X-ray focal point shape evaluation device and X-ray focal point shape evaluation method

Abstract

To provide a device and method which can easily evaluate a focus shape that includes X-ray focus dimensions at an X-ray source target.SOLUTION: An X-ray focus shape evaluation device 10 evaluates an X-ray focus shape that includes X-ray focus dimensions at a target 22 of an X-ray source 20, and includes an imaging unit 11 and a computation unit 12. The imaging unit 11 acquires the phase contrast image in an edge-including range of an object 30 which is located on a propagation path of the X-ray generated at the target 22 of the X-ray source 20. The computation unit 12 evaluates an X-ray focus shape at the target 22 on the basis of at least the phase contrast image, a linear attenuation coefficient of the object 30, and a refractive index of the object 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for evaluating the shape of an X-ray focal spot on a target of an X-ray source. [Background technology]

[0002] Japanese Industrial Standard JIS Z4704 specifies the slit camera method and pinhole camera method as methods for evaluating the X-ray focal size of a medical X-ray source target. The slit camera method uses a shielding object with a long slit in one direction to obtain the intensity profile of X-rays that pass through the slit out of the X-rays emitted from the X-ray source, and determines the focal size based on this intensity profile. The pinhole camera method uses a shielding object with a pinhole to obtain the intensity profile of X-rays that pass through the pinhole out of the X-rays emitted from the X-ray source, and determines the focal size based on this intensity profile.

[0003] JIS Z4615 specifies a method for evaluating the X-ray focal spot size of the target of an industrial X-ray source. However, this standard only specifies a method for evaluating focal spots of 300 μm or more, and does not specify a method for evaluating focal spots of less than 300 μm.

[0004] The knife-edge method is also known as a method for measuring the focal spot size of an X-ray source target. In this method, part of the cross section of the X-ray beam output from the X-ray source is blocked by a shielding object to obtain an edge image, and the focal spot size is calculated based on this edge image.

[0005] Non-Patent Document 1 describes that when a phase contrast image of a range including the edge of a cylindrical object placed on the X-ray propagation path is acquired, the profile shape of the X-ray intensity distribution in the range near the position corresponding to the edge in the phase contrast image correlates with the focal spot size. It is believed that by utilizing this correlation, the focal spot size can be determined based on the profile shape of the X-ray intensity distribution in the range near the edge-corresponding position in the phase contrast image. Below, the focal spot size measurement method based on the description in Non-Patent Document 1 is referred to as a "Comparative Example." [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-57163 [Non-patent literature]

[0007] [Non-Patent Document 1] Akira Ishisaka, et al., "A New Method of Analyzing Edge Effect in Phase Contrast Imaging with IncoherentX-rays," Optical Review, Vol.7, No.6, (2000) 566-572. Summary of the Invention [Problem to be solved by the invention]

[0008] The slit camera method and pinhole camera method have limitations in reducing the slit width and pinhole diameter, making them difficult to use when the focal length is small, but are effective when the focal length is large. In contrast, the knife-edge method can be used even when the focal length is small.

[0009] The slit camera method, pinhole camera method, and knife edge method require that the shielding object be thick enough to adequately block X-rays, and that the cross section of the slit, pinhole, or edge be machined with high precision. However, it is not easy to machine the edge of such a thick shielding object with high precision. These methods require that the shielding object be positioned precisely on the X-ray propagation path to measure the focal spot dimensions with high precision, but this positioning is also not easy. Materials with high X-ray absorption (metals with high atomic numbers) are used as shielding objects, but such materials are expensive.

[0010] The comparative measurement method based on the description in Non-Patent Document 1 is expected to solve the problems associated with the slit camera method, pinhole camera method, and knife-edge method. However, when the inventors attempted to measure focal length using the comparative measurement method, they found that this measurement method had the following problems. That is, the comparative measurement method is difficult to use when the X-ray absorption of a cylindrical object is high. Furthermore, since the comparative measurement method is thought to be significantly affected by distortion of the cylindrical object's shape and variations in surface curvature, it is necessary to machine the cylindrical object with high precision, but such machining is not easy.

[0011] The present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method that can easily evaluate the focal shape, including the X-ray focal dimension, on the target of an X-ray source. [Means for solving the problem]

[0012] The X-ray focal shape evaluation device of the present invention is a device for evaluating the X-ray focal shape on the target of an X-ray source, and includes an imaging unit that acquires a phase contrast image of an area including the edge of an object placed on the propagation path of X-rays generated by the target, and a calculation unit that evaluates the X-ray focal shape based on at least the phase contrast image, the linear attenuation coefficient of the object, and the refractive index of the object.

[0013] The imaging unit preferably acquires a phase contrast image of a flat object. The imaging unit preferably acquires a background image in a state where no object is placed on the propagation path, and the calculation unit preferably corrects the phase contrast image based on the background image and evaluates the X-ray focal shape based on the corrected phase contrast image.

[0014] The calculation unit preferably assumes a function representing the X-ray intensity distribution at the time of X-ray generation in the target, and estimates parameters of the assumed function by fitting the intensity distribution in the direction perpendicular to the edge in the phase contrast image acquired by the imaging unit to the intensity distribution in the direction perpendicular to the edge in the phase contrast image obtained based on this assumed function, thereby evaluating the X-ray focal shape. It is also preferable that the calculation unit obtains the distance between the maximum intensity position and the minimum intensity position in the intensity distribution in the direction perpendicular to the edge in the phase contrast image acquired by the imaging unit, and evaluates the X-ray focal shape based on this distance.

[0015] It is preferable that the imaging unit acquires phase contrast images with the edges of the object set in each of a plurality of orientations, and the calculation unit evaluates the X-ray focal shape based on the phase contrast images for each of the plurality of orientations.It is also preferable that the imaging unit acquires phase contrast images of an object having a plurality of edges with different orientations, and the calculation unit evaluates the X-ray focal shape for each of the plurality of edges based on the phase contrast images.

[0016] The X-ray focal shape evaluation method of the present invention is a method for evaluating the X-ray focal shape in a target of an X-ray source, and includes an imaging step of acquiring, by an imaging unit, a phase contrast image of an area including an edge of an object placed on the propagation path of X-rays generated by the target, and a calculation step of evaluating the X-ray focal shape based on at least the phase contrast image, the linear attenuation coefficient of the object, and the refractive index of the object.

[0017] It is preferable that the imaging step acquires a phase contrast image of a flat object, and that the imaging step acquires a background image by the imaging unit in a state where no object is placed on the propagation path, and that the calculation step corrects the phase contrast image based on the background image and evaluates the X-ray focal point shape based on the corrected phase contrast image.

[0018] In the calculation step, it is preferable to estimate parameters of the assumed function by assuming a function representing an X-ray intensity distribution at the time of X-ray generation in the target and fitting the intensity distribution in the direction perpendicular to the edge in the phase contrast image acquired by the imaging unit to the intensity distribution in the direction perpendicular to the edge in the phase contrast image obtained based on this assumed function, and to evaluate the X-ray focal shape. It is also preferable in the calculation step to determine the distance between the maximum intensity position and the minimum intensity position in the intensity distribution in the direction perpendicular to the edge in the phase contrast image acquired by the imaging unit and evaluate the X-ray focal shape based on this distance.

[0019] It is preferable that in the imaging step, phase contrast images are acquired with the edges of the object set in each of a plurality of orientations, and in the calculation step, the X-ray focal shape is evaluated based on the phase contrast images for each of the plurality of orientations.It is also preferable that in the imaging step, phase contrast images of an object having a plurality of edges with different orientations are acquired, and in the calculation step, the X-ray focal shape is evaluated for each of the plurality of edges based on the phase contrast images. [Effects of the Invention]

[0020] According to the present invention, the focal spot shape including the X-ray focal spot size on the target of the X-ray source can be easily evaluated. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing the configuration of an X-ray focal point shape evaluation device 10. As shown in FIG. [Figure 2] FIG. 2 is a diagram schematically showing a phase contrast image. [Figure 3] FIG. 3 is a diagram showing a schematic diagram of the intensity distribution I(x) near the edge of a phase contrast image. [Figure 4] FIG. 4 is a diagram showing an example of a phase contrast image acquired by the imaging unit 11. As shown in FIG. [Figure 5] FIG. 5 is a diagram showing the intensity distribution I(x) on a straight line L perpendicular to the edge in the phase contrast image shown in FIG. [Figure 6] FIG. 6 is a diagram showing a comparison of the measured intensity distribution I(x) obtained from the phase contrast image acquired by the imaging unit 11, the intensity distribution I(x) obtained by wave optics calculation, and the intensity distribution I(x) obtained by the theoretical formula (5). [Figure 7] FIG. 7 is a flowchart showing a first example of an X-ray focal point shape evaluation method. [Figure 8] FIG. 8 is a flowchart showing a second example of the X-ray focal point shape evaluation method. [Figure 9] FIG. 9 is a flowchart showing a third example of the X-ray focal point shape evaluation method. [Figure 10] FIG. 10 is a diagram showing a comparison of the simulation results of the example and the comparative example. [Figure 11] Figure 11 is a table summarizing the tube voltage and tube current during the experiment. [Figure 12] FIG. 12 is a diagram showing a phase contrast image acquired in the example when the tube voltage was 20 kV and the tube current was 40 μA. [Figure 13] FIG. 13 is a graph showing I(x) obtained from the phase contrast image of FIG. [Figure 14] FIG. 14 is a diagram showing a comparison of the experimental results of the example and the knife-edge method. [Figure 15] 15(a) to 15(d) are diagrams that schematically show phase contrast images when the orientation of the edge of the object 30 is changed. [Figure 16]FIG. 16 is a diagram schematically showing a phase contrast image in the case where an object 30 has a plurality of edges with different orientations. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate explanations will be omitted. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0023] 1 is a diagram showing the configuration of an X-ray focal shape evaluation device 10. In addition to the X-ray focal shape evaluation device 10, this diagram also shows an X-ray source 20, an object 30, and a holder 40. The X-ray focal shape evaluation device 10 is an apparatus for evaluating the X-ray focal shape including the X-ray focal dimension on a target 22 of the X-ray source 20, and includes an imaging unit 11 and a calculation unit 12.

[0024] The X-ray source 20 includes a target 22 inside a housing 21, and a window 23 in a portion of the housing 21 for emitting X-rays generated by irradiating the target 22 with an electron beam to the outside. An object 30 is placed on the X-ray propagation path between the X-ray source 20 and the imaging unit 11. The object 30 is preferably a flat plate with a uniform thickness, which makes it easy to process. The object 30 is a phase object that allows a portion of the X-rays to pass through. The thickness and material of the object 30 may be arbitrary, as long as they allow a portion of the X-rays to pass through. The object 30 is, for example, a metal foil or a resin film. The holding unit 40 holds the object 30 and adjusts the position and orientation of the object 30. The holding unit 40 holds the flat plate-shaped object 30 so that it is perpendicular to the X-ray propagation direction and so that the edge of the object 30 is located within the X-ray beam cross section.

[0025] The imaging unit 11 acquires a phase contrast image of a range including the edge of an object 30 placed on the propagation path of X-rays generated by a target 22 of the X-ray source 20. The imaging unit 11 is placed at a distance from the object 30 required to acquire a phase contrast image of the object 30. The imaging unit 11 outputs data of the phase contrast image to the calculation unit 12.

[0026] The imaging unit 11 may be any device capable of acquiring a two-dimensional X-ray image. The imaging unit 11 may be an X-ray CCD camera that is sensitive to X-rays. The imaging unit 11 may also have a configuration including a scintillator that generates scintillation light when X-rays are incident thereon, and a CCD camera that images the distribution of scintillation light generated in the scintillator.

[0027] The calculation unit 12 receives the phase contrast image data output from the imaging unit 11. The calculation unit 12 evaluates the X-ray focal shape in the target 22 based on at least the phase contrast image, the linear attenuation coefficient of the object 30, and the refractive index of the object 30. The calculation unit 12 includes a CPU that performs processes such as the above evaluation, memory (RAM, ROM, hard disk drive, etc.) that stores various parameters and processing results, a display that displays the image and processing results, etc. The calculation unit 12 may be a computer.

[0028] The X-ray focal shape evaluation method is a method for evaluating an X-ray focal shape including X-ray focal dimensions on a target 22 of an X-ray source 20, and includes an imaging step and a calculation step. In the imaging step, a phase contrast image of an area including an edge of an object 30 placed on a propagation path of X-rays generated by the target 22 of the X-ray source 20 is acquired by the imaging unit 11. The imaging step can be performed by the imaging unit 11. In the calculation step, the X-ray focal shape on the target 22 is evaluated based on at least the phase contrast image, the linear attenuation coefficient of the object 30, and the refractive index of the object 30. The calculation step can be performed by the calculation unit 12.

[0029] In the imaging step, a background image may be acquired by the imaging unit 11 when no object 30 is placed on the X-ray propagation path, and in the calculation step, the phase contrast image may be corrected based on the background image, and the X-ray focal shape may be evaluated based on the corrected phase contrast image. The order in which the phase contrast image and the background image are acquired in the imaging step may be arbitrary. If the background light intensity is non-uniform in the range near the position corresponding to the edge of the object 30 in the background image, the accuracy of the evaluation of the X-ray focal shape will deteriorate. To avoid this, it is preferable to correct the phase contrast image by dividing it by the background image. On the other hand, if the background light intensity can be considered uniform in the range near the position corresponding to the edge of the object 30 in the background image, such correction may not be necessary.

[0030] For convenience of explanation, an xyz Cartesian coordinate system is set as shown in Fig. 1. The direction of X-ray propagation from the target 22 to the imaging unit 11 is set as the z direction, the edge of the object 30 is set as parallel to the y direction, and the edge of the object 30 is set as perpendicular to the x direction.

[0031] The linear attenuation coefficient of the object 30 is μ. The refractive index of the object 30 is 1-δ. Generally, in the X-ray region, δ is a very small positive value (for example, 10 -6 μ and δ are determined by the X-ray energy and the material of the object 30. The thickness of the object 30 is T. The distance between the X-ray generation position of the target 22 and the object 30 is z1. The distance between the object 30 and the imaging surface of the imaging unit 11 is z2. Note that z1 >> T and z2 >> T can be satisfied. The optical magnification M is expressed by the following equation (1).

[0032]

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[0033]

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[0034]

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[0035] When S(x) is a Gaussian function expressed by the following equation (4), I(x) is expressed by the following equation (5). σ is a parameter that represents the shape or size of the X-ray focal spot on the target 22. erf on the right side of equation (5) is an error function. Of the two terms on the right side of equation (5), the second term is sensitive to the value of σ. The x-coordinate value x of the position where equation (5) is maximum is a and the x-coordinate value x of the position where equation (5) is the minimum value. bThe difference between the maximum and minimum intensity positions is Δx edge In this case, σ is Δx edge It is expressed by the following equation (6) using the above formula: Note that the X-ray focal spot size (full width at half maximum) on the target 22 is often defined as 2.35σ.

[0036]

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[0038]

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[0039] 6 is a diagram comparing the measured intensity distribution I(x) obtained from a phase contrast image acquired by the imaging unit 11, the intensity distribution I(x) obtained by wave optics calculation, and the intensity distribution I(x) obtained from the theoretical formula (5). As shown in this diagram, the intensity distribution I(x) obtained by the theoretical formula (5) is in good agreement with both the measured intensity distribution I(x) and the intensity distribution I(x) obtained by the wave optics calculation.

[0040] Next, an example of the flow of an X-ray focal shape evaluation method will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a flowchart showing a first example of an X-ray focal shape evaluation method. The imaging step includes steps S1 and S2. The calculation step includes steps S3, S4, S11, and S12.

[0041] In step S1, the imaging unit 11 acquires a phase contrast image of an area including the edge of an object 30 placed on the propagation path of X-rays generated by the target 22 of the X-ray source 20. In step S2, the imaging unit 11 acquires a background image in a state where the object 30 is not placed on the propagation path of the X-rays. The order of execution of steps S1 and S2 is arbitrary. In step S3, the phase contrast image acquired in step S2 is corrected based on the background image acquired in step S1. In step S4, the intensity distribution I(x) near the edge in the phase contrast image corrected in step S3 is acquired.

[0042] In step S11, a function S(x) is assumed that represents the X-ray intensity distribution at the time of X-ray generation in the target 22. The function S(x) assumed here is arbitrary, but is typically a Gaussian function, and may also be the sum of two or more Gaussian functions with different central positions, peak intensities, or σ. In step S12, the measured intensity distribution I(x) acquired in step S4 is fitted with I(x) in the above equation (3) obtained based on the function assumed in step S11, and the parameters of the function assumed in step S11 are estimated, thereby evaluating the X-ray focal spot shape.

[0043] 8 is a flowchart showing a second example of an X-ray focal point shape evaluation method. The imaging step includes steps S1 and S2. The calculation step includes steps S3, S4, S21, and S22. Steps S1 to S4 are the same as those described in FIG. 7.

[0044] In step S21, it is assumed that the function S(x) representing the X-ray intensity distribution at the time of X-ray generation in the target 22 is a Gaussian function. In step S22, the actually measured intensity distribution I(x) acquired in step S4 is fitted with I(x) in the above equation (5) obtained when the function S(x) is expressed by the above equation (4), and σ in the above equation (4) is estimated, thereby evaluating the X-ray focal shape.

[0045] 9 is a flowchart showing a third example of an X-ray focal point shape evaluation method. The imaging step includes steps S1 and S2. The calculation step includes steps S3, S4, S31, and S32. Steps S1 to S4 are the same as those described in FIG. 7.

[0046] In step S31, it is assumed that the function S(x) representing the X-ray intensity distribution at the time of X-ray generation in the target 22 is a Gaussian function. In step S32, the maximum intensity position x in the actually measured intensity distribution I(x) acquired in step S4 is calculated. a and the minimum intensity position x b The distance Δx between edge Calculate this Δx edge Based on this, σ in the above equation (4) is estimated using the above equation (6), and the X-ray focal spot shape is evaluated using this.

[0047] Next, the simulation results will be described. In this simulation, the X-ray energy was 10 keV, and the object 30 was an aluminum foil with a thickness of 10 μm. z2=1.6 m, and M=10. The function S(x) representing the X-ray intensity distribution at the time of X-ray generation in the target 22 was assumed to be a Gaussian function. Then, for cases where the true 2σ was set to various values within a range of 1 to 20 μm, the 2σ obtained by the X-ray focal point shape evaluation method (Example) shown in the flowchart of FIG. 9 was compared with the 2σ obtained by the measurement method of the comparative example based on the description in Non-Patent Document 1.

[0048] FIG. 10 is a diagram comparing the simulation results of the Example and the Comparative Example. As shown in this figure, in the Comparative Example, the calculated 2σ closely matches the true 2σ in the range where the true 2σ is approximately 5 μm or less, but the difference from the true 2σ becomes larger as the true 2σ increases. In contrast, in the Example, the calculated 2σ closely matches the true 2σ throughout the entire range where the true 2σ is 1 to 20 μm. This difference in the simulation results between the Example and the Comparative Example is thought to be due to the fact that the Comparative Example does not take into account either μ or δ of the object 30, while the Example takes into account both μ and δ of the object 30.

[0049] Next, the experimental results will be described. In this experiment, the object 30 was a 4 μm-thick polypropylene film (X-ray transmittance of 99.9% or more). z1 = 170 mm, and z2 = 1640 mm. An X-ray CCD camera with a pixel size of 10 μm was used as the imaging unit 11. The function S(x) representing the X-ray intensity distribution at the time of X-ray generation in the target 22 was assumed to be a Gaussian function. Then, for each value of the tube voltage and tube current, the focal spot dimensions obtained by the X-ray focal spot shape evaluation method (Example) shown in the flowchart of FIG. 9 were compared with the focal spot dimensions obtained by the knife-edge method.

[0050] FIG. 11 is a table summarizing the tube voltage and tube current used in the experiment. FIG. 12 is a diagram showing a phase contrast image acquired in the example when the tube voltage was 20 kV and the tube current was 40 μA. FIG. 13 is a graph showing I(x) acquired from the phase contrast image of FIG. 12. FIG. 14 is a diagram comparing the experimental results of the example and the knife-edge method. As shown in this figure, the actual measurement results of the focal spot size in the example were in good agreement with the actual measurement results of the focal spot size using the knife-edge method. This shows that the X-ray focal spot shape evaluation method of this embodiment can obtain results equivalent to those obtained using the knife-edge method and is therefore appropriate as a method for evaluating the focal spot size.

[0051] So far, we have explained the case where the edge of the object 30 is assumed to be parallel to the y direction and the X-ray focal shape in the x direction on the target 22 is evaluated. However, it is also possible to evaluate the X-ray focal shapes in multiple directions on the target 22 by doing the following.

[0052] In the imaging step, the imaging unit 11 acquires phase contrast images with the edge of the object 30 set in each of a plurality of orientations by the holding unit 40, and in the calculation step, the calculation unit 12 evaluates the X-ray focal shape based on the phase contrast images in each of the plurality of orientations. Fig. 15 is a diagram schematically showing phase contrast images when the orientation of the edge of the object 30 is changed.

[0053] 15(a), the edge of the object 30 is parallel to the y direction. Based on this phase contrast image, an intensity distribution I on a line L parallel to the x direction is obtained, and the focal shape in the x direction is evaluated based on this intensity distribution I.

[0054] 15(b), the edge of the object 30 is tilted at 30° with respect to the y direction. Based on this phase contrast image, an intensity distribution I on a line L tilted at 30° with respect to the x direction is obtained, and the focal shape in a direction tilted at 30° with respect to the x direction is evaluated based on this intensity distribution I.

[0055] 15(c), the edge of the object 30 is tilted at 60° with respect to the y direction. Based on this phase contrast image, an intensity distribution I on a line L tilted at 60° with respect to the x direction is obtained, and the focal shape in a direction tilted at 60° with respect to the x direction is evaluated based on this intensity distribution I.

[0056] 15(d), the edge of the object 30 is parallel to the x direction. Based on this phase contrast image, an intensity distribution I on a line L parallel to the y direction is obtained, and the focal shape in the y direction is evaluated based on this intensity distribution I.

[0057] In this way, by acquiring phase contrast images with the edge of object 30 set in each of multiple orientations and evaluating the X-ray focal shape based on the phase contrast images in each of these multiple orientations, the X-ray focal shape can be evaluated in more detail.

[0058] In the imaging step, the imaging unit 11 acquires a phase contrast image of the object 30 having multiple edges with different orientations, and in the calculation step, the calculation unit 12 evaluates the X-ray focal shape for each of the multiple edges based on the phase contrast image. FIG. 16 is a diagram schematically illustrating a phase contrast image when the object 30 has multiple edges with different orientations. The object 30 may have, for example, a polygonal (octagonal in this figure) flat plate shape. In this phase contrast image, intensity distributions I along each of the straight lines L1 to L4 perpendicular to each edge are acquired, and the X-ray focal shape in the direction of each of the straight lines L1 to L4 is evaluated. This allows for more detailed evaluation of the X-ray focal shape.

[0059] 15 and 16 can evaluate the X-ray focal shape in multiple directions on the target 22, and therefore can evaluate whether the focal shape is close to a perfect circle or the ellipticity of the focal shape. Furthermore, by using the algorithm described in Patent Document 1, it is also possible to estimate the function F(x, y) of the X-ray intensity distribution on the target 22. This is a method of estimating the point spread function of a certain optical system from the line spread function in multiple directions (the line integral distribution of the point spread function) using a reconstruction algorithm of CT (Computed Tomography).

[0060] As described above, in this embodiment, the object 30 can be a flat plate-shaped object made of any material (e.g., metal foil or resin film), and the object 30 with an edge can be easily prepared. Furthermore, the object 30 does not need to be positioned precisely on the X-ray propagation path. Even if the flat object 30 is positioned at an angle with respect to the xy plane, the X-ray focal spot size can be accurately and easily evaluated. Furthermore, in comparison with the measurement method of the comparative example based on the description of Non-Patent Document 1, this embodiment is similar in that the focal spot shape is evaluated based on a phase contrast image, but differs in that the focal spot shape is evaluated taking into account both the linear attenuation coefficient and refractive index of the object 30, thereby enabling highly accurate evaluation of the focal spot shape. In this way, the focal spot shape, including the X-ray focal spot size, on the target 22 can be easily evaluated. In particular, the X-ray focal spot shape evaluation method shown in the flowchart of FIG. 9 evaluates the maximum intensity position x in the actually measured intensity distribution I(x). a and the minimum intensity position x b The distance Δx between edge Calculate this Δx edge Since σ is estimated based on the above, the focal spot shape including the X-ray focal spot size can be more easily evaluated. [Explanation of symbols]

[0061] 10...X-ray focal point shape evaluation device, 11...imaging unit, 12...calculation unit, 20...X-ray source, 21...casing, 22...target, 23...window, 30...object, 40...holding unit

Claims

1. An apparatus for evaluating an X-ray focal shape on a target of an X-ray source, comprising: an imaging unit for acquiring a phase contrast image of an area including an edge of an object disposed on a propagation path of the X-rays generated by the target; a calculation unit that evaluates the X-ray focal spot shape based on at least the phase contrast image, the linear attenuation coefficient of the object, and the refractive index of the object; An X-ray focal spot shape evaluation device comprising:

2. the imaging unit acquires the phase contrast image of a flat-plate-shaped object. The X-ray focal point shape evaluation device according to claim 1 .

3. the imaging unit acquires a background image in a state where the object is not located on the propagation path, the calculation unit corrects the phase contrast image based on the background image, and evaluates the X-ray focal spot shape based on the corrected phase contrast image.

3. The X-ray focal point shape evaluation device according to claim 1.

4. the calculation unit assumes a function representing an X-ray intensity distribution at the time of X-ray generation in the target, and estimates parameters of the assumed function by fitting an intensity distribution in a direction perpendicular to the edge in a phase contrast image acquired by the imaging unit to an intensity distribution in a direction perpendicular to the edge in a phase contrast image obtained based on the assumed function, thereby evaluating the X-ray focal point shape. The X-ray focal point shape evaluation device according to any one of claims 1 to 3.

5. the calculation unit calculates a distance between a maximum intensity position and a minimum intensity position in an intensity distribution in a direction perpendicular to the edge in the phase contrast image acquired by the imaging unit, and evaluates the X-ray focal spot shape based on the distance. The X-ray focal point shape evaluation device according to any one of claims 1 to 3.

6. the imaging unit acquires the phase contrast image with the edge of the object set in each of a plurality of orientations; the calculation unit evaluates the X-ray focal spot shape based on the phase contrast images in each of the plurality of orientations. The X-ray focal point shape evaluation device according to any one of claims 1 to 5.

7. the imaging unit acquires the phase contrast image of an object having a plurality of edges with different orientations; the calculation unit evaluates the X-ray focal spot shape for each of the plurality of edges based on the phase contrast image. The X-ray focal point shape evaluation device according to any one of claims 1 to 5.

8. 1. A method for evaluating an X-ray focal spot shape on a target of an X-ray source, comprising: an imaging step of acquiring, by an imaging unit, a phase contrast image of an area including an edge of an object disposed on a propagation path of the X-rays generated by the target; a calculation step of evaluating the X-ray focal spot shape based on at least the phase contrast image, the linear attenuation coefficient of the object, and the refractive index of the object; An X-ray focal spot shape evaluation method comprising:

9. In the imaging step, the phase contrast image of the flat-plate-shaped object is acquired. The X-ray focal point shape evaluation method according to claim 8.

10. In the imaging step, a background image is acquired by the imaging unit in a state where the object is not placed on the propagation path; In the calculation step, the phase contrast image is corrected based on the background image, and the X-ray focal spot shape is evaluated based on the corrected phase contrast image. The X-ray focal point shape evaluation method according to claim 8 or 9.

11. In the calculation step, a function representing an X-ray intensity distribution at the time of X-ray generation in the target is assumed, and an intensity distribution in a direction perpendicular to the edge in a phase contrast image acquired by the imaging unit is fitted to an intensity distribution in a direction perpendicular to the edge in a phase contrast image obtained based on this assumed function, thereby estimating parameters of the assumed function and evaluating the X-ray focal point shape. The X-ray focal point shape evaluation method according to any one of claims 8 to 10.

12. In the calculation step, a distance between a maximum intensity position and a minimum intensity position is calculated in an intensity distribution in a direction perpendicular to the edge in the phase contrast image acquired by the imaging unit, and the X-ray focal spot shape is evaluated based on this distance. The X-ray focal point shape evaluation method according to any one of claims 8 to 10.

13. In the imaging step, the phase contrast images are acquired with the edge of the object set in each of a plurality of orientations; In the calculation step, the X-ray focal spot shape is evaluated based on the phase contrast images in each of the plurality of orientations. The X-ray focal point shape evaluation method according to any one of claims 8 to 12.

14. In the imaging step, the phase contrast image of an object having a plurality of edges with different orientations is acquired; In the calculation step, the X-ray focal spot shape is evaluated for each of the plurality of edges based on the phase contrast image. The X-ray focal point shape evaluation method according to any one of claims 8 to 12.

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