JP2023130084A - Evaluation device and evaluation method of x-ray ct apparatus - Google Patents

Abstract

To simplify a structure of an evaluation device for calculating a correct distance between an X-ray source and an X-ray detector.SOLUTION: An evaluation device of an X-ray CT device comprises: an X-ray source; an X-ray detector; a phantom unit for evaluation; and a calculation unit which calculates a distance in a first direction between the X-ray source and the X-ray detector. In the phantom unit, a first pair including two phantoms in four phantoms is arranged at a position closer to the X-ray source than a second pair including the other two phantoms in the four phantoms in the first direction being the direction heading from the X-ray source to the X-ray detector, each phantom included in the first pair and each phantom included in the second pair are arranged along a second direction intersecting the first direction, and the phantoms included in the first pair are arranged so as not to be located on the straight line connecting the phantoms included in the second pair and the X-ray source.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to an evaluation device and evaluation method for an X-ray CT apparatus.

In the technique described in Patent Document 1, in order to evaluate an X-ray CT apparatus, measurement data measured with a reference gauge placed at a first measurement point between an X-ray source and an X-ray detector and , the relationship between the X-ray source and the X-ray detector is based on the measurement data measured with the reference gauge placed at the second measurement point and the distance between the first measurement point and the second measurement point. Calculate the exact distance between

JP 2019-120536 Publication

In the technique described in Patent Document 1, it is necessary to move the reference gauge to the second measurement point after measurement at the first measurement point. Therefore, a mechanism for accurately moving the reference gauge by a predetermined distance is required, and the configuration of the evaluation device becomes complicated.

The present disclosure can be realized as the following forms.
(1) According to one embodiment of the present disclosure, an evaluation device for an X-ray CT device is provided. This evaluation device includes an X-ray source that emits X-rays, and an X-ray detector that is placed in the direction in which the X-rays are emitted from the X-ray source, and that is placed between the X-ray source and the X-ray detector. an X-ray detector for detecting the intensity of X-rays transmitted through a subject and acquiring detection data; and an evaluation phantom unit disposed between the X-ray source and the X-ray detector, the The first pair, which includes two phantoms of the four phantoms, has two phantoms of the four phantoms in the first direction, which is the direction from the X-ray source to the X-ray detector. The phantoms are located closer to the X-ray source than the second pair including the phantoms, and each phantom included in the first pair and each phantom included in the second pair are arranged in a second direction intersecting the first direction. , and the phantom unit included in the first pair is arranged so that it is not located on a straight line connecting the phantom included in the second pair and the X-ray source. and an X-ray detector, the calculation unit calculates the distance between the phantom unit and the X-ray detector, and the calculation unit calculates the distance between the phantom unit and the X-ray detector. A first interval of projections of each of the included phantoms and a second interval of projections of each of the phantoms included in the second pair are determined, and a first interval between the first interval and the second interval and a first interval between the first pair and the second pair are determined. and a calculation unit that calculates a distance in the first direction between the X-ray source and the X-ray detector based on the distance in the first direction.
Since a phantom unit including a plurality of phantoms is used, a CT image including projections of a plurality of phantoms can be acquired without moving the phantom unit. Therefore, the configuration of the evaluation device is simple.
(2) In the evaluation device of the above configuration, the distances between the X-ray source and each phantom included in the first pair in the first direction are set equal, and the distances between the X-ray source and the second pair in the first direction are set equal. The distances to each of the included phantoms may be set equally.
Since the projections of the phantoms for each pair are magnified by the same magnification, it is easy to calculate the first interval and the second interval from the projections of each pair.
(3) In the evaluation device of the above embodiment, the four phantoms may have the same shape.
Since the projections of the four phantoms have the same shape, it becomes easy to calculate the interval between the projections of the respective phantoms.
(4) In the evaluation device of the above embodiment, each of the four phantoms may be a cylinder extending in a direction perpendicular to the first direction and the second direction.
When the phantom is a cylinder, the depth from the side of the cylinder to the central axis is constant. Based on the brightness of the phantom projection, the position of the central axis of the phantom can be determined more accurately. Therefore, the projection interval of each phantom can be calculated with high accuracy.
(5) In the evaluation device of the above embodiment, the base area and height of each cylinder may be equal.
Since the cylinders are all of equal size, the projections of the two cylinders of the first pair at equal distances from the X-ray source have the same shape and size. Therefore, it is easy to calculate the first interval from the brightness of the first pair of projections. Also, the projections of the two cylinders of the second pair at equal distances from the X-ray source have the same shape and size. Therefore, it is easy to calculate the second interval from the brightness of the second pair of projections.
(6) In the evaluation device of the above embodiment, the four phantoms are spherical, and the first pair and the second pair are arranged on a plane formed by a direction perpendicular to the first direction and the second direction and the second direction. The four phantoms are arranged so that when projected, the straight line connecting the centers of the two phantoms included in the first pair is parallel to the straight line connecting the centers of the other two phantoms included in the second pair. A phantom may also be placed.
If the phantom is a sphere, the depth from the surface of the sphere to the center is constant. Based on the brightness of the phantom's projection, the position of the center of the phantom can be determined more accurately. Also, since the straight line connecting the centers of the two phantoms included in the first pair and the straight line connecting the centers of the other two phantoms included in the second pair are parallel, Compared to the case where the straight line connecting the centers of the two phantoms included in the second pair and the straight line connecting the centers of the other two phantoms included in the second pair are not parallel, the relationship between the X-ray source and the X-ray detector It becomes easy to calculate the distance between the two in the first direction.
(7) In the evaluation device of the above embodiment, the radius of each sphere may be equal.
Since the spheres are all of equal size, the projections of the two spheres of the first pair at equal distances from the X-ray source have the same shape and size. Therefore, it is easy to calculate the first interval from the brightness of the first pair of projections. Also, the projections of the second pair of two spheres at equal distances from the X-ray source have the same shape and size. Therefore, it is easy to calculate the second interval from the brightness of the second pair of projections.
(8) In the evaluation device of the above embodiment, the interval in the second direction between the two phantoms included in the first pair may be set to be larger than the interval in the second direction between the two phantoms included in the second pair. .
The distance between the first pair of phantoms, which is closer to the X-ray source, is set larger than the distance between the second pair of phantoms, which is farther from the X-ray source, so that all phantoms are projected onto the light-receiving surface of the X-ray detector. You can avoid the situation where you cannot
(9) In the evaluation device of the above embodiment, the interval between the two phantoms included in the first pair in the second direction is equal to the interval between the two phantoms included in the second pair, and the The distance Δd between the pair and the second pair may be set to satisfy the following formula (1).
Δd≧2r/sinθ...(11)
(The radius of the bottom surface of the phantom is r, and the angle that the straight line connecting the position of the X-ray source and one end in the width direction of the projection plane of the X-ray detector makes with the first direction is θ. do)
If the spacing between the first pair of phantoms closer to the X-ray source is equal to the spacing between the second pair of phantoms farther from the X-ray source, the first pair is By setting the distance between the first pair and the second pair, all the phantoms can be projected onto the light receiving surface of the X-ray detector.
(10) According to another aspect of the present disclosure, there is provided an evaluation method for evaluating an X-ray CT apparatus by irradiating a phantom unit with X-rays. In this evaluation method, the phantom unit includes four phantoms, and a first pair including two phantoms among the four phantoms has a higher X Each of the phantoms included in the first pair and each of the phantoms included in the second pair are arranged close to the X-ray source in the first direction, which is the direction from the radiation source to the X-ray detector. , are arranged along a second direction intersecting the first direction, and the phantom included in the first pair is arranged so as not to be located on a straight line connecting the phantom included in the second pair and the X-ray source. ing. This evaluation method includes the steps of irradiating X-rays to an evaluation phantom unit placed between an X-ray source and an X-ray detector, and generating a CT image based on detection data output from the X-ray detector. obtaining a first interval of projections of each of the phantoms included in the first pair and a second interval of projections of each of the phantoms included in the second pair in the second direction from the CT image; calculating a distance in the first direction between the X-ray source and the X-ray detector based on the spacing and the second spacing and the distance in the first direction between the first pair and the second pair; ,including.
Since a phantom unit including a plurality of phantoms is used, a CT image including projections of a plurality of phantoms can be obtained without moving the phantom unit. Therefore, the X-ray CT apparatus can be evaluated with a simple configuration.

1 is a diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment. FIG. 3 is a diagram showing the appearance of a phantom unit. FIG. 2 is a diagram showing a phantom unit placed between an X-ray source and an X-ray detector, viewed from above. It is a figure which shows the example of the CT image which photographed the phantom unit. FIG. 7 is a diagram showing the appearance of a phantom unit according to another embodiment 2. FIG. FIG. 7 is a diagram showing the appearance of a phantom unit according to another embodiment 3; FIG. 7 is a diagram for explaining requirements for phantom arrangement in another embodiment 6;

A. Embodiment FIG. 1 is a diagram showing a schematic configuration of an X-ray CT apparatus 10 and an evaluation apparatus 100 according to an embodiment. In order to measure the internal or external dimensions of the measurement object, the X-ray CT apparatus 10 irradiates the measurement object with X-rays and detects the X-rays that have passed through the measurement object. The object to be measured is also called the object. Moreover, the X-ray CT apparatus 10 may be used to inspect internal defects or shapes of an inspection target by non-destructive inspection. The evaluation device 100 is used to calibrate the X-ray CT device 10 prior to measuring a measurement target. Furthermore, the evaluation device 100 is used to evaluate whether or not the measurement results include errors. In the following description, an XYZ orthogonal coordinate system will be set for ease of understanding. The X-axis direction and the Y-axis direction are directions parallel to the horizontal plane. The Z-axis direction is a direction perpendicular to the X-axis direction and the Y-axis direction.

The X-ray CT apparatus 10 includes an X-ray source 11, an X-ray source control section 12, a rotary table 13, a rotation mechanism 14, an X-ray detector 15, a detector control section 16, and an image generation section 17. , a tomographic image generation section 18, and a storage section 19. The functions of the X-ray source control section 12, rotation mechanism 14, detector control section 16, image generation section 17, tomographic image generation section 18, and storage section 19 are realized by a computer equipped with a processor and a memory. shall be.

The X-ray source 11 irradiates X-rays toward the inspection target. Specifically, the X-ray source 11 includes an X-ray tube (not shown), and generates X-rays according to the tube voltage and tube current supplied from the X-ray source control section 12. The X-ray source control unit 12 controls the The radiation source 11 is controlled.

The rotating table 13 is a table on which an object to be inspected is placed. The rotary table 13 is rotatable around a central axis in a direction parallel to the Z-axis. The rotation mechanism 14 includes a motor (not shown), and rotates the rotating table 13 by driving the motor.

The X-ray detector 15 is arranged in the X-ray emission direction of the X-ray source 11. The X-ray detector 15 detects the intensity of X-rays that have passed through the inspection object for each pixel, and outputs X-ray transmission data indicating the detection results. X-ray transmission data is also called detection data. The X-ray detector 15 is a combination of a flat panel detector (FPD) or an image intensifier (I.I.) with a CCD image sensor. The light-receiving surface of the X-ray detector 15 is perpendicular to the X-axis direction, which is the direction from the X-ray source 11 to the X-ray detector 15, and is parallel to the YZ plane. The light receiving surface of the X-ray detector 15 is also called a projection surface. The X-axis direction, which is the direction from the X-ray source 11 to the X-ray detector 15, is also referred to as a first direction. The Y-axis direction is also referred to as a second direction. Note that the light-receiving surface of the X-ray detector 15 may be a surface having an inclination within a range of +-10 degrees with respect to the YZ plane. The detector control unit 16 controls the X-ray detector 15 based on the imaging condition data stored in the storage unit 19.

The image generation unit 17 generates a CT image based on the X-ray transmission data output by the X-ray detector 15. Hereinafter, a CT image may be simply referred to as an image. For example, the rotary table 13 is rotated by the rotation mechanism 14 while the X-ray source 11 irradiates the inspection object placed on the rotary table 13 with X-rays. The image generation unit 17 sequentially generates CT images from the X-ray transmission data output by the X-ray detector 15 while the rotating table 13 is rotating. As a result, a CT image corresponding to X-ray transmission data for 360 degrees around the inspection object is generated.

The tomographic image generation unit 18 generates a tomographic image by reconstructing the series of CT images generated by the image generation unit 17. For example, the tomographic image generation unit 18 generates a CT image representing a tomographic image of the test object sliced along a plane along the XY plane by reconstructing an image taken of the test object from 360 degrees around the test object. be done.

The storage unit 19 stores measurement condition data used by the X-ray source control unit 12 to control the X-ray source 11. The storage unit 19 also stores imaging condition data used by the detector control unit 16 to control the X-ray detector 15.

As described above, the X-ray CT apparatus 10 measures the internal or external dimensions of the object to be inspected. Measured values may include errors due to various factors. For example, if the distance between the X-ray source 11 and the X-ray detector 15 is long, the image of the inspection object projected onto the X-ray detector 15 will appear larger than the actual inspection object. Therefore, prior to the inspection, the distance between the X-ray source 11 and the X-ray detector 15 is accurately measured in advance, and the magnification of the image projected onto the light-receiving surface of the X-ray detector 15 is calculated. Accurate measurements of the dimensions of the inspection object can be obtained by calibrating the measurements of the dimensions of the inspection object using a pre-calculated magnification for the projected image of the actual inspection object. I can do it.

The evaluation device 100 uses a part of the configuration of the X-ray CT device 10 to accurately measure the distance between the X-ray source 11 and the X-ray detector 15 for calibration processing. The evaluation device 100 includes a phantom unit 110 and a distance calculation section 120.

The phantom unit 110 is an evaluation phantom placed between the X-ray source 11 and the X-ray detector 15 during calibration. A phantom is a reference device used for calibration and evaluation.

FIG. 2 is a diagram showing the appearance of the phantom unit 110. The phantom unit 110 includes a phantom 111, a phantom 112, a phantom 113, a phantom 114, and a base 115. Each of the phantoms 111 to 114 is formed as a cylinder. The base areas and heights of the phantoms 111 to 114 are all equal. That is, the phantoms 111-114 have the same shape and size. Although any material can be used to form the phantoms 111 to 114, it is preferable to use a material that is less affected by thermal expansion due to temperature changes. The material forming the phantoms 111 to 114 may be the same material as the object to be inspected. Phantoms 111 to 114 are placed on a base 115.

Phantom 111 and phantom 112 are placed at the same position in the X-axis direction and at different positions in the Y-axis direction. That is, the phantoms 111 and 112 are arranged side by side along the Y-axis direction. Phantom 111 and phantom 112 are sometimes referred to as a first pair. The distance between the phantom 111 and the phantom 112 in the Y-axis direction is set to be a distance W1. The interval W1 represents the interval between the central axis of the phantom 111 and the central axis of the phantom 112.

Phantom 113 and phantom 114 are placed at the same position in the X-axis direction and at different positions in the Y-axis direction. That is, the phantoms 113 and 114 are arranged side by side along the Y-axis direction. Phantom 113 and phantom 114 are sometimes referred to as a second pair. Phantoms 113 and 114 are arranged at different positions from phantom 111 and phantom 112 in the X-axis direction. Phantoms 113 and 114 are arranged in a different column from phantom 111 and phantom 112. The distance between the phantoms 113 and 114 in the Y-axis direction is set to be a distance W2. The interval W2 represents the interval between the central axis of the phantom 113 and the central axis of the phantom 114.

In the embodiment, phantom 111 and phantom 112 are located closer to X-ray source 11 than phantom 113 and phantom 114, and phantom 113 and 114 are located farther from X-ray source 11 than phantom 111 and phantom 112. shall be located at. The condition that the phantom 111 in the front row is not located on the straight line connecting the phantom 113 in the rear row and the X-ray source 11, and the phantom 112 in the front row is not located on the straight line connecting the phantom 114 in the rear row and the X-ray source 11. The phantoms 111 to 114 must be arranged so that the following conditions are satisfied. Therefore, it is assumed that the value of the interval W1 and the value of the interval W2 are appropriately set so as to satisfy this condition. The reason why the phantoms 111 to 114 are arranged in this way is to project the phantoms 111 to 114 onto the light receiving surface of the X-ray detector 15 at the same time. This is also to prevent the projections of the phantoms 111 to 114 projected onto the light receiving surface of the X-ray detector 15 from overlapping each other.

In the embodiment, the interval W2 is set to be smaller than the interval W1. Hereinafter, it is assumed that the interval W1 and the interval W2 are set so that W1=2·W2.

The base 115 is a foundation that supports the phantoms 111-114. The base 115 is made of a rectangular plate-like member. The material forming the base 115 is, for example, the same material as the material forming the phantoms 111-114. The phantoms 111 to 114 are arranged to extend vertically from the base 115. The phantoms 111 to 114 are fixed to a base 115. It is assumed that the surface of the base 115 on which the phantoms 111 to 114 are fixed is formed parallel to a horizontal surface.

The distance between the -X side end of the base 115 and the phantom 111 in the X-axis direction and the distance between the -X side end of the base 115 and the phantom 112 in the X-axis direction are set equal. The distance between the -X side end of the base 115 and the phantom 113 in the X-axis direction and the distance between the -X side end of the base 115 and the phantom 114 in the X-axis direction are set equal. As described above, the phantoms 111 to 114 are arranged along the Y-axis direction. In this way, in the XY plane, the straight line connecting the central axis of the phantom 111 and the central axis of the phantom 112 is parallel to the straight line connecting the central axis of the phantom 113 and the central axis of the phantom 114. The phantoms 111 to 114 are placed in the phantoms.

The phantom unit 110 is manufactured within tolerance dimensions by precision machining. The dimensions of each of the phantoms 111 to 114 and their position on the base 115 may be ensured to be within tolerance dimensions by, for example, being measured by a three-dimensional measuring device.

FIG. 3 is a diagram showing a top view of the phantom unit 110 placed between the X-ray source 11 and the X-ray detector 15 during calibration. Note that the illustration of the base 115 is omitted in FIG. 3. Phantom 111 and phantom 112 are placed closer to X-ray source 11 than phantom 113 and 114 in the X-axis direction. Phantom 113 and phantom 114 are arranged farther from X-ray source 11 than phantom 111 and phantom 112 in the X-axis direction. It is assumed that the X-axis direction and the direction from the X-ray source 11 to the X-ray detector 15 match.

Further, the phantom unit 110 is arranged so that the distance between the X-ray source 11 and the phantom 111 and the distance between the X-ray source 11 and the phantom 112 in the X-axis direction are equal. For example, the phantom unit 110 is arranged so that the -X side end of the base 115 and the exit window of the X-ray source 11 are parallel to each other. As described above, the distance between the -X side end of the base 115 and the phantom 113 in the X-axis direction and the distance between the -X side end of the base 115 and the phantom 114 in the X-axis direction are set equal. has been done. Therefore, the distance between the X-ray source 11 and the phantom 113 and the distance between the X-ray source 11 and the phantom 114 in the X-axis direction are equal.

The distance between the X-ray source 11 and the phantoms 111 and 112 in the X-axis direction is defined as a distance d1. The distance d1 is, for example, the distance between the exit window of the X-ray source 11 and the position of the central axis of the phantom 111 in the X-axis direction. Further, the distance in the X-axis direction between the exit window of the X-ray source 11 and the position of the central axis of the phantom 112 is also the distance d1.

The projections of the phantoms 111 to 114 are respectively referred to as projections P1 to P4. The distance in the X-axis direction between phantoms 111 and 112 included in the first pair and phantoms 113 and 114 included in the second pair is defined as distance L1. The distance between the phantoms 111 and 112 and the X-ray detector 15 in the X-axis direction is defined as a distance d2. The distance d2 is, for example, the distance between the position of the central axis of the phantom 111 and the light receiving surface of the X-ray detector 15 in the X-axis direction. Further, the distance in the X-axis direction between the position of the central axis of the phantom 112 and the light receiving surface of the X-ray detector 15 is also the distance d2. The distance between the X-ray source 11 and the X-ray detector 15 is defined as a distance Ld.

FIG. 4 is a diagram showing an example of a CT image taken of the phantom unit 110. The projection of the base 115 is assumed to be P5. The distance calculation unit 120 calculates the distance Ld between the X-ray source 11 and the X-ray detector 15 from the CT image generated by the image generation unit 17. Specifically, first, the distance calculating unit 120 calculates, from the CT image, the distance W1' in the Y-axis direction between the projection P1 of the phantom 111 and the projection P2 of the phantom 112, the projection P3 of the phantom 113, and the projection P4 of the phantom 114. and the distance W2' in the Y-axis direction. The interval W1' is also referred to as a first interval. The interval W2' is also referred to as a second interval.

Hereinafter, a method in which the distance calculation unit 120 calculates the distances d1, d2, and Ld using the interval W1' and the interval W2' will be described with reference to FIG. 3.

The magnification rate G1 of the projection of the phantoms 111 and 112 is expressed by the distance W1 and the distance W1' as G1=W1'/W1. Further, the magnification ratio G1 can also be determined from the distance d1 and the distance d2 using the following formula (1).
G1=W1'/W1=(d1+d2)/d1...(1)
When formula (1) is modified, the interval W1 is expressed as shown in formula (2) below.
W1=(W1'・d1)/(d1+d2)...(2)

The magnification rate G2 of the projection of the phantoms 113 and 114 is expressed by the distance W2 and the distance W2' as G2=W2'/W2. Further, the magnification ratio G2 can also be determined from the distance d1, the distance d2, and the distance L1 using the following formula (3).
G2=W2'/W2={(d1+L1)+(d2-L1)}/(d1+L1)=(d1+d2)/(d1+L1)...(3)
When formula (3) is modified, the interval W2 is expressed as in formula (4) below.
W2=W2'・(d1+L1)/(d1+d2)...(4)

As described above, in the embodiment, the interval W1 and the interval W2 are set so that W1=2·W2. In this case, by modifying equation (2) in which W1=2·W2 is substituted, the interval W2 is expressed as equation (5).
W2=(W1'・d1)/{2・(d1+d2)}...(5)
Since the left sides of both equations (4) and (5) are the same, equation (6) holds true.
W2'・(d1+L1)/(d1+d2)=(W1'・d1)/{2・(d1+d2)} ...(6)

When formula (6) is transformed, the distance d1 is expressed as in formula (7) below.
d1=(2W1'・L1)/(W1'-2W2')...(7)
Further, when formula (1) is modified, distance d2 is expressed as in formula (8) below.
d2=d1・(W1'/W1-1)...(8)

The distance calculation unit 120 inputs the respective values of the interval W1' and the interval W2' calculated from the image projected by the phantom unit 110, and the known distance L1 into the above equation (7), and calculates the distance. d1 can be calculated.

The distance calculation unit 120 calculates the distance W1' and the distance W2', which are calculated from the image projected by the phantom unit 110, into the equation (9) obtained by substituting the equation (7) into the equation (8). The distance d2 can be calculated by substituting each value of a certain interval W1.
d2={(2W1'・L1)/(W1'-2W2')}・(W1'/W1-1)...(9)

As shown in FIG. 3, the distance Ld between the X-ray source 11 and the X-ray detector 15 is the sum of the distance d1 and the distance d2. Therefore, using equations (7) and (9), the distance Ld is expressed as shown in equation (10) below.
Ld=d1+d2=(2W1'・L1)/(W1'-2W2')+{(2W1'・L1)/(W1'-2W2')}・(W1'/W1-1)={(2W1'・L1)/(W1'-2W2')}・(W1'/W1)...(10)

The distance Ld between the X-ray source 11 and the X-ray detector 15 is also referred to as focus-to-detector distance (FDD). The calculated distance Ld is an accurate distance between the X-ray source 11 and the X-ray detector 15.

Next, a method of calibrating the X-ray CT apparatus 10 will be explained. The operator places the phantom unit 110 on the rotary table 13. Specifically, the operator places the phantom unit 110 on the rotating No. 13 so that the -X side end of the base 115 shown in FIG. 2 and the exit window of the X-ray source 11 are parallel to each other. . Therefore, the distance from the X-ray source 11 to the central axis of the phantom 111 is equal to the distance from the X-ray source 11 to the central axis of the phantom 112. Furthermore, the distance from the X-ray source 11 to the central axis of the phantom 113 is equal to the distance from the X-ray source 11 to the central axis of the phantom 114.

The operator sets the X-ray source control section 12 and the detector control section 16 appropriately, and then causes the X-ray source 11 to irradiate the phantom unit 110 with X-rays. When the X-ray detector 15 outputs the X-ray transmission data, the image generation unit 17 generates an image based on the X-ray transmission data. The generated image is supplied to the distance calculation unit 120. Therefore, the distance calculating section 120 calculates the distance Ld between the X-ray source 11 and the X-ray detector 15 from the supplied image of the phantom unit 110 using the method described above. The distance calculation unit 120 supplies the calculated distance Ld to the tomographic image generation unit 18. The tomographic image generation unit 18 changes parameters necessary to generate a tomographic image based on the value of the distance Ld, which is the accurate distance between the X-ray source 11 and the X-ray detector 15. Therefore, accurate measurement values of the dimensions of the object to be inspected can be obtained.

As described above, in the embodiment, the phantom unit 110 includes a pair of phantoms 111 and 112 and a pair of phantoms 113 and 124 arranged at different positions in the first direction. Therefore, a CT image including the first pair of projections and the second pair of projections located at different positions can be acquired by one imaging operation. Unlike the conventional method, there is no need to move the phantom, so the configuration of the evaluation device 100 is simple. Additionally, X-ray CT equipment can be evaluated with a simple configuration.

Further, the first pair of phantoms 111 to 112 are arranged at equal distances from the X-ray source 11. Therefore, the projections of the phantoms 111-112 are magnified by the same magnification. Furthermore, the phantoms 111 to 112 are formed as cylinders with the same base area and height. Since the projections of the first pair of phantoms 111-112 have the same shape and size, it is easy to calculate the interval W1' from the brightness of the first pair of projections. Further, the second pair of phantoms 113 to 114 are arranged at equal distances from the X-ray source 11. Therefore, the projections of the phantoms 113-114 are magnified by the same magnification. Further, the phantoms 113 to 114 are formed as cylinders having the same base area and height. Since the projections of the second pair of phantoms 113-114 have the same shape and size, it is easy to calculate the interval W2' from the brightness of the second pair of projections.

Furthermore, the phantoms 111 to 114 are formed as cylinders extending in the Z-axis direction, which is a direction perpendicular to the horizontal plane. Therefore, since the depth from the side surfaces of the phantoms 111 to 114 to the central axes is constant, the positions of the central axes of the phantoms 111 to 114 can be determined more accurately based on the brightness of the projections of the phantoms 111 to 114. . Thereby, the interval W1' and the interval W2' can be calculated with high accuracy.

In the embodiment, the distance W1 between the phantoms 111 and 112 included in the first pair located near the X-ray source 11 is greater than the distance W1 between the phantoms 113 and 112 included in the second pair located far from the X-ray source 11. and 114 is set larger than the interval W2. This is because the X-rays emitted from the X-ray source 11 spread radially, so if the interval W2 is larger than the interval W1, it may not be possible to project all of the phantoms 111 to 114 onto the light-receiving surface of the X-ray detector 15. . Since the interval W1 between the first pair of phantoms 111 and 112, which is closer to the X-ray source 11, is set larger than the interval between the second pair of phantoms 113 and 114, which is farther from the X-ray source 11, all phantoms It is possible to avoid a situation where the image cannot be projected onto the light receiving surface of the ray detector.

B1. Other embodiment 1:
In the embodiment, an example has been described in which the phantoms 111 to 114 included in the phantom unit 110 are formed as cylinders having the same size. However, the examples of the phantoms 111 to 114 are not limited to this. Hereinafter, a description will be given focusing on configurations that are different from the embodiment.

The heights and bottom areas of the phantoms 111 to 114 formed as cylinders do not necessarily have to be equal. In this case, it is preferable that the first pair of phantoms 111 and 112 have the same height and base area. This is because each of the first pair of projections has the same shape and size, making it easy to calculate the interval W1'. Further, it is preferable that the second pair of phantoms 113 and 114 have the same height and base area. This is because the second pair of projections each have the same shape and size, making it easy to calculate the interval W2'.

Also in the first embodiment, the phantom 111 in the front row is not located on the straight line connecting the phantom 113 in the rear row and the X-ray source 11, and the phantom 112 in the front row connects the phantom 114 in the rear row and the X-ray source 11. It is assumed that the phantoms 111 to 114 are arranged so that the condition that they are not located on the connecting straight line is satisfied. This is to simultaneously project the phantoms 111 to 114 onto the light receiving surface of the X-ray detector 15. This is also to prevent the projections of the phantoms 111 to 114 projected onto the light receiving surface of the X-ray detector 15 from overlapping each other.

B2. Other embodiment 2:
FIG. 5 is a diagram showing the appearance of a phantom unit 110A according to another embodiment 2. The phantom unit 110A includes phantoms 111a to 114a and support parts 116 to 119. Each of the phantoms 111a to 114a is formed as a sphere with the same radius. The phantoms 111a to 114a are fixed to the base 115 by cylindrical support parts 116 to 119, respectively. Note that the support parts 116 to 119 are arranged to extend vertically from the base 115. It is assumed that the surface of the base 115 to which the supporting parts 116 to 119 are fixed is formed parallel to a horizontal surface. In another embodiment 2, the support parts 116 to 119 are used to support the phantoms 111a to 114a. The projections of the supports 116-119 are not used to calculate the distance W1' and the distance W2'.

The support parts 116 to 119 have the same base area and height. The phantoms 111a to 114a are arranged at the same position in the Z-axis direction. Therefore, when the phantoms 111a to 114a are projected onto the light receiving surface of the X-ray detector 15, a straight line connecting the centers of the phantoms 111a and 112a and a straight line connecting the centers of the phantoms 113a and 114a are The phantoms 111a to 114a are arranged parallel to each other. With this arrangement, the straight line connecting the centers of phantoms 111a and 112a included in the first pair is not parallel to the straight line connecting the centers of phantoms 113a and 114a included in the second pair. It is easier to calculate the distance Ld between the X-ray source 11 and the X-ray detector 15 than in the case of the above case.

In the second embodiment as well, the phantom 111 in the front row is not located on the straight line connecting the phantom 113 in the rear row and the X-ray source 11, and the phantom 112 in the front row is located on the straight line connecting the phantom 114 in the rear row and the X-ray source 11. It is assumed that the phantoms 111 to 114 are arranged such that the condition that they are not located on a straight line connecting the phantoms 111 to 114 is satisfied. This is to simultaneously project the phantoms 111 to 114 onto the light receiving surface of the X-ray detector 15. This is also to prevent the projections of the phantoms 111 to 114 projected onto the light receiving surface of the X-ray detector 15 from overlapping each other.

The spherical bodies of the phantoms 111a to 114a are all equal in size, and the distances from the X-ray source 11 of the first pair of phantoms 111a to 112a are equal. Therefore, the projections of the phantoms 111a to 112a are magnified by the same magnification. Since the projections of the first pair of phantoms 111a-112a have the same shape and size, it is easy to calculate the interval W1' from the brightness of the first pair of projections. Further, the distances of the second pair of phantoms 113a to 114a from the X-ray source 11 are equal. Therefore, the projections of the phantoms 113a to 114a are magnified by the same magnification. Since the projections of the second pair of phantoms 113a-114a have the same shape and size, it is easy to calculate the interval W2' from the brightness of the second pair of projections.

Further, since the depth from the surface to the center of the phantoms 111a to 114a is constant, the positions of the centers of the phantoms 111a to 114a can be determined more accurately based on the brightness of the projections of the phantoms 111a to 114a. Thereby, the interval W1' and the interval W2' can be calculated with high accuracy.

The heights of the supports 116 to 119 do not necessarily have to be equal. In this case, among the supports 116 to 119, the heights of the supports 116 and 117 that support the first pair of phantoms 111a and 112a are preferably equal. This is because the positions of the first pair of projections in the Z-axis direction are the same, making it easier to calculate the interval W1'. Further, it is preferable that the heights of the support parts 118 and 119 that support the second pair of phantoms 113a and 114a are equal. This is because the positions of the second pair of projections in the Z-axis direction are the same, making it easier to calculate the interval W2'.

The radii of the phantoms 111a to 114a do not necessarily have to be equal. In this case, the radii of the first pair of phantoms 111a and 112a are preferably equal. This is because the first pair of projections have the same shape and size, making it easy to calculate the interval W1'. Moreover, it is preferable that the radii of the second pair of phantoms 113a and 114a are equal. This is because the second pair of projections have the same shape and size, making it easier to calculate the interval W2'.

B3. Other embodiment 3:
FIG. 6 is a diagram showing the appearance of a phantom unit 110B according to another third embodiment. The phantom unit 110B has phantoms 111b to 114b. Unlike the other embodiment 2, the phantom unit 110B does not have a support portion that supports each of the phantoms 111b to 114b. Each of the phantoms 111b to 114b is directly fixed to the base 115.

It is assumed that the surface of the base 115 to which the phantoms 111b to 114b are fixed is formed parallel to a horizontal surface. Therefore, the phantoms 111b to 114b are arranged at the same position in the Z-axis direction. Therefore, when the phantoms 111b to 114b are projected onto the light-receiving surface of the X-ray detector 15, a straight line connecting the centers of the phantoms 111b and 112b and a straight line connecting the centers of the phantoms 113b and 114b are the same. The phantoms 111b to 114b are arranged in parallel. With this arrangement, the straight line connecting the centers of phantoms 111b and 112b included in the first pair is not parallel to the straight line connecting the centers of phantoms 113b and 114b included in the second pair. The interval W1' and the interval W2' can be calculated more easily than in the case where the distance W1' and the interval W2' are calculated easily.

In the third embodiment as well, the phantom 111b in the front row is not located on the straight line connecting the phantom 113b in the rear row and the X-ray source 11, and the phantom 112b in the front row is located on the straight line connecting the phantom 114b in the rear row and the X-ray source 11. It is assumed that the phantoms 111b to 114b are arranged such that the condition that they are not located on a straight line connecting the phantoms 111b to 114b is satisfied. This is to simultaneously project the phantoms 111b to 114b onto the light receiving surface of the X-ray detector 15. This is also to prevent the projections of the phantoms 111b to 114b projected onto the light receiving surface of the X-ray detector 15 from overlapping each other.

Furthermore, since the respective sizes of the spheres that are the phantoms 111b to 114b are all equal, similarly to the second embodiment, the interval W1' is calculated from the brightness of the first pair of projections, and the interval W1' is calculated from the brightness of the second pair of projections. It is easy to calculate the interval W2'.

Further, since the depth from the surface to the center of the phantoms 111b to 114b is constant, the position of the center of the phantoms 111b to 114b is determined based on the brightness of the projection of the phantoms 111b to 114b, as in the second embodiment. can be determined more accurately. Thereby, the interval W1' and the interval W2' can be calculated with high accuracy.

The radii of the phantoms 111b to 114b do not necessarily have to be equal. In this case, the radii of the first pair of phantoms 111b and 112b are preferably equal. This is because the first pair of projections have the same shape and size, making it easy to calculate the interval W1'. Moreover, it is preferable that the radii of the second pair of phantoms 113b and 114b are equal. This is because the second pair of projections have the same shape and size, making it easier to calculate the interval W2'.

B4. Other embodiment 4:
In the embodiment, an example has been described in which the phantoms 111 to 114 formed as cylinders extend in the Z-axis direction, which is a direction perpendicular to the horizontal plane. Alternatively, the phantoms 111 to 114 formed as cylinders may extend in other directions inclined with respect to the Z axis within the YZ plane. Since the projections of the phantoms 111 to 114 extend in the same direction in the YZ plane, the interval W1' and the interval W2' can be calculated from the projections, similarly to the embodiment.

B5. Other embodiment 5:
In other embodiments 2 and 3, an example has been described in which the surface of the base 115 on which the phantom is fixed is formed to be parallel to the horizontal surface. Alternatively, the surface of the base 115 on which the phantom is fixed may be a surface inclined with respect to the Y axis.

In this case, similarly to the embodiment, when the phantoms 111 to 114 are projected onto the light receiving surface of the X-ray detector 15 that is parallel to the YZ plane, the centers of each of the phantoms 111 and 112 included in the first pair The phantoms 111 to 114 are arranged so that the straight line connecting the phantoms 111 to 114 is parallel to the straight line connecting the centers of the phantoms 113 and 114 included in the second pair. By arranging them in this way, the straight line connecting the centers of the phantoms 111 and 112 included in the first pair is not parallel to the straight line connecting the centers of each of the phantoms 113 and 114 included in the second pair. The interval W1' and the interval W2' can be calculated more easily than in the case where the distance W1' and the interval W2' are calculated easily.

B6. Other embodiment 6
In the embodiment, an example has been described in which the interval W1 between the first pair of phantoms 111 and 112 is different from the interval W2 between the second pair of phantoms 113 and 114. Alternatively, the interval W1 and the interval W2 may be equal. In this case, the phantom 111 needs to be placed so as not to be located on a straight line connecting the X-ray source 11 and the phantom 113. Furthermore, the phantom 112 needs to be placed so as not to be located on a straight line connecting the X-ray source 11 and the phantom 114.

FIG. 7 is a diagram for explaining requirements for arrangement of phantoms 111 to 114 in another embodiment 6. FIG. 7 shows the X-ray source 11, the phantoms 111 to 114, and the X-ray detector 15 viewed from above. The distance W1 between the phantoms 111 and 112 is equal to the distance W2 between the phantoms 113 and 114.

Even if the interval W1 and the interval W2 are equal, the distance Δd is set to satisfy the following formula (11) in order to project onto the light receiving surfaces of the X-ray detectors 15 of all the phantoms 111 to 114. There is a need. The distance Δd is the distance in the X-axis direction between the first pair of phantoms 111 and 112 and the second pair of phantoms 113 and 114. Let r be the radius of the bottom surface of the phantoms 111 to 114.

Assume that the angle that the straight line A2 makes with the straight line A1 is θ. The straight line A1 is a straight line connecting the center of the X-ray source 11 and the center of the light-receiving surface of the X-ray detector 15 in the XY plane. A straight line A1 represents the path along which the X-rays output from the X-ray source 11 reach the X-ray detector 15 without being interfered with by the phantoms 111 and 113. The straight line A2 is a straight line connecting the center of the X-ray source 11 and the end of the light-receiving surface of the X-ray detector 15 in the width direction. The Y-axis direction of the projection plane of the X-ray detector 15 is also referred to as the width direction.
Δd≧2r/sinθ...(11)

By setting the distance Δd so as to satisfy the above formula (1), even if the distance W1 and the distance W2 are equal, the phantoms 111 to 114 can be projected onto the light receiving surfaces of all the X-ray detectors 15. I can do it.

B7. Other embodiment 7
Furthermore, in order to accurately measure the intervals W1' and W2', it is necessary to calculate the position of the central axis of the phantom 111 from the brightness distribution of the projection P1 of the phantom 111. Therefore, it is necessary to accurately specify the contours of the projections P1 to P4. Here, in the CT image, the contour line is displayed with a spread of about several pixels. Therefore, variations occur in the luminance distribution. For this reason, it is difficult to uniquely define the central axis. Therefore, the position where the absolute value of the brightness gradient of the contour portion of the projection P1 is maximum may be determined as the position of the contour line. The center of the left and right contour lines of the phantom 111 along the Z-axis can be set as the position of the central axis.

Alternatively, an approximate curve of a graph representing the brightness distribution may be drawn, and the coordinates of the pixel with the lowest brightness value may be determined as the position of the central axis. Methods for drawing an approximate curve include the least squares method, the N-point moving average method, and Greville's method.

B8. Other embodiment 8
In the embodiment, the distance between the X-ray source 11 and the phantom 111 and the distance between the X-ray source 11 and the phantom 112 were set to be equal. Further, the distance between the X-ray source 11 and the phantom 113 and the distance between the X-ray source 11 and the phantom 114 were set to be equal. However, the distance between the X-ray source 11 and the phantom 111 and the distance between the X-ray source 11 and the phantom 112 are not equal; The distance between and does not have to be equal.

Also in this case, the first pair and the second pair are arranged along the same direction. The phantom 111 is arranged so that the straight line connecting the central axis of the phantom 111 and the central axis of the phantom 112 and the straight line connecting the central axis of the phantom 113 and the central axis of the phantom 114 are parallel in the XY plane. ~114 are arranged.

Since the distance between the X-ray source 11 and the phantom 111 is not equal to the distance between the X-ray source 11 and the phantom 112, the magnification of the projection of the phantom 111 and the magnification of the projection of the phantom 112 are different. However, the interval W1' can be calculated from the central axis of the phantom 111 shown by the projection of the phantom 111 and the central axis of the phantom 112 shown by the projection of the phantom 112. Further, since the distance between the X-ray source 11 and the phantom 113 is not equal to the distance between the X-ray source 11 and the phantom 114, the magnification of the projection of the phantom 113 and the magnification of the projection of the phantom 114 are different. . However, the interval W2' can be calculated from the position of the central axis of projection of the phantom 113 and the position of the central axis of projection of the phantom 112.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each form described in the column of the summary of the invention may be used to solve some or all of the above-mentioned problems, or to achieve one of the above-mentioned effects. In order to achieve some or all of the above, it is possible to replace or combine them as appropriate. Further, unless the technical feature is described as essential in this specification, it can be deleted as appropriate.

A1...straight line, A2...straight line, G1...magnification rate, G2...magnification rate, L1...distance, Ld...distance, W1...interval, W1'...interval, W2...interval, W2'...interval, d1...distance, d2... Distance, Δd...Distance, 10...X-ray CT device, 11...X-ray source, 12...X-ray source control unit, 13...rotating table, 14...rotating mechanism, 15...X-ray detector, 16...detector control unit , 17... Image generation section, 18... Tomographic image generation section, 19... Storage section, 100... Evaluation device, 110... Phantom unit, 110A... Phantom unit, 110B... Phantom unit, 111, 111a, 111b... Phantom, 112, 112a , 112b... Phantom, 113, 113a, 113b... Phantom, 114, 114a, 114b... Phantom, 115... Base, 116, 117, 118, 119... Support section, 120... Distance calculation section

Claims (10)

An evaluation device for an X-ray CT device,
an X-ray source that emits X-rays;
an X-ray detector disposed in the emission direction of the X-rays in the X-ray source, the intensity of the X-rays passing through a subject disposed between the X-ray source and the X-ray detector; an X-ray detector that detects and acquires detection data;
An evaluation phantom unit disposed between the X-ray source and the X-ray detector,
Contains 4 phantoms,
A first pair comprising two phantoms of the four phantoms connects the other two phantoms of the four phantoms in a first direction, which is the direction from the X-ray source to the X-ray detector. is located closer to the X-ray source than the second pair containing the X-ray source,
Each of the phantoms included in the first pair and each of the phantoms included in the second pair are arranged along a second direction intersecting the first direction,
The phantom included in the first pair is arranged so as not to be located on a straight line connecting the phantom included in the second pair and the X-ray source.
phantom unit,
A calculation unit that calculates a distance between the X-ray source and the X-ray detector,
From a CT image based on the detection data obtained by irradiating the phantom unit with the X-ray, the first interval of projection of each of the phantoms included in the first pair in the second direction and the second determining a second interval of projections of each of the phantoms included in the pair;
The distance between the X-ray source and the X-ray detector is based on the first spacing, the second spacing, and the distance in the first direction between the first pair and the second pair. calculating a distance in a first direction;
A calculation section,
An evaluation device comprising: The evaluation device according to claim 1,
The distances between the X-ray source and each of the phantoms included in the first pair in the first direction are set equal;
distances between the X-ray source and each of the phantoms included in the second pair in the first direction are set equal;
Evaluation device. The evaluation device according to claim 1 or 2,
the four phantoms have the same shape,
Evaluation device. The evaluation device according to claim 3,
Each of the four phantoms is a cylinder extending in a direction perpendicular to the first direction and the second direction,
Evaluation device. The evaluation device according to claim 4,
The base area and height of each of the cylinders are equal;
Evaluation device. The evaluation device according to claim 3,
The four phantoms are spherical,
When the first pair and the second pair are projected onto a plane formed by the second direction and a direction perpendicular to the first direction and the second direction, the two included in the first pair The four phantoms are arranged such that a straight line connecting the centers of the phantoms is parallel to a straight line connecting the centers of the other two phantoms included in the second pair.
Evaluation device. The evaluation device according to claim 6,
The radius of each of the spheres is equal;
Evaluation device. The evaluation device according to any one of claims 1 to 7,
The distance between the two phantoms included in the first pair in the second direction is set to be larger than the distance in the second direction between the two phantoms included in the second pair.
Evaluation device. The evaluation device according to claim 4 or 5,
The distance between the two phantoms included in the first pair and the distance between the two phantoms included in the second pair in the second direction are equal,
A distance Δd between the first pair and the second pair in the first direction is set to satisfy the following formula (11),
Δd≧2r/sinθ...(11)
(The radius of the bottom surface of the phantom is r, and the angle that the straight line connecting the position of the X-ray source and one end in the width direction of the projection plane of the X-ray detector makes with the first direction is θ. do)
Evaluation device. An evaluation method for evaluating an X-ray CT device by irradiating a phantom unit with X-rays, the method comprising:
The phantom unit is
Contains 4 phantoms,
A first pair comprising two phantoms of the four phantoms comprises the other two phantoms of the four phantoms in a first direction, which is the direction from the X-ray source to the X-ray detector. is located closer to the X-ray source than the second pair;
Each of the phantoms included in the first pair and each of the phantoms included in the second pair are arranged along a second direction intersecting the first direction,
The phantom included in the first pair is arranged so as not to be located on a straight line connecting the phantom included in the second pair and the X-ray source.
A phantom unit,
The evaluation method is
irradiating the X-ray to an evaluation phantom unit disposed between the X-ray source and the X-ray detector;
acquiring a CT image based on detection data output from the X-ray detector;
determining a first interval of projections of each of the phantoms included in the first pair and a second interval of projections of each of the phantoms included in the second pair in the second direction from the CT image;
The distance between the X-ray source and the X-ray detector is based on the first spacing, the second spacing, and the distance in the first direction between the first pair and the second pair. calculating a distance in a first direction;
Evaluation methods including.

Images