JP2018102565A - X-ray phase contrast imaging device - Google Patents

Abstract

Provided is an X-ray phase contrast imaging apparatus capable of generating an X-ray phase contrast image in which the contrast of a specific part of a subject is enhanced. An X-ray phase contrast imaging apparatus (100) is arranged between an X-ray source (1), a detector (5) for detecting X-rays, and between the X-ray source (1) and the detector (5). From the plurality of gratings including the phase grating 2 irradiated with X-rays and the absorption grating 4 irradiated with X-rays passing through the phase grating 2 and the intensity distribution of X-rays detected by the detector 5, the X-ray phase An image processing unit 6 for generating a contrast image, wherein the image processing unit 6 is based on the amount of change in the phase of X-rays at the specific portion 3 a of the subject 3, and the periodic direction of the grating that contributes relatively strongly to the contrast generation Is configured to generate an X-ray phase contrast image in which the specific portion 3a is emphasized from an image captured by selecting a plurality of relative positions in. [Selection diagram] FIG.

Description

  The present invention relates to an X-ray phase contrast imaging apparatus, and in particular, an X-ray phase contrast image is obtained by a method of creating a reconstructed image (a fringe scanning method) from a plurality of images obtained by scanning a grating at regular intervals. The present invention relates to an X-ray phase contrast imaging apparatus.

  2. Description of the Related Art Conventionally, an X-ray phase contrast imaging apparatus that obtains an X-ray phase contrast image by a method of creating a reconstructed image from a plurality of images obtained by scanning a grid at regular intervals (a fringe scanning method) is known. (For example, refer to Patent Document 1).

  Patent Document 1 discloses an X-ray phase contrast imaging apparatus that obtains an X-ray phase contrast image from nine images obtained by translating a grating at regular intervals of 1/9 period in the periodic direction. The X-ray phase contrast image includes an absorption image, a phase differential image, and a dark field image. The “phase differential image” is an image formed based on a phase shift of the X-ray generated when the X-ray passes through the subject. A “dark field image” is a Visibility image obtained by a change in Visibility based on small-angle scattering of an object. A dark field image is also called a small angle scattered image. “Visibility” refers to the sharpness of interference fringes.

JP 2012-16370 A

  However, there is a need for more clearly grasping the internal structure of a subject in a medical field or nondestructive inspection, and a phase generated by a conventional X-ray phase contrast imaging apparatus as described in Patent Document 1 above. There has been a demand for an image in which the characteristic points of the phase differential image and the dark field image (contrast of phase shift and change in visibility (change in interference fringe definition)) are more emphasized than the differential image and the dark field image.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to generate an X-ray phase contrast image in which the contrast of a specific part of a subject is emphasized. A line phase contrast imaging apparatus is provided.

  As a result of intensive studies by the inventors of the present application, when generating an X-ray phase contrast image using the fringe scanning method, the grating is scanned so as to be at a predetermined relative position that is non-uniformly spaced with respect to the period of the grating. In this case, the knowledge that an X-ray phase contrast image in which the contrast of a specific part of the subject is enhanced can be generated can be obtained. Based on this knowledge, the following invention has been conceived. That is, an X-ray phase contrast imaging apparatus according to one aspect of the present invention is disposed between an X-ray source, a detector that detects X-rays emitted from the X-ray source, and the X-ray source and the detector. A plurality of gratings including a first grating for forming a self-image and a second grating for causing interference with the self-image of the first grating by X-rays emitted from the X-ray source, and detection by a detector And an image processing unit that generates an X-ray phase contrast image from the intensity distribution of the X-rays, and the image processing unit is relative to the contrast generation based on the amount of X-ray phase change at a specific part of the subject. An X-ray phase contrast image in which a specific part is emphasized is generated from an image obtained by selecting a plurality of relative positions in the periodic direction of the grating that strongly contribute to the frequency and arranging a plurality of gratings at the plurality of relative positions. It is configured.

  Here, the X-ray phase contrast image is generated based on the change amount of the X-ray phase and the change in Visibility (definition of interference fringes) due to the specific part of the subject. Therefore, if the amount of change in the X-ray phase at a specific part of the subject is known, the approximate phase that contributes to the generation of contrast can be obtained. Therefore, in the X-ray phase contrast imaging apparatus according to one aspect of the present invention, as described above, the grating structure that contributes relatively strongly to the generation of contrast based on the amount of change in the phase of the X-ray at a specific part of the subject. A plurality of relative positions in the periodic direction can be selected. As a result, an X-ray phase contrast image in which a specific part of the subject is emphasized can be generated from an image captured by arranging a plurality of grids at a plurality of relative positions that contribute relatively strongly to the generation of contrast.

  In the X-ray phase contrast imaging apparatus according to the above aspect, the image processing unit is preferably located at a position that contributes relatively strongly to the generation of contrast selected based on the amount of change in the X-ray phase at a specific part of the subject. An X-ray phase contrast image in which a specific part is emphasized is generated from an image obtained by scanning at least one of the plurality of gratings at non-uniform intervals in the periodic direction of the grating. Here, in the present invention, “non-uniform spacing” refers to an interval at which each relative position does not become a position for equally dividing the period of the grating as a whole when the grating is scanned at a plurality of relative positions. In addition, when an X-ray phase contrast image is generated from an image captured by arranging a plurality of grids at the position where the contrast is most emphasized, the contrast is enhanced in a specific portion of the subject, but the other portions are included in the image. Disappears. With this configuration, it is possible to prevent a plurality of grids from being arranged at a position where the contrast is most emphasized based on a change in the phase of the X-ray at a specific part of the subject. As a result, it is possible to generate an image in which the contrast of a specific part is emphasized while grasping the entire image of the subject.

  In this case, preferably, the image processing unit determines a reference phase based on the amount of change in the phase of the X-ray, and a reference for generating a contrast determined based on the amount of change in the X-ray of the specific part. The X-ray phase contrast image in which a specific part is emphasized is generated from a plurality of images captured by scanning at least one of a plurality of gratings at a predetermined phase at an equal interval from . With this configuration, it is possible to clearly determine the relative positions of a plurality of gratings that contribute to the generation of contrast.

  More preferably, the reference phase is determined by the period of the intensity signal curve obtained from the X-ray intensity distribution and the amount of change in the X-ray phase of the specific part. Here, in the present invention, the “intensity signal curve” is a curve that represents a change in the luminance value of the detected X-ray by scanning the lattice when attention is paid to a certain pixel. According to this configuration, it is possible to determine a reference phase that contributes to the generation of contrast without imaging a plurality of gratings at a large number of relative positions in advance.

  More preferably, the predetermined phase is set in a range less than 1/8 of the period of the intensity signal curve from the vicinity of the reference phase. If comprised in this way, it can prevent arrange | positioning a some grating | lattice in the relative position which divides | segments 1 period of an intensity | strength signal curve equally. As a result, when moving at least one of the plurality of gratings from the reference phase, the plurality of gratings can be arranged at a plurality of relative positions that contribute to the generation of contrast.

  In a configuration in which one of a plurality of gratings is scanned at non-uniform intervals by a predetermined phase from a reference phase for contrast generation determined based on the amount of change in X-rays of the specific part, preferably a plurality of The grating determines a reference phase based on the amount of change in the X-ray phase, and is arranged at a plurality of relative positions scanned by a predetermined phase from the reference phase. If a plurality of grids are arranged in this way, a plurality of predetermined relative positions that contribute to the generation of contrast can be determined in advance, so that a plurality of grids are arranged at a plurality of determined predetermined positions for shooting. Can do. As a result, it is possible to generate a contrast-enhanced image without previously performing imaging by arranging grids at a number of relative positions in advance, so that the imaging time can be shortened and the amount of X-ray exposure can be reduced. .

  Preferably, the image processing unit selects a plurality of images photographed at a position scanned by a predetermined phase from a reference phase, from a plurality of images photographed by scanning any of the plurality of grids. It is configured as follows. With this configuration, it is possible to obtain an image captured by arranging a plurality of grids at a number of relative positions in advance, so that an image scanned by a plurality of predetermined phases from a reference phase (contributes strongly to the generation of contrast). Multiple images can be generated by emphasizing the contrast of a specific part of the subject.

ここで、ｋは、画素値の変化を表す信号曲線の所定点である。また、Ｍは、所定点の総数である。また、Ｉ_k（ｘ、ｙ）は、被写体を配置した場合における所定点の強度信号値であり、下記の式（８）で定義される。また、Ｉ_OK（ｘ、ｙ）は、被写体を配置しない場合における所定点の強度信号値である。また、ｘ、ｙは、検出器５の検出面上におけるＸ線の照射軸方向に直交する面内の座標位置である。また、Θ_kは、強度信号曲線の所定点の位相である。

ここで、ａ_nは、干渉縞の各周波数成分の量である。また、ｄ₁は、第１格子の周期である。また、ｚ₀は、第１格子と第２格子との距離である。
このように構成すれば、上記式（１）および（２）を定義することにより、非等間隔に格子を走査させた場合でも、従来の縞走査法において使用する上記式（５）〜（７）を用いて、被写体の特定部位のコントラストを強調した画像を生成することができる。 In the X-ray phase contrast imaging apparatus according to the above aspect, preferably, when the following expressions (1) to (4) are defined, the image processing unit is specified using the following expressions (5) to (7): An X-ray phase contrast image in which the region is emphasized is generated.

Here, k is a predetermined point of a signal curve representing a change in pixel value. M is the total number of predetermined points. I _k (x, y) is an intensity signal value at a predetermined point when the subject is arranged, and is defined by the following equation (8). I _OK (x, y) is an intensity signal value at a predetermined point when no subject is arranged. X and y are coordinate positions in a plane orthogonal to the X-ray irradiation axis direction on the detection surface of the detector 5. Θ _k is the phase of a predetermined point of the intensity signal curve.

Here, a _n is the amount of each frequency component of the interference fringes. D ₁ is the period of the first grating. Z ₀ is the distance between the first grating and the second grating.
With this configuration, by defining the above formulas (1) and (2), the above formulas (5) to (7) used in the conventional fringe scanning method even when the grid is scanned at unequal intervals. ) Can be used to generate an image in which the contrast of a specific part of the subject is emphasized.

In the X-ray phase contrast imaging apparatus according to the above aspect, preferably, the plurality of relative positions are represented by the sign of arg [S (x, y)] in formula (5) and arg [S ₀ (x, y)]. Is determined at a position where the sign of is opposite. By determining the relative position of the lattice in this way, the value of arg [S (x, y)]-arg [S ₀ (x, y)] in equation (5) is increased. That is, the phase shift between when the subject is present and when it is absent increases. Alternatively, since S ₀ (x, y) in Expression (7) is determined to be a position where the minimum value is obtained, S ₀ (x, y) in Expression (7) becomes minimum, so that the entire Expression (7) The value of becomes the maximum. That is, the ratio of Visibility (the sharpness of interference fringes) with and without the subject is maximized. Therefore, contrast can be enhanced. As a result, by generating an X-ray phase contrast image using the images at these relative positions, it is possible to generate an image in which the contrast of a specific part of the subject is emphasized.

  In the X-ray phase contrast imaging apparatus according to the above aspect, preferably, the plurality of gratings further include a third grating disposed between the X-ray source and the first grating. If comprised in this way, the coherency of the X-ray irradiated from an X-ray source can be improved with a 3rd grating | lattice. As a result, it is possible to generate an X-ray phase contrast image in which the contrast of a specific part is enhanced using an X-ray source with a small focal length.

  According to the present invention, as described above, an X-ray phase contrast imaging apparatus capable of generating an X-ray phase contrast image in which the contrast of a specific part of a subject is emphasized can be provided.

1 is a diagram illustrating an overall configuration of an X-ray phase contrast imaging apparatus according to a first embodiment of the present invention. It is the graph (A) which shows an example with a small phase difference in the phase differential image of 1st Embodiment of this invention, and the graph (B) which shows an example with a large phase difference. Graph (A) showing an example where the difference in Visibility (definition of interference fringes) is small in the dark field image of the first embodiment of the present invention and graph showing an example where the difference between Visibility (definition of interference fringes) is large (B ). FIG. 2 is an image view (A) of the subject according to the first embodiment of the present invention viewed from the X-ray irradiation axis direction and an image view (B) of the subject viewed from the X direction. They are a graph (A) in which values calculated based on luminance values with and without an object are plotted on a complex plane, and a graph (B) in which the center of gravity is enlarged. The graph (A) showing the relationship between the phase differential contrast when the phase angle serving as the reference of the first embodiment of the present invention is changed and the case where the predetermined phase is changed, and the relationship between the dark field image contrast and It is a graph (B) shown. FIG. 3 is an image diagram of a phase differential image (A) generated by scanning a grating at equal intervals and a phase differential image (B) generated by scanning a grating at non-uniform intervals in the first embodiment of the present invention. FIG. 3 is an image diagram of a dark field image (A) generated by scanning a grid at equal intervals and a dark field image (B) generated by scanning a grid at non-uniform intervals in the first embodiment of the present invention. It is another example of the image figure of the phase differential image (A) produced | generated by scanning a grating | lattice at equal intervals, and the phase differential image (B) produced | generated by scanning a grating | lattice at non-equal intervals in 1st Embodiment of this invention. . It is another example of the image figure of the dark field image (A) produced | generated by scanning a grating | lattice at equal intervals, and the dark field image (B) produced | generated by scanning a grating | lattice at non-equal intervals in 1st Embodiment of this invention. . It is a figure which shows the whole structure of the X-ray phase contrast imaging device of 3rd Embodiment of this invention.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.

[First Embodiment]
The configuration of the X-ray phase contrast imaging apparatus 100 according to the first embodiment of the present invention will be described with reference to FIGS.

(Configuration of X-ray phase contrast imaging apparatus)
First, the configuration of the X-ray phase contrast imaging apparatus 100 according to the first embodiment will be described with reference to FIG.

  As shown in FIG. 1, an X-ray phase contrast imaging apparatus 100 includes an X-ray source 1, a phase grating 2, an absorption grating 4, a detector 5, an image processing unit 6, a control unit 7, and grating movement. And a mechanism 8. In this specification, the direction from the X-ray source 1 to the phase grating 2 is the Z2 direction, and the opposite direction is the Z1 direction. Further, the left-right direction in the plane orthogonal to the Z direction is defined as the X direction, the direction toward the back of the sheet is defined as the X2 direction, and the direction toward the front side of the sheet is defined as the X1 direction. Also, the vertical direction in the plane orthogonal to the Z direction is the Y direction, the upper direction is the Y1 direction, and the lower direction is the Y2 direction. The phase grating 2 and the absorption grating 4 are examples of “first grating” and “second grating” in the claims, respectively.

  The X-ray source 1 is configured to generate X-rays and irradiate the generated X-rays when a high voltage is applied.

  The phase grating 2 includes a plurality of slits 2a arranged in the Y direction at a predetermined period (pitch) d1, and an X-ray phase change unit 2b. Each slit 2a and the X-ray phase change portion 2b are formed so as to extend in the X direction.

  The phase grating 2 is installed between the X-ray source 1 and the absorption grating 4 and is irradiated with X-rays. The phase grating 2 is provided for forming a self-image by the Talbot effect. When coherent X-rays pass through a grating in which slits are formed, an image of the grating (self-image) is formed at a position away from the grating by a predetermined distance (Talbot distance). This is called the Talbot effect. The self-image is an interference fringe generated by X-ray interference.

  The absorption grating 4 has a plurality of slits 4a and an X-ray absorption part 4b arranged in the Y direction at a predetermined period (pitch) d2. Each slit 4a and X-ray absorbing portion 4b are formed to extend in the X direction.

  The absorption grating 4 is disposed between the phase grating 2 and the detector 5 and is irradiated with X-rays that have passed through the phase grating 2. Further, the absorption grating 4 is disposed at a position away from the phase grating 2 by a Talbot distance.

When the distance between the X-ray source 1 and the phase grating 2 is R1, the distance between the phase grating 2 and the absorption grating 4 is R2, and the distance between the X-ray source 1 and the absorption grating 4 is R (= R1 + R2), The positional relationship among the source 1, the phase grating 2, and the absorption grating 4 is expressed by the following formula (9).

  The detector 5 is configured to detect X-rays, convert the detected X-rays into electric signals, and read the converted electric signals as image signals. The detector 5 is, for example, an FPD (Flat Panel Detector). The detector 5 includes a plurality of conversion elements (not shown) and pixel electrodes (not shown) arranged on the plurality of conversion elements. The plurality of conversion elements and the pixel electrodes are arranged side by side in the X direction and the Y direction at a predetermined cycle (pixel pitch).

  The detection signal of the detector 5 is sent to the image processing unit 6. The image processing unit 6 is configured to generate an X-ray phase contrast image in which the contrast of the specific part 3a of the subject 3 is emphasized from images captured by arranging the absorption grating 4 at a plurality of predetermined positions. Here, in the phase differential image, the change in the X-ray phase becomes large at the boundary of the subject 3. In the dark field image, the change in Visibility (definition of interference fringes) becomes large in a fine structure portion such as a scratch inside the subject 3. Therefore, the specific part 3a is set near the boundary of the subject 3 if it is a phase differential image, and is set near the scratch inside the subject 3 if it is a dark field image.

  The control unit 7 is configured to generate an X-ray phase contrast image in which the contrast of the specific part 3 a of the subject 3 is enhanced using the image processing unit 6. Further, the control unit 7 is configured to move the absorption grating 4 to a predetermined position using the grating moving mechanism 8.

  The grating moving mechanism 8 includes a grating holding unit (not shown) that holds the absorption grating 4 and a grating moving stage (not shown) that moves the held grating in the Z direction and the Y direction. The grating moving mechanism 8 is configured to move the absorption grating 4 held by the grating holding unit in a predetermined direction in the Z direction and the Y direction based on a signal sent from the control unit 7.

ここで、ａ_nは、干渉縞の各周波数成分の量である。また、Ｚ₀は、位相格子２と吸収格子４との距離である。また、ｄ₁は、位相格子２の周期（ピッチ）ｄ１である。また、ｘ、ｙは検出器５の検出面上における、Ｘ線の照射軸に直交する面内の座標位置である。 (Generating method of X-ray phase contrast image by conventional fringe scanning method)
Here, a method of generating an absorption image and a dark field image in the conventional fringe scanning method will be described. In the conventional fringe scanning method, an X-ray phase contrast image is generated from an image obtained by translating a grating at equal intervals in 1 / M periods in the period direction of the grating. For example, when M-step fringe scanning is performed, the X-ray intensity I _k (x, y) at each step k is expressed by the following equation (10).

Here, a _n is the amount of each frequency component of the interference fringes. Z ₀ is the distance between the phase grating 2 and the absorption grating 4. D ₁ is the period (pitch) d ₁ of the phase grating 2. Further, x and y are coordinate positions in a plane orthogonal to the X-ray irradiation axis on the detection surface of the detector 5.

If the intensity when the subject 3 is arranged is I _k (x, y), and the intensity when the subject 3 is not arranged is I _0k (x, y), the following equations (11) and (12) are given. Define S (x, y) and S ₀ (x, y).

Further, the phase differential image Φ _x (x, y) is expressed by the following equation (13).

また、被写体３を配置した場合のＶｉｓｉｂｉｌｉｔｙ（干渉縞の鮮明度）をＶ（ｘ，ｙ）とし、被写体３を配置しない場合のＶｉｓｉｂｉｌｉｔｙ（干渉縞の鮮明度）をＶ₀（ｘ，ｙ）とすると、Ｖ（ｘ，ｙ）およびＶ₀（ｘ，ｙ）は以下の式（１５）および（１６）により表される。

Further, the absorption image T (x, y) is represented by the following formula (14).

In addition, Visibility (interference fringe definition) when the subject 3 is arranged is V (x, y), and Visibility (interference fringe definition) when the subject 3 is not arranged is V ₀ (x, y). Then, V (x, y) and V ₀ (x, y) are expressed by the following equations (15) and (16).

The dark field image D (x, y) is expressed by the following equation (17).

In the conventional fringe scanning method, based on these equations, S (x, y) and S ₀ (x, y) are calculated by the above equations (11) and (12) using all the pixel values for M steps. The phase differential image and the dark field image are generated according to the above equations (13) and (17).

(Contrast enhancement effect of X-ray phase contrast image)
Next, a mechanism for enhancing the contrast of the X-ray phase contrast image will be described with reference to FIGS. In FIG. 2 and FIG. 3, pixel values detected by scanning the absorption grating 4 at the position of the phase that divides one period of the intensity signal curve into 16 are plotted.

  First, the mechanism for enhancing the contrast of the phase differential image will be described with reference to FIG. FIG. 2 shows X-ray intensity signal curves focusing on predetermined pixels with and without the subject 3. The pixel value obtained by stepping the grid shows a step curve like a sine wave. This is the intensity signal curve. Further, the number of steps of the grating corresponds to the phase of the intensity signal curve. FIG. 2A shows an example in which the absorption grating 4 is arranged at a relative position where the phase difference represented by the equation (13) becomes small. FIG. 2B shows an example in which the absorption grating 4 is arranged at a position where the phase difference expressed by the equation (13) becomes large.

Consider a case where the absorption grating 4 is arranged at the phase position of the straight line 20 and the straight line 21 in FIG. A straight line 22 represents the angle of deviation between the two phases detected by arranging the subject 3 and is descending to the right (Φ _{x in} equation (18) is a minus sign). A straight line 23 represents the angle of deviation between the two phases detected without the subject 3 being arranged, and this is also downwardly sloping. The phase differential image is calculated by the above equation (13), and among these, is determined by the value of the following equation (18).

  That is, when the deviation angle when the subject 3 is arranged and the deviation angle when the subject 3 is not arranged have the same sign, the value of the above equation (18) becomes small, so that the contrast of the obtained phase differential image is become weak.

On the other hand, as shown in FIG. 2B, when the absorption grating 4 is arranged at the phase position of the straight line 24 and the straight line 25, the straight line 26 representing the declination when the subject 3 is arranged is downwardly sloping. On the other hand, the straight line 27 representing the declination when the subject 3 is not arranged rises to the right (Φ _{x in} equation (18) is a plus sign). Therefore, since the value of the above equation (18) becomes large, the contrast of the obtained phase differential image becomes strong.

  That is, it can be seen that when the absorption grating 4 is arranged at the phase positions of the straight lines 24 and 25 in FIG. 2B, the contrast of the phase differential image is enhanced.

  Next, a mechanism for enhancing the contrast of the dark field image will be described with reference to FIG. FIG. 3A is a graph showing an example in which the contrast is weak (the difference in visibility (visibility of interference fringes) is small), and FIG. 3B is a graph in which the contrast is strong (visibility (definition of interference fringes)). It is a graph showing an example).

The dark field image is calculated using the above equation (17). When the absorption grating 4 is arranged at the position of the phase corresponding to the straight line 30 and the straight line 31 in FIG. 3 (A), the value (2) obtained by the equation (11) using the pixel values of the two points connected by the straight line 32 ( A value (S ₀ (x, y)) obtained by Expression (12) using S (x, y)) and the two pixel values connected by the straight line 33 becomes a finite value. Therefore, the value of D (x, y) represented by the above equation (17) is a finite value.

On the other hand, in FIG. 3B, when the absorption grating 4 is arranged at the phase positions of the straight line 34 and the straight line 35, the two points connected by the straight line 37 have the same pixel value and the opposite phase sign. Since the value (S ₀ ) calculated by the equation (12) is substantially 0, the value of D (x, y) becomes a maximum regardless of the two values (S) connected by the straight line 36. Therefore, in the state shown in FIG. 3B, the contrast of the obtained dark field image becomes strong.

  That is, it can be seen that when the absorption grating 4 is arranged at the phase position of the straight line 34 and the straight line 35 in FIG. 3B, the contrast of the dark field image is enhanced. Therefore, in the present embodiment, an X-ray contrast image in which the contrast of the specific part 3a of the subject 3 is emphasized is generated based on the above knowledge.

(Generation method of X-ray phase contrast image)
Next, a method for generating an X-ray phase contrast image will be described with reference to FIGS.

  FIG. 4 is an image diagram showing an example of the shape of the subject 3, and FIG. 4A is an image diagram when the subject 3 is viewed from the X2 direction (the direction from the detector 5 to the subject 3). FIG. 4B is an image diagram when the subject 3 is viewed from the X direction.

  As shown in FIG. 4B, the subject 3 has an inclined portion 3a that decreases in size in the Y direction as it proceeds from the Z1 direction to the Z2 direction. In the first embodiment, the contrast of the inclined portion 3a on the Y2 side of the subject 3 is enhanced.

In the first embodiment, the amount of change in the phase of the X-ray of the specific part 3a of the subject 3 (see FIG. 6) from a plurality of images taken by scanning the absorption grating 4 in advance at a number of relative positions (for example, 40 locations). An X-ray phase contrast image is generated from a plurality of images selected based on the angle α) in (B). FIG. 6 shows the following equation (19) based on the pixel values detected by the detector 5 by scanning the absorption grating 4 at 40 relative positions when the subject 3 is arranged and when the subject 3 is not arranged. ) And (20) and a graph (FIG. 6A) in which the integrands of S (x, y) and S ₀ (x, y) shown on the complex plane are plotted, and the center of gravity | S | 7 is a graph (FIG. 6B) obtained by enlarging / M, | S ₀ | / M.

Each plot in FIG. 6A is _obtained by changing Θ _k in the above equations (19) and (20). The slope of the straight line 40 passing through the origin in FIG. 6A corresponds to the value of Θ _k (that is, the phase).

  A straight line 40 indicates a reference phase that contributes to the generation of contrast determined based on the amount of change in the X-ray phase of the specific part 3a of the subject 3 (angle α in FIG. 5B). The straight line 41 indicates the position of the phase detected by scanning the grating for a predetermined phase (difference 42 between the straight line 40 and the straight line 41) from the reference phase (straight line 40).

The angle α shown in FIG. 5B indicates a phase shift between when the subject 3 is present and when it is not present, and corresponds to a phase differential image. Further, the ratio of | S | / M and | S ₀ | / M represents the ratio of Visibility (the sharpness of interference fringes) with and without the subject 3 and corresponds to a dark field image. To do. M is the total number of times the grid is scanned. Here, regarding the phase shift of the subject 3, a value measured in advance may be stored in a CPU (not shown) connected to the control unit 7 or accumulated data may be used. .

Here, when it is desired to enhance the contrast of the X-ray phase contrast image, absorption is performed at a position that contributes to the generation of contrast based on the phase shift (angle α) between when the subject 3 is placed and when the subject 3 is not placed. What is necessary is just to produce | generate an X-ray phase contrast image from the image image | photographed by arrange | positioning the grating | lattice 4. FIG. That is, as shown in FIG. 6, the image processing unit 6 uses a phase (straight line 40) serving as a reference that contributes to the generation of contrast based on the amount of change (angle α) in the X-ray phase of the specific part 3 a of the subject 3. ), S and S ₀ at positions separated by a predetermined phase (width 42 between the straight line 40 and the straight line 41) are obtained. A phase differential image 11 and a dark field image 13 are generated using the obtained S and S ₀ .

ここで、πは強度信号曲線の周期の半周期であり、Φｘは、被写体３の特定部位３ａのＸ線の吸収格子４のピッチに対する自己像シフトの割合（自己像シフト［ｕｍ］／吸収格子４のピッチ［ｕｍ］×２π［ｒａｄ］、図５（Ｂ）に示す角度α）である。 The reference phase (straight line 40) is determined by the following equation (21).

Here, π is a half period of the period of the intensity signal curve, and Φx is a ratio of the self-image shift to the pitch of the X-ray absorption grating 4 of the specific part 3a of the subject 3 (self-image shift [um] / absorption grating). 4 pitch [um] × 2π [rad], and angle α) shown in FIG.

  FIG. 6 shows the contrast when the angle of the reference phase (straight line 40) and the predetermined phase (the width 42 between the straight line 40 and the straight line 41) scanned from the reference phase (straight line 40) are changed. It shows a change. Note that “binD” is a predetermined phase (width 42 between the straight line 40 and the straight line 41) scanned from the reference phase (straight line 40). FIG. 6A shows the angle when the reference phase (straight line 40) and the predetermined phase (the width 42 between the straight line 40 and the straight line 41 and the unit is 1 step of fringe scanning) are changed in the phase differential image. FIG. 6B shows the change of contrast when the angle of the reference phase (straight line 40) in the dark field image and the predetermined phase are changed.

  As shown in FIG. 6, it can be seen that the smaller the value of binD, the more the contrast is enhanced. However, when binD is 0, that is, when an image photographed by scanning the absorption grating 4 at a position in the reference phase (straight line 40) is used, the value is 0 except where the contrast is emphasized. It has become. That is, in the reference phase (straight line 40), the strongest enhancement effect can be obtained in the specific part 3a of the subject 3, but the other places cannot be obtained as an image. Further, it can be seen that the contrast of the obtained image does not change even if the angle of the reference phase (straight line 40) is changed in an image taken by scanning the absorption grating 4 at positions where binD is equally spaced. (Assuming that the intensity modulation signal is close to a sine curve).

  Therefore, the value of binD may be set to a value larger than the reference phase (straight line 40) and less than a value that is equally spaced. In FIG. 5A, since the values detected by making the absorption grating 4 40 steps are plotted, the value of binD may be set to less than 5. That is, it may be set to less than 1/8 of the total number of steps of the absorption grating 4.

  In the first embodiment, the image processing unit 6 generates an X-ray phase contrast image from images captured by arranging the absorption grating 4 at a plurality of relative positions corresponding to the straight line 41. Specifically, the image processing unit 6 generates the phase differential image 11 using the above equation (13), and generates the dark field image 13 using the above equation (17). FIG. 7A shows a phase differential image 10 generated from an image captured by scanning the absorption grating 4 at equal intervals. FIG. 7B is a phase differential image 11 generated from an image captured by scanning the absorption grating 4 at non-equal intervals. It can be seen that the specific portion 3a of the phase differential image 11 generated by the configuration of the present embodiment has higher contrast than the specific portion 3a of the phase differential image 10 generated by the conventional method. The phase differential image 11 is an example of an “X-ray phase contrast image in which the contrast of a specific part is emphasized” in the claims.

  FIG. 8A shows a dark field image 12 generated from an image captured by scanning the absorption grating 4 at equal intervals. FIG. 8B is a dark field image 13 generated from an image captured by scanning the absorption grating 4 at non-equal intervals. It can be seen that the contrast of the specific part 3a of the dark field image 13 generated by the configuration of the present embodiment is enhanced compared to the specific part 3a of the dark field image 12 generated by the conventional method. The dark field image 13 is an example of an “X-ray phase contrast image in which the contrast of a specific part is emphasized” in the claims.

  Further, in the first embodiment, the image processing unit 6 uses the images captured by arranging the absorption grating 4 at a plurality of relative positions corresponding to the straight line 41 in FIGS. 9B and 10B. An X-ray phase contrast image is generated. FIG. 9 is an image diagram of a phase differential image obtained by photographing a cylindrical container 50 in which cartilage 3 is inserted and the inside is immersed in water. 9A is a phase differential image 15 generated by a conventional fringe scanning method, and FIG. 9B is a phase differential image 16 generated from an image captured by scanning the absorption grating 4 at non-uniform intervals. It is.

  9 and 10 are image diagrams of an X-ray phase contrast image obtained by photographing a cylindrical container 50 in which the cartilage 3 is inserted and the inside is immersed in water. 9A is a phase differential image 15 generated by a conventional fringe scanning method, and FIG. 9B is a phase differential image 16 generated from an image captured by scanning the absorption grating 4 at non-uniform intervals. It is. FIG. 10A shows a dark field image 17 generated by a conventional fringe scanning method, and FIG. 10B shows a dark field image 18 generated from an image taken by scanning the absorption grating 4 at non-uniform intervals. It is.

  Compared with the phase differential image 15 generated by the conventional method, it can be seen that the contrast of the cartilage 3 is enhanced in the phase differential image 16 generated by scanning the absorption grating 4 at non-uniform intervals. It can also be seen that the contrast of the cartilage 3 is emphasized in the dark field image 18 generated by scanning the absorption grating 4 at non-uniform intervals as compared with the dark field image 17 generated by the conventional method.

  The image processing unit 6 is based on the amount of change in the X-ray phase (angle α) of the specific part 3a of the subject 3 and the position of the phase that contributes relatively strongly to the generation of contrast, that is, the relationship in FIG. An X-ray contrast image in which the specific portion 3a is emphasized is generated from an image captured by scanning the absorption grating 4 at non-uniform intervals at such positions. Specifically, when the expressions (19) and (20) are defined, the image processing unit 6 generates the phase differential image 11 and the dark field image 13 using the expressions (13), (14), and (17). To do.

Here, at the phase positions indicated by the straight line 24 and the straight line 25 in FIG. 2B, signs of arg [S (x, y)] and arg [S ₀ (x, y)] in the equation (13). Therefore, the absolute value of arg [S (x, y)]-arg [S ₀ (x, y)] in the equation (18) becomes large. That is, the contrast of the phase differential image is increased. Further, at the phase positions indicated by the straight line 34 and the straight line 35 in FIG. 3B, the value of S _{0 in} the equation (17) is a minimum value. That is, since the value of the entire expression (17) is a maximum value, the contrast of the dark field image is increased. Therefore, the image processing unit 6 determines the relative position where the absolute value of arg [S (x, y)] − arg [S ₀ (x, y)] in Expression (18) becomes large, or S in Expression (17). _A phase differential image 11 and a dark field image 13 are generated from an image captured by scanning the absorption grating 4 at a relative position where the value of ₀ is a minimum value.

  Further, the relative position that contributes relatively strongly to the generation of contrast is based on the reference phase calculated by equation (21) based on the amount of change in the X-ray phase (angle α) of the specific part 3a of the subject 3 ( The phase is determined to be binD (predetermined phase) away from the straight line 40).

(Effect of 1st Embodiment)
In the first embodiment, the following effects can be obtained.

  In the first embodiment, as described above, the X-ray phase contrast imaging apparatus 100 includes the X-ray source 1, the phase grating 2, the absorption grating 4, the detector 5, the image processing unit 6, the control unit 7, and the grating moving mechanism 8. And the Y direction (lattice direction of the lattice) that contributes relatively strongly to the generation of contrast based on the amount of change (angle α) of the X-ray phase in the specific part 3a (see FIG. 4) of the subject 3 The phase differential image 11 in which the specific portion 3a of the subject 3 is emphasized and the dark image are obtained from an image taken by selecting the relative positions of the plurality of gratings in FIG. A field image 13 is generated. As a result, a plurality of relative positions in the Y direction (lattice direction of the lattice) that contribute relatively strongly to the generation of contrast are selected based on the amount of change in the X-ray phase (angle α) in the specific part 3a of the subject 3 can do. As a result, a phase differential image 11 and a dark field image 13 in which the specific portion 3a of the subject 3 is emphasized from an image photographed by arranging the absorption grating 4 at a plurality of relative positions that contribute relatively strongly to the generation of contrast. Can be generated.

  In the first embodiment, the phase differential generated from the image captured by scanning the absorption grating 4 at non-equal intervals is compared with the phase differential image 15 generated from the image captured by scanning the absorption grating 4 at equal intervals. In the image 16, the contrast of the cartilage 3 is emphasized. Further, in the dark field image 17 generated from the image captured by scanning the absorption grid 4 at equal intervals, the cartilage 3 is hardly shown, but is generated from the image captured by scanning the absorption grid 4 at non-uniform intervals. In the dark field image 18, the cartilage 3 can be confirmed.

  In the first embodiment, as described above, the image processing unit 6 has an absorption grating at a position that contributes relatively strongly to the generation of contrast selected based on the amount of change in the X-ray phase (angle α). An X-ray phase contrast image in which a specific portion 3a is emphasized is generated from an image captured by scanning 4 in the Y direction (periodic direction of the absorption grating 4) at non-uniform intervals. Thereby, it is possible to prevent the absorption grating 4 from being arranged at a position where the contrast is most emphasized based on the amount of change (angle α) of the X-ray phase in the specific part 3a of the subject 3. As a result, it is possible to generate the phase differential image 11 and the dark field image 13 in which the contrast of the specific portion 3a is enhanced while grasping the entire image of the subject 3.

  In the first embodiment, as described above, the image processing unit 6 determines a reference phase (straight line 40) based on the amount of change (angle α) in the phase of the X-ray, and determines the specific portion 3a. From the phase (straight line 40) serving as a reference for generating a contrast determined based on the amount of change in X-ray phase (angle α), the absorption grating 4 is separated by a predetermined phase (width 42 between the straight line 40 and the straight line 41). An X-ray phase contrast image in which the specific part 3a is emphasized is generated from a plurality of images photographed by scanning at non-equal intervals. Thereby, the relative position of the absorption grating 4 that contributes to the generation of contrast can be clearly determined.

  In the first embodiment, as described above, the predetermined phase (the width 42 between the straight line 40 and the straight line 41) is less than 1/8 of the period of the intensity signal curve from the vicinity of the reference phase (the straight line 40). Is set in the range. Thereby, it can prevent arrange | positioning the absorption grating 4 in the relative position which divides | segments 1 period of an intensity | strength signal curve equally. As a result, when the absorption grating 4 is moved from the reference phase (straight line 40), the absorption grating 4 can be arranged at a plurality of relative positions that contribute to the generation of contrast.

  In the first embodiment, as described above, the image processing unit 6 selects a reference phase (straight line 40) from a reference phase (straight line 40) from a plurality of images captured by scanning the absorption grating 4. A plurality of images taken at positions scanned by the width 42) with respect to the straight line 41 are selected. As a result, it is possible to obtain an image captured by arranging the absorption gratings 4 at a number of relative positions in advance, so that a plurality of predetermined phases (width 42 between the straight line 40 and the straight line 41) from the reference phase (straight line 40). A plurality of patterns in which the contrast of the specific part 3a of the subject 3 is emphasized can be generated by combining the images that have been scanned in minutes (images that greatly contribute to the generation of contrast).

  In the first embodiment, as described above, when the expressions (19) and (20) are defined, the image processing unit 6 uses the expressions (13), (14), and (17) to specify the specific part 3a. Are generated so as to generate a phase differential image 11 and a dark field image 13. Thus, by defining the above equations (19) and (20), even when the absorption grating 4 is scanned at non-uniform intervals, the above equations (13), (14), Using (17), the phase differential image 11 and the dark field image 13 in which the contrast of the specific part 3a of the subject 3 is enhanced can be generated.

In the first embodiment, as described above, the plurality of relative positions are represented by the sign of arg [S (x, y)] and the sign of arg [S ₀ (x, y)] in Expression (17). Is determined to be the opposite position, or S ₀ (x, y) in Expression (17) is determined to be a minimum value. As a result, the absolute value of arg [S (x, y)]-arg [S ₀ (x, y)] in the equation (18) increases. That is, the phase shift between when the subject 3 is present and when it is absent is large. In addition, since S ₀ (x, y) in Expression (17) is minimized, the value of Expression (17) as a whole is maximized. That is, the ratio of Visibility (interference fringe definition) with and without the subject 3 is maximized. Therefore, contrast can be enhanced. As a result, by generating an X-ray phase contrast image using the images of these relative positions, the phase differential image 11 and the dark field image 13 in which the contrast of the specific part 3a of the subject 3 is enhanced can be generated.

[Second Embodiment]
Next, an X-ray phase contrast imaging apparatus 200 according to the second embodiment of the present invention will be described with reference to FIG. The first embodiment is configured to generate a phase differential image 11 and a dark field image 13 in which the contrast of the specific part 3a of the subject 3 is emphasized from an image captured by arranging the absorption grating 4 at a number of relative positions in advance. Unlike the form, in the second embodiment, the reference phase (straight line 40) is calculated based on the amount of change (angle α) in the X-ray phase of the specific part 3a of the subject 3, and the absorption grating 4 is arranged. A plurality of relative positions are determined in advance. In addition, about the structure similar to the said 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

(How to find multiple relative positions)
In the second embodiment, the image processing unit 6 determines the reference phase (straight line 40) calculated by the equation (21) based on the change amount (angle α) of the X-ray phase of the specific part 3a of the subject 3. To do. Then, the image processing unit 6 reads the phase differential image 11 and the dark image from the image obtained by scanning the absorption grating 4 at the position of the phase (straight line 40) that is determined as the reference and the phase separated by binD (predetermined phase). A field image 13 is generated.

  That is, instead of scanning the 40-step absorption grating 4, the absorption grating 4 is scanned at four positions that are binD (predetermined phase) away from the reference phase (straight line 40).

  In addition, the other structure of 2nd Embodiment is the same as that of the said 1st Embodiment.

(Effect of 2nd Embodiment)
In the second embodiment, the following effects can be obtained.

  In the second embodiment, the reference phase (straight line 40) is determined by the period of the intensity signal curve obtained from the X-ray intensity distribution and the amount of change (angle α) in the X-ray phase of the specific part 3a. The This makes it possible to determine the reference phase (straight line 40) that contributes to the generation of contrast without arranging the absorption gratings 4 at a large number of relative positions in advance.

  [Third Embodiment]

  Next, an X-ray phase contrast imaging apparatus 300 according to the third embodiment of the present invention will be described with reference to FIG. In the third embodiment, in addition to the configuration of the first embodiment, a multi-slit 9 is further provided between the X-ray source 1 and the phase grating 2. In addition, about the structure similar to the said 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

(Configuration of X-ray phase contrast imaging apparatus)
In the third embodiment, as shown in FIG. 11, the X-ray phase contrast imaging apparatus 300 further includes a multi-slit 9 disposed between the X-ray source 1 and the phase grating 2. The multi slit 9 is an example of the “third grating” in the claims.

  The multi slit 9 has a plurality of slits 9a and an X-ray absorber 9b arranged in the Y direction at a predetermined period (pitch) d0. Each slit 9a and the X-ray absorber 9b are configured to extend in the X direction.

  The multi-slit 9 is installed between the X-ray source 1 and the phase grating 2 and is irradiated with X-rays from the X-ray source 1. The multi-slit 9 is configured so that the X-rays that have passed through each slit 9a serve as a line light source corresponding to the position of each slit 9a. Thereby, the multi slit 9 can improve the coherence of the X-rays irradiated from the X-ray source 1.

When the distance between the multi slit 9 and the phase grating 2 is R1, the distance between the phase grating 2 and the absorption grating 4 is R2, and the distance between the X-ray source 1 and the absorption grating 4 is R, the multi slit 9 and the phase grating 2 and the absorption grating 4 are represented by the following formula (22).

  The remaining configuration of the third embodiment is similar to that of the aforementioned first embodiment.

(Effect of the third embodiment)
In the third embodiment, the following effects can be obtained.

  The third embodiment further includes a multi slit 9 disposed between the X-ray source 1 and the phase grating 2. Thereby, since the coherency of the X-rays emitted from the X-ray source 1 can be improved, even when the focal length of the X-ray source 1 is not very small, the phase differentiation that emphasizes the contrast of the specific part 3a of the subject 3 An image 11 and a dark field image 13 can be generated.

(Modification)
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims, and further includes meanings equivalent to the scope of claims and all modifications (variants) within the scope.

  For example, in the first embodiment, the configuration in which the phase differential image 11 and the dark field image 13 are generated from the images captured by scanning the absorption grating 4 at four locations corresponding to binD of 1 is shown. The invention is not limited to this. For example, the phase differential image 11 and the dark field image 13 may be generated from an image captured by arranging the absorption grating 4 at a position where binD is less than 5. Further, the absorption grating 4 may be scanned at a plurality of locations (in this case, a total of 8 locations) such as binD = 1, 2, or the absorption grating 4 may be scanned at a larger number.

  In the first to third embodiments, the example in which the absorption grating 4 is moved in the Y direction (the periodic direction of the grating) by the grating moving mechanism 8 is shown. However, the present invention is not limited thereto. Absent. For example, the grating moving mechanism 8 may be configured to move the phase grating 2 in the Y direction for imaging. Moreover, the multi-slit 9 may be moved in the Y direction by the lattice moving mechanism 8 so as to be photographed.

  In the first to third embodiments, the example in which the X-ray phase contrast image is generated from the image photographed without rotating the subject 3 is shown, but the present invention is not limited to this. For example, a rotation mechanism for rotating the subject 3 is further provided, and tomography (CT imaging) is performed from a plurality of images taken at a predetermined rotation angle (for example, 9 degrees) while the subject 3 is rotated 360 degrees. It may be configured as follows.

  In the first to third embodiments, the example in which the reference phase (straight line 40) is obtained to determine the relative position of the absorption grating 4 has been described, but the present invention is not limited to this. For example, the absorption angle 4 may be arranged at the phase position where the declination is calculated and the sign is reversed.

  Moreover, in the said 1st Embodiment, although the example which image | photographs 40 steps of scanning of the absorption grating 4 was shown, this invention is not limited to this. The number of steps of the absorption grating 4 may be an arbitrary number. The size of binD may be varied according to the number of steps.

  In the first and second embodiments, the grating provided for forming the self-image by the Talbot effect is the phase grating 2, but the present invention is not limited to this. In the present invention, the self-image of the phase grating 2 only needs to be a stripe pattern. Therefore, the shadow of the absorption grating may be used as the stripe pattern of the self-image using an absorption grating instead of the phase grating 2.

1 X-ray source 2 Phase grating or absorption grating (first grating)
3 Subject 4 Absorption grating (second grating)
5 Detector 6 Image processor 8 Multi slit (3rd lattice)
40 Reference phase 42 Predetermined phase 100, 200, 300 X-ray phase contrast imaging apparatus α Amount of change of X-rays at specific part of subject

Claims (10)

An X-ray source;
A detector for detecting X-rays emitted from the X-ray source;
A first grating that is disposed between the X-ray source and the detector and is irradiated with X-rays from the X-ray source, and a second grating that is irradiated with the X-rays that have passed through the first grating. A plurality of grids including,
An image processing unit that generates an X-ray phase contrast image from an X-ray intensity distribution detected by the detector;
The image processing unit selects a plurality of relative positions in a periodic direction of a grating that contributes relatively strongly to contrast generation based on a change amount of an X-ray phase in a specific part of a subject, and the plurality of relative positions An X-ray phase contrast imaging apparatus configured to generate an X-ray phase contrast image in which the specific portion is emphasized from an image captured by arranging the plurality of gratings on the X-ray phase contrast image.   The image processing unit scans at least one of the plurality of gratings at non-uniform intervals in the periodic direction of the grating at a position relatively contributing to the contrast selected based on the amount of change in the phase of the X-ray. The X-ray phase contrast imaging apparatus according to claim 1, wherein the X-ray phase contrast imaging apparatus is configured to generate an X-ray phase contrast image in which the specific part is emphasized from an image photographed in this manner.   The image processing unit scans at least one of the plurality of gratings at unequal intervals by a predetermined phase from a phase serving as a reference for generating a contrast determined based on a change amount of X-rays at the specific part. The X-ray phase contrast imaging apparatus according to claim 2, wherein the X-ray phase contrast imaging apparatus is configured to generate an X-ray phase contrast image in which the specific part is emphasized from a plurality of images captured in this manner.   4. The X-ray phase contrast according to claim 3, wherein the reference phase is determined by a period of an intensity signal curve obtained from the X-ray intensity distribution and a change amount of an X-ray phase of the specific part. Shooting device.   The X-ray phase contrast imaging apparatus according to claim 4, wherein the predetermined phase is set in a range less than 1/8 of a period of the intensity signal curve from the vicinity of the reference phase.   The plurality of gratings are arranged at a plurality of relative positions obtained by determining the reference phase based on the amount of change in the phase of the X-ray and scanning the predetermined phase from the reference phase. The X-ray phase contrast imaging apparatus according to 3 or 4.   The image processing unit selects a plurality of images photographed at a position scanned by the predetermined phase from the reference phase from a plurality of images photographed by scanning any of the plurality of grids. The X-ray phase-contrast imaging apparatus according to claim 3, which is configured as follows. When the following expressions (1) to (4) are defined, the image processing unit generates an X-ray phase contrast image in which the specific portion is emphasized using the following expressions (5) to (7). The X-ray phase contrast imaging device according to claim 1, which is configured.

here,
a _n : amount of each frequency component of interference fringes;
k: a predetermined point of a signal curve representing a change in pixel value;
M: total number of predetermined points;
I (x, y): intensity signal value at a predetermined point when the subject is arranged;
I _OK (x, y): intensity signal value at a predetermined point when no subject is arranged;
x, y: coordinate position in a plane perpendicular to the irradiation axis direction of X-rays in the second grating;
Θ _k : phase of a predetermined point of the intensity signal curve;

here,
d ₁ : period of the first grating;
z ₀ : distance between the first grating and the second grating;
It is. The plurality of relative positions are positions where the sign of arg [S (x, y)] in Expression (5) is opposite to the sign of arg [S ₀ (x, y)], or Expression (7) The X-ray phase-contrast imaging apparatus according to claim 1, wherein S ₀ (x, y) is determined to be a position where the local minimum value is obtained.   The X-ray phase contrast imaging apparatus according to claim 1, wherein the plurality of gratings further include a third grating disposed between the X-ray source and the first grating. .

Images