JP4058523B2 - Calibrator and calibration method - Google Patents

Description

  The present invention relates to a calibrator and a calibration method for determining a reference direction independent of an apparatus used for radiography.

In recent high-magnification imaging by X-ray fluoroscopy, imaging is performed at a geometric magnification of several tens to several hundreds in order to achieve micron-order resolution. At this time, it is necessary to adjust the position and orientation of the detector for detecting X-rays and the sample stage, the X-ray source and the relative positional relationship thereof with high accuracy.
Examples of documents disclosing methods for adjusting these apparatuses for X-ray imaging include Patent Document 1 and Patent Document 2.

  In Patent Document 1, a linear phantom in which metal wires are embedded at a certain interval is installed on the surface of an X-ray image intensifier (see FIG. 11) to correct an alignment shift between the image intensifier and the X-ray source. Proposed method. However, with this method, even if correction of the upper and lower tilts (see FIG. 12) and left / right shake (see FIG. 13) of the image intensifier is possible, the rotation of the detection surface (see FIG. 14) can be corrected. Since the linear phantom and the image intensifier do not move relative to each other, it is not possible to detect a shift. Further, even if the alignment between the image intensifier and the X-ray source can be adjusted, there is no mention of a verification method as to whether or not the sample stage is orthogonal to the alignment. The adjustment of the position and direction of the sample stage becomes more important for high-magnification high-magnification fluoroscopic imaging and tomographic imaging using a microfocus X-ray source or the like. Posture adjustment is essential.

  Patent Document 2 provides a method of projecting a thin pin-shaped phantom onto a detector and identifying a pixel position where a line connecting an X-ray and a rotation axis intersects the detector from the unevenness of the luminance value distribution. In this method, calibration is performed on the premise that the sample stage on which the pin-shaped phantom is mounted and the central axis of the X-ray fan beam are set vertically (see FIG. 15A). However, the accuracy of the sample stage position and tilt is not guaranteed only by mechanical attachment (see FIG. 15B). When performing high-magnification fluoroscopic imaging that requires micron-order resolution, such as industrial sample imaging, slight deviations and inclinations of the sample rotation axis are geometrically enlarged to several tens to several hundreds times. It leads to deterioration of image quality. Therefore, it is necessary to adjust the position and inclination of the sample table and the rotating table more strictly as the magnification becomes higher.

As described above, when determining the relative positional relationship between the detector and the sample stage, if the position and orientation of the detector are used as a reference, even if the phantom described in Patent Document 1 is used, the rotation direction of the detection surface is corrected. I can't. In addition, the positional relationship with the sample stage cannot be corrected by correcting only the detector. In Patent Document 2, a detector pixel position at the projection center is obtained using a pin phantom. However, the relative positional relationship between the detector and the sample stage cannot be corrected only by this. Also, the determination of whether the pin phantom is vertical depends on whether the detection surface is vertical, and therefore cannot be determined uniquely. Therefore, a method for determining the vertical direction and the horizontal direction independent of the position and orientation of the apparatus is required.
JP 2000-32219 A JP 58-41532 A

  The positions and postures of the X-ray detector, the sample stage, and the rotary table are relative to the support table on which they are fixed. If the processing accuracy of the support base or the positioning accuracy of the drive mechanism is low or the installation is misaligned, even if you try to align with this support base as a reference, the accuracy may be reduced or there may be no freedom of setting. is there. For example, if a phantom is placed on a slightly tilted sample stage and an attempt is made to adjust the detector with the sample stage as a reference, the detector is rotated or tilted to correct the position of the device relative to the tilted reference. The need to come out. Although it is possible to correct this in software, there is a demerit that calculation takes time and the accuracy of the image is lowered.

  For example, when the inside of a measurement object is visualized by X-ray radiography and the dimensions are obtained, it is difficult to obtain the exact dimensions from the luminance distribution unless the detector surface and the installation orientation and direction of the sample are set correctly. Therefore, it is difficult to correct later in software. In industrial X-ray CT (computed tomography), when looking at the internal structure of electronic components, bones, rocks, etc., a large enlargement factor of several tens to several hundreds is required, but a slight error is also enlarged at the same time. Therefore, it is necessary to accurately adjust the position of the sample stage and the detector.

  The same adjustment work is required for the X-ray CT apparatus. In the X-ray CT apparatus, after a fan beam or cone beam-like X-ray generated from an X-ray source passes through a sample, the X-ray intensity is recorded by a detector installed on the opposite side of the sample. At this time, the sample or the combination of the X-ray source and the detector is rotated to collect projection data of various angles of the sample. An image of one angle is equivalent to X-ray radiography, but X-ray CT is composed of a convolution (superimposition integration) with a filter function and a back projection process based on the plurality of angle data. This technology reproduces one or more object tomographic planes by performing image reconstruction calculation. If the detector is a one-line line sensor, a tomographic image is reproduced using two-dimensional reconstruction. If the detector is a two-dimensional image intensifier or flat panel sensor, Feldkamp et al. A three-dimensional image composed of a plurality of tomographic planes can be reproduced using an image reconstruction algorithm. In these image reconstruction algorithms, the distance between the X-ray focal point and the detector, the distance between the X-ray focal point and the sample rotation axis, the size of the detector, the center line of the X-ray fan beam and the detection surface intersect perpendicularly. Since it is necessary to give the upper position as an input, it is necessary to accurately measure these positions. In addition, since the calculation is performed on the assumption that there is no inclination of the detector, pixel displacement, sample rotation axis, displacement, etc., and there is a contradiction between the measured data and the calculated numerical value, As a result, it appears as an artifact and a high-quality tomographic image cannot be reproduced. For example, if the pixel at the position where the center line of the X-ray fan beam and the detection surface intersect perpendicularly is not accurate, the superimposition at the time of back projection shifts, resulting in a blurred image. In addition, if the rotation axis of the sample stage is inclined, an accurate back projection is obtained in a certain cross section, but a tomographic image is blurred above and below. As countermeasures, either the hardware correction or the data correction by measuring the deviation amount can be taken. In either case, the deviation amount is quantitatively measured using a phantom or a calibrator. Work is required. The amount of deviation is a result of the mutual influence of the deviation of the detector and the deviation of the sample stage, so it is difficult to adjust because the cause of the deviation cannot be specified unless there is a guarantee that either one is installed correctly. It becomes. These problems occur because a plurality of reference positions of the sample stage and the detector are set or the reference is ambiguous. If a reference direction independent of the device is determined, the alignment of the entire device can be adjusted based on this.

  The present invention has been made in view of such problems, and a calibrator capable of calibrating the inclination of each apparatus based on an absolute reference direction independent of each apparatus constituting the radiation imaging apparatus, and The purpose is to provide a calibration method.

In order to solve the above-mentioned problem, the invention according to claim 1 is arranged at a position facing the radiation source across the sample stage, a radiation source for irradiating radiation, a sample stage on which the sample is placed, and the sample In a calibrator for calibrating the inclination of the sample stage in a radiation imaging apparatus comprising a detector for detecting the intensity of radiation that has passed through , one end is fixed to the calibrator built in the sample stage , and radiation A linear member formed of a material whose transmittance is smaller than that of the surrounding material, and fixed to the calibrator so as to form a cross crossing the linear member perpendicularly in the horizontal state of the calibrator , and A thin metal plate made of a material whose radiation transmittance is smaller than that of the surrounding material,
Based on the result detected by the detector by irradiating the linear member and the metal thin plate with radiation, the inclination of the sample stage with respect to the vertical plane parallel to the radiation irradiation direction is orthogonal to the radiation irradiation direction. Provided is a calibrator that detects and calibrates an inclination with respect to a vertical plane at the same time.

  According to invention of Claim 1, since the said calibrator is equipped with the said linear member and the said metal thin plate, the absolute which does not depend on an apparatus shown with the said linear member and the said metal thin plate is shown. Since the inclination of the sample stage can be calibrated using the reference, the adjustment accuracy can be increased. Further, since the inclination of the sample stage with respect to the radiation irradiation direction and the inclination with respect to the plane orthogonal to the radiation irradiation direction can be detected at the same time, the sample stage can be adjusted with a small number of repetitions, and adjustment is required. Labor can be greatly reduced.

According to a second aspect of the present invention, in the calibrator according to the first aspect, an identification for identifying in which direction the sample stage is inclined with respect to the radiation irradiation direction is provided on a part of the thin metal plate. It is characterized by being processed.
According to the invention described in claim 2, since the identification processing applied to the metal thin plate can identify which direction the sample stage is inclined with respect to the radiation irradiation direction, there is little The adjustment of the sample stage can be completed by the number of repetitions.

The invention according to claim 3 is the calibrator according to claim 1 or 2, wherein a weight is joined to the other end of the linear member.
According to invention of Claim 3, since the weight is joined to the other end of the said linear member, the said linear member does not shake or bend. For this reason, an accurate vertical direction can be shown by the linear member.

According to a fourth aspect of the present invention, in the calibrator according to any one of the first to third aspects, the linear member and the thin metal plate have a radiation transmittance higher than that of the linear member and the thin metal plate. It is characterized by being installed in a container into which a large liquid is injected.
According to the fourth aspect of the present invention, the linear member can be prevented from shaking due to the viscosity of the liquid injected into the container, and can be prevented from being attracted to the container wall by static electricity or the like. Therefore, an accurate vertical direction can be indicated by the linear member.

The invention according to claim 5 provides the calibrator according to any one of claims 1 to 4, to which the sample stage is attached.
According to the fifth aspect of the present invention, since the sample stage is attached to the calibrator, the sample stage is placed and photographed while holding the alignment adjusted by the calibrator. Therefore, a high-quality image can be obtained.

The invention according to claim 6 is a calibration method for calibrating the inclination of the radiation imaging apparatus using the calibrator according to any one of claims 1 to 5, wherein the radiation transmittance is higher than that of a surrounding substance. A step of installing a flat plate that is pivotally supported by a rotary shaft whose end is perpendicular to the detection surface and another flat plate that intersects the flat plate perpendicularly, and By irradiating the flat plate and the other flat plate with radiation, based on the result detected by the detector, the pixel arrangement of the detector becomes parallel to the projection image of the flat plate and the other flat plate. The projected image of the intersection of the flat plate and the other flat plate is based on the result detected by the detector by irradiating the flat plate and the other flat plate with radiation. Calibrating the orientation of the detection surface to be visible as a point; and Based on the result detected by the detector by irradiating the main device with radiation, the radiation focus of the radiation source and the midpoint of the intersection line of the rotation axis of the calibrator and the metal thin plate are connected. There is provided a calibration method including a step of calibrating a normal line set at a position where a line obtained by extending a line and a detection surface of the detector intersect with each other so as to face the radiation focus direction.

  According to the invention described in claim 6, first, based on the result detected by the detector by irradiating the flat plate and the other flat plate with radiation, the rotational deviation of the detector and the detection surface are detected. In order to calibrate the tilt, and then calibrate the sample stage based on the result detected by the detector by irradiating the calibrator with radiation, and further adjust the orientation of the detection surface, The radiation imaging apparatus can be calibrated with high accuracy and efficiency based on absolute standards indicated by flat plates, linear members, and metal thin plates that are orthogonal to each other.

According to the present invention, the calibrator includes a linear member having one end fixed, and a metal thin plate fixed in the vicinity of the linear member. Since the inclination of the sample stage can be calibrated using an absolute reference that does not depend, the sample stage can be calibrated with high accuracy. In addition, since the tilt of the sample stage relative to the radiation irradiation direction and the tilt relative to the plane perpendicular to the radiation irradiation direction can be detected simultaneously, the calibration of the sample stage can be completed with a small number of repetitions, and the labor required for adjustment Can be greatly reduced.
In addition, if a sample stage equipped with a calibrator is used, the sample can be photographed while maintaining the adjusted alignment, so that a high-quality image can be obtained.

Next, the best mode for carrying out the present invention will be described with reference to the drawings. In each drawing referred to in the following description, the same reference numerals are given to the same parts as in the other drawings.
FIG. 1 is a diagram for explaining the overall configuration of the X-ray CT apparatus 1. As shown in the figure, an X-ray CT apparatus 1 includes an X-ray source 11 that irradiates X-rays, a sample table 12 on which a sample to be X-rayed, a rotating table 13 that rotates the sample table 12, and a sample A calibrator 14 for measuring and calibrating the tilt of the table 12, an X-ray detector 15 installed at a position facing the X-ray source 11 with the sample table 12 interposed therebetween, and an X-ray detector A calibrator 16 for measuring and calibrating the inclination of the device 15, a data processing device (not shown) for reconstructing an image based on the X-ray intensity detected by the X-ray detector 15, and a reconstructed image A display screen (not shown). The X-ray detector 15 includes a detection surface 151 for detecting X-rays, and a plurality of pixel matrices are arranged on the detection surface 151 in the vertical direction and the horizontal direction. Here, the detector 15 is a two-dimensional planar detector such as an X-ray image intensifier or a flat panel detector.

Next, a method for creating the calibrator 14 according to the present embodiment will be described. In the following description, when the state of the calibrator 14 and the calibrator 16 and the projection image are described, the state of the X-ray projection image displayed on the display screen is described.
First, as shown in FIG. 2, a metal ball 142 having a high density is joined to the tip of a thin metal wire 141 having a high X-ray attenuation rate, and the other end is a lid of a cylindrical container 143 having a low X-ray attenuation rate. It joins to 144 and hangs down inside the cylindrical container 143. Thereby, tension is always applied to the metal thin wire 141 in the direction of gravity, that is, the direction perpendicular to the ground. The material of the metal thin wire 141 having a large X-ray attenuation factor is preferably tungsten, molybdenum, or the like, and a material that can clearly detect an X-ray projection image even with a thickness of about 10 μm. Further, the thickness of the thin metal wire 141 is sufficiently thin so that the rigidity can be ignored when the metal ball 142 is suspended.

The metal sphere 142 is made of a material having a high density, such as copper, lead, iron, etc., capable of applying tension to make the metal thin wire 141 straight even with a diameter of several millimeters and not breaking the metal thin wire 141. To do.
If the projection image of the thin metal wire 141 is projected onto the X-ray detector 15 while the metal sphere 142 is stationary, the vertical projection image can be obtained without depending on the installation method of the apparatus and the sample stage 12. It has become a direction.
A thin donut-shaped thin metal plate 145 is installed in a part of the cylindrical container 143 so as to be perpendicular to the central axis in the longitudinal direction of the cylindrical container 143.

  A part of the thin metal plate 145 is subjected to identification processing for identifying in which direction the thin metal plate 145 is inclined with respect to the X-ray irradiation direction. Here, the identification processing is processing performed so that the projected image of the metal thin plate 145 changes depending on the direction of inclination, and for example, projections, holes, slits, and the like are conceivable. Here, as will be described later, the diameter of the metal thin plate 145 is used to calculate the inclination of the metal thin plate 145. Therefore, as the identification processing, processing that does not change the diameter of the metal thin plate 145, or metal thin plate 145 A process capable of recognizing the diameter is suitable.

In addition, the thin metal plate 141 is installed so that the fine metal wire 141 passes through the hollow portion at the center of the thin metal plate 145. When the cylindrical container 143 is placed on a horizontal plane and seen from the side, the thin metal plate 145 looks straight, so that when the metal ball 142 is stationary, the thin metal wire 141 and the side surface of the thin thin metal plate 145 intersect each other vertically. Forming a cross. As shown in FIGS. 3A and 3B, when the calibrator 14 is tilted to the left and right (tilt with respect to a plane orthogonal to the X-ray irradiation direction), the cross intersects at 90 degrees. Therefore, the left / right inclination can be detected from the angle θ between the thin metal wire 141 and the thin metal plate 145. Further, as shown in FIGS. 4A and 4B, when the sample stage 12 is tilted beyond the X-ray irradiation direction, the metal thin plate 145 cannot be seen in a straight line (FIG. 4B). Reference), the inclination angle θ is obtained and adjusted from the diameter D of the thin metal plate and the short axis S of the projected disk by θ = sin ⁻¹ (S / D). 4A and 4B, the calibrator 14 is inclined to the far side in the X-ray irradiation direction, but the calibrator 14 is inclined to the near side in the X-ray irradiation direction. Similarly, the inclination angle θ is obtained and adjusted. Since these cross projection images are based on the direction of gravity, they give vertical and horizontal directions independent of the apparatus. The thin metal thin plate 145 is desirably the same thickness as the thin metal wire 141, and has a high processing accuracy and a high X-ray attenuation factor such as copper. As the diameter D of the metal thin plate 145 is larger, the accuracy of determining the angle is improved. However, when the diameter is increased, the enlargement ratio cannot be obtained. Therefore, the diameter D is determined according to the target enlargement ratio.

When the metal ball 142 is greatly shaken and does not stand still for a short time, or when the distance from the cylindrical container 143 is small and is attracted to the wall by static electricity or the like, as shown in FIG. Enclose high liquid 146. The liquid 146 reduces the vibration of the metal sphere 142 within a short time, prevents static charge between the metal sphere 142 and the cylindrical container 143, and the metal sphere 142 is stationary. It is desirable that the liquid 146 to be sealed has a high viscosity, a low surface tension, and a small X-ray attenuation. For example, glycerin or silicone oil is used.
The calibrator 14 thus created is placed vertically on the sample stage 12 and the turntable 13, and the heights of the X-ray detector 15, the sample stage 12 and the turntable 13 are adjusted, and the fine metal wires of the calibrator 14 are adjusted. The position and orientation of the turntable 13 are set so that 141 and the thin metal plate 145 can be seen as a cross in the approximate center of the screen. What is corrected here is the inclination of the rotation axis of the turntable 13.

Next, when the turntable 13 is rotated once, if the angle between the thin metal plate 145 and the thin metal wire 141 changes or there is an angle at which the thin metal plate 145 does not look straight, the calibrator 14 and the turntable 13 are not attached correctly. First, the mounting of the turntable 13 is corrected. At this time, the inclination with respect to the X-ray irradiation direction is adjusted using the identification processing of the thin metal plate 145. Further, when the turntable 13 is rotated once, the deflection width of the fine metal wire 141 is recorded, and the median value becomes the true rotation axis. A line connecting the midpoint of the intersection of the true rotation axis and the thin metal plate 145 and the focal point of the X-ray source 11 is a reference line for radiation projection. However, even if the metal thin plate 145 is not horizontal with respect to the ground, the projected image may appear to be a straight line because the X-rays are emitted conically from the focal point. To correct this, both the turntable 13 and the calibrator 14 are moved horizontally by a certain distance in the X-ray irradiation direction, and the change in the thickness of the thin metal plate 145 in the process is examined. If the thin metal plate 145 is inclined with respect to the horizontal plane, the projected thickness should increase as the distance from the X-ray source 11 increases. In this case, the irradiation direction of the thin metal plate 145 again in that position. What is necessary is just to adjust inclination. If there is no change in the thickness of the thin metal plate 145 even if it is moved horizontally, it indicates that the thin metal plate 145 is installed horizontally.

The vertical and horizontal deflections of the detection surface 151 of the X-ray detector 15 and the horizontal deflection (inclination with respect to the plane orthogonal to the X-ray irradiation direction) are obtained using a calibrator 16 as shown in FIGS. Calibrate. As shown in the figure, the calibrator 16 affixes a thin metal plate 161 having a width of about one pixel and perpendicular to each other to a cross-shaped plastic material 162, and attaches the end of the plastic material 162 to the mounting plate 163. Is pivotally supported on a rotating shaft 164 provided perpendicular to the surface. As a specific calibration method, first, the calibrator 16 is attached to the surface of the detection surface 151 of the X-ray detector 15. At this time, it is attached so that the intersecting portion 165 of the orthogonal thin metal plates 161 is approximately at the center of the screen. Then, the rotational deviation of the detector 15 is corrected so that the projected image of the metal thin plate 161 is parallel to the two-dimensional pixel array (see FIG. 7). Then, the position of the X-ray detector 15 and the inclination of the detection surface 151 are adjusted so that the two thin metal plates 161 appear to be orthogonal lines. At this time, the inclination of the detection surface 151 is adjusted by regarding the pixel position A on which the end point closer to the detection surface 151 of the intersecting portion 165 of the thin metal plate 161 is projected as the rotation center (see FIG. 8). When the detection surface 151 is swung up and down or left and right, the thin metal plate 161 of the calibrator 16 does not look linear but looks like a trapezoid or a parallelogram (see FIG. 8). Since the deflection angle can be obtained by θ = sin ⁻¹ (L / H) from the width H of the metal thin plate 161 and the width L obtained from the projection image, the detection surface 151 is corrected. When adjustment is made so that the thin metal plate 161 looks like a cross and the intersecting portion 165 of the thin metal plate 161 looks like a point, the normal vector with respect to the detection surface 151 at the point position is directed to the focus of the X-ray source 11. The pixel at the normal line position is A (see FIGS. 8 and 9). Next, the detection surface is centered on the point B so that the normal line set to the projection position point B of the projection position point of the true rotation center point E of the thin metal plate 145 faces the focus S direction of the X-ray source 11. The direction of 151 is adjusted. By doing so, the condition that the focal point S and the extension line of the true rotation center point E of the thin metal plate 145 intersect the detection surface 151 at the position point B of the detection surface 151 is achieved.

  If the sample stage 12 is replaced after the calibration is completed, the adjusted alignment may be shifted. Therefore, as shown in FIG. 10, the calibration unit 14 is built in the sample stage 12 and is integrated with the sample stage 12. 14 (hereinafter referred to as “calibrator 17 with sample stage”) is provided. At the time of calibration, the calibrator 17 with the sample table is raised and calibrated by the above method using the thin metal wire 141 and the thin metal plate 145. At the time of actual photographing, the calibrator 17 with the sample table is lowered and moved to the sample table 12. By photographing the placed sample, it is possible to photograph without losing the adjusted alignment.

Next, specific examples will be described.
A tungsten wire having a diameter of about 10 to 20 μm is used as a metal thin wire 141 made of a material having a large X-ray attenuation factor and having an appropriate strength. A metal ball 142 having a diameter of 1-2 mm is joined to the tip of this tungsten wire by spark welding or the like, and the other end is adhered to the center of the lid 144 of the acrylic cylindrical container 143.
The acrylic cylindrical container 143 is hollow with a thickness of about 1 mm and has an outer diameter of about 8 mm and is divided into two. A doughnut-shaped thin copper metal thin plate 145 is embedded so that the dividing position comes to a position about 5 mm above the metal ball 142. At this time, it is processed so as to be parallel to the end surface of the acrylic cylindrical container 143.
Acrylic cylindrical container 143 is joined, and liquid 146 such as high-viscosity glycerin or silicon oil is injected into cylindrical container 143. A lid 144 to which a fine metal wire 141 formed of tungsten wire is bonded is attached to enclose the liquid 146. Thereby, the calibrator 14 is completed.

  The calibrator 16 affixes a thin metal plate 161 such as aluminum or iron having a thickness of about 0.1 mm and a length of about 40 mm so as to intersect at 90 degrees by using a side surface such as a plastic material 162 having a high radiation transmittance. Therefore, it is assumed that the vertical plastic material 162 can be freely rotated about the smooth rotation shaft 164 by lengthening the plastic material 162 in the vertical direction. Since the rotation shaft 164 is installed perpendicularly to the mounting plate 163 parallel to the detection surface 151, the rotational movement is limited to a two-dimensional plane parallel to the detection surface 151, and the vertical direction is caused by gravity. Is a structure that can be determined naturally. Therefore, the plastic material 162 and the metal thin plate 161 need to have a symmetrical structure around a vertical line passing through the rotation shaft 164. After attaching this to the detection surface 151 and correcting the rotational deviation so that the pixel arrangement of the detector 15 and the projection data are parallel, the detection surface 151 is projected so that the intersection 165 of the thin metal plate 161 is projected as a point. Adjust the angle. Here, the detection surface 151 is rotated around the rotation axes aa and bb around the point A in FIG. 9, and the direction of the detection surface 151 is corrected so that the intersecting portion 165 of the thin metal plate 161 becomes a point.

  Next, the calibrator 14 is projected, and the inclination of the turntable 13 with respect to the X-ray irradiation direction is adjusted so that the thin metal wire 141 and the thin metal plate 145 are projected in a line shape by using the identification processing of the thin metal plate 145. To do. Further, the turntable 13 is adjusted with respect to the direction perpendicular to the X-ray irradiation direction so that the thin metal wire 141 and the thin metal plate 145 are orthogonal to each other. Further, when the turntable 13 is rotated once and the deflection width of the thin metal wire 141 is obtained, the center position thereof becomes the true rotation axis of the calibrator 14. The midpoint of the intersection line between the true rotation axis and the thin metal plate 145 is called the true rotation center point of the thin metal plate 145 (point E in FIG. 9). In FIG. 9, the positions and lengths of points are defined as follows.

A: Projection point of the end point on the side close to the detection surface 151 in the intersecting portion 165 of the thin metal plate 161 B: Projection image of the midpoint of the intersection of the thin metal wire 141 and the thin metal plate 145 C: Intersection of the intersecting portion 165 of the thin metal plate 161 Projection line D at the upper end of the virtual normal that is the same length as the line length D: upper end of the virtual normal that is raised from the point B E: midpoint of the intersection of the thin metal wire 141 and the thin metal plate 145 S: Focal point L1 of X-ray source 11 AS length L2: Intersection length 165 of intersecting portion 165 of metal thin plate 161 of calibrator 16 L3: AB length, measurable from projection image L4: BC length, measurement Find from data

If the projected point of the end point near the detection surface 151 in the intersecting portion 165 of the thin metal plate 161 is at the point B, a projected image is virtually indicated by BC. In order for the virtual normal line BD of the point B to be directed to the focal point S, that is, to be seen as a point, the vertical and horizontal shake amounts of the detector 15 with respect to the point B are represented by the rotation axis a Rotate around 'a' and b'b 'and adjust so that the projected image of BD moves by Δx' and Δy '. Point B has only a virtual normal, and there is actually no projection image. However, if Δx ′ and Δy ′ are obtained, the amount of rotation about the a′a ′ axis and the amount of rotation about b′b ′. Can be determined uniquely. By doing so, the detection surface 151 is adjusted so that the normal of the point B faces the focal point S. Here, Δx ′ and Δy ′ are expressed as a function of components Δx and Δy (measurable) on the detection surface 151 of the distances L1, L2, and L3 and the points A and B as follows.

Δx ′ = L4 × cos α, Δy ′ = L4 × sin α, where α = tan ⁻¹ (Δy / Δx) and L4 = L2 × L3 / (L1−L2).
Here, in order to correct the left / right and up / down deflection angles of the detector 15 around the point B, a rotation axis passing through the point B is required, but if these are not mechanically equipped, they are parallel. Equivalent movement may be realized by combining movement and rotational movement.

With the above procedure, the alignment of the X-ray detector 15, the sample stage 12, and the X-ray focal point can be corrected based on an absolute reference independent of the apparatus. For this reason, the correction of the detection surface 15 is first performed by the calibrator 16, and then the detection surface 15 is adjusted in accordance with the sample stage 12 installed horizontally by the calibrator 14, so that the correction can be performed in a one-through manner. It can be carried out efficiently in time. In actual projection, the calibrator 16 is removed, the sample stage 12 is moved downward, and a sample is placed on the sample stage 12 and photographed. The position of the point B is known, and the beam from the focal point of the X-ray source 11 intersects the detection surface 15 perpendicularly at the point B.
In the embodiment described above, the shape of the metal thin plate 145 is not limited to a circular plate, and may be, for example, a polygonal thin plate. Moreover, although X-ray CT was demonstrated in embodiment mentioned above, it is also possible to change an X-ray into a gamma ray.

  The present invention is for nondestructive inspection, industrial X-ray CT, high-magnification fluoroscopy, microfocus X-ray CT, fluoroscopy of bones, rocks, electronic parts, etc., medical X-ray CT, and manufacture of phantoms for X-ray CT Can be used.

It is a figure for demonstrating the X-ray CT apparatus 1 which concerns on embodiment of this invention. It is a side view of the calibrator 14 which concerns on the same embodiment. (A) is a side view when the calibrator 14 in FIG. 2 is tilted in the YL direction, and (b) is a side view when the calibrator 14 in FIG. 2 is tilted in the YR direction. (A) is the side view of the calibrator 14 seen from the direction orthogonal to the X-ray irradiation direction when the sample stage 12 according to the embodiment is tilted away from the X-ray irradiation direction. b) is a front view of the calibrator 14 viewed from the X-ray irradiation direction. It is a side view of the calibrator 14 at the time of enclosing the highly viscous liquid 146 which concerns on the embodiment. (A) is a front view of the calibrator 16 according to the embodiment, and (b) is a plan view of the calibrator 16. It is a figure for demonstrating a mode that the rotational deviation of the X-ray detector 15 is correct | amended using the calibrator 16 which concerns on the embodiment. It is a figure for demonstrating a mode that the inclination of the detection surface 151 is adjusted using the calibrator 16 which concerns on the embodiment. It is a figure for demonstrating the positional relationship required in order to adjust the inclination of the detection surface 151 which concerns on the embodiment. It is a side view of the calibrator 17 with a sample stage concerning the embodiment. It is a figure for demonstrating the example of installation to the phantom and its X-ray image intensifier in patent document 1. FIG. It is a figure which shows the example of the up-and-down shake and projection image of the X-ray image intensifier in patent document 1. FIG. It is a figure which shows the example of the right-and-left shake and projection image of the X-ray image intensifier in patent document 1. FIG. It is a figure which shows the direction of the deviation | shift which cannot correct | amend the X-ray image intensifier in patent document 1 with a phantom. (A) is a figure which shows the example of installation of the pin phantom of the sample stand proposed in patent document 2, (b) is for demonstrating the deviation which cannot be corrected with the pin phantom of the sample stand proposed in patent document 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 11 X-ray source 12 Sample stand 13 Turntable 14 Calibrator 141 Metal fine wire 142 Metal sphere 143 Cylindrical container 144 Lid 145 Metal thin plate 146 Liquid 15 X-ray detector 151 Detection surface 16 Calibrator 161 Metal thin plate 162 Plastic Material 163 Mounting plate 164 Rotating shaft 165 Crossing portion 17 Calibrator with sample stage

Claims (6)

Radiography including a radiation source for irradiating radiation, a sample stage on which a sample is placed, and a detector that is disposed at a position facing the radiation source across the sample stage and detects the intensity of the radiation that has passed through the sample. In a calibrator for calibrating the inclination of the sample stage in the apparatus,
One end is fixed to a calibrator built in the sample stage , and a linear member formed of a material whose radiation transmittance is smaller than that of the surrounding material,
A thin metal plate fixed to the calibrator so as to form a cross crossing perpendicularly to the linear member in the horizontal state of the calibrator and having a radiation transmittance smaller than that of the surrounding material. Prepared,
Based on the result detected by the detector by irradiating the linear member and the metal thin plate with radiation, the inclination of the sample stage with respect to the vertical plane parallel to the radiation irradiation direction is orthogonal to the radiation irradiation direction. A calibrator that detects and calibrates inclination with respect to a vertical plane at the same time.   2. The calibrator according to claim 1, wherein a part of the metal thin plate is subjected to identification processing for identifying in which direction the sample stage is inclined with respect to the radiation irradiation direction. .   The calibrator according to claim 1 or 2, wherein a weight is joined to the other end of the linear member.   The said linear member and the said metal thin plate are installed in the container in which the liquid whose radiation transmittance is larger than this linear member and this metal thin plate is inject | poured. The calibrator according to item 1.   The calibrator according to any one of claims 1 to 4, wherein the sample stage is attached. In the calibration method which calibrates the inclination of the radiographic apparatus using the calibrator according to any one of claims 1 to 5,
Both have a lower radiation transmission than the surrounding material,
A step of installing a flat plate whose end is pivotally supported by a rotary shaft perpendicular to the detection surface, and another flat plate perpendicular to the flat plate;
By irradiating the flat plate and the other flat plate with radiation, based on the result detected by the detector, the pixel arrangement of the detector is parallel to the projection image of the flat plate and the other flat plate. The process of calibrating so that
By irradiating the flat plate and the other flat plate with radiation, based on the result detected by the detector, the detection is performed so that the projected image of the intersection of the flat plate and the other flat plate can be seen as a point. Calibrating the orientation of the surface;
Based on a result detected by the detector by irradiating the calibrator with radiation, a radiation focal point of the radiation source, and a midpoint of an intersection line of the rotation axis of the calibrator and the metal thin plate, A calibration method comprising a step of calibrating a normal line set at a position where a line obtained by extending a connecting line and a detection surface of the detector intersect with each other so as to face the radiation focus direction.

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