JP2006334069A - X-ray imaging method and apparatus - Google Patents

Abstract

An X-ray imaging method and apparatus capable of displaying an X-ray phase-difference image transmitted through a subject at a low exposure dose without the need to construct and adjust an optical system with an accuracy equal to or less than the wavelength of X-rays. To do.
An X-ray source that emits a coherent beam-like X-ray 2 and a plane orthogonal to the optical axis of the X-ray at a plurality of positions along the optical axis after the X-ray 2 passes through a subject 3 An X-ray imaging device 4 for measuring an intensity distribution, a phase difference calculating device 5 for calculating an X-ray phase distribution from the X-ray intensity distribution, and an image display device 6 for displaying an image of the subject by the phase distribution. It is set as the structure provided with.
[Selection] Figure 1

Description

  The present invention relates to an X-ray image capturing method and apparatus for capturing an image of a subject by X-ray phase change caused by the dielectric constant of the subject when X-rays pass through the subject.

  The technique for photographing an object such as a human body using X-rays has been rapidly developed until recently. Image processing technology using a computer plays a major role in this field. Conventional X-ray imaging apparatuses project the difference in the X-ray absorption rate of a subject on a detector such as a film or an imaging plate. Recently, however, the use of coherent X-rays with a single energy, such as synchrotron radiation, has been developed. In X-ray imaging, not only detection of intensity difference due to absorption but also imaging attempts using local phase plane distortion of transmitted X-rays due to the difference in dielectric constant of the subject have been started. .

  Imaging by phase difference detection has received the following advantages compared to the absorption method. (1) The detection sensitivity is greatly improved compared to the conventional absorption method. (2) As a result, abnormalities in the soft tissue can be detected, and blood flow can be observed without using a sensitizer. (3) Since it is not necessary for the subject to absorb X-rays, the exposure dose to the human body is greatly reduced.

  Hereinafter, conventional X-ray phase difference imaging will be described with reference to the drawings. In the conventional example shown in FIG. 8, the X-ray 2 is divided into two using the splitter 10, one is projected onto the subject 3, the other is guided to another path, and both are made to interfere with each other by the analyzer 12. A change in the phase of the X-rays observed is observed by the detector 13. This technique is common in the wavelength region of microwaves and the like.

  As described in Non-Patent Document 1 below, Mr. Momose and others demonstrated phase contrast imaging by interferometry in 1995 using a semi-transparent mirror made from a single crystal of silicon. However, since the wavelength of X-ray is about 1 mm, a highly accurate mirror system is required. At present, since the X-ray optical system is cut out from a single crystal of silicon as a single unit, the system is very expensive, and the production of mirrors with an area of about 3cm x 3cm is the limit. The desired 10cm x 10cm image capture is still far away.

  FIG. 9 shows a schematic diagram of a phase contrast imaging apparatus of a second conventional example. This is described in Non-Patent Document 2 below, but with the configuration of FIG. 9A, the X-ray 2 that has been monochromated using the monochromator 9 is localized when passing through the subject 3. Refracted. The refraction angle of the X-ray after transmission is measured by the analyzer 12 and the detector 13 installed downstream of the subject 3, and the result is as shown in FIG. 9B. In this method, since the refraction angle is very small, a high-intensity monochromatic X-ray source is required for accurate measurement, and a long exposure time is required. As a result, the exposure dose increases.

Further, FIG. 10 shows a schematic diagram of the phase contrast imaging method of the third conventional example. In FIG. 10, the monochromatic X-ray 2 is locally refracted when passing through the subject 3. At a position sufficiently away from the subject 3, the transmitted X-ray beam is distorted in the intensity distribution as a result of interference with itself. This distortion includes a change in phase plane that occurs during transmission of the subject 3 as information. Development of a method for deriving phase information from such intensity distribution is expected, but no effective method has been reported so far.
A. Momose, “Demonstration of phase-contrast X-ray Computed tomography using an X-ray interferometer,” Nucl. Instrum. Meth. A352 (1995), 622. R. Fitzgerald, “Phase-sensitive X-ray imaging,” Physics today, Vol. 53 (2000), No. 7, 23.

  As described above, the conventional image capturing apparatus using the phase difference of the X-rays needs to configure the optical system with an accuracy equal to or less than the wavelength of the X-rays. Requires precise work.

  Accordingly, the present invention provides an X-ray imaging method capable of imaging and displaying an X-ray phase difference image transmitted through a subject with a low exposure dose without the need to construct and adjust an optical system with an accuracy equal to or less than the wavelength of X-rays. And an object to provide an apparatus.

  In order to achieve the above object, the invention of claim 1 irradiates a subject with coherent beam-shaped X-rays having a single energy toward a subject and transmits light at a plurality of positions along the optical axis of the X-rays transmitted through the subject. An X-ray imaging method is provided in which an X-ray intensity distribution in a plane orthogonal to the axis is measured, an X-ray phase distribution is calculated from the intensity distribution, and an image of the subject is displayed by the phase distribution.

  According to a second aspect of the present invention, there is provided an X-ray source that emits a coherent beam-shaped X-ray, and an intensity at a plane orthogonal to the optical axis of the X-ray at a plurality of positions along the optical axis after the X-ray is transmitted through the subject. X comprising: an X-ray imaging device for measuring a distribution; a phase difference calculating device for calculating an X-ray phase distribution from the X-ray intensity distribution; and an image display device for displaying an image of the subject by the phase distribution. A line image photographing device is assumed.

  According to a fourth aspect of the present invention, a plurality of coherent beam-shaped X-rays having energy levels are irradiated toward a subject, and the plurality of X-ray intensity distributions on a plane orthogonal to the optical axis of the X-rays transmitted through the subject are obtained. The X-ray imaging method is to measure each energy level, calculate the X-ray phase distribution from the intensity distribution, and display the image of the subject by the phase distribution.

  According to a fifth aspect of the present invention, an X-ray source that emits a plurality of coherent beam-shaped X-rays having a plurality of energy levels, and an intensity distribution on a plane orthogonal to the optical axis after the X-rays are transmitted through the subject, An X-ray imaging device that measures each X-ray, a phase difference calculation device that calculates an X-ray phase distribution from the X-ray intensity distribution, and an image display device that displays an image of the subject by the phase distribution A line image photographing device is assumed.

  According to the present invention, an X-ray imaging method capable of displaying an X-ray phase-difference image transmitted through a subject at a low exposure dose without the need to construct and adjust an optical system with an accuracy equal to or less than the wavelength of X-rays, and An apparatus can be provided.

Hereinafter, first to fifth embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing an X-ray imaging method and apparatus according to the first embodiment of the present invention. That is, the X-ray imaging apparatus of the present embodiment includes an X-ray generator 1 that generates monochromatic X-rays toward the subject 3 and a subject that is movable in the propagation direction of the X-ray 2 and at least two different positions. 3, an X-ray two-dimensional imaging device 4 capable of capturing three-dimensional images, a phase difference calculation device 5 and an image display device 6.

  The intensity distribution of the X-ray 2 at the position of the subject 3 is measured in advance and is assumed to be known. Since the dielectric constant inside the subject 3 changes locally, the phase plane of the X-ray 2 changes locally as it propagates inside the subject 3. As a result, the phase plane of the X-ray 2 transmitted through the subject 3 is distorted in accordance with the dielectric constant distribution in the subject 3. Therefore, as a result of self-interference resulting from distortion of the phase plane during transmission, the two-dimensional intensity distribution in the plane perpendicular to the optical axis of the transmitted X-ray changes along the propagation direction. This intensity distribution is measured by the imaging device 4.

  In order to obtain the phase distribution from the two-dimensional intensity distribution that changes along the propagation direction, the phase difference calculation device 5 performs the following calculation. Here, the first and second positions from the side closer to the subject 3 and the intensity distributions at the respective positions are referred to as first and second intensity distributions. First, assuming a uniform phase distribution with respect to the first intensity distribution, the distribution at the second position is calculated by solving the wave equation. Next, the phase calculated from the first intensity distribution is given to the second intensity distribution, and the distribution at the position of the subject 3 is calculated.

  This process is repeated until the phase distribution converges in all cross sections. The phase distribution converged at the position of the subject 3 represents the phase changed by the subject transmission. This phase change is displayed on the image display device 6 as an image of the subject 3.

  In principle, in order to calculate a phase distribution from a single energy X-ray beam, intensity distributions photographed at three locations are required. In X-ray imaging, the intensity distribution of X-rays at the subject position can be measured in advance and does not change with each imaging, so the intensity distributions in two cross sections that are substantially perpendicular to the X-ray axis are additionally captured. That's fine.

のように求めることができる。 A flowchart shown in FIG. 2 shows a method for calculating the phase distribution from three distributions of the intensity distribution measured in advance at the subject position and the intensity distribution measured on the first and second imaging planes along the X-ray optical axis. Will be described. If the wave function of the X-ray passing through the subject position is U (x, y, z), this U (x, y, z) is obtained. From the subject position and the power distributions P ₀ (x, y), P ₁ (x, y), and P ₂ (x, y) measured at the first and second imaging planes, the amplitude of the X-ray beam at each position , U ₀ (x, y), U ₁ (x, y), U ₂ (x, y),

Can be obtained as follows.

と仮定して、第１撮影面における振幅分布Ｕ₀ ¹(x,y,z₁)を計算する（ステップＳ２）。（文書作成ソフトの制約によりギリシャ文字ファイの大文字と小文字を併用する。）ここでiは純虚数である。被写体位置の派動関数から第１撮影面における振幅分布を計算する場合には、Ｘ線の自由空間における伝播計算を用いて行なう。ここでは２つの方法について説明する。 The convergence calculation is performed according to the following procedure. First, the phase distribution Φ ₀ ¹ (x, y) of the X-ray beam at the subject position is set using an appropriate trial function (step S1). Hereinafter, the subscript of the function represents the subject position (subscript 0), the first photographing surface (subscript 1), and the second photographing surface (subscript 2), and the superscript represents the number of iterations. In the flowchart, the phase distribution is uniform and 0 is assumed. Using the assumed Φ ₀ ¹ (x, y) and the amplitude U ₀ (x, y) at the subject position, the wave function of the X-ray beam at the subject position is obtained.

Assuming that, the amplitude distribution U ₀ ¹ (x, y, z ₁ ) on the first imaging plane is calculated (step S2). (The uppercase and lowercase letters of the Greek letter Phi are used together due to restrictions in the document creation software.) Here, i is a pure imaginary number. When calculating the amplitude distribution on the first imaging surface from the subject function, the propagation calculation in the X-ray free space is performed. Here, two methods will be described.

と表せる。ここでｋはＸ線の自由空間における波数である。 The first is a method using Fourier transform.
The amplitude distribution U ₀ ¹ (x, y, z ₁ ) on the first imaging plane is obtained by using the amplitude U ₀ (x, y).

It can be expressed. Here, k is the wave number in the free space of X-rays.

The amplitude distribution U ₀ ¹ (x, y, z ₁ ) can be calculated by obtaining this set by general numerical integration. Although it was described in the infinite integration range on the equation, the integration range is limited due to numerical integration. At this time, it is desirable to integrate over a region that is about four times the area of the imaging surface of the imaging device. The same applies to the following numerical integration.

と表せる。この式を一般的な数値積分により求めることにより、振幅分布Ｕ₀ ¹(x,y,z₁)を計算する。 The second method uses the Fresnel-Kirchhoff diffraction integration formula.
The amplitude distribution U ₀ ¹ (x, y, z ₁ ) on the first imaging plane is obtained by using the amplitude U ₀ (x, y).

It can be expressed. The amplitude distribution U ₀ ¹ (x, y, z ₁ ) is calculated by obtaining this equation by general numerical integration.

このようにして求められた振幅分布Ｕ₀ ¹(x,y,z₁)から第１撮影面における位相分布Φ₁ ¹(x,y)を
Φ₁ ¹(x,y)=arg{Ｕ₀ ¹(x,y,z₁)}
のように求める（ステップＳ３）。 When the X-ray beam is localized in the vicinity of the Z axis, it can also be obtained using the following equation.

From the amplitude distribution U ₀ ¹ (x, y, z ₁ ) obtained in this way, the phase distribution Φ ₁ ¹ (x, y) on the first imaging plane is obtained as Φ ₁ ¹ (x, y) = arg {U ₀ ¹ (x, y, z ₁ )}
(Step S3).

と仮定し、第２撮影面における振幅分布Ｕ₁ ¹(x,y,z₂)を計算する（ステップＳ４）。得られた分布から第２撮影面における位相分布Φ₂ ¹(x,y)を
Φ₂ ¹(x,y)=arg{Ｕ₁ ¹(x,y,z₂)}
のように計算する（ステップＳ５）。 Next, using the obtained phase distribution Φ ₁ ¹ (x, y) and the amplitude U ₁ (x, y) measured on the first imaging plane, the wave function of X-rays on the first imaging plane is obtained.

And the amplitude distribution U ₁ ¹ (x, y, z ₂ ) on the second imaging surface is calculated (step S4). From the obtained distribution, the phase distribution Φ ₂ ¹ (x, y) on the second imaging plane is expressed as Φ ₂ ¹ (x, y) = arg {U ₁ ¹ (x, y, z ₂ )}
(Step S5).

を仮定し、被写体位置の波動関数から第１撮影面における振幅分布を求めた時と同様にＸ線の自由空間における伝播計算により撮影位置における分布Ｕ₂ ¹(x,y,z₀)を計算する（ステップＳ７）。さらに位相分布Φ₀ ²(x,y)を
Φ₀ ²(x,y)=arg{Ｕ₂ ¹(x,y,z₀)}
のように計算する（ステップＳ８）。 Subsequently, using the phase distribution Φ ₂ ¹ (x, y) and the amplitude distribution U ₂ (x, y) on the second imaging plane, an X-ray wave function on the second imaging plane.

And the distribution U ₂ ¹ (x, y, z ₀ ) at the imaging position is calculated by the propagation calculation in the X-ray free space in the same manner as when the amplitude distribution on the first imaging surface is obtained from the wave function of the subject position. (Step S7). Further, the phase distribution Φ ₀ ² (x, y) is changed to Φ ₀ ² (x, y) = arg {U ₂ ¹ (x, y, z ₀ )}
(Step S8).

を仮定して、Ｘ線の自由空間における伝播計算により第１撮影面における分布Ｕ₀ ²(x,y,z₁)および位相分布Φ₁ ²(x,y)を算出する。以下計算が収束するまで反復する。 Similarly, the X-ray wave function at the subject position using the phase distribution Φ ₀ ² (x, y) and the amplitude distribution U ₀ (x, y) at the subject position.

As a result, the distribution U ₀ ² (x, y, z ₁ ) and the phase distribution Φ ₁ ² (x, y) on the first imaging plane are calculated by propagation calculation in the free space of X-rays. Repeat until the calculation converges.

ここでそれぞれ、j-1回目に算出された位相分布とj回目に算出された位相分布の差の分散がεよりも小さくなることを意味している。 Various convergence determinations can be considered. Here, the convergence determination focusing on the phase distribution will be described. In the series of iterative calculations described above, the following various quantities are calculated for the phase distribution, and the iteration is terminated when all the evaluation quantities become smaller than the preset determination condition ε.

Here, it means that the variance of the difference between the phase distribution calculated at the j-1th time and the phase distribution calculated at the jth time becomes smaller than ε.

  In this method, an axis through which X-rays propagate is necessary when calculating the phase distribution. However, since the center of gravity of the X-ray power density can be obtained numerically from the measurement data, the installation accuracy of the imaging device 4 is not so important. is not. As a result, the manufacturing cost of the optical system can be greatly reduced. The imaging device 4 may shoot at at least two different locations. However, by further moving the imaging device 4 and shooting at three or more positions, the calculation accuracy of the phase distribution is improved.

  Thus, according to the present embodiment, it is possible to obtain phase information from the change in intensity distribution along the optical axis of the X-ray and obtain an image of the subject 3. In addition, the optical system can be simplified, and manufacturing and photographing costs can be greatly reduced.

(Second Embodiment)
Next, an X-ray imaging method and apparatus according to the second embodiment of the present invention will be described with reference to FIG. That is, the X-ray imaging apparatus according to the present embodiment includes an X-ray generator 1 that generates monochromatic X-rays and two-dimensionally arranged at at least two different positions along the propagation direction of the X-ray 2. X-ray imaging devices 4a and 4b, a phase difference calculation device 5 and an image display device 6 are included.

  This embodiment is effective when the energy of the X-ray 2 is sufficiently high and the influence of the imaging apparatus transmission is small. In the first embodiment, the intensity distribution at different positions is photographed by moving the imaging device 4, but in the present embodiment, photographing is possible at the same time. The method for deriving the phase change at the sample position from the position of the subject 3 and the intensity distribution in the first and second imaging devices 4a and 4b is the same as in the first embodiment.

(Third embodiment)
FIG. 4 shows an X-ray imaging apparatus according to the third embodiment of the present invention. In the third embodiment, the X-ray 2 after passing through the subject 3 is divided by using a semi-transparent mirror 7 that reflects a part of the X-ray and passes a part thereof, so that the X-rays at different propagation positions are divided. Measure the intensity distribution. The method for calculating the phase distribution from the obtained intensity distribution is the same as in the first embodiment. The X-ray imaging apparatus of this embodiment is effective when the influence of X-ray scattering when passing through the imaging apparatus can be ignored.

(Fourth embodiment)
Next, an X-ray imaging method and apparatus according to a fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, the intensity of the X-ray 2 at the location of the subject 3 is changed using the slit device 8 placed in front of the X-ray generator 1. X-ray imaging is performed at least at one location. The intensity distribution of the X-rays after passing through the subject 3 changes along the propagation direction due to self-interference, but if the intensity at the location of the subject 3 is different, the intensity distribution after passing through the subject 3 is also different. FIG. 4 shows some examples of different slits 8a, 8b, and 8N. Among them, at least two types are used.

  The phase difference calculation method is slightly different from that in the first to third embodiments. For example, an example using the slit 8a and the slit 8b among the slits shown in FIG. 4 will be described. The intensity distribution of the X-ray 2 at the position of the subject 3 with respect to the slit 8a and the slit 8b is measured in advance and is known. First, a uniform phase distribution is given to the intensity distribution at the position of the subject 3 with respect to the slit 8a, and the intensity distribution at the position of the imaging device 4 is calculated. Next, the phase distribution calculated from the intensity distribution at the subject 3 position is given to the intensity distribution at the position of the imaging device 4 to calculate the phase distribution at the subject 3 position.

  Subsequently, a phase distribution calculated from the intensity distribution of the imaging position of the slit 8a is given to the intensity distribution of the subject 3 position with respect to the slit 8b, and the intensity distribution at the imaging position of the slit 8b is calculated. Further, the phase distribution at the subject 3 position is calculated by giving the phase calculated from the intensity distribution at the subject 3 position to the intensity distribution at the imaging position. The above is regarded as one series and it moves to iterative calculation.

  The phase distribution calculated from the intensity distribution at the imaging position with respect to the slit 8b is given to the intensity distribution at the position of the subject 3 with respect to the slit 8a to calculate the phase distribution at the imaging position. The above procedure is repeated until the phase distribution converges at all positions. The phase distribution finally obtained at the position of the subject 3 is obtained. This phase distribution is displayed on the image display device 6 as an image of the subject 3.

A phase distribution calculation method according to the present embodiment will be described with reference to the flowchart shown in FIG. In this embodiment, an example using slits 8a and 8b among the slits shown in FIG. 5 will be described. The X-ray distribution at the subject position with respect to the slit 8a and the slit 8b is assumed to be known in both the intensity distribution and the phase distribution, and the distribution function of the X-ray at the subject position when the slits 8a and 8b are used is U ₀ (x, y), Let V ₀ (x, y). Unlike the first to third embodiments, U ₀ (x, y) and V ₀ (x, y) are complex numbers. The phase distribution can also be calculated by measuring the intensity distribution at a plurality of locations with no subject placed using the devices of the first to third embodiments.

と仮定し（ステップＳ２）、撮影面における分布Ｕ₀ ¹(x,y,z₁)を計算する。（文書作成ソフトの制約によりギリシャ文字ファイの大文字と小文字を併用する。）得られた分布から位相分布を
Φ₀ ¹(x,y)=arg{Ｕ₀ ¹(x,y,z₁)}
のように算出する（ステップＳ３）。次に、スリット８ａに対して撮影面で得られた電力分布Ｐ_A(x,y)から求めた振幅分布Ｕ₁(x,y)と上で求めた位相分布Φ₁ ¹(x,y)を用いて、撮影面における分布を

と仮定し（ステップＳ４）、被写体位置における分布Ｕ₁ ¹(x,y,z₀)を計算し、位相分布
φ₀ ¹(x,y)=arg{Ｕ₁ ¹(x,y,z₀)}-arg{Ｕ₀(x,y)}
を求める（ステップＳ５）。ここで被写体位置におけるＸ線Bの分布を、

と仮定し（ステップＳ６）、撮影面における分布Ｖ₀ ¹(x,y,z₁)を計算し、撮影面における位相分布
φ₁ ¹(x,y)=arg{Ｖ₀ ¹(x,y,z₁)}
を得る（ステップＳ７）。続いて、スリット８ｂに対して撮影面で得られた電力分布Ｐ_B(x,y)から求めた振幅分布Ｖ₁(x,y)と上で求めた位相分布φ₁ ¹(x,y)を用いて、撮影面における分布を

と仮定し（ステップＳ９）、被写体位置における分布Ｖ₁ ¹(x,y,z₀)を計算し、位相分布
Φ₀ ²(x,y)=arg{Ｖ₁ ¹(x,y,z₀)}-arg{Ｖ₀(x,y)}
を得る（ステップＳ１０）。以上が反復計算の１シリーズとなる。 In the following description, the wave function of the X-ray A when using the slit 8a is U (x, y, z), and the wave function of the X-ray B when using the slit 8b is V (x, y, z). And First, Φ ₀ ¹ (x, y) = 0 as a trial function of the phase distribution for the slit 8a
(Step S1) and the distribution of the X-ray A at the subject position

(Step S2) and the distribution U ₀ ¹ (x, y, z ₁ ) on the imaging plane is calculated. (Uppercase and lowercase letters of Greek letter Phi are used together due to restrictions of the document creation software.) Φ ₀ ¹ (x, y) = arg {U ₀ ¹ (x, y, z ₁ )} from the obtained distribution
(Step S3). Next, the amplitude distribution U ₁ (x, y) obtained from the power distribution P _A (x, y) obtained on the imaging surface with respect to the slit 8a and the phase distribution Φ ₁ ¹ (x, y) obtained above. To

(Step S4), the distribution U ₁ ¹ (x, y, z ₀ ) at the subject position is calculated, and the phase distribution φ ₀ ¹ (x, y) = arg {U ₁ ¹ (x, y, z ₀₎ )}-arg {U ₀ (x, y)}
Is obtained (step S5). Here, the distribution of X-rays B at the subject position is

(Step S6), the distribution V ₀ ¹ (x, y, z ₁ ) on the imaging plane is calculated, and the phase distribution φ ₁ ¹ (x, y) = arg {V ₀ ¹ (x, y) on the imaging plane is calculated. , z ₁ )}
Is obtained (step S7). Subsequently, the amplitude distribution V ₁ (x, y) obtained from the power distribution P _B (x, y) obtained on the imaging surface with respect to the slit 8b and the phase distribution φ ₁ ¹ (x, y) obtained above. To

(Step S9), the distribution V ₁ ¹ (x, y, z ₀ ) at the subject position is calculated, and the phase distribution Φ ₀ ² (x, y) = arg {V ₁ ¹ (x, y, z ₀₎ )}-arg {V ₀ (x, y)}
Is obtained (step S10). The above is one series of iterative calculations.

を仮定して（ステップＳ２）、撮影面の分布Ｕ₀ ²(x,y,z₁)を計算し、位相を求めてから被写体位置の分布を計算、以下Ｘ線ＡとＸ線Ｂについての反復計算を収束するまで交互に繰り返す。微小な実数εを判定条件とし、

が満たされた時点（ステップＳ８）で反復計算を終了する。 The second series of calculations is based on the known distribution U ₀ (x, y) at the subject position and Φ ₀ ² (x, y) obtained above.

(Step S2), the distribution U ₀ ² (x, y, z ₁ ) of the imaging plane is calculated, and the distribution of the subject position is calculated after obtaining the phase. Hereinafter, the X-ray A and X-ray B are calculated. Iterative calculation is repeated alternately until convergence. Using a small real number ε as a judgment condition,

When the above is satisfied (step S8), the iterative calculation ends.

(Fifth embodiment)
Next, an X-ray imaging method and apparatus according to a fifth embodiment of the present invention will be described with reference to FIG. The fifth embodiment includes a multi-energy X-ray generator 1a that generates X-rays of at least two types of energy levels, an X-ray imaging device 4, a phase difference calculation device 5, and an image display device 6. .

  Since the phase distortion in the subject 3 varies depending on the wavelength, the local dielectric constant inside the subject 3 can be estimated by observing changes in the intensity distribution for a plurality of types of X-ray energy. The algorithm of the phase difference calculation performed in the phase difference calculation device 4 is as follows.

  X-rays of a plurality of types of X-ray energy are respectively referred to as first and second X-rays, and the wavelengths of the X-rays corresponding thereto are respectively referred to as first and second X-ray wavelengths. The intensity distribution of the first and second X-rays at the position of the subject 3 is measured in advance and is assumed to be known.

  First, a uniform phase distribution is given to the intensity distribution at the subject position of the first X-ray, and the distribution at the position of the imaging device 4 is calculated. Next, the phase distribution calculated from the distribution of the subject position is given to the intensity distribution observed at the position of the imaging device 4, and the distribution at the subject position is calculated.

  If the two types of X-ray energy are selected to be relatively close, it can be considered that the dielectric constant of the subject shows almost the same value for both X-rays. Therefore, as the next process, the intensity distribution of the second X-ray at the object position is changed to the phase distribution of the object position calculated from the imaging position to the first X-ray (first X-ray wavelength) / (first 2), the distribution of the second X-ray at the imaging position is calculated.

  Further, the phase calculated from the subject position is given to the intensity distribution of the second X-ray measured at the imaging position, and the second X-ray distribution at the subject position is calculated. Subsequently, the second X-ray phase distribution at the subject position calculated from the imaging position is calculated as (second X-ray wavelength) / (first X-ray intensity distribution). X-ray wavelength) is given, and the distribution of the first X-ray at the imaging position is calculated.

  Thereafter, this procedure is repeated, and is finished when the two types of X-ray phase distributions converge at all positions. The obtained phase distribution represents a change in the dielectric constant inside the subject 3, and this is displayed as an image on the image display device 6.

  As described above, in all the embodiments, by obtaining the center of gravity of the X-ray intensity distribution, the optical axis of X-ray propagation can be obtained, and the coordinate system for distribution calculation can be accurately adjusted at each position. As a result, the optical system can be simplified, and the system can be manufactured at a very low cost. In the first and second embodiments, there are two imaging positions. In the third, fourth, and fifth embodiments, an example in which the imaging position is one is shown. By photographing at the position, it is possible to improve the phase distribution estimation and hence the accuracy of the image.

1 is a diagram illustrating a configuration of an X-ray imaging apparatus according to a first embodiment of the present invention. 3 is a flowchart showing an X-ray image capturing method according to the first embodiment of the present invention. The figure which shows the structure of the X-ray imaging apparatus of the 2nd Embodiment of this invention. The figure which shows the structure of the X-ray imaging apparatus of the 3rd Embodiment of this invention. The figure which shows the structure of the X-ray imaging apparatus of the 4th Embodiment of this invention. The flowchart which shows the X-ray-image imaging method in the 4th Embodiment of this invention. The figure which shows the structure of the X-ray imaging apparatus of the 5th Embodiment of this invention. The figure explaining the 1st prior art example regarding X-ray phase contrast imaging. The 2nd prior art example regarding a X-ray phase contrast imaging is demonstrated, (a) is a figure which shows the structure of an apparatus, (b) is a graph which shows the relationship between the angle with respect to the optical axis of a X-ray, and a reflectance. The figure explaining the 3rd prior art example regarding X-ray phase contrast imaging.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... X-ray generator, 1a ... Multiple energy X-ray generator, 2 ... X-ray, 3 ... Subject, 4, 4a, 4b ... X-ray two-dimensional imaging device, 5 ... Phase difference calculating device, 6 ... Image display apparatus 7, translucent mirror, 8, 8a, 8b, 8N ... slitting device, 9 ... monochromator, 10 ... splitter, 11 ... semi-transparent mirror, 12 ... analyzer, 13 ... detector.

Claims (6)

  A single energy coherent beam-shaped X-ray is irradiated toward the subject, and the X-ray intensity distribution in a plane orthogonal to the optical axis is measured at a plurality of positions along the optical axis of the X-ray transmitted through the subject. An X-ray imaging method comprising: calculating an X-ray phase distribution from the intensity distribution and displaying an image of the subject by the phase distribution.   X-ray source that emits coherent beam-like X-rays, and X-ray imaging that measures intensity distribution in a plane orthogonal to the optical axis of the X-rays at a plurality of positions along the optical axis after the X-rays are transmitted through the subject An X-ray image comprising: an apparatus; a phase difference calculation device that calculates an X-ray phase distribution from the X-ray intensity distribution; and an image display device that displays an image of the subject by the phase distribution. Shooting device.   The X-ray imaging apparatus according to claim 2, further comprising a semi-transmissive mirror that reflects a part of the X-ray and passes a part between the subject and the X-ray imaging apparatus.   A plurality of energy levels of coherent beam-shaped X-rays are irradiated toward the subject, and the X-ray intensity distribution in a plane perpendicular to the optical axis of the X-rays transmitted through the subject is measured for each of the plurality of energy levels. An X-ray imaging method comprising: calculating an X-ray phase distribution from the intensity distribution and displaying an image of the subject by the phase distribution.   X-ray imaging for measuring, for each of the plurality of energy levels, an X-ray source that emits a coherent beam-shaped X-ray having a plurality of energy levels, and an X-ray intensity distribution on a plane orthogonal to the optical axis after the subject is transmitted An X-ray image comprising: an apparatus; a phase difference calculation device that calculates an X-ray phase distribution from the X-ray intensity distribution; and an image display device that displays an image of the subject by the phase distribution. Shooting device.   6. The X-ray imaging apparatus according to claim 5, further comprising a slit device that changes an X-ray intensity distribution at a subject position between the X-ray source and the subject.

Images