JP2017083413A - X-ray Talbot interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a talbot interferometer with which it is possible to acquire test object information having a higher spatial resolution than by a two-dimensional Fourier transform method, even from fewer detection results than by a two-dimensional phase shift method.SOLUTION: The talbot interferometer comprises: a diffraction grating 130 for forming a first interference pattern 180 having a cycle in a first and a second direction; and a shield grid 140 for shielding some of X-rays that form an interference pattern and forming a second interference pattern having a cycle in two intersecting directions. In addition, the talbot interferometer includes a detector 150 for detecting an X-ray having passed through the shield grid, and an arithmetic unit 160 for acquiring test object information using the detection result of the detector. The detector 150 detects X-rays a plural number of times. The arithmetic unit 160 acquires information on a test object in the first direction using the results of a plural number of times of detection, and acquires information on a test object in the second direction using a frequency spectrum obtained by Fourier-transforming the detection result.SELECTED DRAWING: Figure 1

Description

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

  As an example of applying the wavefront measurement method using interference to X-ray phase imaging, there is a Talbot interferometry using X-rays (referred to as X-ray Talbot interferometry). The X-ray Talbot interferometer is a differential interferometer using X-rays, and X-rays irradiated from an X-ray source pass through the subject, and the X-ray phase changes accordingly. X-rays transmitted through the subject are diffracted by a grating having a periodic pattern called a diffraction grating, thereby forming a first interference pattern at a position away from the diffraction grating by a predetermined distance called a Talbot distance. To do. By analyzing the change in the first interference pattern due to the subject, the change in the incident light wavefront described above can be measured.

  The pattern period of a diffraction grating having the above-described periodic pattern varies depending on conditions such as the apparatus length and the wavelength of X-rays. In the case of general X-rays, the cycle is on the order of several μm. It is also known that the first interference pattern generated thereby has a period of the order of several μm. Even though a commonly used X-ray detector has a high resolution, the resolution is about several tens of μm, so it is difficult to detect the first interference pattern. For this reason, a shielding grating having substantially the same period as the first interference pattern is arranged at a position where the interference pattern is formed, and a part of the X-rays forming the first interference pattern is shielded by the shielding grating so that the number of periods is reduced. A second interference pattern (so-called moire) of about 100 μm is formed. A change in the first interference pattern can be indirectly measured by detecting the second interference pattern with a detector.

  The phase information of the subject can be acquired by subjecting the second interference pattern detected by the detector to phase recovery processing by a computing unit such as a computer. As a phase recovery processing method used for an X-ray Talbot interferometer, a phase shift method (also called a fringe scanning method) and a Fourier transform method are known.

  Patent Document 1 describes an X-ray Talbot interferometer that acquires phase information of a subject using a phase shift method. The phase shift method is a technique for measuring the wavefront of X-rays transmitted through a subject using a plurality of periodic patterns whose phases are shifted from each other, and obtaining information about the subject. From the intensity of light detected at each pixel, Information on the subject can be obtained independently. In Patent Document 1, a diffraction grating having a period in two directions and a shielding grating are used, and the first interference pattern is scanned in two directions with respect to the first interference pattern, whereby the phase of the second interference pattern (second The light and dark positions of the interference pattern are shifted in each of the two directions. Information obtained by differentiating the phase change of incident X-rays by the subject (hereinafter referred to as differential phase information) is recovered by using a plurality of detection results whose phases are shifted in each direction. Has been acquired. The acquisition of information in two directions by shifting the phase of the interference pattern in two directions is called a two-dimensional phase shift method.

  Patent Document 2 describes an X-ray Talbot interferometer that acquires phase information of a subject using a Fourier transform method. The Fourier transform method can acquire the differential phase information of the subject in two directions even from a single detection result, and can acquire the differential phase information of the subject without shifting the phase of the second interference pattern. it can. Note that acquiring information in two directions using an interference pattern having a period in two directions is called a two-dimensional Fourier transform method.

JP 2012-005820 A WO2010 / 050484 gazette

  As described in Patent Document 1, the two-dimensional phase shift method requires five or more detection results.

  On the other hand, the two-dimensional Fourier transform method can obtain information on the subject in two directions even from one interference pattern. However, using the information on the second interference pattern for a plurality of pixels, Get information. Therefore, the spatial resolution of the differential position information obtained as compared with the two-dimensional phase shift method is low.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a Talbot interferometer that can acquire subject information having a spatial resolution higher than that of the two-dimensional Fourier transform method even from a detection result smaller than that of the two-dimensional phase shift method. .

  A Talbot interferometer according to one aspect of the present invention diffracts X-rays from an X-ray source to form a first interference pattern having a period in a first direction and a second direction intersecting each other. A shielding grating for forming a second interference pattern having a period in two directions intersecting by shielding a part of the X-rays forming the interference pattern, and a detector for detecting the X-rays transmitted through the shielding grating And a calculation unit that acquires information on an object disposed between the X-ray source and the shielding grating using a detection result of the detector, and the detector transmits the shielding grating The X-ray detection is performed a plurality of times to obtain a plurality of detection results, and the calculation unit analyzes the intensity change between the plurality of detection results for each pixel to thereby analyze the first direction of the subject. Obtaining information on at least one of the plurality of detection results Parts and obtains the information in the second direction of the subject using a frequency spectrum obtained by Fourier transform.

  According to the present invention, it is possible to provide a Talbot interferometer capable of acquiring subject information having a higher spatial resolution than the two-dimensional Fourier transform method even from a detection result less than the two-dimensional phase shift method.

Diagram showing the principle of the Talbot interferometer Diagram showing interference pattern and grating used in Talbot interferometer FIG. 4 is a diagram for explaining the first embodiment of the present invention. The figure which represented the information acquired in 1st Example of this invention by the plot FIG. 6 is a diagram for explaining the second embodiment of the present invention. The figure showing the grating | lattice and interference pattern which are used in the 3rd Example of this invention

  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.

Embodiment 1
The Talbot interferometer in this embodiment is a two-dimensional Talbot that forms a first interference pattern having a period in a first direction (referred to as the y direction) and a second direction (referred to as the x direction) that intersect each other. It is an interferometer. In addition, the calculation unit included in the Talbot interferometer of the present embodiment acquires information about the subject in the x direction using the Fourier transform method, and acquires information about the subject in the y direction using the phase shift method. . Therefore, the direction in which the phase of the second interference pattern is shifted may be one direction (y direction), and the information of the subject can be transmitted in two directions even from the same number of detection results as the Talbot interferometer that performs the phase shift method in one direction. Can be obtained at Also, since the direction of shifting the phase of the second interference pattern may be one direction, the moving means for moving the relative position between the first interference pattern and the shielding grating is the first interference pattern or shielding grating in one direction. As long as you can move. Therefore, a moving means simpler than the moving means for moving the relative position in two directions can be used. As moving means for shifting the phase of the second interference pattern, for example, moving means for moving the shielding grating in the y direction can be used. In addition, the spatial resolution of the differential phase information in the y direction can be increased compared to the case where the differential phase information in the x direction and the y direction is acquired by the Fourier transform method. When phase information is acquired by integrating differential phase information with a one-dimensional Talbot interferometer, a blank area (area where no subject is arranged) that is a reference for integration may be required for one pixel column. Are known. On the other hand, since the two-dimensional Talbot interferometer does not require an integration reference string, the Talbot interferometer of this embodiment can acquire integration information even if the subject is placed over the entire measurement range. That is, when this embodiment is used, the same number of detections as the one-dimensional phase shift method and the same moving means are used, and the subject is placed over the entire measurement range, and the information more than the one-dimensional phase shift method and the two-dimensional Fourier transform method. Can be obtained. Note that when the object information that can be acquired is compared with the one-dimensional shift method, the present embodiment is superior in that information in the x direction can be acquired. Further, when the object information that can be acquired is compared with the two-dimensional Fourier transform method, the present embodiment is superior in that the spatial resolution of information in the y direction is high.

  A configuration of an imaging system including the Talbot interferometer according to the present embodiment will be described with reference to FIG. The imaging system includes a display unit 170 that displays information on a subject acquired by a Talbot interferometer and an X-ray Talbot interferometer. The Talbot interferometer includes an X-ray source 110 that generates X-rays, and a diffraction grating 130 that diffracts X-rays from the X-ray source to form a first interference pattern (hereinafter sometimes referred to as a self-image). And a shielding grating 140 that blocks a part of the X-rays forming the first interference pattern. With these configurations, a second interference pattern (hereinafter sometimes referred to as moire) is formed. The Talbot interferometer further acquires information on the object 120 disposed between the X-ray source and the shielding grating from the detector 150 that detects the X-rays that have passed through the shielding grating, and the detection result of the detector. And a calculation unit 160 for acquiring information on the subject from the second interference pattern. Examples of information that can be acquired include absorption information indicating the amount of X-ray absorption by the subject, phase information indicating the amount of X-ray phase change by the subject, and scattering information indicating the amount of X-ray scattering by the subject. It is done. Since the Talbot interferometer is a differential interferometer, differential phase information and differential scattering information are acquired as phase information and scattering information, and phase information and scattering information are acquired by integrating these. x In the present invention and this specification, subject information in the x direction is phase information or scattered information differentiated in the x direction, which is x shear information of the subject, and information on the subject in the y direction. Is the phase information or the scattering information differentiated in the y direction, which is the y shear information of the subject. Further, in the present invention and the present specification, the term phase information and scattering information includes both differential phase information and differential scattering information. Each configuration will be described below.

  The X-ray source 110 can be used as long as it emits X-rays having coherency (coherence) enough to form the self-image 180 by being diffracted by the diffraction grating. Further, even if the X-ray source alone does not have coherency, an array of minute X-ray sources is virtually formed in combination with the source grating, and this virtually formed minute X-ray source Each of these should have coherency. A Talbot interferometer using a source grating is called a Talbot-Lau interferometer, but a Talbot-Lau interferometer is a type of Talbot interferometer. Includes total. In the present invention and specification, in the case of a Talbot-Lau interferometer, the source grating shall be considered part of the X-ray source. In the present embodiment, the Talbot interferometer includes the X-ray source 110. However, the X-ray source 110 is configured separately from the Talbot interferometer, and may be combined with the Talbot interferometer for measurement. good. When the X-ray source is configured separately from the Talbot interferometer, the X-ray source can be easily replaced, and the X-ray source can be easily changed depending on the measurement target. In the present invention and the present specification, X-rays are electromagnetic waves having energy of 2 keV or more and 100 keV or less. X-rays from the X-ray source 110 are diffracted by the diffraction grating 130 to form a self-image 180 in which the bright part 204 and the dark part 203 are arranged in the arrangement direction at a predetermined distance called a Talbot distance. The diffraction grating 130 can be either a phase type diffraction grating or an amplitude type diffraction grating, but the X-ray Talbot interferometer uses a phase type diffraction grating with little attenuation of irradiated X-rays. There are many. In FIG. 1, the subject 120 is disposed between the X-ray source 110 and the diffraction grating 130, but if the subject 120 is disposed between the X-ray source 110 and the shielding grating 140. Alternatively, it may be between the diffraction grating 130 and the shielding grating 140.

Here, a case where a phase type diffraction grating having a π type checkerboard pattern as shown in FIG. 2A is used as a grating pattern of the diffraction grating 130 will be described as an example. In the checker pattern, two types of areas 201 and 202 are arranged in a checkerboard shape, and the X-ray transmitted through one area 201 is shifted in phase by π radians with respect to the X-ray transmitted through the other area 202. Use material and thickness. For example, assuming that the pattern is made of silicon for X-rays having an effective energy of 17.5 keV, the area 201 is formed so as to have a thickness of 21 μm compared to the area 202, so that the transmitted X-rays It is known that the phase difference is π radians. The shape of the self-image 180 formed using a diffraction grating having such a grating pattern varies depending on the distance from the diffraction grating. For example, when the pattern period of the diffraction grating 130 is p ₁ and the wavelength of the X-ray is λ, a self-image 180 formed at a position of p ₁ ² / (8λ) from the diffraction grating 130 is shown in FIG. It becomes like a grid pattern. The self-image 180 has a period in the x direction and the y direction.

Since the period p _{2 of the} self-image is usually on the order of μm, the magnification (the value obtained by dividing the distance (L1 + L2) between the X-ray source and the self-image by the distance (L1) between the X-ray source and the diffraction grating) is also used. However, the normal detector 150 cannot detect. Therefore, a moire is formed by installing a shielding grid 140 at a position where the self-image 180 is formed. The shielding grating 140 is the same as the shape of the self-image 180 or slightly shifted in period, and often has a pattern in which the bright portion 204 of the self-image is a transmission portion and the dark portion 203 of the self-image is a shielding portion. . That is, when using a self-image in which bright portions are discretely arranged in dark portions as shown in FIG. 2B, a self-image in which a plurality of transmission portions are discretely arranged in shielding portions is used. The shielding part is preferably capable of shielding 80% or more of X-rays perpendicularly incident on the shielding part, and is formed of gold having a thickness of, for example, about several tens of μm. The period of moire formed by the self-image 180 and the shielding grating 140 is a period that can be detected by the detector 150 at least in the x direction. The moire period is preferably at least twice the pixel size of the detector, and more preferably at least three times the pixel size. For the formation of moiré, a method using the fact that the period of the shielding grating 140 is different from that of the self-image (enlarged moire) and a method of forming the shielding grating 140 so that the periodic direction of the shielding grating 140 intersects the periodic direction of the self-image 180 ) And both.

  The detector 150 is an area sensor that can detect X-rays, and can detect moire as shown in FIG. The detector 150 may be an indirect conversion type detector composed of a scintillator and a light receiving element that detects light generated by the scintillator, or a direct conversion type using a detection layer in which an electric charge is generated by the incidence of X-rays. The detector may be used.

  Note that the moire shown in FIG. 2C is an enlarged moire. In the case of magnified moire, the periodic direction of the self-image coincides with the periodic direction of the moire, the x shear information is superimposed on the intensity distribution of the moire in the x direction, and the y shear information is superimposed on the intensity distribution of the moire in the y direction. It is known to do. When the rotation moire or the rotation moire and the enlargement moire are combined, the periodic direction of the self-image and the periodic direction of the moire may not coincide with each other. In this case, the x shear information is superimposed on the moire y direction, and the y shear information is superimposed on the moire x direction.

  The Talbot interferometer of the present embodiment performs detection a plurality of times by shifting the phase of moire in order to perform the phase shift method. In order to shift the phase of moiré, the shielding grating 140 is scanned by the moving unit 190 in this embodiment. The configuration of the moving unit 190 is not particularly limited as long as the shielding grid can be moved, but an actuator, a gear, or the like can be used.

  The scanning direction is the x direction, which is one of the two periodic directions of the self-image. However, since the phase only needs to be shifted in the x direction, scanning may be performed in a direction other than the direction perpendicular to the x direction. In general, in order to efficiently scan, it is preferable to be parallel or substantially parallel to the periodic direction (the angle formed with the periodic direction is 10 degrees or less). In order to shift the phase, it is only necessary to scan the shielding grating with respect to the self-image. Instead of scanning the shielding grating, the X-ray source (the source grating) or the diffraction grating is moved to move the self image. The image may be scanned.

  When rotating moiré is formed, the periodic direction of the moire may be different from the periodic direction of the self-image, but since the phase needs to be shifted in the periodic direction of the self-image, the period of the self-image is generally used. In many cases, scanning is performed in a direction parallel to or substantially parallel to the direction.

  The calculation unit 160 can be configured by a general-purpose computer having hardware resources such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and an auxiliary storage device. Image processing, various operations, and control described later are realized by the CPU reading and executing a program stored in the auxiliary storage device. Note that some or all of the functions of the arithmetic unit 160 may be configured by a circuit such as an ASIC (Application Specific Integrated Circuit).

  The arithmetic device 160 acquires information about the subject 120 in the x direction and information about the subject 120 in the y direction using the detection result of the detector 150. As described above, information about the subject 120 in the y direction is acquired using the phase shift method, and information about the subject 120 in the x direction is acquired using the Fourier transform method.

First, a specific example of a method for acquiring subject information in the y direction using the phase shift method will be described. For example, the differential phase information P _y in the y direction and the differential scattering intensity information V _y in the y direction of the subject by the phase shift method using N detection results of I ₁ , I ₂ ... I _N−1 , I _N. The following formulas can be given as formulas for obtaining.

Here, i is an imaginary unit, n is an integer of 1 or more, and (x, y) indicates a position on the xy coordinates. Equations 1 and 2 are examples, and the calculation method for acquiring the differential phase information and the differential scattering information is not limited to this. For example, a term for correcting the phase shift error may be added to the right side of Equations 1 and 2. Also, using the formula that integrates the distribution of the differential phase information and differential scattering information obtained in Equations 1 and 2, the phase information obtained by integrating these values (not differential) and the scattering information (not differential) are acquired. May be. In that case, even if the arithmetic device 160 does not output the differential phase information and the differential scattering information, the differential phase information and the differential scattering information are acquired as the primary information. In the present invention and the present specification, obtaining information on an object by analyzing a change in intensity due to a phase shift for each pixel using a plurality of detection results obtained by shifting the phase is regarded as a phase shift method. In general, N is preferably 3 or more in the phase shift method.

Next, a specific example of a method for acquiring subject information in the x direction using the Fourier transform method will be described. The Fourier transform method can acquire information on a subject even from one detection result. However, in the case of this embodiment, in order to acquire N detection results (I _{1 to} I _N ) in order to acquire subject information in the y direction, the information I obtained by adding the N detection results is used. It is preferable to acquire information on the subject. By adding the N detection results, information on the subject can be acquired using information having a higher signal-to-noise ratio (hereinafter, S / N ratio) than using any of the N detection results. It is considered that accurate subject information can be acquired.

  I is represented by the following formula.

By performing phase recovery by a one-dimensional Fourier transform method on I (x), the differential phase P _x in the x direction and the scattering intensity V _x in the x direction are acquired. A typical Fourier transform method is represented by the following equation.

Here, F of calligraphy indicates the operation of Fourier transform, and F- ¹ of calligraphy indicates the operation of inverse Fourier transform. Further, the omega _x is the angular frequency in the x direction of the moire, the period of the x-direction of the moire upon a p _x, a ω _{x =} 2π / p _x. Note that ω _x can be calculated from the self-image, the period of the shielding grating, and the angle in the period direction in the same manner as the general moire period. G (k _x , k _y ) is a window function that represents a spectrum cut performed in Fourier space, and a path that limits the range in order to separate a desired spectrum from other spectra in Fourier space. Filter function. It should be noted that the spectrum cut by G (k _x , k _y ) is used for acquiring object information, and the spectrum that is not cut is not used here for acquiring object information.

  There are various types of window functions. For example, a Hann window represented by the following equation is one of the window functions that are often used.

In addition, Formula 4-6 is also an example which shows a Fourier-transform method, For example, using the Fourier-transform method using window Fourier transform as shown in Unexamined-Japanese-Patent No. 2011-163937 and Unexamined-Japanese-Patent No. 2013-002845, for example. Also good. In the present invention and the present specification, a spatial change in the intensity of moire is analyzed using a frequency spectrum obtained by performing Fourier transform on at least a part of the detection result (however, data of two pixels or more). Acquiring the information of the subject in step 4 is regarded as the Fourier transform method.

  Finally, the absorption information A is for I (x, y)

It becomes. The absorption information A is not differentiated information, and thus has no directionality.

  As shown in FIG. 2C, the moire of this embodiment has the same period in the x direction and the y direction. However, like the moire 301 in FIG. 3B, the moire has a period in the x direction and the y direction. It may be different. In particular, it is preferable that the cycle in the y direction (the direction in which the subject information is acquired by the phase shift method) is larger than the cycle in the x direction (the direction in which the subject information is acquired by the Fourier transform method).

  In the Fourier transform method, it is important to improve the spatial resolution to reduce the period of moire. However, if the moire period is reduced, the amplitude of the moire also decreases due to a blurring factor of the detector or the like (MTF is smaller than 1 or the like), and the S / N ratio of the detection result used for phase recovery decreases. On the other hand, since the spatial resolution does not decrease even if the moire period is increased in the phase shift method, the S / N ratio can be improved by increasing the moire period. Therefore, if the moire period in the direction (y direction) in which the subject information is acquired by the phase shift method is made larger than the direction (x direction) in which the subject information is acquired by the Fourier transform method, a reduction in spatial resolution in the x direction is prevented. However, the signal-to-noise ratio in the y direction can be increased. Thus, it can be said that the use of the fringe scanning method in only one direction is advantageous in terms of both spatial resolution and signal-to-noise ratio, and is a method balanced with throughput. The period with respect to the x direction is preferably about several pixels, but the period with respect to the y direction may be infinite. It should be noted that when the period and the period direction of the self-image and the shielding grating are exactly the same, the moire period becomes infinite.

By using the above phase recovery method, five types of parameters, A, P _x , P _y , V _x , and V _y in the two-dimensional Talbot interferometer can be acquired. As described above, in the present embodiment, the detection results I _{1 to} I _N obtained by scanning the shielding grating in one direction with respect to the self image using the shielding grating moving unit that is a moving unit that shifts the phase of the moire. Thus, information on the subject in two directions can be acquired.

[Embodiment 2]
The second embodiment will be described with reference to FIG. In this embodiment, two-dimensional moire having different periods in the x direction and the y direction is formed, a line sensor is used as the detector 150, and a transport unit 121 that transports the subject 120. Is different from the first embodiment. In addition, description is abbreviate | omitted about the structure similar to Embodiment 1. FIG.

  One of the applications of the Talbot interferometer is an inspection application. In the inspection application, in order to improve the throughput, the subject 120 is installed on a transport means 121 such as a belt conveyor, and the subject is transported between detections by the detector, or detection is performed while transporting the subject. Although the form which scans a measurement range with the subject fixed may be considered, in the present embodiment, an example in which the subject 120 is transported will be described. The transport unit 121 transports the subject 120 in one direction.

  FIG. 3A is a bird's-eye view schematically showing the configuration of the present embodiment. However, since the configuration of the calculation unit 160, the image display unit 170, and the shielding grid moving unit 190 is the same as that of the first embodiment, it is omitted. In addition, since the detector 150 of the present embodiment is a line detector, X-rays emitted from the X-ray source 110 are only in the region corresponding to the detection area of the detector 150 by the collimator 111 in the subject 120. Collimated to irradiate. Thereby, it is possible to prevent excessive exposure of the subject. The subject 120 is moved in the direction of the arrow by the transport means 121. In this embodiment, the direction of the arrow is parallel to the y direction (the direction in which the subject information is acquired by the phase shift method), but the direction in which the position of the subject moves in the y direction, that is, perpendicular to the y direction. If it is a direction other than the intersecting direction, it can be the transport direction. However, in order to efficiently carry in the y direction, the angle formed with the y direction is preferably 45 degrees or less, and more preferably 10 degrees or less. As the conveying means, for example, a belt conveyor can be used.

  FIG. 3B is a diagram comparing data acquired by the line sensor with data acquired by the area sensor. If the collimator 111 is not used and an area sensor is used as in the first embodiment, a two-dimensional moire 301 is detected. On the other hand, when a line sensor is used as in this embodiment, the detected result is a one-dimensional moire 302. FIG. 3C shows the relationship between the intensity of the one-dimensional moire obtained by one detection and the coordinates in the x direction. In FIG. 3C, the horizontal axis indicates coordinates in the x direction, and the vertical axis indicates the intensity of X-rays.

  In the present embodiment, the period of the moire 301 in the x direction is smaller than the period in the y direction, but the difference in the period is not an essential problem in terms of implementation, and various ratios can be used.

  In the present embodiment, the subject is transported by the transport unit 121, whereby the subject is scanned with respect to the measurement range of the interferometer, and information on the subject in a region wider than the measurement range is acquired. Note that the measurement range of the interferometer is a range corresponding to a range where moire is formed in the detection range of the detector. Here, the range corresponding to the range where moiré is formed refers to a range projected onto the range where moiré is formed when X-rays are irradiated, and diverges like between X-rays. When using X-rays, the size varies depending on the distance from the detector. In the present embodiment, the diffraction grating 130 and the shielding grating 140 are sufficiently larger than the detection range of the line sensor, and moire can be formed on the entire detection range of the line sensor. Therefore, the measurement range includes the opening of the collimator and the line sensor. It matches the square frustum that is formed by connecting the detection range.

  When measuring the subject, it is preferable to repeat the detection of moire with different phases and the conveyance of the subject alternately until the measurement of the entire measurement location is completed. In other words, the measurement process is as follows.

First, the first region of the subject is placed in the measurement range, detection is performed by the line sensor, and the intensity distribution I ₁ (x) is acquired as a detection result. Next, the shield grating is moved in the y direction, and the shield grating is scanned with respect to the self-image to shift the moire phase in the y direction, and detection by the line sensor is performed again, and the intensity distribution I ₂ (x) To get. As in a general phase shift method, the amount of phase shift that occurs during detection is preferably 2π / N when the number of detections is N, and N is preferably 3 or more. The shift of the moire phase and the detection by the line sensor are repeated N times, and after obtaining I ₁ (x) to I _n (x), the measurement of the first region is finished. Then, the subject 120 is transported by the transport means 121, and the second region of the subject is measured in the same manner as the first region. In this way, the scanning of the subject and the fringe scanning in the y direction in each measurement range are repeated to measure the entire desired range.

  Next, a procedure for performing phase recovery from the acquired data will be described. In the present embodiment, similarly to the first embodiment, the phase shift method is used to acquire subject information in the y direction, and the Fourier transform method is used to acquire subject information in the x direction. In the first embodiment, the two-dimensional intensity distribution is a target for phase recovery. However, in the present embodiment, the one-dimensional intensity distribution is a target for phase recovery, and a phase is set for each of the first region, the second region, and the measurement range. By performing recovery and adding up the results, information on the subject in the entire measured range is acquired.

FIG. 4 shows a set of detection results I ₁ (x) to I ₄ (x) acquired in the first region. The vertical axis represents the X-ray intensity, and the horizontal axis represents the position (coordinates) in the x direction. FIG. 4 shows an example in which N is 4. Because of the line sensor, each detection result is shown as a one-dimensional plot. For each detection result I ₁ (x) to I ₄ (x) obtained by four detections, the differential phase P _y and the scattering intensity V _y are:

Is required. Expressions (8) and (9) indicate that the detection results I ₁ (x) to I ₄ (x) to be used and the object information P _y (x) and V _y (x) to be acquired are one-dimensional (the y coordinate is Except for the point, it is the same formula as formulas (1) and (2).

The object information in the x direction is acquired by the Fourier transform method. The differential phase P _x (x) and the scattering intensity V _x (x) in the x direction are acquired as the detection results I ₁ (x, y) to I ₄ (x, y) of the expressions (3) to (5). The object information P _y (x, y) and V _y (x, y) can be obtained by the following formulas (10) to (12) in which the object information is replaced with one dimension.

The one-dimensional Hann window is represented by the following formula (13).

Finally, the absorption image A can also be acquired using the following formula (14) in which the formula (7) is replaced with one dimension.

As described above, according to this embodiment, even when a line sensor as a detector, the detection results I ₁ ~I _n obtained by scanning the absorption grating in one direction relative to the self-image, two directions Information (A, P _x , P _y , V _x , V _y ) on the subject can be acquired. Information on the subject in two directions can be acquired in each region, and if the information is added, information on the subject in two directions over the entire measurement range can be acquired.

  Note that, as in this embodiment, a Talbot interferometer having two optical systems as a Talbot interferometer that scans the subject in one direction with respect to the measurement range and acquires information on the subject in two directions. Is described in Japanese translations of PCT publication No. 2015-503988. However, since this Talbot interferometer is substantially provided with two one-dimensional Talbot interferometers, the configuration of the apparatus becomes more complicated than that of one Talbot interferometer as in the present embodiment. Is expected to become expensive.

[Embodiment 3]
The present embodiment is different from the second embodiment in that a plurality of line sensors or area sensors are used as detectors and a moving unit that scans the shielding grid is not provided. When a plurality of line sensors are used as detectors, detection results of different line sensors are used as I ₁ (x) to I _n (x), respectively. Similarly, when an area sensor is used as a detector, each of detection results from pixels in different columns of the area sensor is used as each of I ₁ (x) to I _n (x). Thus, even if there is no moire phase shift in the y direction in the second embodiment, information on the subject in the y direction can be obtained by the phase shift method. For this reason, the measurement process can be executed only by the transport mechanism that transports the subject as the moving mechanism. In addition, description is abbreviate | omitted about the structure similar to Embodiment 2. FIG.

  FIGS. 5A and 5C are bird's-eye views schematically showing the configuration of the present embodiment. However, since the configurations of the calculation unit 160 and the image display unit 170 are the same as those in the first embodiment, they are omitted. FIG. 5A shows a Talbot interferometer having four line sensors 151 a to 151 d as the detector 150, and FIG. 5C shows a Talbot interferometer having an area sensor as the detector 150.

A Talbot interferometer having a plurality of line sensors 151a to 151d will be described with reference to FIGS. The number of line sensors is the number of detection results used in the phase shift method, that is, the number of N or more in the first and second embodiments. When the Talbot interferometer has N line sensors, the detection results detected by the first to Nth line sensors at different timings are used as I ₁ (x) to I _n (x), respectively. As shown in FIGS. 5A and 5B, the Talbot interferometer using the first to fourth line sensors 151a to 151d as detectors will be described in more detail. FIG. 5B shows the relationship between the moire 301 formed in this embodiment and the detection ranges of the first to fourth line sensors 151a to 151d. The detection range of the first line sensor 151a is shown in FIG. 302a, the detection range of the second line sensor 151b is 302b, the detection range of the third line sensor 151c is 302c, and the detection range of the fourth line sensor 151d is 302d.

The plurality of line sensors are defined as first, second, third, and fourth line sensors from the upstream side in the subject conveyance direction (the arrow direction in the drawing). When the first area of the subject is arranged in the measurement range of the first line sensor 151a, the first line sensor 151a performs detection, thereby obtaining the detection result I _1-1 (x). The object 120 is conveyed in the direction of the arrow by the conveying means 121, and the second line sensor 151b performs detection when the first region is arranged in the measurement range of the second line sensor 151b. I _1-2 (x) is acquired. At this time, the second region of the subject is arranged in the measurement range of the first line sensor 151a, and the detection result I ₂₋ is also obtained by detecting the first line sensor simultaneously with the second line sensor. ₁ (x) is acquired. The subject is transported again in the direction of the arrow by the transport means. The first region is the third line sensor 151c, the second region is the second line sensor 151b, and the third region is the first line sensor 151a. The first to third line sensors detect when they are arranged in the detection range. Thereby, detection results I _1-3 (x), I _2-2 (x), and I _3-1 (x) are acquired. The subject is transported again in the direction of the arrow by the transport means, the first region being the fourth line sensor 151d, the second region being the third line sensor 151c, the third region being the second line sensor 151b, The first to fourth line sensors perform detection when the fourth region is arranged in the detection range of the first line sensor 151a. Thereby, detection results I _1-4 (x), I _2-3 (x), I _3-2 (x), and I _4-1 (x) are acquired. With this series of detection results, four detection results of I _1-1 (x) _, I _1-2 (x) _, I _1-3 (x) _{, and} I _1-4 (x) are obtained for the first region. did it. Then, using these four detection results, phase recovery is performed as in the second embodiment. As a result, for the first region, it is possible to acquire subject information using the phase shift method in the y direction and the Fourier transform method in the x direction. Similarly, by repeating the conveyance and the detection by the line sensor, four detection results can be obtained for the second, third, and fourth regions, and information on the subject can be acquired in the same manner.

period p _y of moire with respect to the y direction is adjusted to the extent that it is possible to perform the phase shift method using the detection result of the line sensor of the first to N. Specifically period p _y moire when a distance (the distance between the centers of the detection range) in the y direction of the line sensors and D is
p _y = DN Formula (15)
Is desirable. The amount of phase shift of each detection in a general phase shift method corresponds to the amount of phase shift between moires formed on line sensors separated by a distance D. That is, satisfying Equation (15) is equivalent to the amount of phase shift occurring during detection in the second embodiment being 2π / N.

  Since the position of the object detected at the same timing by each line sensor is different, the data of the detection result is retained by some method such as a storage device, and the detection result obtained by measuring the same position of the object later is taken out Phase recovery.

  The first to fourth line sensors perform detection at the same timing, but by shifting the detection timing, the distance between the areas to be measured (for example, the first area and the second area) (Distance) may be adjusted. However, since the control of the detection timing by the line sensors becomes complicated, it is easier to adjust the distance between the areas to be measured by adjusting the distance between the line sensors. In addition, although conveyance of the subject and detection by the line sensor were alternately performed, the line sensor may detect X-rays while conveying the subject. By doing so, not only can the measurement throughput be increased, but the control of the conveying means is facilitated.

  The above is a case where a line sensor is used, but the detection range of the line sensor is only one line for the pixel width in the subject. Therefore, when measuring the entire subject, the feed amount (conveyance distance) is defined by the width of the line sensor.

As shown in FIG. 5C, when an area sensor is used as the detector 150 instead of the line sensor, such a point can be improved. Since the area sensor can measure multiple lines at once, the throughput can be significantly improved. FIG. 5D shows the relationship between the moire 301 formed in this embodiment and the detection range of the area sensor. Detection range of the area sensor, pixel size d × m _y pixels in the y-direction, the x-direction and pixel size d × m _x pixels.

In this case, by using the period p _y of moire in the _y-direction, of the detection range in the y-direction of the area sensor length dm _y, conveying distance D between one of the detection

It is preferable that At this time, n × N detections are performed on the same region before the subject moves from the end of the area sensor to the other end. When data of detection results obtained by detecting the same region on the subject are collected, the subject information in the y direction can be acquired using the phase shift method, and the subject information in the x direction can be obtained by using the Fourier transform method. Can be obtained using. In addition, when n is 2 or more, it is preferable to add the detection results having the same moire phase among the detection results obtained by measuring the same region of the subject because the S / N ratio can be improved.

As described above, according to the present embodiment, the information (A, P _x ) of the subject in two directions is used without using the moving means (the means for moving the shielding grating with respect to the self-image) that shifts the moire phase. , P _y , V _x , V _y ). The information (P _y , V _y ) on the subject in the y direction acquired by the present embodiment is obtained by a two-dimensional Fourier transform method that obtains information on the subject in the x direction and the y direction by a Fourier transform method. Compared with the information of the subject in the direction, the spatial resolution is high.

[Embodiment 4]
In the present embodiment, a Talbot interferometer having a different moire pattern from the first to third embodiments will be described. This embodiment can be combined with any of Embodiments 1 to 3, and can be used in place of the moire shown in FIGS. 2 (c), 3 (b), 5 (b), and (d). .

  In the first to third embodiments, a π-type phase grating having a checker pattern is used as the diffraction grating 130. In these embodiments, moire as shown in FIGS. 2C, 3B, 5B, and 5D is generated. These moires have different S / N ratios depending on places (lines), and artifacts are more likely to occur in places where the S / N ratio is small than in places where the S / N ratio is large. For example, in FIG. 3B, the signal intensity is different between the line 311 and the line 312, and the line 311 has a small S / N ratio. Therefore, in the measurement range corresponding to the line 311, artifacts are likely to occur in the obtained subject information.

  In this embodiment, as shown in FIG.6 (c), even if it is a line with a small S / N ratio variation and a small S / N ratio, it is compared with the line with a small S / N ratio of Embodiment 1-3. Forms a moire with a large S / N ratio. A configuration for forming such moire will be described.

  In this embodiment, a diffraction grating having a π / 2 type checkerboard pattern as shown in FIG. In the checkerboard pattern, two types of areas 201 and 202 are arranged like a checkerboard, and the X-ray transmitting one is configured to be shifted in phase by π / 2 radians with respect to the X-ray transmitting the other. Yes.

Using this diffraction grating, when the pattern period of the diffraction grating 130 is p ₁ and the wavelength of the incident X-ray is λ, a first interference pattern formed at a position of p ₁ ² / (2λ) from the diffraction grating 130. 180 is shown in FIG. The first interference pattern 180 in FIG. 6B is a pattern in which the bright part 204 and the dark part 203 are arranged in a checkerboard shape. In this case, the brightness ratio between the bright part and the dark part in the line is lower than that in FIG. However, the amplitude of the moire in the direction perpendicular to the line formed thereby becomes almost uniform at any position in the line.

6C is formed by a diffraction grating having a π / 2 type checker pattern, and a shielding grating having a pattern in which a shielding part and a transmission part correspond to each of a bright part and a dark part of the moire pattern in FIG. 6B. It is a schematic diagram of the moire. The formed moire also has a pattern in which bright portions and dark portions are arranged in a checkerboard shape. FIG. 6D shows a pattern in which the moire pattern is tilted 45 degrees with respect to the y direction to change the ratio of the cycle in the y direction to the cycle in the x direction. In FIG. 6D, although the average brightness of lines 411 and 422 is different, the amplitude in the line direction is the same as in lines 311 and 312, and when the S / N ratio is calculated for each line, the minimum value is It is larger than the moire shown in FIG. Therefore, artifacts are unlikely to occur during phase recovery. However, as shown in FIG. 6D, when the moire has a pattern in which the bright part and the dark part are arranged in a checkerboard shape, the arrangement direction of the pixels is inclined 45 degrees with respect to the periodic direction of the moire. It is necessary to arrange a diffraction grating, a shielding grating, and a detector.
When the moire having such a pattern is used, the subject information of the area corresponding to the line 311 is acquired when the moire in which the bright portions are discretely arranged as in the pattern of FIG. The problem that it is difficult to solve can be solved.

  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.

DESCRIPTION OF SYMBOLS 110 X-ray source 120 Subject 130 Diffraction grating 140 Shielding grating 150 Detector 160 Calculation part 170 Image display apparatus 180 First interference pattern 190 Moving part

Claims (10)

A diffraction grating that diffracts X-rays from an X-ray source and forms a first interference pattern having a period in a first direction and a second direction intersecting each other;
A shielding grating for forming a second interference pattern having a period in two directions intersecting by shielding a part of the X-rays forming the interference pattern;
A detector for detecting X-rays transmitted through the shielding grating;
A calculation unit that obtains information of a subject disposed between the X-ray source and the shielding grid using a detection result of the detector,
The detector acquires a plurality of detection results by performing detection of X-rays transmitted through the shielding grid a plurality of times,
The computing unit is
Obtaining information in the first direction of the subject by analyzing the intensity change between the plurality of detection results for each pixel,
A Talbot interferometer characterized in that information in the second direction of the subject is acquired using a frequency spectrum obtained by Fourier transforming at least a part of the plurality of detection results. A moving unit that moves a relative position between the first interference pattern and the shielding grating;
The detector is
X-ray detection is performed when the first interference pattern and the shielding grating are in a first relative position and when the second interference pattern and the shielding grating are in a second relative position. The Talbot interferometer according to claim 1. Moving means for moving the relative position of the subject and the measurement range;
The detector is
X-ray detection is performed when the subject and the detector are in a first relative position and when the subject and the detector are in a second relative position. Item 3. The Talbot interferometer according to Item 1 or 2. While moving the relative position of the subject and the measurement range by the moving means,
The Talbot interferometer according to claim 3, wherein X-ray detection is performed by the detector. The detector is a line detector;
Among each of the subjects, when the first region is arranged in the measurement range and when the second region is arranged in the measurement range,
The moving unit moves a relative position between the first interference pattern and the shielding grating, and the detector has the first interference pattern and the shielding grating at a first relative position. Detecting X-rays when the second interference pattern and the shielding grating are in a second relative position;
The computing unit is
A detection result detected by the detector when the first interference pattern and the shielding grating are in a first relative position when the first region is arranged in a measurement range; and the second Using the detection result detected by the detector when the interference pattern and the shielding grating are in the second relative position, to obtain information in the first direction of the first region,
A detection result detected by the detector when the first interference pattern and the shielding grating are in a first relative position when the second region is arranged in the measurement range; and the second Information in the first direction of the second region is obtained using a detection result detected by the detector when the interference pattern and the shielding grating are in a second relative position. The Talbot interferometer according to any one of claims 1 to 4. The detector is a plurality of line detectors;
5. The Talbot interferometer according to claim 3, wherein each piece of information for each pixel of the subject is acquired using detection results acquired by different line detectors. The detector comprises a first line detector and a second line detector;
The computing unit is
A detection result detected by the first line detector when the first region of the subject is arranged in a detection range of the first line detector;
A detection result detected by the second line detector when the first region of the subject is arranged in a detection range of the second line detector;
5. The Talbot interferometer according to claim 3, wherein information on the first region of the subject is acquired using the Talbot interferometer. The detector is an area sensor;
5. The Talbot interferometer according to claim 3, wherein each piece of information for each pixel of the subject is acquired using detection results acquired from different pixel rows of the area sensor. The detector is an area sensor having a first pixel column and a second pixel column;
The computing unit is
A detection result detected by the first pixel column when the first region of the subject is arranged in a detection range of the first pixel column;
A detection result detected by the second pixel column when the first region of the subject is arranged in a detection range of the second pixel column;
5. The Talbot interferometer according to claim 3, wherein information on the first region of the subject is acquired using the Talbot interferometer. The detector is an area sensor;
The length of the detection range of the detector direction definitive relative position between the detector and the object is moved is dm _y,
The detector performs N detections,
The computing unit is
Using the detection results N times by the detector to obtain information on the subject in the first direction;
The moving unit is
5. The Talbot interferometer according to claim 3, wherein the relative position between the subject and the measurement range is moved by dm _y / n × N during each detection by the detector.
However, n is an integer of 1 or more, and N is an integer of 2 or more.