WO2007125833A1

WO2007125833A1 - X-ray image picking-up device and x-ray image picking-up method

Info

Publication number: WO2007125833A1
Application number: PCT/JP2007/058645
Authority: WO
Inventors: Atsushi Momose; Wataru Yashiro
Original assignee: The University Of Tokyo
Priority date: 2006-04-24
Filing date: 2007-04-20
Publication date: 2007-11-08

Abstract

An X—ray image picking-up device and its method are provided to use a continuous X-ray for picking up an image with a high sensitivity based on X-ray phase information. An object (2) is set in a space existing from an X-ray source (1) to a third grid (5) (e.g., a space defined between a second grid (4) and the third grid (5)). A continuous X-ray beam is irradiated from the X-ray source (1) to the first grid (3). The second grid (4) diffracts an X-ray diffracted by the first grid (3). The first and second grids (3) and (4) selectively make an X-ray with a specific band wavelength penetrate. Further, an X-ray diffracted by the second grid (4) forms its own image. The image is observed through the third grid (5). In consequence, based on the principle of Talbot interferometer, a contrast of the object is generated. An X-ray diffracted by the third grid (5) is detected by an X-ray image detector (6). With this, such a structure of the object that an absorbed contrast does not depict can be observed.

Description

Specification

X-ray imaging apparatus and X-ray imaging method

Technical field

The present invention relates to an X-ray imaging apparatus and an X-ray imaging method for observing the internal structure of a subject with high sensitivity using the phase of X-rays.

Background art

[0002] Since X-rays have high penetrating power, they are widely used in medical image diagnosis, nondestructive inspection, security check, and the like as probes for seeing through the inside of an object. The contrast of the X-ray fluoroscopic image depends on the difference in the X-ray attenuation rate, and the portion that strongly absorbs X-rays is rendered as X-ray shadows. X-ray absorption capacity is stronger as more elements with higher atomic numbers are included. On the other hand, it can be pointed out that contrast is difficult for substances whose atomic numbers are small! /, Which is made up of only elements, and this is also a fundamental drawback of fluoroscopic images. Therefore, sufficient sensitivity cannot be obtained with X-ray fluoroscopic images for biological soft tissues or soft materials.

[0003] On the other hand, it is known that using X-ray phase information can achieve a sensitivity higher by 3 digits or more than a general conventional X-ray fluoroscopic image. Since it can be applied to observation of substances consisting of light elements that do not absorb X-rays very much (biological soft tissues, organic materials, etc.), its practical use is expected. Research on high-sensitivity imaging using this X-ray phase information is a field that has emerged since the first half of the 1990s. Usually, advanced X-ray sources are required. Not in. In other words, the mainstream of research so far uses an X-ray optical system that uses monochromatic plane wave X-rays, which is premised on the use of extremely high-intensity X-ray sources. In addition to the huge synchrotron radiation facility, it is difficult to imagine what can actually be used as such an X-ray source. This is a major obstacle when considering the practical use of imaging methods using X-ray phase information.

[0004] A general X-ray source is a type that extracts X-rays by irradiating a metal target with an electron beam or a laser. When such an X-ray source is used, the X-rays included in the spectrum include “continuous X-rays” due to bremsstrahlung and “special characteristics due to electron orbit transitions” depending on the X-ray generation principle. Sex X-ray "exists. Characteristic X-rays are monochromatic as a spectrum. Continuous X-rays contain a continuous spectrum, ie, various wavelengths (photon energies). If monochromatic X-rays are required, the characteristic X-ray part of the spectrum can be used. The wavelength of the characteristic X-ray depends on the type of metal target (ie the type of element). However, for example, in medical applications, X-rays of several tens of keV are required, but targets for elements that generate characteristic X-rays, particularly in the range of 30 to 50 keV, have not been developed so much. In addition, although it is possible in principle to select and use monochromatic X-rays of arbitrary energy with continuous X-ray force, sufficient strength cannot be ensured in that case. However, the intensity problem can be greatly reduced if a spectral part with a much wider energy width than continuous X-rays can be extracted and used.

[0005] The general X-ray source described above emits X-rays radially. In other words, it is a corn beam. Although it is possible in principle to extract and use a parallel beam (plane wave), sufficient strength cannot be ensured.

[0006] As described above, even when a method that requires a monochromatic plane wave is combined with the above-described general X-ray source, the X-ray utilization efficiency is extremely deteriorated, and imaging within a substantial imaging time is difficult. A phase-based imaging method that works with cone-beam X-rays with a window width is desired. If this is realized, an apparatus using a compact X-ray source other than synchrotron radiation is expected.

[0007] The inventor of the present invention has already proposed an X-ray phase imaging method using an X-ray Talbot interferometer that uses two diffraction gratings (Patent Document 1 below). Since this method works with cone beams, it can be combined with a compact X-ray source in this respect. Further, in the technique described in Patent Document 1, it is difficult to use the continuous X-rays as it is, around the energy E and the energy width delta E, remarkably than typical energy spread Δ EZE~10- ³ characteristic X-ray Wide, it functions with spectral quasi-monochromatic X-rays (X-rays with a spectral width of about Δ E / E <1Z8!). That is, if continuous X-ray force can also extract the quasi-monochromatic X-ray described above, an X-ray Talbot interferometer that uses a continuous X-ray source can be realized relatively efficiently, that is, fusion with a compact X-ray source is greatly achieved. It can be expected.

Patent Document 1: WO2004 / 058070

Disclosure of the invention Problems to be solved by the invention

The present invention has been made in view of the above circumstances. An object of the present invention is to provide an apparatus and method that enables X-ray imaging with high sensitivity using phase information of X-rays even when continuous X-rays are used.

Means for solving the problem

The X-ray imaging apparatus according to the present invention includes an X-ray source, a first grating, a second grating, a third grating, and an X-ray image detector. The X-ray source is configured to irradiate an X-ray cone beam toward the first grating. The first grating is a phase type diffraction grating or an amplitude type diffraction grating. The second grating is an amplitude type diffraction grating. The second grating is configured to diffract the X-ray diffracted by the first grating. The period of the lines in the second grating is substantially the same as the period of the periodic intensity pattern formed by the X-rays diffracted by the first grating. Furthermore, the second grating has a configuration in which a periodic intensity pattern can be formed by X-rays diffracted from the second grating. The third grating is an amplitude type grating. The third grating is disposed at substantially the same position as the position where the periodic intensity pattern formed by the X-rays diffracted by the second grating is formed. The period of the lines in the third grating is substantially the same as the period of the periodic intensity pattern formed by the second grating. The X-ray image detector is configured to detect X-rays that pass through the third grating from the force of the periodic intensity pattern formed by the second grating.

In this apparatus, a subject to be subjected to X-ray imaging is arranged at any position between the X-ray source and the third grating. The X-ray cone beam is irradiated to the arranged subject.

[0011] In the X-ray imaging apparatus according to the present invention, the X-rays emitted from the X-ray source can be continuous X-rays.

In the X-ray imaging apparatus according to the present invention, the third grating can be translated along the plane of the grating and in the direction in which the periodic structure is formed. Further, the X-ray image detector may sequentially measure the intensity of X-rays transmitted through the third grating, which changes as the third grating translates. With this configuration, depending on the subject The X-ray phase shift derivative can be detected.

In the X-ray imaging method according to the present invention, an X-ray source, a first grating, a second grating, a third grating, and an X-ray image detector are used. Furthermore, the subject is arranged at any position between the X-ray source and the third lattice. The first grating is a phase type diffraction grating or an amplitude type diffraction grating. The second grating is an amplitude type diffraction grating. The period of the line in the second grating is substantially the same as the period of the periodic intensity pattern formed by the X-rays diffracted by the first grating. The third lattice is an amplitude lattice. The period of the lines in the third lattice is substantially the same as the period of the periodic intensity pattern formed by the X-rays that are diffracted by the second lattice.

[0014] Furthermore, the X-ray imaging method according to the present invention comprises the following steps:

(1) irradiating a cone beam including continuous X-rays toward the first grating;

(2) The second grating is arranged at a position where a periodic intensity pattern is formed by the first grating with respect to a quasi-monochromatic X-ray having a spectrum centered on a desired energy contained in the continuous X-ray. Step, but this step may be before step (1);

(3) the second grating diffracts the quasi-monochromatic X-ray diffracted by the first grating and forms a periodic intensity pattern by the quasi-monochromatic X-ray diffracted by the second grating;

(4) A step of placing the third grating at a position where the periodic intensity pattern of the second grating is formed, provided that this step is performed even before step (1) or (3). Good;

(5) A step of detecting X-rays transmitted through the third grating from the periodical intensity pattern formed by the second grating.

The invention's effect

[0015] According to the X-ray imaging apparatus and the X-ray imaging method of the present invention, even when the X-rays from the radiation source are continuous X-rays by using the first to third gratings. It can function as an X-ray Talbot interferometer.

[0016] In the present invention, even when continuous X-rays are used, high-sensitivity using X-ray phase information is used. X-ray imaging is possible.

[0017] Further, in the present invention, the first and second gratings generate X-rays (quasi-monochromatic X-rays) that are much wider than the monochromatic X-rays and have an energy bandwidth from the continuous X-rays, and image these images. Available to: For this reason, the energy of continuous X-rays with a wide band can be used effectively. In addition, since various X-ray sources can be used, X-ray imaging devices can be put to practical use and applications can be expanded.

BEST MODE FOR CARRYING OUT THE INVENTION

[0018] (Configuration of Embodiment)

Hereinafter, an X-ray imaging apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. The X-ray imaging apparatus of the present embodiment includes an X-ray source 1, a first grating 3, a second grating 4, a third grating 5, and an X-ray image detector 6 (see FIG. 1). ). This device is for observing the internal structure of the subject 2. The subject 2 is, for example, a biological sample, a polymer material, an organic substance such as a human body, or an object including an inorganic substance such as a semiconductor device.

The X-ray source 1 is configured to irradiate an X-ray cone beam toward the first grating 2.

Here, continuous X-rays are used as X-rays. The cone beam is a spherical wave radiated from a point light source (hereinafter referred to as a “pseudo point light source” t ヽぅ) having an aperture necessary for the operation of the X-ray Talbot interferometer. The theoretical condition of the aperture diameter in the pseudo point light source will be described later using mathematical formulas. Note that the X-ray Talplo interferometer operates even if the X-ray emission area is linear. In that case, the conditional force on the line width exists in the same way as in the case of the opening diameter (described later). Further, such linear X-ray radiation site forces may be arranged at substantially equal intervals and substantially parallel to each other. To obtain such an X-ray source effectively, the X-ray emission site is large! You can use a conventional X-ray source and an X-ray mask that transmits only the part of the above shape. The X-ray beam obtained in this way is also widely called a cone beam.

[0020] The first grating 3 is a phase type diffraction grating. The first grating 3 is provided with a plurality of lines 31 for exerting a diffraction effect (see FIG. 2). The period of line 31 is shown in FIG. The first grating 3 diffracts continuous X-rays emitted from the X-ray source 1. Downstream of the first grating 3 is a periodic intensity pattern (i.e. a so-called `` self-image '' (Sometimes called “self-image”). However, the position depends on the wavelength of the X-ray. The line 31 is made of a material or a structure that gives a phase difference to the X-ray when the first grating 3 is a phase type. The first grating 3 may be an amplitude type. In this case, the line 31 is a material that absorbs X-rays and has a structure.

[0021] The second grating 4 is an amplitude type diffraction grating. The second grating 4 is provided with a plurality of lines 41 for exhibiting a diffractive action (see FIG. 2). The period of line 41 is shown in FIG. When looking at quasi-monochromatic X-rays with the desired center wavelength, the second grating 4

2

Are arranged at positions where self-images of the center wavelength are formed. The period d of the second lattice 4 is the first case

The period of the self-image formed by two children 3 is substantially the same. If the part where the intensity of the self-image is large coincides with the gap between the lines 41 of the second grating 4, the quasi-monochromatic X-ray having the above-noted center wavelength, which is most efficient, passes through the second grating. it can. At the same time, for X-rays with other wavelengths, since the self-images are formed in different places, the rate of passing through the second grating 4 is relatively small. Thus, the second grating 4 functions as an energy filter. At the same time, the second grating 4 is configured such that a self-image can be formed by the quasi-monochromatic X-ray diffracted from the second grating 4. Also, by adjusting the position or period d of the second grating 4, the wavelength of X-rays passing through the second grating can be adjusted to some extent.

2

Is possible.

[0022] The third grating 5 is an amplitude type grating. The third grid 5 is provided with a plurality of lines 51 for exhibiting an absorption filter action (see FIG. 2). The cycle of line 51 is indicated by d in FIG. The third lattice 5 is almost the same as the position where the self-image of the second lattice 4 is formed.

Three

Placed in position. The third grating 5 can be regarded as a spatial filter that partially transmits the self-image by the second grating 4. Period d in third lattice 5 (see Fig. 2)

Three

Is almost the same period as the self-image of the second lattice 4. Here, substantially the same period means that the period is approximated to the extent that moire fringes can be formed by the self-image of the second diffraction grating 4 and the third diffraction grating 5. Also, even if both periods are completely equal, moire fringes occur if they are slightly deviated from the parallel arrangement. The subject 2 and its internal structure can be detected as a moire fringe deformation approximately proportional to the angle at which the X-ray is bent by refraction by the subject 2. The period of self-image by the second lattice 4 and the period d of the third lattice 5 are If they are completely equal and both are completely parallel, the detected shade will be proportional to the cosine of an amount proportional to the angle of the X-ray bent by refraction.

Note that the subject 2 may be placed between the X-ray source 1 and the first grating 3 or between the first grating 3 and the second grating 4. However, in this case, since the energy filter function of the first grid 3 and the second grid 4 may be affected, the subject 2 is located between the second grid 4 and the third grid 5. desirable.

[0024] As explained above, the set of the first lattice 3 and the second lattice 4 functions as an energy filter based on the Talbot effect (that is, a filter that also generates a quasi-monochromatic X-ray with continuous X-ray force). The combination of 4 and the third grating 5 becomes a Talbot interferometer using the above quasi-monochromatic X-rays! That is, the second grating 4 is configured to contribute to both the energy filter and the Talbot interferometer.

The X-ray image detector 6 is configured to form a self-image with the second grating 4 and detect X-rays transmitted through the third grating 5. Since the X-ray image detector 6 itself may be the same as that conventionally used, detailed description thereof is omitted.

[0026] (Principle of X-ray Talbot interferometer)

The X-ray imaging apparatus of this embodiment uses the principle of the Talbot interferometer. Therefore, the principle of the Talbot interferometer will be described below.

[0027] The X-ray Talbot interferometer is an interferometer using the X-ray Talbot effect. The Talbot effect is as follows: `` If an object with a periodic structure such as a grating is irradiated with light with high spatial coherence, it will be measured at a position where the grating force is separated by a certain distance determined by the wavelength of the light and the period of the grating. This is a phenomenon where the same intensity pattern (ie, “self-image”) as the intensity transmittance of the grating appears in the light transmitted through the grating. The position z from the lattice where the narrow self-image appears is that the lattice is of amplitude type.

T

Well,

[Equation 1] md ² R

= — ~~ (Formula 1)

This is the case where m is an even number when Λ.Κ-ma. D, λ, and R are the period of the lattice, X The wavelength of the line and the X-ray source force are also the distance to the grating. For plane wave X-rays, R → infinity

I think that. When m is an odd number, a self-contrast image is inverted, which is also called a self-image in a broad sense. If the lattice is phase type, a periodic intensity pattern appears when m is a fraction (fractional Talbot effect). This is also called a self-image in a broad sense. In the present embodiment, the term “self image” includes not only a narrow sense but also a broad sense. Note that the self-image does not appear only at the position given by Equation 1. Equation 1 gives the position where the contrast of the self-image periodic pattern is maximized. Therefore, if it is in the vicinity of the position given by Equation 1, the self-image is observed. Figure 3 shows an example.

[0028] Here, the spatial coherence required for the X-ray source will be mentioned. First, let a be the size (opening diameter) of the X-ray source (X-ray generating part). At this time, spatial coherence is proportional to a / R, and some degree of coherence is required to form a self-image. Here, R has the same meaning as described above. In order to obtain high coherence, the X-ray source should be small or far away from the X-ray source. As a relation with the period d of the diffraction grating

[Equation 2] a <~ (Formula 2)

It is desirable to satisfy a. This condition relates to the direction of the grating period (up and down in the figure in FIG. 3), and need not be applied in the direction perpendicular to it (the direction perpendicular to the paper in FIG. 3). Therefore, the X-ray generation part may be linear with a width a. In addition, a plurality of such linear X-ray generators are arranged at almost equal intervals and almost in parallel.

[0029] Now, when an X-ray is irradiated to an object, it is considered that there is a sufficient phase shift even if the X-ray absorption by the object is weak. In other words, X-rays are refracted by an object. If there is a phase shift, the self-image that should be formed in an orderly manner is distorted. If you observe this distortion, you can get information about the phase shift caused by the object. Can do. However, it is desirable that the period of the X-ray diffraction grating is smaller than the coherence distance of the X-ray, and it is typically on the order of several microns. Since self-images have a periodic intensity distribution that depends on them, a specially high resolution X-ray detector is required to resolve them. In the X-ray Talbot interferometer, in order to avoid this annoyance, another grating is placed on the self-image. This other grating is of the amplitude type whose period is almost equal to the average period of the self-image. At this time, moire fringes are generated by superimposing the self-image and the periodic pattern of another grating, and the distortion of the self-image is visualized as the bending of the moire fringes. Moire fringe spacing is generally much wider than the self-image period. The spatial resolution requirements for X-ray image detectors are greatly reduced.

[0030] The configuration of this X-ray Talbot interferometer is described in Equation 1 using the wavelength λ!

However, it can be pointed out that even if it has a certain energy width (ie, wavelength width), it functions in the same configuration. Given the center wavelength, and considering the wavelength width of λ

0 0

The position where the image is formed changes in the range of ζ and Δ ζ. Where Δζ is based on Equation 1,

Τ Τ Τ

[Equation 3] (Formula 3)

Given in. For example, if the center wavelength is 0.05 nm and then there is a 5% wavelength change, the change in the position where the self-image is formed when calculating in the case of R = lm, d = 5 μm and m = l / 2 Δ ζ is about 2cm (ζ is about 33cm). In other words, it is slightly away from the center wavelength.

T T

It can be said that the position of the self-image formed by the X-rays with the specified wavelength is not so different from that of the X-rays with the central wavelength. It can be said that the X-ray Talbot interferometer functions not only for monochromatic X-rays but also for quasi-monochromatic X-rays having a relatively wide energy width.

[0031] However, as described above, when using an X-ray source having a continuous spectrum in combination with a Talbot interferometer, the X-ray must be guided to the Talbot interferometer after some spectroscopic means. Don't be. In general, X-ray spectroscopy is performed using crystals. Its performance is very high, on the other hand, monochrome degree 10 ⁴ about an X-ray, since parallelism is ^10-4 ~ - ⁵ rad, efficiency is very poor. However, since the X-ray Talbot interferometer is composed of a diffraction grating, Such high monochromaticity and parallelism are not required. In other words, the combination of an X-ray Talbot interferometer and a crystal spectrometer will unnecessarily reduce the X-ray dose available for imaging. Then, except when using an X-ray source with very high parallelism and brightness, such as a synchrotron radiation source, the X-ray intensity is insufficient, and a practical apparatus configuration cannot be performed. In addition, since the synchrotron radiation source is a huge facility, there are too many obstacles to make it a practical machine, such as cost and installation space.

(Operation of X-ray imaging apparatus according to this embodiment)

The apparatus of this embodiment performs spectroscopy suitable for an X-ray Talbot interferometer based on the same principle as that of an X-ray Talbot interferometer. As described above, the Talpau interferometer described in Patent Document 1 uses two gratings. On the other hand, in this embodiment, three lattices are used. The side force of the X-ray source 1 also has a spectroscopic function in the Talbot interferometer consisting of the first grating 3 and the second grating 4, and the second grating 4 and the third grating 5 as another Talbot interferometer. Thinking about it, it performs the original contrast generation function described above.

Hereinafter, the operation of the present embodiment having the three-grid configuration will be described in detail with reference to FIG. Assume that X-ray source 1 emits a continuous spectrum of X-rays in the shape of a cone beam. The phase type first grating 3 is located at a distance R from the X-ray source 1 and the period of the grating is d. This first lattice 3

1

For example, the line 31 in FIG.

[0034] FIG. 3 shows the result of calculating the state of self-image generation at this time. The intensity of X-rays from the position of the first grating 3 (π-type phase diffraction grating) (m = 0) to the rear is expressed in black and white. If we focus on the position of m = 0.75, we can see that X-rays are locally strong. Here, the second grating 4 (amplitude diffraction grating) is arranged so that only the portion where the X-ray is strong can pass through the gap of the line 41. Note that the pattern in Figure 3 changes as the X-ray wavelength changes. In other words, behind the second grating 4, more X-rays in a specific wavelength region that cause a remarkable intensity concentration at the position of the gap of the line 41 pass.

[0035] Here, the distance between the first lattice 3 and the second lattice 4 is z, and the distance between the second lattice 4 and the third lattice 5 is

12

If Z, the following conditions must be satisfied. In the following equation,

23 0

The heart wavelength.

[Equation 4]

[Equation 5] One m'd ^ (R + ∑ _u )

¾ _{+ ½} ) — ' ² (Equation ⁵ )

[Equation 6]

^{R: d} i = (R + z _n ) d ₂ = (R + z + z ₂₃ ): d ₃ (Formula 6)

Specifically, a configuration example in which the first grating 3 and the second grating 4 selectively transmit X-rays having a central wavelength of 0.05 nm is as follows.

X-ray source: Microfocus X-ray source

Target: Tungsten, focal size: 5 μτη

Distance from X-ray source to first grating: R = 1.5 m

First lattice: Consists of a gold pattern on a silicon wafer

First grating period: d = 4.31 / zm, gold line width: d / 4, gold line height: 4.9 / zm (determined to be a π-type phase diffraction grating for X-rays with a center wavelength of 0.05 nm) )

First grid force Distance to second grid: z = 0.34 m

12

Second lattice: Consists of a gold pattern on a silicon wafer

Second grating period: d = 5.30 μm, gold line width: d X 0.8, gold line height: 60 μm

twenty two

Determined to be regarded as a width diffraction grating)

Distance from second grid to third grid: _Z = 0.81 m

twenty three

Third lattice: Consists of a gold pattern on a silicon wafer

Period of third grating: d = 7.62 μm, gold line width: d 11, gold line height: 60 m (almost amplitude case)

3 3

Decided to be considered a child)

[0037] In this configuration example, an X-ray spectrum transmitted through the set of the first grating 3 and the second grating 4 is measured. Figure 4 shows the result. In this example, the half width of the spectrum can be reduced to about 1/4 of the center wavelength. Here, the calculation was made on the assumption that the incidence of a completely uniform spectrum was used. However, in practice, low-energy components were cut by using an appropriate filter, and the absorption edge of the filter and the high-energy cutoff of the X-ray source were When used together, the spectrum width can be effectively narrowed.

[0038] At the same time, the second grating 4 can also function as the X-ray source side diffraction grating of the Talbot interferometer, and if the third grating 5 is arranged at a position where the self-image of the second grating 4 is generated. The moire fringes can be observed by the detector 6.

In the present embodiment, the position of the subject 2 is not particularly limited as long as it is between the X-ray source 1 and the third grating 5. However, if the subject 2 is placed closer to the X-ray source than the second grating 4, it is considered that the wavelength selection performance is slightly deteriorated. Therefore, it is desirable that the position of the subject 2 is between the second grating 4 and the third grating 5. . However, since the wavelength selection performance required for the Talbot interferometer is not very sharp, it is possible to place an object closer to the X-ray source than the second grating 4. In particular, if the subject 2 is placed between the X-ray source 1 and the first grating 3, there is a practical advantage that the work of placing the subject becomes easy. The sensitivity is almost proportional to the distance between the subject 2 and the third grid 5.

[0040] The aperture ratio (line width Z period) of the second lattice 4 is preferably 1Z2 or more. This is because when the aperture ratio is less than 1Z2, other wavelength components increase in the transmitted X-ray and the wavelength selectivity deteriorates. For example, in the example of Fig. 3, the wavelength selectivity is improved by setting the aperture ratio to 4Z5.

[0041] According to the X-ray imaging apparatus and the X-ray imaging method according to the present embodiment, even when the X-ray of the source power is a continuous X-ray by using the first to third gratings. As described above, there is an advantage that it can function as an X-ray Talbot interferometer!

In addition, according to the present embodiment, even when continuous X-rays are used as the X-ray source 1, high-sensitivity X-ray imaging using X-ray phase information is possible.

Furthermore, in the present embodiment, the first and second gratings 3 and 4 generate X-rays (quasi-monochromatic X-rays) that are far wider than monochromatic X-rays and have an energy bandwidth from continuous X-rays. This can be used for imaging. For this reason, effective use of continuous X-ray energy with a wide bandwidth Can do. In addition, since various X-ray sources can be used, the X-ray imaging device can be put into practical use and expanded in use.

In addition, the second grating 4 in the present embodiment has both the energy filter effect by the first and second gratings 3 and 4 and the Talbot interference effect by the second and third gratings 4 and 5. Since this also serves as a function, the entire apparatus can be reduced in size.

[0045] (Example of tomography)

In the configuration of the present embodiment described above, if the third lattice is translatable along the direction in which the periodic structure of the lattice is formed on the surface of the lattice (vertical direction in FIG. 2), an X-ray It is possible to image the distribution of the angle at which the object is bent by refraction. This image corresponds to the differentiation of the X-ray phase shift by the subject. If this measurement is performed on a subject in a plurality of projection directions, acquisition of a slice image and further a three-dimensional image can be realized based on the principle of tomography.

In tomography using the apparatus of the present embodiment, the following three procedures are required. Procedure 1 is based on the X-ray image detected by the X-ray image detector 6 (hereinafter referred to as the “moire fringe image”) and the “distribution image of the angle at which the X-ray is bent by the refraction effect of the subject 2” (hereinafter “ This is referred to as “phase shift differential image”. Step 2 is to acquire an image representing the phase shift itself (hereinafter referred to as “phase shift image”) by integrating the phase shift differential image. Step 3 is to reconstruct a solid image by tomography using phase shift images obtained in multiple projection directions.

[0047] For the procedure 1, a fringe scanning method is used. In this method, the third lattice 5 is translated relative to the self-image of the second lattice 4. The translation direction is a direction substantially along the grating surface and the periodic direction of the grating. Therefore, when tomography is performed by the apparatus of this embodiment, it is preferable that the apparatus of this embodiment further includes a moving mechanism that moves the third lattice 5.

[0048] The moire fringe moves as the lattice moves, and the moire fringe image is restored when the translation distance reaches one period of the lattice. The fringe scanning method records the change of moire fringes in multiple images while translating the grating by an integer of one period, and obtains a phase-shift differential image φ (x, y) by processing them. It is. (X, y) is a coordinate indicating the position of the pixel. Above average Moire fringe image I (x, y)

[Equation 7] 2 + γ) + ζ ₂₂ φ {χ, γ) + ξ}

(Formula 7)

Given in. Where A (k = 0, 1, ...) is a constant k determined by the cross-sectional shape of the lattice lines.

It is. A (x, y) represents the contribution of contrast generated regardless of the subject due to lattice distortion, manufacturing error, and placement error. d of the third lattice 5 to translate

Three

The period, z, is the distance between the second lattice 4 and the third lattice 5. Now, step d / M (M: integer)

23 3

Suppose you want to acquire M moiré fringe images while changing with. In Equation 7, if the term k> N is small enough to be ignored, choose M so that M> N + 1.

[Equation 8]

(Formula 8)

Is satisfied. The arg port means extraction of declination. I (x, y) is the formula when = pd / M

P

A value of 7. d and z are known, A (x, y) when there is no object (i.e. _φ (χ, Υ)

twenty three

= 0) can be obtained in advance by performing the same measurement. Therefore, φ (x, y) can be obtained from the above.

However, arc tangent calculation is performed in the extraction of the declination of Equation 8. Since the range of the arc tangent is -π to π, when the refraction by the subject is somewhat large (in the case of a moire image, when the amount of deformation of the moire fringes exceeds the interval of the moire fringes), In adjacent pixels, a jump from -π to π (or π force is also -π) may appear. In this case, 2 π is added (or subtracted) to one of the adjacent pixels to remove the jump (called unwrapping) for the entire image.

FIG. 5 shows a phase shift fine image acquired by computer simulation under the conditions of the above-described embodiment. Figure 6 shows the configuration of the phantom used at this time. This is a model of a phantom that is used for accuracy control of general breast cancer diagnostic equipment. It is. This phantom consists of a homogeneous base material (matrix) in which an object (structure) with the composition and shape shown in Fig. 6 (b) is mixed. The schematic shape of the tissue is shown in Fig. 6 (a). Each organization in Fig. 6 (a) is numbered corresponding to the explanation in Fig. 6 (b).

[0051] On the other hand, an X-ray absorption image simulated with the same exposure dose as in Fig. 5 is shown in Fig. 7 for comparison. Compared to Fig. 5, it can be seen that X-ray absorption clearly makes the image unclear.

[0052] What is phase shift image Φ (x, y) and phase shift differential image φ (x, y)?

[Equation 9]

Are related. X is the direction in which the diffraction grating is translated by the fringe scanning method. Thus, the phase shift image Φ (χ, γ) is given by integrating φ (φ, _Υ ) along the X axis. This is Page 2 of Tagawa.

[0053] The phase-shifted image Φ (χ, γ) has a refractive index distribution of the subject as n (x, y, z)

[Equation 10]

^z (Equation 1 0). Here, the z axis is the direction in which the X-ray travels. Tomography is a technique for reconstructing a 3D image of a subject from two or more projection images that can be acquired from multiple projection directions. Since the phase shift image Φ (χ, γ) corresponds to the projected image of ln (x, y, z), if a phase shift distribution image is obtained from multiple projection directions, a solid that represents n ( _X , y, z) The image is reconstructed (step 3). Note that step 2 can be incorporated into step 3. In this case, it is realized by devising the filter function used in the tomograph reproduction algorithm.

[0054] The imaging method described above is not meaningless unless it proceeds to step 3. An image (raw image) directly obtained by the X-ray image detector 4 of the above-described embodiment, a phase shift differentiation. Both image Φ (x, y) and phase shift image Φ (χ, γ) are fully utilized depending on the purpose of imaging. It can be done.

It should be noted that the description of the above-described embodiment and examples is merely an example, and does not indicate a configuration essential to the present invention. The configuration of each part is not limited to the above as long as the gist of the present invention can be achieved.

[0056] For example, the components in each of the embodiments described above may be integrated with other elements as devices or parts as long as they exist as functional elements, and may be integrated by a plurality of parts. One element has been realized!

Brief Description of Drawings

FIG. 1 is an explanatory diagram showing a schematic configuration of an X-ray imaging apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the apparatus shown in FIG.

FIG. 3 is an explanatory diagram showing an intensity distribution and an arrangement position of the second grating when an X-ray having a wavelength of 0.05 passes through the first grating.

FIG. 4 is a graph showing the spectral transmittance of X-rays transmitted through the first grating and the second grating of the present embodiment. The vertical axis represents the transmittance at each wavelength (the X-ray intensity before transmission is 1). The horizontal axis is the wavelength (unit: nm).

FIG. 5 is a diagram showing a phase shift differential image obtained by simulation based on the apparatus of the present embodiment.

6 is an explanatory diagram showing a phantom configuration assumed in the simulation of FIG. 5. FIG.

FIG. 7 is a simulation of an X-ray absorption image for the phantom of FIG.

Explanation of symbols

[0058] 1 X-ray source

2 Subject (object)

3 First lattice

d Period at the line of the first lattice

4 Second lattice

d Period at the line of the second lattice

2

5 Third lattice Periodic X-ray image detector in the third grating line.

Claims

Claims [1] An X-ray source, a first grating, a second grating, a third grating, and an X-ray image detector are provided, and the X-ray source is directed toward the first grating. It is configured to irradiate an X-ray cone beam, the first grating is a phase type diffraction grating or an amplitude type diffraction grating, and the second grating is an amplitude type diffraction grating, The second grating is configured to diffract the X-ray diffracted by the first grating, and the period of the line in the second grating is formed by the X-ray diffracted by the first grating. The period of the periodic intensity pattern is substantially the same, and the second grating is configured to be able to form a periodic intensity pattern by X-rays diffracting the second grating, The third lattice is an amplitude-type lattice, and the third lattice is the second case. The periodic intensity pattern formed by the X-rays diffracted at is arranged at substantially the same position as the position where the periodic pattern is formed, and the period of the line in the third grating is the period formed by the second grating The X-ray image detector detects X-rays transmitted through the third grating from the periodic intensity patterns formed by the second grating. An X-ray imaging apparatus characterized by the above. [2] The X-ray imaging apparatus according to [1], wherein the X-rays irradiated from the X-ray source are continuous X-rays. [3] The third grating can be translated along the plane of the grating and along the direction in which the periodic structure is formed, and the X-ray image detector has the third grating translated. The X-ray imaging apparatus according to claim 1 or 2, wherein the intensity of X-rays transmitted through the third grating, which changes depending on the measurement, is sequentially measured. [4] Using an X-ray source, a first grating, a second grating, a third grating, and an X-ray image detector, the subject is either between the X-ray source and the third grating. The first grating is a phase type diffraction grating or an amplitude type diffraction grating, the second grating is an amplitude type diffraction grating, and the period of the line in the second grating is: The period of the periodic intensity pattern formed by the X-rays diffracted by the first grating is substantially the same; the third grating is an amplitude-type grating; The period of the line is substantially the same as the period of the periodic intensity pattern formed by the X-ray diffracted by the second grating, and further includes the following steps:

(2) The second grating is arranged at a position where a periodic intensity pattern is formed by the first grating with respect to a quasi-monochromatic X-ray having a spectrum centered on a desired energy contained in the continuous X-ray. Step;

(4) disposing the third grating at a position where the periodic intensity pattern of the second grating is formed;