JP7366467B2 - Evaluation equipment for X-ray CT equipment - Google Patents

Description

The present invention relates to an X-ray CT evaluation instrument.

X-ray CT (Computed Tomography) devices developed for medical use have recently been used for measuring industrial products, that is, measuring dimensions and shapes. Conventionally, contact-type coordinate measuring machines (CMMs) have been used to measure the shape of industrial products, and the ISO 10360-2 standard has been used to evaluate their accuracy. Regarding X-ray CT, there is also a demand for the establishment of an accuracy evaluation method standard, and discussions are underway to publish it as ISO 10360-11.

Here, the measurement principle of X-ray CT will be briefly explained using FIG. 1. The X-ray CT apparatus for three-dimensional shape measurement includes an X-ray irradiation section 11, an X-ray detector 12, and a rotation stage 13. This X-ray CT apparatus uses a non-destructive method in which an object to be measured (also referred to as a workpiece) is placed on a rotating stage 13 placed between an X-ray irradiator 11 and an X-ray detector 12, which are arranged opposite to each other. This is used to observe the interior and measure the three-dimensional shape.

The X-ray irradiation unit 11 includes an X-ray tube as an X-ray source therein, and causes the X-ray tube to generate X-rays according to the tube voltage and tube current supplied from the high voltage generator 15. This high voltage generator 15 is controlled by an X-ray control section 16, and the X-ray control section 16 is connected to a PC (Personal Computer) in which control software for controlling the entire X-ray CT apparatus is installed. The X-ray detector 12 is a combination of an image intensifier and a CCD (Charge Coupled Device) camera, or an FPD (Flat Panel Detector), and is connected to a PC via a CT image reconstruction calculation device 18. . Note that the X-ray detector 12 is configured to be movable toward and away from the rotation stage 13 in order to enlarge and reduce the fluoroscopic imaging area. Furthermore, the rotation stage 13 can also be moved toward and away from the X-ray irradiation section 11 .

The rotation stage 13 rotates about a Z-axis that is perpendicular to the X-axis along the X-ray optical axis L connecting the X-ray irradiation unit 11 to the X-ray detector 12 as a rotation axis R, and is rotated by a stage drive mechanism 14 to rotate the It is possible to move horizontally and vertically in the Z direction. The stage drive mechanism 14 is connected to and controlled by the PC via the stage control section 17.

During X-ray CT imaging, the object to be inspected placed on the rotary stage 13 is irradiated with X-rays from the X-ray irradiation unit 11 while the rotary stage 13 is rotated about the rotation axis R. Then, the X-ray detector 12 detects the X-rays transmitted from all directions over 360 degrees around the object to be inspected, and the X-ray transmission data is taken into the CT image reconstruction calculation device 18.

The CT image reconstruction calculation unit 18 constructs a three-dimensional reconstructed image (CT image) of the object to be inspected sliced along the XY plane using the captured 360 degrees of X-ray transmission data. be done. The CT image is transmitted from the CT image reconstruction calculation device 18 to the PC, and is used for three-dimensional imaging by a three-dimensional image construction program installed on the PC.

A display device 23 such as a liquid crystal display, and an input device 22 including a keyboard 22a and a mouse 22b are connected to the PC. Note that the keyboard 22a and mouse 22b are used for input by the operator in various operations. The display device 23 displays the CT image transmitted from the CT image reconstruction calculation device 18 to the PC, and also displays a three-dimensional image constructed using the CT image. The PC also measures the dimensions and shape of the object to be measured. Note that the functions of the CT image reconstruction calculation device 18 may be integrated with a PC and realized in one computer as a computer peripheral device or software.

If such an X-ray CT device is used, it becomes possible to obtain a transmitted image of the object to be measured, but if the object is thick or dense, the amount of X-rays that can be transmitted will be limited. The amount of light decreases, and the transmitted image appears dark.

In addition, as the X-ray detector 12, as described above, a two-dimensional detector (area detector) is used (Fig. 2A: cone beam CT), and a one-dimensional detector (line detector) is used. There is a case where it is used (FIG. 2B: fan beam CT). When using a line detector, the reconstructed image obtained is only a one-dimensional cross section, so in order to obtain a three-dimensional reconstructed image, the object to be measured must be moved slightly upward or downward with each rotation. It turns out. On the other hand, when using an area detector, a three-dimensional reconstructed image can be generated by one rotation of the measurement target, but the quality of the obtained reconstructed image is better when using a one-dimensional detector.

Unlike a CMM, an X-ray CT apparatus is capable of measuring the inside of an object to be measured, but for this reason, there are two points that should be considered when evaluating the accuracy of X-ray CT. The first is whether the moving mechanism and parts of the X-ray CT apparatus are properly aligned. If there is an error due to this factor, the dimensions may not be measured correctly, or the entire object to be measured may be observed to be distorted. The second reason is that a nonlinear effect occurs on the attenuation of X-rays when they pass through the object to be measured, and when this factor exists, the measurement results in the object being measured as if there were local irregularities. I end up. Although the standard is under discussion, ISO/2CD 10360-11 requires E-testing for the first consideration and P-testing for the second consideration, and both should be evaluated independently as much as possible. This is desirable. That is, when performing the E test, in order to avoid the influence of the material of the object to be measured, it is preferable that the X-rays do not pass through anything other than the object to be measured as much as possible.

In the E test, which evaluates mechanical errors in X-ray CT, accuracy is evaluated by arranging many spheres or cylinders in space and measuring the distances between them. The distance between spheres is calibrated in advance using a high-precision measuring instrument such as a CMM, and the accuracy is evaluated by comparing the calibration results with the measurement results of X-ray CT.

Note that in this application, assigning an accurate value to a gauge (evaluation instrument) for evaluating the accuracy of X-ray CT is referred to as "calibration." On the other hand, evaluating errors and confirming performance of an X-ray CT apparatus using a calibrated evaluator is referred to as a "test" or "test." As schematically shown in FIG. 3, in the prior art, evaluation instrument A used to test a highly accurate X-ray CT apparatus is calibrated with a highly accurate CMM. On the other hand, evaluation instrument B for a popular X-ray CT device that is not very accurate is calibrated using a CMM or a highly accurate X-ray CT device.

Evaluation instruments used in the E-test include something called a forest (Figure 4), in which balls are placed in space, and a hole plate, which is a board with many holes. Since the Hall plate allows many X-rays to pass through the material, it is not suitable as an evaluator for the E test in that respect, but it is used because it has other advantages.

Here, we will explain a little about forests. X-ray CT equipment is limited in the materials and thickness that it can penetrate depending on the energy of the X-ray source used, so it is difficult to measure iron with the generally widely used medium-energy X-rays of about 225 kV. Much of the material is aluminum. The forest includes a base, a shaft, and a ball to be measured. Low-expansion metals and ceramics are often used as the base material. In the case of an evaluation instrument for a medium-energy X-ray CT device, the sphere to be measured is made of aluminum or a material with an X-ray transmittance close to that (for example, ruby or ceramic).

As can be seen from FIG. 4, the X-rays that pass through the balls during measurement, except for the highest ball in the middle, will also necessarily pass through the shaft. Considering the purpose of the E-test, a material that allows X-rays to pass through as easily as possible, such as resin, is suitable for the shaft. However, since such materials lack mechanical strength, ceramics and carbon fibers are unavoidably used. Therefore, the material of the ball and the material of the shaft have approximately the same X-ray transmittance. As a result, the results of the E-test, which is intended to eliminate the influence of materials, are affected, which is not desirable for manufacturers of X-ray CT apparatuses who want to indicate measurement errors as small as possible.

Evaluation instruments that are not forest-based include those in which multiple spheres to be measured are embedded in a cylindrical resin, and those in which only half of the spheres to be measured are embedded in the side of a cylindrical resin. Existing. If the evaluation device has multiple spheres half-embedded in the side of a cylinder-shaped resin, the positions of the spheres can be measured by CMM, making calibration possible, but the spheres cannot be placed unless they are on the side of the cylinder. Internal evaluation is not possible. On the other hand, in the case of an evaluation instrument in which multiple spheres to be measured are embedded in a cylindrical resin, CMM cannot measure the position of the spheres and cannot be calibrated, so another method must be introduced. . On the other hand, there is a degree of freedom in the placement of the balls.

In the conventional technology, requirements for evaluation instruments for industrial X-ray CT apparatuses have not been sorted out, and evaluation instruments preferable for high-precision X-ray CT apparatuses have not been proposed. The same applies to popular X-ray CT.

International Publication 2018/193800 Japanese Patent Application Publication No. 2012-189517 Japanese Patent Application Publication No. 2014-190933 Japanese Patent Application Publication No. 2018-179983

Junpei Aizawa, “Evaluation of error in dimension measurement using X-ray XT device”, Nagano Prefectural Technical Center Report, No.7, p.M39-M41 (2012)

Therefore, one aspect of the present invention is to provide a new evaluation instrument for an X-ray CT apparatus that is suitable for calibration and testing.

Another object of the present invention is to provide a new evaluation instrument for X-ray CT apparatuses, which is suitable for testing.

The evaluation instrument for an X-ray CT apparatus according to the first aspect of the present invention is capable of realizing a first state in which at least two adjacent side surfaces have a flat outer shape and a second state in which the outer shape is cylindrical. , an evaluation instrument for an X-ray CT apparatus, which includes a plurality of balls inside. In the first state, the plurality of spheres are optically observable from each of the two sides without overlapping each other, and in the second state, the spheres are rotated about the long axis of the cylinder. In this case, the plurality of spheres are arranged so that, at any angle of rotation, any X-ray emitted from an X-ray source at a predetermined position relative to the cylinder passes through the cylinder without passing through two or more spheres. This is what is being done.

An evaluation instrument for an X-ray CT apparatus according to a second aspect of the present invention is a cylindrical evaluation instrument for an X-ray CT apparatus, and includes a plurality of balls inside. When the cylinder is rotated about its long axis, at any rotation angle, any X-rays emitted from the X-ray source at a predetermined position relative to the cylinder will not pass through two or more spheres. A plurality of balls are arranged so as to pass through an evaluation instrument.

FIG. 1 is a diagram showing an outline of an X-ray CT apparatus. FIG. 2A is a diagram showing an outline of the X-ray CT apparatus. FIG. 2B is a diagram showing an outline of the X-ray CT apparatus. FIG. 3 is a diagram for explaining calibration and testing in the present application. FIG. 4 is a perspective view of an evaluation instrument called Forest. FIG. 5 is a perspective view of the first instrument in the first embodiment. FIG. 6 is a perspective view of the second instrument in the first embodiment. FIG. 7A is a diagram for explaining how to use it during calibration in the first embodiment. FIG. 7B is a diagram for explaining how to use it during calibration in the first embodiment. FIG. 8 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 9 is a diagram for explaining the arrangement of the first sphere. FIG. 10 is a diagram for explaining the arrangement of the first sphere. FIG. 11 is a diagram for explaining the arrangement of the second sphere. FIG. 12 is a diagram for explaining the arrangement of the second sphere. FIG. 13 is a diagram for explaining the arrangement of the second sphere. FIG. 14 is a diagram for explaining the arrangement of the third ball. FIG. 15 is a diagram for explaining the arrangement of the third ball. FIG. 16 is a diagram for explaining the arrangement of the third ball. FIG. 17 is a diagram for explaining the arrangement of the fourth ball. FIG. 18 is a diagram for explaining the arrangement of the fourth ball. FIG. 19 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 20 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 21 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 22 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 23 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 24 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 25 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 26 is a diagram for explaining the arrangement of a plurality of spheres. FIG. 27 is a diagram for explaining the arrangement of a plurality of spheres. FIGS. 28A to 28C are diagrams for explaining a case where the condition that each sphere can be observed from two directions without being obstructed by other spheres is satisfied. FIG. 29 is a diagram for explaining the calibration method. FIGS. 30(a) to 30(c) are perspective views for explaining the evaluation instrument in the second embodiment. FIGS. 31(a) to 31(c) are perspective views for explaining other evaluation instruments according to the second embodiment. FIGS. 32(a) to 32(c) are diagrams for explaining the method for manufacturing the first instrument according to the first embodiment. FIGS. 33(a) to 33(c) are diagrams for explaining another method of manufacturing the first instrument according to the first embodiment. FIG. 34 is a diagram for explaining problems when using columns. FIG. 35 is a diagram for explaining problems when using columns. FIG. 36 is a diagram for explaining problems when using struts. FIG. 37 is a diagram for explaining another embodiment. FIG. 38 is a diagram for explaining another embodiment. FIG. 39 is a diagram for explaining another embodiment.

[Basic idea regarding embodiments of the present invention]
Here, preferable conditions for evaluation instruments such as evaluation instrument A that can be used for calibration and testing (particularly E-test) will be summarized.

1. An evaluation device in which multiple balls with X-ray transmittances different from the X-ray transmittance of the evaluation device are embedded.In a case where the balls are supported by a shaft like a forest, the influence of the shaft is Since the ball will come out, it is preferable that multiple balls are floating without any support. In order to realize this, condition 1 can be considered.

Furthermore, the sensitivity of X-ray CT depends on the X-ray transmittance of the material. For example, the X-ray transmittance of a ruby ball and air differs greatly, so a ball can be viewed as a sphere. On the other hand, when the sphere is encapsulated in resin, that is, when resin is used as the exterior body of the sphere, the difference in X-ray transmittance is smaller compared to when it is floating in the air, but the ruby sphere and the resin Since the X-ray transmittance of the two objects differs considerably, it is possible to capture the sphere correctly. Here, the materials for the ball and the exterior body may be materials that have different X-ray transmittances, and the X-ray transmittance of the sphere may be relatively high or low.

2. The shape of the outer body of the sphere is cylindrical.When performing a test, the evaluation instrument is rotated once in X-ray CT for measurement. When a cylinder made of some material is rotated around its long axis, the transmitted image does not change at all during one revolution. As mentioned above, it is desirable that the X-rays do not pass through anything other than the object to be measured, but in the case of a cylinder, although the X-rays pass through it, the length of the passage does not change, so it is the same as if there were no exterior body. Therefore, this condition 2 can be considered.

3. When placed on the sample stage of an X-ray CT device and rotated, at any rotation angle, any X-rays emitted from the X-ray source at a predetermined position will form a cylindrical column without passing through two or more spheres. When measuring with X-rays by rotating the evaluation instrument to conduct a test, if the X-rays that have passed through one sphere also pass through other spheres, the transmittance will change as a result. This results in an undesirable transmission image being obtained by the detector. That is, it is preferable to avoid a situation in which the X-rays that have passed through the sphere pass through another material other than the exterior body. Other materials include other balls.

4. Optical Calibration Possible When the outer body of the sphere is transparent and cylindrical, as shown in FIG. 5, when optically observed from the outside, the sphere appears distorted. This is because the light rays are refracted on the surface of the cylinder, and it looks like this even if the sphere inside is a perfect sphere. When embedding a sphere inside the exterior body, it is difficult to calibrate the position of the sphere using a CMM, and the position of the sphere must be calibrated optically, but this is impossible if the sphere remains cylindrical.

In order to prevent the sphere from being observed as distorted, it is preferable to make the side surfaces flat, but when measuring with X-rays, it is preferable that the sphere be cylindrical, so a special configuration is required to satisfy conditions 3 and 4. It will be adopted. This point will be explained in a specific embodiment.

5. It is possible to optically observe any of the multiple spheres from any of two different directions without overlapping each other.Even if it is possible to observe without distortion, if they overlap, it cannot be observed, and if it cannot be observed. This is because it becomes impossible to calibrate. Note that the two directions do not have to be orthogonal, but it is assumed that their angles are known.

Below, an evaluation instrument having a specific configuration that satisfies such conditions will be described in detail.

[Embodiment 1]
The evaluation instrument in this embodiment includes a cylindrical first instrument as shown in FIG. 5 and a second instrument as shown in FIG. 6. The first instrument is used for testing with an X-ray CT machine, and the arrangement of the plurality of balls inside it will be described below. On the other hand, the second instrument has a substantially rectangular parallelepiped shape in the example of FIG. 6, and has a hole in which the first instrument can be accommodated from the top. However, it does not necessarily have to be a rectangular parallelepiped as long as at least two side surfaces are flat. Further, it is preferable that the second instrument is made of a material (for example, resin) having the same refractive index as the first instrument.

As shown in FIG. 7A, the second instrument is an instrument for storing the first instrument in the hole so that the ball can be optically observed from at least two sides without being distorted. . The sphere is also distorted and does not appear in Figure 7A. For this reason, it is preferable that the first instrument and the second instrument are optically integrated. Also, it is undesirable for the cylindrical first instrument to move within the hole of the second instrument. Therefore, the inner surface of the hole of the second instrument may be in contact with the outer surface of the first instrument. For example, if a gap is provided between the inner surface of the hole of the second instrument and the outer surface of the first instrument in order to facilitate handling, a marker (black in FIG. 7B) may be provided as shown in FIG. 7B. It is possible to achieve optical integration of the first instrument and the second instrument by aligning the first instrument and the second instrument with the same refractive index as the first and second instruments into the gap. preferable.

Next, the specific arrangement of the spheres to satisfy conditions 3 and 5 will be explained using FIGS. 8 to 18.

FIG. 8 shows a state in which a ball is placed on the central axis (the long axis of the cylinder, herein referred to as the Z axis) of the cylindrical first instrument. No other spheres are located in any of the X-ray shadows created by the spheres. In addition, it is possible to optically observe them without overlapping at any rotation angle. However, as an evaluation instrument for X-ray CT equipment, there is another demand for distributing the spheres as three-dimensionally as possible within the measurement area, and the arrangement of the balls shown in Figure 8 is for evaluation of X-ray CT equipment. Not very suitable as a device.

In addition, if there are at least two balls, the above E test can be carried out by measuring the distance between them and comparing it with the calibration value, but the three-dimensional measurement performance of the X-ray CT device can be investigated in more detail. For this purpose, two pieces are not enough. For example, ISO/2CD 10360-11, which is a standard under discussion, specifies at least eight.

Therefore, a procedure for sequentially arranging eight balls one by one will be explained. Assuming that four devices are arranged in each of the upper and lower halves of the cylindrical first instrument, only the arrangement of the upper half will be described here.

As shown in FIG. 9, the first ball is placed directly above the upper and lower intermediate planes 101 and on the Z axis. It is assumed that the second, third, and fourth spheres are installed at locations with a phase shift of 120 degrees within the XY plane indicated by the dotted line.

FIG. 10 is a side view of the state shown in FIG. In FIG. 10, the X-rays tangent to the sphere are shown as solid lines. To the right of the sphere, a shadow is created by the X-rays. No subsequent balls can be placed in this shadow area. Since this sphere is placed on the Z axis, when the evaluation instrument is rotated, a shadow of the same shape is cast over 360 degrees. Therefore, in FIG. 10, the second and subsequent balls cannot be installed in the area below the dotted line, which is the height at which X-rays are emitted from the cylindrical first instrument. Strictly speaking, the trajectory created by the shadow is not a low cylindrical shape, but a shape with a concave center on the top surface, and it is possible to place the second or subsequent ball in the concave area, but Here, for the sake of simplicity, it is assumed that the shadow area is cylindrical.

The second ball is placed directly above the shadow area created by the first ball. FIG. 11 shows a side view of the state in which the second ball is placed, and FIG. 12 shows a perspective view. The second ball rests on the top surface 103 of the area 102 of the shadow caused by the first ball. The second ball is placed away from the Z axis. Although the separation distance is arbitrary, considering the purpose of testing a wider measurement area, it is desirable to separate them as much as possible. Although the azimuth angle of the arrangement position with respect to the Z axis is arbitrary, for example, for the following explanation, the azimuth in which the second sphere is arranged is assumed to be 0°. Further, this direction is assumed to be the X-axis direction.

FIG. 13 shows the area of the X-ray shadow caused by the second sphere. The size of the shadow changes as the evaluation instrument rotates, but the largest shadow is formed when the sphere is closest to the X-ray source, so the shadow is largest in the state shown in FIG. 13. That is, the third and subsequent balls cannot be placed within the area below the dotted line.

FIG. 14 shows an X-ray shadow area 104 of the first and second spheres, and a third sphere is placed on the upper surface 105 of this area 104. Furthermore, as shown in FIG. 15, the second sphere is placed at a position deviated from the second sphere by 120 degrees within the XY plane. Note that the distance from the Z-axis is here the same as the distance from the Z-axis of the second ball.

FIG. 16 shows the area of the X-ray shadow caused by the third sphere. The size of the shadow changes as the first instrument rotates, but the largest shadow is formed when the sphere is closest to the X-ray source, so the shadow is largest in the state shown in FIG. 16. That is, the fourth ball cannot be placed within the area below the dotted line.

FIG. 17 shows a shadow region 106 of the first to third balls by X-rays, and a fourth ball is placed on the upper surface 107 of this region 106. Further, as shown in FIG. 18, it is placed at a position shifted by 120 degrees from the third sphere within the XY plane. Note that the distance from the Z-axis is here the same as the distance from the Z-axis of the second ball.

As can be seen from FIG. 18, the four spheres are three-dimensionally distributed within the cylindrical first instrument. In addition, with the arrangement shown in Figure 18, even if the spheres are rotated around the Z axis, the Z coordinate values of all the spheres are different, so it is not possible to optically observe all the spheres at any rotation angle. can do. That is, conditions 3 and 5 are satisfied.

In addition, according to the procedure shown in FIGS. 9 to 18, starting from the center of the cylinder, the first area of the shadow that occurs when the sphere is placed at the very edge of the side of the cylinder and on the X-ray source side, and the first area of the shadow. Above (or below) the area, the second area of the shadow that occurs when the sphere is placed close to the side of the cylinder and on the X-ray source side, and above (or below) the third area of the shadow. If you create a shadow area such as the fourth area of the shadow that occurs when the sphere is placed on the edge of the side of the cylinder and on the side of the X-ray source, you can determine the position of each shadow area in the XY plane on the sphere placement surface. It is also possible to place a ball in the If it is a distributed arrangement, the distance from the Z axis may be changed randomly.

Note that the possible placement positions of the sphere are generally limited by the size of the evaluation instrument, the size of the sphere, and the distance between the X-ray source and the evaluation instrument. When designing an evaluation instrument, the distance between the X-ray source and the evaluation instrument must be determined in advance. The number of balls that can be placed is also limited. For example, if the size of the evaluation instrument is fixed and you want to arrange many balls, you have no choice but to use small balls.

If you want to arrange as many balls as possible or as large as possible, the degree of freedom regarding arrangement increases by considering the size of the evaluation instrument and the distance between the evaluation instrument and the X-ray source. In the above example, the area of the sphere's shadow caused by X-rays is approximated to a cylindrical shape, but since it actually has a more complicated shape, it may be used. The shadow area will be specifically explained below.

First, as shown in FIG. 19, consider a case where only two balls are enclosed in a cylindrical first instrument. The Z coordinate values of the spheres are the same. That is, two spheres are arranged on a plane that is perpendicular to the long axis of the cylinder and is close to the top surface of the cylinder. However, the number of balls "2" is an example. FIG. 20 is a top view of FIG. 19, and when X-rays are irradiated from the direction shown in this figure, each sphere will not fall into the shadow of the other sphere. On the other hand, in the case of FIG. 21 in which the first instrument is rotated 90 degrees, the right ball falls into the X-ray shadow created by the left ball, so the arrangement of these two balls appears unfavorable. However, as shown in Figure 22, if the sphere is placed away from the line connecting the X-ray source and the detector, the size of the evaluation instrument, the size of the sphere, and the distance between the X-ray source and the evaluation instrument will change. Depending on the positional relationship, even if two balls are placed at the same height on the Z axis, it is possible that one ball will not fall into the shadow of the other ball. Note that balls other than these two balls may be placed, for example, in the lower half region of the cylinder, for example, by the method described above.

This situation is schematically shown in FIG. 23, where the shaded area shows the shadow of the sphere caused by X-rays. When the first instrument is rotated on the stage of an X-ray CT device, the shadow traces a three-dimensional trajectory, but since the diagram becomes very complicated, here we show the case observed from the side. . When placing the first ball and then considering the placement of the second ball, the second ball is placed in an area other than this shadow. Also, the first ball must not be in the shadow created by the second ball. However, the shadows may overlap.

FIG. 24 shows this state two-dimensionally. In this way, each time you place a sphere, you draw the shadow created by it, and by repeating the process of placing the next sphere in a position that does not touch any of the shadows created by all the spheres that have already been placed, you can improve the condition. 3, and it is possible to arrange more balls. Note that whether or not Condition 5 is satisfied is a different matter.

Note that although the explanation has been made on a plane in FIG. 24, the explanation will actually be made on a three-dimensional basis. The three-dimensional locus of the shadow created by one sphere will be explained using FIGS. 25 to 27. As shown in FIG. 25, consider the case where only one sphere is enclosed in a cylinder and the rotary stage is in a certain rotational phase. X-rays from the lower left cast a shadow toward the upper right of the sphere. Another ball must not enter this shadow. FIG. 26 shows the situation when the rotational phase changes. However, in order to facilitate understanding of the three-dimensional positional relationship, FIG. 26 is drawn with the rotational phase unchanged but with the X-ray irradiation direction changed. X-rays coming from the lower right cast a shadow on the upper left of the sphere.

When the first instrument is rotated once, the shadow also rotates once, and its trajectory resembles an upside-down umbrella. Another ball must not enter this trajectory. In other words, the second ball may be placed anywhere other than this trajectory, as shown in FIG. 27. However, whether or not Condition 5 is satisfied is a different matter.

Regarding condition 3, as mentioned above, the actual placement of the sphere is determined by considering factors such as the positional relationship between the X-ray source and the first instrument, the size of the first instrument, and the size of the sphere. It turns out. On the other hand, if only condition 5 is considered, for example, each surface to be observed is divided into more squares than the number of balls to be placed, and the balls are arranged so that no more than two balls fit into each square. Deploy. As shown in FIG. 28(a), assume that there are three spheres, and the side surface of the cylinder is observed from two directions: a first direction and a second direction perpendicular to the first direction. . When viewed from the first direction, as shown in FIG. 28(b), one ball is arranged in each of three of the four squares. Furthermore, when viewed from the second direction, as shown in FIG. 28(c), one ball is arranged in each of three of the four squares. In such a case, condition 5 is satisfied. Although the method of using such grids is just one example, Condition 5 can be easily satisfied if the coordinate values in the Z-axis direction are different.

In addition, as shown in FIG. 29, the calibration is performed with the first instrument housed in the hole on the top of the second instrument, and the camera 300 observing the inner sphere from two sides A and B of the second instrument. This is done by taking pictures. Although FIG. 29 shows a scene in which a photograph is taken from the front of side A, when photographing from the front of side B, the camera 300 may be moved, but the stage on which the first and second instruments are mounted may be rotated. You can let me. For the images taken from side A and the images taken from side B, the information processing device 200 calculates the three-dimensional coordinates of each internal sphere from the angles of sides A and B and the images taken from both directions. do. This will result in calibration. Since the specific contents of the calculation are already known, their explanation will be omitted here.

Note that the material of the ball is preferably ruby, ceramic, glass, or the like. The material of the exterior body of the ball (that is, the first device and the second device other than the ball) is preferably epoxy resin or the like. However, these materials are merely examples, and the ball may be of any material as long as it has a large difference in X transmittance with the outer body and can obtain a highly accurate shape. In addition, other resins may be used for ease of forming the first device and the second device.

[Embodiment 2]
In the first embodiment, the shape of the first instrument serving as the base is cylindrical, and when calibrating, the first instrument and the second instrument are combined and deformed into a rectangular parallelepiped shape. In this case, the first instrument serving as the base has a rectangular parallelepiped shape, and is deformed into a cylindrical shape using the second instrument serving as an auxiliary member when testing.

Specifically, FIG. 30(a) shows the first instrument serving as the base. In this embodiment, it is a vertically elongated rectangular parallelepiped, and includes a plurality of spheres arranged so as to satisfy Conditions 3 and 5 inside. In this state, calibration is performed by optically observing from two adjacent sides and measuring the position of the sphere. On the other hand, FIG. 30(b) shows an example of a second instrument that is an auxiliary member. The second instrument is divided into four members that are the difference between the first instrument and the smallest cylinder that contains the first instrument. As shown in FIG. 30(c), during the test, each of the second instruments is attached to either side of the first instrument to form a cylinder. The first instrument and the second instrument in this embodiment may have the same or negligible difference in X-ray transmittance, and the second instrument may not be transparent.

By introducing the first instrument and the second instrument in this manner, it becomes possible to satisfy conditions 1 to 5 and perform calibration and testing appropriately.

Note that it is sufficient if the inner sphere can be observed optically from two adjacent sides, so modifications can be made from that point of view. That is, as shown in FIG. 31(a), the first device is a three-dimensional object in which only two adjacent sides are flat and the remaining sides are part of the cylindrical side, and conditions 3 and 5 are satisfied inside. Contains multiple spheres arranged to fill. In this state, calibration is performed by optically observing from two flat sides. On the other hand, as shown in FIG. 31(b), an example of a second instrument that is an auxiliary member is shown. The second device is divided into two members that are the difference between the first device and the smallest cylinder that contains the first device. Then, as shown in FIG. 31(c), during the test, each of the second instruments is attached to either of the two sides of the first instrument to form a cylinder. Such an evaluation instrument can also be used for calibration and testing as in the first embodiment.

[About manufacturing method]
The first device containing a plurality of spheres is made of, for example, a resin that becomes transparent when cured. For example, as shown in FIG. 32(a), resin is poured into the mold to the height at which the first ball is to be placed. After the resin hardens, the first ball is placed on the surface of the resin (the shaded surface). Then, as shown in Fig. 32(b), further resin is poured into the formwork to the height at which the second ball should be placed, and after the resin hardens, the second ball is placed on the surface of the resin (the diagonal lined side). Place. Furthermore, as shown in Figure 32(c), resin is further poured into the formwork to the height at which the third ball should be placed, and after the resin has hardened, the third ball is placed on the surface of the resin (the diagonal lined surface). Place. After that, the process is similar, and if only three balls are to be placed, the resin is poured to a predetermined height (for example, to the upper edge of the mold) and allowed to harden. This forms the first device in the first embodiment. Note that for the first instrument in the second embodiment, a rectangular parallelepiped may be cut out from a cylinder created by the procedure shown in FIGS. 32(a) to 32(c). At this time, make sure that no spheres are included in parts other than the rectangular parallelepiped.

This method has a problem in that it takes time to manufacture the resin because it takes time to harden the resin. In addition, resin is poured into the mold many times, but since resin is usually made by mixing two types of liquids, mixing is performed many times, and the composition of the resin differs slightly each time. As a result, there is also the problem that the refractive index is not constant and a resin layer appears.

Therefore, a method of placing the balls at desired three-dimensional positions within the mold and then pouring the resin all at once may be considered. In order to place the ball in the desired three-dimensional position, it is possible to either suspend it from the top or support it from below with a support. For example, as shown in FIG. 33(a), a support for supporting the ball at the desired three-dimensional position is installed on the base, and the ball is attached to the end of the support as shown in FIG. 33(b). 33(c), the resin is poured all at once. In this way, the resin layer will not appear.

On the other hand, since a support column must be prepared separately, this poses a problem. If the struts are made of the same material as the resin, the refractive index and X-ray transmittance will be the same, but in reality they are not exactly the same. Although the difference in X-ray transmittance is considered to be negligible, the difference in refractive index may cause a problem in which the sphere cannot be observed due to the pillars.

For example, consider a case where a cylindrical first instrument is observed from the first direction and is in a state as shown in FIG. 34. In this example, the third and fourth balls are lined up on a straight line parallel to the Z axis. However, since the third ball is located in front of the support for the fourth ball, the third ball can be observed without being obstructed by the support.

On the other hand, when the cylindrical first instrument is observed from the second direction, it may be in a state as shown in FIG. 35. In other words, the first and second balls are lined up on a straight line parallel to the Z axis, and the support for the second ball is in front of the first ball, so the first ball is obstructed by pillars and cannot be observed. Such a situation is not desirable.

Therefore, the following condition 6 is added to condition 5 when the ball is arranged so as to be supported by a support.
6. All of the plurality of spheres can be optically observed from any of two different directions without being obstructed by any of the supports. In other words, as shown in FIG. The first balls are lined up on a straight line parallel to the Z-axis, but since the first ball is in front of the pillar that supports the second ball, all balls can be observed. . Note that there is no problem even if the pillars overlap each other.

As long as condition 6 is satisfied, the material of the resin and the material of the support may be different. However, unless the X-ray transmittance of the resin and the X-ray transmittance of the support are the same or have a negligible difference, there will be an effect during the test. That is, when using struts, it is also required that the X-ray transmittances of the struts and the resin be the same or have a negligible difference.

[Modifications of Embodiments 1 and 2]
In the first embodiment, the two sides of the rectangular parallelepiped second instrument that can accommodate the first instrument through the hole in the top surface can be used as they are during calibration, but these surfaces are not necessarily perfectly flat. Any deviation from the plane gives an error in the calibration of the position of the sphere. Therefore, as shown in the top view of FIG. 37, an optical plane glass is brought close to the two side surfaces used for measurement, and in the gap between the two sides, a material having the same refractive index as the material (for example, resin) of the first and second instruments is placed. Fill with matching oil. Then, the two become optically integrated, and the observation surface becomes a glass surface with good flatness, making it possible to perform more accurate calibration.

Note that since the second instrument is used during calibration, as shown in the top view of FIG. 38, optical flat glass may be brought into close contact with two sides of the second instrument to integrate them. .

Furthermore, in the second embodiment as well, the two adjacent sides of the first instrument, which is a rectangular parallelepiped, can be used as they are during calibration, but these surfaces are not necessarily perfectly flat. Any deviation from the plane gives an error in the calibration of the position of the sphere. Therefore, as shown in the top view of Fig. 39, an optical flat glass is placed close to the two sides used for measurement, and the gap between the two is filled with matching oil having the same refractive index as the material (for example, resin) of the first instrument. . Then, the two become optically integrated, and the observation surface becomes a glass surface with good flatness, making it possible to perform more accurate calibration.

[others]
Above, we have explained the evaluation equipment for X-ray CT equipment that can be used for calibration and testing. Since this is only a test, the conditions for calibration do not need to be met. That is, conditions 4 and 5 do not need to be satisfied.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and other shapes of the first and second instruments that satisfy the conditions described above may be adopted. good.

In particular, regarding the arrangement of the balls, various patterns other than those illustrated in the present application can be adopted. In particular, if they are arranged regularly, a configuration in which they are placed on a spiral curve is also conceivable. For example, if the radius of rotation gradually expands from the center and the increments in the height direction (Z-axis direction) gradually increase, it is relatively easy to create an arrangement that satisfies conditions 3 and 5 above. Realized.

Further, when arranging the balls using supports, only some of the balls may be supported by the supports. Furthermore, a 3D printer may be used in the manufacturing method. In this way, it becomes possible to manufacture the balls without hardening the resin each time the balls are placed and without using supports. Although an example in which eight balls are arranged is described, the number of balls may be three or more.

The embodiments described above can be summarized as follows.

The evaluation instrument for an X-ray CT apparatus according to the first aspect of the present embodiment is capable of realizing a first state having an external shape in which at least two adjacent side surfaces are flat and a second state having a cylindrical shape. This is an evaluation instrument for an X-ray CT apparatus, and includes a plurality of balls inside. In the first state, the plurality of spheres are optically observable from each of the two sides without overlapping each other, and in the second state, the spheres are rotated about the long axis of the cylinder. In this case, the plurality of spheres are arranged so that, at any angle of rotation, any X-ray emitted from an X-ray source at a predetermined position relative to the cylinder passes through the cylinder without passing through two or more spheres. has been done.

In this way, an evaluation instrument containing multiple balls can be calibrated and tested by realizing the two states described above and arranging the multiple balls as described above. It can now be used for both. Regarding the arrangement of the plurality of balls, it is preferable that the balls be arranged in a dispersed manner within the instrument, and it is preferable to avoid arranging them in one straight line. Moreover, it is preferable that the two side surfaces touch perpendicularly.

The evaluation instrument includes a cylindrical first instrument that includes the plurality of balls, and a second instrument that can accommodate the first instrument and has at least two adjacent sides that are flat. You can do it like this. For example, it is an aspect like the first embodiment.

Furthermore, transparent flat plates may be added to at least two adjacent sides of the second device. In order to improve the flatness of the side surface of the second device, for example, a glass plate may be attached closely or matching oil may be added between the sides.

The evaluation device includes a first device that includes a plurality of spheres and has at least two adjacent side surfaces that are flat, and a first device that is attached to the at least two adjacent side surfaces of the first device. The second device may have a cylindrical outer shape. For example, it is an aspect like the second embodiment.

Even in such an embodiment, transparent flat plates may be added to at least the two adjacent side surfaces. This is to improve the flatness of the side surface of the first instrument.

In addition, if at least one of the plurality of balls is supported by the support, it is possible to optically observe each of the plurality of balls from each of the above two sides without being obstructed by the support. , so that multiple balls are placed. This makes it possible to properly perform calibration even when a support is used. Note that the support column is preferably made of a material having substantially the same X-ray transmittance as the X-ray transmittance of the evaluation instrument. Substantially the same X-ray transmittance or the same X-ray transmittance applies if the difference is indiscernible in the transmission image.

The evaluation instrument for an X-ray CT apparatus according to the second aspect of the present embodiment is a cylindrical evaluation instrument for an X-ray CT apparatus, and includes a plurality of balls inside. When the cylinder is rotated about its long axis, at any rotation angle, any X-rays emitted from the X-ray source at a predetermined position relative to the cylinder will not pass through two or more spheres. A plurality of balls are arranged so as to pass through an evaluation instrument. It can be used to test popular X-ray CT devices.

Note that the cylindrical first instrument according to the first aspect is accommodated in the accommodation section of the second instrument, and a plurality of balls are observed from each of the two sides, and the observation results are as follows. The position of each of the plurality of balls may be determined from the following. In this case, matching oil may be injected into the gap between the housing part and the evaluation instrument. Furthermore, a plurality of spheres may be observed after adding a transparent flat plate to each of the two side surfaces or adding a transparent flat plate to each of the two side surfaces with matching oil sandwiched therebetween.

Furthermore, in the evaluation instrument for an X-ray CT apparatus according to the first or second aspect, a plurality of spheres may be provided on a plane that is perpendicular to the long axis of the cylinder and that is included in the upper half or lower half area of the cylinder. Two or more of the balls may be arranged, and balls other than the two or more balls among the plurality of balls may be arranged in an area outside the above-mentioned area within the cylinder. It is also effective to arrange a plurality of balls using this simple method.

Claims (8)

An evaluation instrument for an X-ray CT apparatus, which is capable of realizing a first state having an outer shape in which at least two adjacent side surfaces are flat and a second state having a cylindrical shape,
Contains multiple spheres inside,
In the first state, the plurality of spheres are optically observable from each of the two side surfaces without overlapping each other, and
When the cylinder is rotated about its long axis in the second state, any X-rays emitted from the X-ray source at a predetermined position with respect to the cylinder at any rotation angle will have two or more so as to pass through the cylinder without passing through the sphere,
An evaluation instrument for an X-ray CT apparatus, in which the plurality of balls are arranged. a cylindrical first instrument including the plurality of balls;
a second instrument having a accommodating portion capable of accommodating the first instrument, and at least two adjacent side surfaces are flat;
An evaluation instrument for an X-ray CT apparatus according to claim 1. The X-ray CT apparatus evaluation instrument according to claim 2, wherein a transparent flat plate is added to the at least two adjacent side surfaces of the second instrument. a first instrument that includes the plurality of spheres and has at least two adjacent sides that are flat;
a second device that is attached to the at least two adjacent side surfaces of the first device to make the first device have a cylindrical outer shape;
An evaluation instrument for an X-ray CT apparatus according to claim 1. The X-ray CT apparatus evaluation instrument according to claim 4, wherein transparent flat plates are added to at least two adjacent side surfaces. When at least one of the plurality of spheres is supported by a support, all of the plurality of spheres can be optically observed from each of the two side surfaces without being obstructed by the support. The X-ray CT apparatus evaluation instrument according to any one of claims 1 to 5, wherein the plurality of balls are arranged. The evaluation instrument for an X-ray CT apparatus according to claim 6, wherein the support column has the same X-ray transmittance as the X-ray transmittance of a portion of the evaluation instrument other than the plurality of spheres. In the second state, two or more of the plurality of spheres are arranged on a plane that is perpendicular to the long axis of the cylinder and included in the upper half or lower half area of the cylinder, and The evaluation instrument for an X-ray CT apparatus according to claim 1, wherein balls other than the two or more balls among the plurality of balls are arranged in a region outside the region within the cylinder.

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