of scattering, it is necessary to perform imaging a plurality of times while rotating the subject or the grating around the optical axis.

  On the other hand, when the information on the anisotropy of scattering is acquired according to the disclosure of Non-Patent Document 2 using the scattering forces obtained in Non-Patent Document 1, the reliability of the anisotropy information becomes low. It has become clear by the inventors of the present invention. That is, since the periodic component in the oblique direction has a shorter period than the periodic component in the x and y directions, the amplitude change rate for the same scattering changes (usually the change becomes large), that is, the sensitivity to the scattering changes ( (It usually becomes higher). That is, there are cases where the magnitude of the acquired scattering force is measured to be larger in the oblique direction, although the scattering force is actually the same in the x direction and the oblique direction. Thus, even if it is going to acquire the anisotropy of scattering force like a nonpatent literature 2 using a square lattice, since the scattering sensitivity changes with measurement directions, there is a problem that the reliability of anisotropy information is low. is there.

  Therefore, the present invention can acquire the scattering force in three or more directions without rotating the grating or the subject around the optical axis, and is more suitable for each direction than the Talbot interferometer described in Non-Patent Document 1. An object of the present invention is to provide a Talbot interferometer with a small difference in scattering sensitivity.

  One aspect of the X-ray Talbot interferometer of the present invention includes a beam splitter grating that diffracts X-rays to form a hexagonal lattice-like interference pattern, an X-ray detector that detects the interference pattern, and the X-ray detection And an arithmetic device that calculates information related to X-ray scattering by the subject arranged in the X-ray optical path using a detection result by the detector, and the arithmetic device has the same period in the interference pattern and a different period direction. The information about the X-ray scattering is calculated using the amplitude change of the three period components, and the information about the X-ray scattering includes at least one of information on the degree of anisotropy of scattering and information on the main scattering direction. Features.

  Other aspects of the invention are described in the detailed description.

  According to the present invention, it is possible to obtain the scattering force in three or more directions without rotating the grating or the subject around the optical axis, and more than the Talbot interferometer described in Non-Patent Document 1. A Talbot interferometer with a small difference in scattering sensitivity in each direction can be provided.

1 is a schematic diagram of an X-ray imaging system of an embodiment. The example of a lattice pattern of each lattice in an embodiment. The interference pattern example obtained by embodiment. The schematic diagram of scattering intensity distribution and a two-dimensional modulation transfer function. An example of a scattered intensity distribution of an object.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  The X-ray Talbot interferometer of this embodiment forms a hexagonal lattice-like interference pattern. Thereby, the scattering force of the subject in three directions can be acquired without rotating the grating or the subject about the optical axis. Furthermore, since the hexagonal lattice-like interference pattern has the same period in the three directions, it is possible to reduce variations in the scattering sensitivity due to the period variations.

  FIG. 1 is a schematic diagram of an X-ray Talbot interferometer system 100 of the present embodiment. The X-ray Talbot interferometer system 100 includes an X-ray source 1 and a Talbot interferometer 10. The Talbot interferometer includes a source grating 2, a beam splitter grating 3, an analyzer grating 4, an X-ray detector 5, an arithmetic device 6, and a beam splitter grating moving unit 7. The source grid 2 has an X-ray shielding part and a transmission part, and virtually forms an array of minute X-ray sources. The beam splitter grating diffracts X-rays from the source grating 2 to form an interference pattern. The analyzer grating 4 has an X-ray shielding part and a transmission part, and shields a part of the interference pattern to form moire. The X-ray detector 5 is an area sensor that detects the intensity distribution of X-rays transmitted through the analyzer grating 4. The computing device 6 acquires information on the anisotropy of scattering by the subject using the detection result by the X-ray detector 5. The beam splitter grating moving unit 7 moves the beam splitter grating. Each configuration will be described below. As shown in FIG. 1, the subject 8 is disposed at an upstream position very close to the beam splitter grating 3 at the time of imaging. However, the subject 8 may be arranged on the downstream side of the beam splitter grating 3.

  The X-ray source 1 emits X-rays and the details are not particularly limited as long as the X-ray source 1 emits X-rays to the source grating 2 or the beam splitter grating 3. Specifically, it may emit continuous X-rays or emit characteristic X-rays. The wavelength is generally selected appropriately from about 0.1 to 5 mm. Further, a wavelength selection filter, a shutter, a diaphragm, or the like may be provided as appropriate downstream of the X-ray source 1. The X-ray source 1 can constitute an X-ray Talbot interferometer system 100 together with the X-ray Talbot interferometer 10.

  The radiation source grating 2 is an amplitude modulation grating (absorption grating) used to make it possible to use an X-ray source whose light emitting point (focal point) size is not sufficiently small. This lattice is usually arranged near the emission point (focal point) of the X-ray source, and plays a role of virtually dividing the X-ray emission point having a certain spatial extent into a large number of fine emission points by its periodic structure. . The individual virtual light emitting points are small enough to maintain the fringe visibility of the interference patterns generated by the action of the beam splitter grating 3, and the interference patterns formed by the adjacent virtual light emitting points are shifted by an integral multiple of the period. Arrange at regular intervals. As a result, when the actual light emitting point size is large, it is possible to form a periodic intensity distribution with high visibility even though many interference patterns are superimposed. A Talbot interferometer using a source grating based on such a principle is generally called a Talbot-Lau interferometer, and is a periodic that is formed by superimposing many interference patterns in the Talbot-Lau interferometer. The intensity distribution is also called an interference pattern. Although the interferometer 10 of the present embodiment includes the radiation source grating 2, the radiation source grating 2 is not necessary when an X-ray source having a small emission point to such an extent that an interference pattern can be formed by the beam splitter grating 3.

FIG. 2A shows a lattice pattern of the source lattice 2 of the present embodiment. The source grid 2 includes an X-ray shielding part 21 and an X-ray transmission part 22, and has a structure in which X-ray transmission parts 22 separated between the uniform X-ray shielding part 21 are arranged in a hexagonal lattice shape. . In the present specification, when the lattice pattern formed by the X-ray shielding portion and the X-ray transmission portion has a hexagonal lattice (regular triangular lattice) periodicity, the lattice is a hexagonal lattice shape. Expressed as having an X-ray transmittance distribution. The pitch d ₀ of the source grid 2 is the distance shown in FIG. The pitch d ₀ is a length corresponding to the height of one equilateral triangle constituting the hexagonal lattice pattern. The pitch d ₀ of the source grating 2 is also the length of one cycle of the three fundamental wave components that make up the X-ray transmittance pattern.
The X-ray shielding unit does not need to shield all the incident X-rays, and an X-ray transmitted through the source grating may be diffracted by the beam splitter grating 3 to form an interference pattern. Generally, 80% of the X-rays incident perpendicularly to the X-ray shielding part may be shielded. Generally, the X-ray shielding part is made of a heavy metal having a high X-ray absorption coefficient, and the X-ray transmission part is made of a material made of a light element such as silicon or a resin material having a low X-ray absorption coefficient. Or a void.

  The beam splitter grating 3 diffracts the X-rays from the source grating 2 by a periodic structure, and forms a fine interference pattern due to the Talbot effect at a predetermined position downstream of the X-rays. The beam splitter grating 3 is usually arranged in the vicinity of the subject 8. Due to the presence of the subject 8, not only an amplitude change due to X-ray absorption by the subject but also a phase shift occurs in the X-rays transmitted through the subject 8. In addition, scattering due to spatially minute changes in the amplitude and phase distributions causes distortion and visibility (contrast) degradation reflecting the characteristics of the subject in the interference pattern. By measuring changes in the interference pattern caused by the subject and performing various analyzes, it is possible to acquire more information than with conventional imaging using only absorption contrast. Since more X-rays can be used by increasing the X-ray transmittance of the grating, a phase modulation grating (phase grating) is often used for the beam splitter grating rather than an amplitude modulation grating.

  The grating pattern of the beam splitter grating 3 of this embodiment is shown in FIG. The beam splitter grating 3 diffracts X-rays to form a hexagonal lattice-like interference pattern as shown in FIG. If the X-ray intensity distribution of the hexagonal lattice-like interference pattern is expressed in the frequency domain by Fourier transform, the distribution has six peaks corresponding to the fundamental wave component on one circle centered on the origin. Become. However, the peak position may deviate from the circle due to a manufacturing error of the lattice. Even when the peak position deviates from the circle, the deviation is 10% or less (the distance between the peak and the origin is 0.9 to 1.1 times the radius r of the circle). For example, the performance of obtaining the scattering anisotropy is not greatly reduced. Therefore, in the present invention and the present specification, when the distance between the six peaks corresponding to the fundamental wave component and the origin is in the range of 0.9r to 1.1r, the six peaks are on a circle of radius r. It is considered to exist. Here, r is an arbitrary spatial frequency value. In other words, the periods corresponding to these peaks are considered equal at this time. More preferably, the deviation of the peak position is 5% or less, that is, the distance between the peak of the six fundamental wave components and the origin is in the range of 0.95r to 1.05r. In the case of a square lattice interference pattern, the period in the oblique direction is about 0.7 times the period in the x and y directions.

  The beam splitter grating 3 of this embodiment has a phase advancement unit 31 and a phase delay unit 32, and has a pattern in which the phase delay units 32 are arranged in a hexagonal lattice between the uniform phase advancement unit 31. Yes. Further, the regular hexagon indicated by a broken line in FIG. 2B indicates the unit phase modulation pattern 33. The beam splitter grating 3 has a grating pattern in which regular hexagonal unit phase modulation patterns 33 are spread without gaps.

The pitch d ₁ of the beam splitter grating 3 is a distance shown in FIG. The pitch d ₁ is a length corresponding to the height of one equilateral triangle constituting the hexagonal lattice pattern, similarly to the pitch d ₀ of the source grid 2. Further, the pitch d ₁ of the beam splitter grating 3 is also the length of one period of the three fundamental wave components constituting the pattern of the beam splitter grating 3.

  The phase advancing unit 31 is an area configured such that the phase of X-rays transmitted through the phase advancing unit 31 proceeds relatively with respect to X-rays transmitted through the phase delay unit 32. Further, the beam splitter grating pattern shown here is merely an example, and other patterns such as a pattern in which the phase advancement unit and the phase delay unit are inverted may be used.

  In order to give a phase difference to transmitted X-rays, the phase advancing unit 31 and the phase delay unit 32 can be configured, for example, by changing the thickness of the X-ray incident direction with the same material. For example, such a configuration can be realized by finely processing the surface of a silicon substrate using a semiconductor processing technique. In the present specification, the thicker one is called the phase advance portion, and the smaller thickness is called the phase delay portion. Further, instead of making a difference depending on the thickness, the phase advancing portion and the phase delay portion can be made of materials having different refractive indexes.

  The analyzer grating 4 is disposed at a position where an interference pattern is formed, and moire is formed by overlapping the analyzer grating and the interference pattern. In the present invention and this specification, moire having a period longer than the detection surface of the X-ray detector 5 is also referred to as moire. If the period and direction of the interference pattern exactly match the period and direction of the analyzer grating, the moire period is infinite, but the moire has such a large period that it cannot be detected by the X-ray detector. Is also referred to as moire in the present invention and this specification. The period direction is defined in the range of 0 ° to 180 °.

  Since the interference pattern formed by the beam splitter grating is usually a fine pattern having a period of about several μm, an analyzer grating is often used to facilitate pattern detection by an X-ray detector. By making the period and direction of the analyzer grating and the interference pattern closer, it is possible to generate a moire with a longer period than the interference pattern, and to acquire information on the interference pattern even with a detector that is not particularly high in spatial resolution. It becomes possible. In addition, the phase of each periodic component that makes up the moire can be shifted by changing the relative position between the interference pattern and the analyzer grating, so that the pattern is analyzed using the phase stepping method (also called fringe scanning method). Is possible. In the case of the phase stepping method, even if the moiré period is very large, the detailed structure of the subject can be imaged with a spatial resolution independent of the moiré period. Note that an amplitude modulation grating (absorption grating) is often used as the analyzer grating. If the period of the interference pattern is large enough to be detected by the X-ray detector 5 (when the spatial resolution of the X-ray detector is high), the use of the analyzer grating 4 is not essential.

A lattice pattern of the analyzer lattice 4 of the present embodiment is shown in FIG. The analyzer grating 4 has an X-ray shielding part 41 and a transmission part 42, and has an X-ray transmittance distribution in a hexagonal lattice shape like the source grating 2. The pitch d ₂ of the analyzer grating 4 is determined in the same manner as the source grating 2. The shielding part 41 does not need to shield all the incident X-rays, and moiré may be formed by the X-rays transmitted through the analyzer grating 4. Generally, 80% of the X-rays incident perpendicularly to the shielding part 41 may be shielded. Generally, the X-ray shielding part is made of a heavy metal having a high X-ray absorption coefficient, and the X-ray transmission part is made of a material made of a light element such as silicon or a resin material having a low X-ray absorption coefficient. Or a void. The distance between the gratings is such that a relatively highly visible interference pattern formed by the Talbot effect on the analyzer grating 4 is formed by X-rays diffracted by the periodic structure of the beam splitter grating 3. It is adjusted to become.

  A Talbot interferometer using elements called capillary plates as a beam splitter grating and an analyzer grating, respectively, Momose and S.M. Kawamoto “X-ray Talbot Interferometry with Capillary Plates”, Japan Journal of Applied Physics, Vol. 45, no. 1A, 314-316 (2006). According to this document, this element has a lattice pattern that is partially hexagonal. However, similarly, according to this document, the capillary plate used in the experiment does not have a quality sufficient as a lattice for performing a normal imaging experiment. Therefore, in order to obtain high imaging performance, it is preferable to use a higher quality element as a grating, for example, designed and manufactured exclusively for a Talbot interferometer. That is, for example, a grating in which the period and the direction of the structure are aligned over the entire surface of the element is desirable.

  The X-ray detector 5 is an area sensor that can detect a two-dimensional intensity distribution of X-rays transmitted through the analyzer grating 4. When the analyzer grating 4 is not used, the detection surface of the X-ray detector 5 is arranged at a position where an interference pattern is formed. Regardless of whether or not the analyzer grating 4 is used, the X-ray detector 5 detects an interference pattern. If the analyzer grating 4 is not used, the X-ray detector may directly detect the interference pattern. If the analyzer grating 4 is used, the X-ray detector may indirectly detect the interference pattern. May be distinguished.

  The beam splitter grating moving unit 7 is a moving unit that can move the beam splitter grating 3 in a plane, and can be configured by an actuator such as a piezoelectric element. The beam splitter grating moving unit 7 moves the beam splitter grating 3 in the plane, so that the phase stepping method can be performed. Since the phase stepping method can be performed by changing the relative positional relationship between the interference pattern and the analyzer grating, the analyzer grating 4 or the source grating 2 can be moved instead of moving the beam splitter grating 3. good.

  The arithmetic device 6 uses the detection result by the X-ray detector 5 to calculate information related to X-ray scattering by the subject placed in the optical path of the X-ray. Although details will be described later, the information regarding X-ray scattering is calculated mainly from the amplitude change of the periodic component included in the detection result by the subject. This amplitude change is calculated for each small region of the detected X-ray intensity distribution. That is, the arithmetic device 6 acquires information related to X-ray scattering by the subject from a local amplitude change of the periodic component included in the detection result. Then, by arranging the amplitude change calculated for each small region or other information related to X-ray scattering calculated from the amplitude change for each small region, an image of the amplitude change or other information related to X-ray scattering Can be obtained. That is, the small region corresponds to, for example, one pixel in the image of information regarding X-ray scattering.

  The computing device 6 of this embodiment, as information related to X-ray scattering by the subject, is at least one of information on the degree of scattering anisotropy (sometimes referred to as scattering anisotropy) and information on the main scattering direction. Is calculated. The degree of anisotropy of scattering indicates how much anisotropy exists in X-ray scattering by the subject. The lower the degree of anisotropy of scattering, the more isotropic the scattering is. . For example, when the scattering anisotropy is 0, the X-ray scattering force by the subject is completely isotropic, that is, when the X-ray is incident on a certain position of the subject. In the plane perpendicular to the incident direction, X-ray scattering occurs at the same scale in all 360 ° directions. Further, the main scattering direction is a direction in which the scattering force is maximized in a plane perpendicular to the X-ray incidence direction. A method for calculating the information of the scattering anisotropy and the information of the main scattering direction using the detection result by the X-ray detector 5 will be described later.

  The arithmetic device 6 can be composed of a CPU (central processing unit), a main storage device (RAM, etc.), an auxiliary storage device (HDD, SSD, etc.), and a computer having various I / Fs. Various operations performed by the arithmetic device are realized by loading a program stored in the auxiliary storage device into the main storage device and executing it by the CPU. Of course, this configuration is merely an example, and does not limit the scope of the present invention. For example, instead of the auxiliary storage device, the program may be loaded into the main storage device via a network or various storage media. The arithmetic device 6 receives the detection result from the X-ray detector 5, but the reception method of the detection result is not particularly limited, and may be via a wired or wireless network, or may be via various storage media. Further, the X-ray scattering information by the subject acquired by the arithmetic device 6 may be transmitted to an image display device (not shown). A printer or a display can be used as the image display device. The image display apparatus can constitute an X-ray Talbot interferometer system together with the X-ray Talbot interferometer. The image display device may display, for example, the magnitude of the scattering force of the subject as a value, but it is preferable to display an image created based on the acquired X-ray scattering value. Images and values may be displayed.

  In the present embodiment, a method for imaging a subject and calculating information related to X-ray scattering by the subject using the obtained detection result will be described.

FIG. 3 shows an example of an interference pattern obtained by the interferometer of this embodiment. Due to the effects of the source grating and the beam splitter grating shown in FIGS. 2A and 2B, a hexagonal lattice-like interference pattern as shown in FIG. 3 is formed on the analyzer grating 4. This interference pattern includes a total of 3 periodic components having a periodic direction parallel to the x-axis and two periodic components having a periodic direction in the direction of 60 ° and 120 ° counterclockwise from the x-axis direction. It is composed of two periodic components. Incidentally, all of the period of these periodic components are equal, it is expressed as follows d _IP. At this time, the X-ray intensity distribution g _IP (x, y) of the interference pattern in a small area that is detected by a certain unit detection area of the detector, for example, one pixel of the built-in image sensor, is

と書ける。ここで、ａ_０はこの領域における平均Ｘ線強度、ａ_{１＿０００}、ａ_{１＿０６０}、ａ_{１＿１２０}はそれぞれ、ｘ軸方向から反時計回りに０°、６０°、１２０°回転させた方向に沿った周期成分の振幅を表す。ｘ_ＩＰ、ｙ_ＩＰはそれぞれ、ｘｙ座標系における干渉パターンの位置を表す。尚、ここでは、対象としている小領域における干渉パターンの平均Ｘ線強度や振幅・位相の変化は無視できる程度に小さいと仮定している。尚、周期成分の周期方向とは、その周期成分の位相が位置に対して最も早く変化する方向を指す。

Can be written. Here, a ₀ is the average X-ray intensity in this region, and a 1 — ₀₀₀ , a 1 — ₀₆₀ , and a _{1 —} 120 are periodic components along directions rotated 0 °, 60 °, and 120 ° counterclockwise from the x-axis direction, respectively. Represents the amplitude of. x _IP and y _IP each represent the position of the interference pattern in the xy coordinate system. Here, it is assumed that changes in the average X-ray intensity, amplitude, and phase of the interference pattern in the target small region are small enough to be ignored. The period direction of the periodic component indicates a direction in which the phase of the periodic component changes earliest with respect to the position.

Next, consider the X-ray intensity detected at the pixel. In the present embodiment, the grating pitch d ₂ of the analyzer grating 4 is equal to d _IP , and the period direction also coincides with the interference pattern, so that the period of moire formed by the interference pattern and the analyzer grating becomes infinite. Assume the case. However, in practice, if the period and the direction of the two are substantially the same, the moire period is sufficiently larger than the pixel size of the detector, so that the period is approximately the same as when the period is infinite. Can be considered.

  In the present embodiment, the average X-ray intensity and the amplitude of each periodic component are measured by performing a phase stepping method by scanning the beam splitter grating 3 two-dimensionally by the beam splitter grating moving unit 7, and Get information about X-ray scattering by. Note that various calculations described later based on the control of the beam splitter grating moving unit 7 and the X-ray intensity information acquired by the X-ray detector 5 are both performed by the arithmetic unit 6. At this time, the intensity I of X-rays detected at the pixel is

と概ね表せる。ここで、ｂ_０はアナライザー格子４の平均透過率（透過率分布の平均値）、ｂ_１はアナライザー格子４の透過率分布を構成する３つの周期成分の振幅（３周期成分は同一振幅とする）を表す。ｘ_ｄ、ｙ_ｄはそれぞれ、ビームスプリッター格子３の走査量がゼロである時のアナライザー格子４に対する干渉パターンのｘ、ｙ方向に関する位置ずれ量を表す。ｘ_ＳＴ（ｋ，ｌ）、ｙ_ＳＴ（ｋ，ｌ）はそれぞれ、位相ステッピング法の一連の手順のうちのｋ，ｌの２整数により表される検出回における、ビームスプリッター格子３の走査による干渉パターンのｘ，ｙ方向に関する移動量を表す。

It can be generally expressed as follows. Here, b ₀ is the average transmittance of the analyzer grating 4 (average value of the transmittance distribution), and b ₁ is the amplitude of the three periodic components constituting the transmittance distribution of the analyzer grating 4 (the three periodic components have the same amplitude). ). x _d and y _d represent the amount of displacement in the x and y directions of the interference pattern with respect to the analyzer grating 4 when the scanning amount of the beam splitter grating 3 is zero, respectively. x _ST (k, l) and y _ST (k, l) are interferences caused by scanning of the beam splitter grating 3 in the detection times represented by two integers k and l in a series of steps of the phase stepping method, respectively. This represents the amount of movement in the x and y directions of the pattern.

The scanning of the beam splitter grating 3 in this embodiment will be described with reference to FIG. The two axes u and v shown in FIG. 2B are coordinate axes parallel to a straight line connecting the centers of the nearest unit phase modulation patterns 33. The u-axis is an axis along the direction in which the x-axis is rotated 30 degrees counterclockwise, and the v-axis is an axis along the same direction as the y-axis. In other words, the v-axis is an axis perpendicular to the periodic direction parallel to the x-axis, and the u-axis is an axis perpendicular to the periodic direction parallel to the direction obtained by rotating the x-axis by 30 degrees clockwise. That is, each of the u axis and the v axis is an axis perpendicular to two periodic directions among the three periodic directions of the beam splitter grating. The directions along the u-axis and the v-axis are the first direction and the second direction, respectively. In this embodiment, the beam splitter grating 3 is scanned two-dimensionally along the u axis and the v axis. Specifically, a lattice movement position obtained by equally dividing one period of the lattice along the u-axis toward the negative direction of the u-axis by N, and 1 of the lattice along the v-axis toward the negative direction of the v-axis. Image acquisition is performed under a total of N ² types of lattice movement position conditions configured by lattice movement positions obtained by dividing the period into N equal parts. These image acquisitions may be performed in any order.

  Here, an example in the case of N = 3 will be described. The stepping operation of the lattice is performed as in the following formulas (3) and (4).

尚、ここではｘ_ＳＴ、ｙ_ＳＴにおける第ｋ行第ｌ列の成分がそれぞれｘ_ＳＴ（ｋ，ｌ）、ｙ_ＳＴ（ｋ，ｌ）を表すものとする。この時、式（２）における各項の係数部はそれぞれ、

Here, it is assumed that the components in the k-th row and the l-th column in x _ST and y _ST represent x _ST (k, l) and y _ST (k, l), respectively. At this time, the coefficient part of each term in Equation (2) is

により計算できる。尚、式（５）〜（８）はＩ（ｋ，ｌ）を２次元フーリエ変換することと基本的に等価であるため、ＦＦＴ等を用いて計算しても良い。尚、ビームスプリッター格子を2次元走査する場合はビームスプリッター格子の３つの周期方向のうち２つの周期方向のそれぞれと略垂直に交わる２つの軸に沿ってビームスプリッター格子を移動させるが、アナライザー格子を2次元走査しても良い。その場合は、アナライザー格子の３つの周期方向のうち２つの周期方向のそれぞれと略垂直に交わる２つの軸に沿ってアナライザー格子を移動させる。尚、本発明及び本明細書において、略垂直とは垂直±５度程度の誤差である。５度程度であれば2次元走査の際の移動方向がずれていても影響が少ない。好ましくは、誤差は±２度の範囲内であり、更に好ましくは±1度の範囲である。

Can be calculated by Note that equations (5) to (8) are basically equivalent to two-dimensional Fourier transform of I (k, l), and may be calculated using FFT or the like. In the case of two-dimensional scanning of the beam splitter grating, the beam splitter grating is moved along two axes that intersect each of the two periodic directions of the beam splitter grating substantially perpendicularly. Two-dimensional scanning may be performed. In that case, the analyzer grating is moved along two axes that intersect each of the two periodic directions of the analyzer grating substantially perpendicularly. In the present invention and this specification, the term “substantially vertical” refers to an error of about ± 5 degrees vertical. If it is about 5 degrees, there is little influence even if the moving direction in the two-dimensional scanning is shifted. Preferably, the error is in the range of ± 2 degrees, more preferably in the range of ± 1 degree.

In the present embodiment, the X-ray scattering force of the subject is measured by measuring the change in visibility by the subject with respect to the three periodic components constituting the interference pattern. Visibility is defined as the ratio of the amplitude of the periodic component to the average X-ray intensity. Here, it is assumed that the result of measurement of each quantity with the subject placed in the X-ray optical path and the result of measurement without the subject placed are represented by subscripts s and r, respectively. . At this time, normalized visibility V ₀₀₀ , V ₀₆₀ , V ₁₂₀ for each periodic component constituting the interference pattern is

と定義できる。これらの値は式（５）〜（８）により得られる結果を元に計算可能である。

Can be defined. These values can be calculated based on the results obtained from the equations (5) to (8).

Further, to simplify the discussion here, in the target small region, the X-ray scattering by the subject can be approximated as a convolution of the interference pattern g _IP (x, y) by the scattering intensity distribution h _SC (x, y). Assume that Then, the relationship between g _IPs (x, y) and g _IPr (x, y) is

と書ける。尚ここで＊はコンボリューションを表している。この時、ξ、ηをそれぞれｘ、ｙ方向に関する空間周波数とし、ｈ_ＳＣ（ｘ，ｙ）の２次元フーリエ変換をＨ_ＳＣ（ξ，η）とすれば、畳み込み定理などにより、

Can be written. Here, * represents convolution. At this time, if ξ and η are spatial frequencies in the x and y directions, respectively, and the two-dimensional Fourier transform of h _SC (x, y) is H _SC (ξ, η), the convolution theorem

の関係がある（但しＨ_ＳＣ（０，０）＝１と想定している）。このように、規格化ビジビリティＶ_０００、Ｖ_０６０、Ｖ_１２０は、散乱による干渉パターンの変化を表す２次元変調伝達関数｜Ｈ_ＳＣ（ξ，η）｜のうち、干渉パターンの周期成分の空間周波数座標に相当する６点（独立した情報としては３点）の値を示す。図４（Ａ）（Ｂ）はそれぞれ、散乱強度分布ｈ_ＳＣ（ｘ，ｙ）及び２次元変調伝達関数｜Ｈ_ＳＣ（ξ，η）｜の例を模式的に表している。図４では、色の濃い部分がそれぞれの関数の値が大きいことを示している。また、図４（Ｂ）中に示した６つの点は、Ｖ_０００、Ｖ_０６０、Ｖ_１２０の測定により値を得ることのできる６つの周波数座標を示している。このように、六角格子パターンを構成する３つの周期成分に関するビジビリティを測定することで、散乱の特徴を表現する変調伝達関数に関して、半径１／ｄ_ＩＰの円周上において６０°間隔で６点（独立した情報としては３点）の値を取得することが可能となる。

(However, it is assumed that H _SC (0,0) = 1). Thus, the standardized visibility V ₀₀₀ , V ₀₆₀ , V ₁₂₀ is the spatial frequency of the periodic component of the interference pattern of the two-dimensional modulation transfer function | H _SC (ξ, η) | representing the change of the interference pattern due to scattering. The values of 6 points corresponding to coordinates (3 points as independent information) are shown. 4A and 4B schematically illustrate examples of the scattering intensity distribution h _SC (x, y) and the two-dimensional modulation transfer function | H _SC (ξ, η) |. In FIG. 4, dark portions indicate that each function value is large. In addition, six points shown in FIG. 4B indicate six frequency coordinates from which values can be obtained by measuring V ₀₀₀ , V ₀₆₀ , and V ₁₂₀ . In this way, by measuring the visibility related to the three periodic components constituting the hexagonal lattice pattern, six points (60 ° intervals) on the circumference of the radius 1 / d _IP are obtained with respect to the modulation transfer function expressing the characteristics of scattering. As independent information, it is possible to obtain a value of 3 points).

  Here, the scattering force S (θ) with respect to the counterclockwise angle θ with respect to the x-axis direction is expressed as follows:

と定義すると、Ｖ_０００、Ｖ_０６０、Ｖ_１２０の測定結果を元に、Ｓ（０°）、Ｓ（６０°）、Ｓ（１２０°）を、

And S (0 °), S (60 °), and S (120 °) based on the measurement results of V ₀₀₀ , V ₀₆₀ , and V ₁₂₀ ,

と算出できる。

And can be calculated.

  Here, assuming that S (θ) changes in a sinusoidal shape with a period of 180 ° with respect to θ,

と表現できる。この時、右辺の中の各変数については、Ｓ_ｍｅａｎが全方向に関する平均散乱力、Ｖ_Ｓが散乱の異方性の度合い（散乱異方度）、θ_Ｓが主散乱方向をそれぞれ表しているとみなせる。Ｓ_ｍｅａｎの値はＳ_０００、Ｓ_０６０、Ｓ_１２０を元に、

Can be expressed. At this time, for each variable on the right side, S _mean represents the average scattering force in all directions, V _S represents the degree of scattering anisotropy (scattering anisotropy), and θ _S represents the main scattering direction. Can be considered. The value of S _mean is based on S ₀₀₀ , S ₀₆₀ , S ₁₂₀ ,

と計算でき、散乱の異方性の度合いＶ_Ｓと主散乱方向θ_Ｓとは、

The degree of scattering anisotropy V _S and the main scattering direction θ _S are:

と計算できる。

Can be calculated.

As described above, information on the X-ray scattering having anisotropy is measured by measuring the amplitude change and average X-ray intensity change of the three periodic components constituting the interference pattern using a hexagonal lattice Talbot interferometer. Can be obtained. Further, as is clear from the example of the analysis method used in this description, even when the simplest model is adopted for S (θ) representing the direction dependency of the scattering force, an average is used to express the feature. Three variables are required: scattering force S _mean , scattering anisotropy V _S , and main scattering direction θ _S. In other words, in order to obtain information on anisotropic scattering, it is necessary to measure the scattering force in at least three directions. For example, the reliability of anisotropic scattering can be determined only from the measurement results of the scattering forces in two orthogonal directions. High information cannot be obtained. For example, as a result of obtaining the scattering force in the x direction and the scattering force in the y direction using a square lattice Talbot interferometer in which both the interference pattern and the analyzer grating have a square lattice pattern, the x direction and the y direction are obtained. Consider the case where the scattering power is the same value. The scattering intensity distribution h _SC (x, y) at this time may not have anisotropy as shown in FIG. 5A, or 45 in the x and y directions as shown in FIG. 5B. In some cases, it has anisotropy so as to have a maximum scattering force in a direction intersecting at a degree. However, information on the degree of anisotropy of X-ray scattering by the subject and information on the main scattering direction cannot be obtained accurately only by acquiring the scattering force in two directions.

  In the present embodiment, the scattering force in three directions can be acquired, and the period of the interference pattern is substantially the same in the three directions. Therefore, the reliability is higher than using a square lattice Talbot interferometer. High anisotropic scattering information can be acquired.

  In the present embodiment, the case where the scattering force in each direction is acquired using the phase stepping method has been described. However, the acquisition method of the scattering force is not limited to that using the phase stepping method. As other methods, for example, M.M. Takeda et al. “Fourier-transform method of fringe-pattern analysis for computer-based topography and information”. Opt. Soc. Am. , Vol. 72, no. 1, 156-160 (1982), the Fourier transform method described in detail may be used. By using the Fourier transform method, it is possible to measure the scattering force in three directions from only one imaging. In this case, the beam splitter grating moving unit 7 is not necessary.

  In addition, the hexagonal lattice Talbot interferometer has the same period of the three periodic components in the moire pattern as a carrier wave, so it has an affinity with a general X-ray detector having an isotropic modulation transfer function. Is higher than the square lattice system.

In addition, the ternary spatial distribution of the _mean scattering force S _mean , the scattering anisotropy degree V _S , and the main scattering direction θ _S representing the characteristics of anisotropic scattering, which is obtained through a series of processes, is expressed by a single image. Therefore, conversion to color image information may be performed to display / record an image. An example of a conversion method to color image information is described in Non-Patent Document 2 and the like. For example, the main scattering direction θ _S , the scattering anisotropy V _S , with respect to hue, saturation, and brightness in the HSV color space, It is possible to carry out by a method such as associating the acquired values of the average scattering force S _mean with each other.

  Example 1 is a specific example of the above-described embodiment. The Talbot interferometer 10 of Example 1 includes an X-ray tube having a tungsten anode as the X-ray source 1. The X-ray tube generates X-rays having an energy spectrum having a certain width centered on photon energy in the vicinity of 25 keV by adjusting the tube voltage and filter type. In addition, the optical system of the Talbot interferometer in the present embodiment is designed specifically assuming the use of X-rays having a wavelength of 0.05 nm (photon energy is about 25 keV). The grating patterns of the source grating 2, the beam splitter grating 3, and the analyzer grating 4 are as shown in FIG. The X-ray shielding portions of the source grating 2 and the analyzer grating 4 are gold having a thickness of 100 μm, and the X-ray transmitting portion is an opening. The material of the beam splitter grating 3 is silicon and the phase thickness of the substrate of the phase delay portion is 32 μm thinner than that of the phase advance portion, thereby relatively delaying the phase of transmitted X-rays having a wavelength of 0.05 nm by π. The X-ray detector is a flat panel detector having a pixel size of 50 μm, and measures a two-dimensional intensity distribution of incident X-rays.

The grating pitches d ₀ , d ₁ , and d ₂ of the source grating, beam splitter grating, and analyzer grating are 12 μm, 4 μm, and 6 μm, respectively. The distance between the source grating and the beam splitter grating and the distance between the beam splitter grating and the analyzer grating are 960 mm and 480 mm, respectively. At this time, the period d _IP of the periodic component of the interference pattern is 6 μm.

  The interferometer includes a grating moving mechanism using an actuator as a beam splitter grating moving unit, and measures the scattering force of the subject in three directions corresponding to the periodic direction of the interference pattern by the phase stepping method as described in the embodiment. By performing a series of measurements with and without the subject in the optical path, and performing the above-mentioned calculations based on the obtained results, the average scattering force and scattering characteristics that characterize anisotropic scattering Three quantities of the anisotropic degree and the main scattering direction are calculated.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

3 Beam splitter grating 5 X-ray detector 6 Arithmetic unit

Claims (12)

A beam splitter grating that diffracts X-rays to form a hexagonal lattice-like interference pattern;
An X-ray detector for detecting the interference pattern;
An arithmetic device that calculates information about X-ray scattering by a subject arranged in an X-ray optical path using a detection result by the X-ray detector,
The arithmetic unit calculates information on the X-ray scattering by using an amplitude change of three period components having the same period and different period directions in the interference pattern,
The X-ray Talbot interferometer characterized in that the information on the X-ray scattering includes at least one of information on the degree of scattering anisotropy and information on the main scattering direction. Comprising an analyzer grating that shields a portion of the interference pattern;
2. The X-ray Talbot interferometer according to claim 1, wherein the analyzer grating has a hexagonal lattice X-ray transmittance distribution, and the X-ray detector detects X-rays from the analyzer grating. 3. . A source grating that shields part of the X-rays between the X-ray source that irradiates the beam splitter grating with X-rays and the beam splitter grating;
3. The X-ray Talbot interferometer according to claim 1, wherein the source grating has a hexagonal lattice-like X-ray transmittance distribution. 4.   The X-ray Talbot interferometer according to any one of claims 1 to 3, wherein the three-period components are three-period components whose period directions are different by 60 °.   The X-ray Talbot interferometer according to claim 1, wherein the beam splitter grating is a phase modulation grating.   6. The phase modulation grating has a lattice pattern in which regular hexagonal unit phase modulation patterns are laid, and the unit phase modulation pattern includes a phase advancement unit and a phase delay unit. X-ray Talbot interferometer described in 1. The arithmetic device has a plurality of X-ray intensity distributions acquired by scanning at least one of the source grating, the beam splitter grating, and the analyzer grating along a first direction and a second direction. The amplitude change of the periodic component is calculated by a predetermined calculation based on
4. The X according to claim 1, wherein each of the first direction and the second direction is a direction substantially perpendicular to a periodic direction of a grating pattern of a grating to be scanned. 5. Wire Talbot interferometer. The arithmetic unit is:
The X-ray according to any one of claims 1 to 6, wherein the amplitude change of the periodic component is calculated from a local X-ray intensity distribution of the interference pattern detected by the X-ray detector. Talbot interferometer. The arithmetic unit is:
The amplitude change of the periodic component is calculated from a local X-ray intensity distribution of a moire pattern formed by superimposing the interference pattern and the analyzer grating detected by the X-ray detector. Item 7. The X-ray Talbot interferometer according to any one of Items 2 to 6.   The arithmetic device calculates three values of the average scattering power, which is the average value of the scattering power in all directions, as the main scattering direction, the degree of scattering anisotropy, and the space of these values as information on X-ray scattering. Color image information is calculated based on the distribution, and the color image information represents the main scattering direction by hue, the degree of scattering anisotropy by saturation, and the average scattering power by brightness. The X-ray Talbot interferometer according to any one of claims 1 to 9.   An X-ray Talbot interferometer according to any one of claims 1 to 10, and an image display device that displays information about the X-ray scattering acquired by the arithmetic device. Interferometer system. 11. An X-ray Talbot interferometer system comprising: the X-ray Talbot interferometer according to claim 1; and an X-ray source that irradiates the beam splitter grating with X-rays.

Images