JP2010204060A - X-ray inspection device, and inspection method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of an inspection device for obtaining transparent data of an inspecting object from various angles by moving a radiation source and a detector in parallel and for obtaining a tomographic image of the inspecting object by reconstituting this data wherein an image cannot be reconstituted when geometric arrangement of the segments for connecting the radiation source to respective detecting elements of the detector is not previously accurately recognized, and information on image reconstitution depends on obtaining of data and an error occurs when vibration occurs in a device under inspection. <P>SOLUTION: In this inspection device including the radiation source and the detector, phantom for calibration is installed between the radiation source and the detector, and a transmission image of a thin line included in the phantom for calibration is obtained synchronously with obtaining of transmission data of a specimen. Using the transmission image of the thin line, the position of the radiation source during data obtaining and the distance between the radiation source and detector are derived. In an imaging data correction method and the inspection device, a correction data of a transmission route is calculated based on the geometric arrangement, and the image reconstitution is executed using this. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray inspection apparatus and an X-ray inspection method.

  Pipes that have been used for a long time at power plants, etc., cause internal thinning. Internal thinning is a phenomenon in which the fluid flowing inside the pipe repeatedly collides with the inner wall surface of the pipe, causing the surface to be mechanically damaged and partly detaching (erosion) and corrosion due to chemical action ( It is generated by interaction with (corrosion). In particular, many internal thinnings occur at places where the flow of fluid is disturbed, such as bent places and orifices. If the amount of thinning exceeds the limit value, the pipe cannot withstand the operating pressure, resulting in damage to the pipe and a serious accident.

  In order to prevent such accidents, piping inspections are regularly performed. In the conventional pipe inspection, an ultrasonic flaw detector or the like is used to perform a test by bringing a probe into direct contact with the pipe. However, piping is often covered with a heat insulating material on the outside. Therefore, ultrasonic flaw detection had to be tested with the coating material removed. The removal and remounting of the covering material takes time and expense, and further there is a problem that the disposal cost of the covering material is required.

  On the other hand, the pipe internal inspection by the combination of the radiation source and the detector is an effective means for improving the inspection efficiency because the internal state inspection is possible even when the heat insulating material is coated on the pipe (Patent Document 1). . However, in transmission imaging, since information on a three-dimensional object is projected on a two-dimensional plane, it is difficult to grasp the position and shape of the thinning and to quantitatively evaluate the thinning.

  Therefore, CT (Computed Tomography) is one of effective methods for obtaining the pipe internal information three-dimensionally. CT is a method for obtaining transmission data from the entire circumference of an inspection object by rotating a radiation source and a detector around the inspection object and obtaining a cross-sectional image by image reconstruction calculation. As a result, an image having a resolution of millimeters or less can be obtained. However, a plant such as a power plant often does not have a space around which a radiation source and a detector can be rotated. In view of this, an inspection method based on a CL (Computed Laminography) method has been developed in which a tomographic image of an inspection object is obtained by translating a radiation source and a detector to obtain three-dimensional information (Non-Patent Document 1).

JP-A-9-89810

S. Gondrom, S. Schropfer: “Digital computed laminography and tomosynthesis-functional principles and industrial applications” Proceedings BB 67-CD, Computerized Tomography for Industrial Applications and Image Processing in Radiography (1999)

  The CL method obtains imaging data from various angles of the inspection object by moving the radiation source and the detector in parallel. By reconstructing this imaging data, a tomographic image of the inspection object is obtained. However, unlike the normal CT method, the CL method does not acquire data by rotating operation. In the CT method, if the rotation center is obtained, the imaging data detected by each detection element can be rearranged according to the distance and angle between the line segment connecting each detection element and the radiation source and the rotation center axis. On the other hand, since the CL method does not have a rotation center, image reconstruction cannot be performed unless the geometrical arrangement of line segments connecting the radiation source and each detector element of the detector is accurately grasped. In addition, when vibration occurs during inspection, information necessary for reconstructing an image differs at each imaging time point, and an error occurs. Due to this error, there is a problem that the accuracy of the reconstructed image is lowered.

  Accordingly, an object of the present invention is to make the reconstruction of an image more accurate.

  The present invention includes a calibration phantom installed in an X-ray irradiation area irradiated by an X-ray source, and a correction unit that corrects imaging data of the inspection object based on the inspection object and a transmission image of the calibration phantom. It is characterized by providing.

  According to the present invention, the reconstruction of an image can be made with higher accuracy.

1 is a diagram illustrating a device configuration of Example 1. FIG. It is the schematic diagram which showed the image reconstruction area | region of the test | inspection apparatus. It is a schematic diagram which shows the principle which derives | leads-out the position of an X-ray source from the transmission image of a perpendicular | vertical thin line. It is a schematic diagram which shows an example of the arrangement place of the calibration phantom. It is a schematic diagram which shows the principle which derives | leads-out the distance between an X-ray source and a detector using the transmission image of a perpendicular | vertical thin line. It is a schematic diagram which shows the principle which derives | leads-out the distance between an X-ray source and a detector using the transmission image of a horizontal fine line. It is a schematic diagram which shows the X-ray attenuation amount of a fine wire diameter direction in the transmission image of a horizontal fine wire. It is a schematic diagram which shows the permeation | transmission image of piping. It is a figure which shows the piping inspection method by the inspection apparatus of a present Example. It is a schematic diagram which shows the manufacturing method of the phantom for calibration. FIG. 6 is a schematic diagram illustrating a device configuration of Example 3. FIG. 6 is a schematic diagram illustrating a device configuration of Example 4.

  Examples will be described below.

  FIG. 1 shows the configuration of this embodiment. The CL-type X-ray inspection apparatus 1 includes an X-ray tube 202 having an X-ray source 201 therein and a detector 203 that is a two-dimensional detection element. The X-ray source 201 and the detector 203 are arranged so as to face each other with the inspection object 230 interposed therebetween. The relative position of the X-ray source 201 and the detector 203 is fixed by the support member 231, and the X-ray source 201 and the detector 203 are moved with respect to the inspection object 230 by the moving mechanism 232. In this example, the inspection object 230 is a pipe, and the X-ray inspection apparatus 1 moves in the pipe longitudinal direction.

  The detector 203 is a thin film such as a scintillator or silicon, and detects X-rays to emit visible light. The photodiode then converts this visible light into an electrical signal. An electronic circuit 221 including a photodiode is disposed below the detector. A cover material 220 that protects the detection surface is provided on the upper surface of the detector.

  The calibration phantom 101 is disposed between the X-ray source 202 and the detector 203. The calibration phantom 101 includes a member having high rigidity, such as acrylic, and a relatively low radiation attenuation rate, and fine wires 102, 103a, 103b made of a material having a high radiation attenuation rate, such as tungsten. Prepare. The thin wire | line 102 is arrange | positioned perpendicularly | vertically inside the member. The two thin wires 103a are disposed horizontally and parallel to the upper surface of the member. The two thin wires 103b are disposed horizontally and parallel to the lower surface of the member. The upper and lower surfaces of the member are preferably smooth and parallel surfaces. The calibration phantom 101 is in a position parallel to the detection surface of the detector 203, and X-rays 204 emitted from the X-ray source cause transmission images of the vertical fine lines 102 and the horizontal fine lines 103a and 103b inside the phantom. It is desirable to be in an X-ray irradiation region that can be detected by the detector 203. Further, it is desirable that the calibration phantom 101 be installed at a position other than the path through which the vertical thin wire 102 and the horizontal thin wires 103a and 103b transmit an object having a large amount of X-ray attenuation such as piping.

  The X-ray tube 202 is connected to a high-voltage power source 205 and a cooler 206, and the X-ray tube system control unit 207 always realizes a stable tube voltage and tube current. The detector control unit 208 adjusts the timing for fetching data from the electronic circuit 221 of the detector 203 and collects data. The X-ray tube system control unit 207 and the detector control unit 208 are connected to the central control unit 209. The central control unit 209 adjusts the operation timing of each device. In addition, the arithmetic device inside the central control unit 209 performs data processing. The monitor 210 displays the operation state of the apparatus and the inspection result.

  In the X-ray inspection apparatus of this embodiment, the X-ray tube 202 and the detector 203 are simultaneously translated, or only one of them is translated in the length direction of the pipe, the imaging data of the inspection object is acquired, and the imaging data is obtained. Reconstruct and obtain a tomogram. FIG. 2 shows an example in which the image reconstruction area is divided into grids 301. As in the present embodiment, the CL-type inspection apparatus does not perform a rotational movement unlike a normal CT apparatus. Therefore, when the CL inspection apparatus derives the geometric arrangement of the apparatus, the relative position cannot be calculated from the rotation center. Image reconstruction consists of the position where the line segment connecting the X-ray source 201 and each detector element of the detector 203 intersects the grid 301 in the image reconstruction area, the length of the line segment passing through the grid 301, and the image reconstruction. The position of the inspection object 230 in the configuration area must be calculated. Therefore, an inspection flow for calculating the position and distance between the X-ray source 201 and the detector 203, the position of the inspection object 230, and the position change due to the apparatus vibration during translation will be described.

  FIG. 9 is a diagram showing an inspection flow of this embodiment. First, the device (except for the calibration phantom) is assembled locally (procedure 801). Next, the calibration phantom 101 is attached to the cover material 220 of the detector 203. Here, the calibration phantom is installed on the front surface of the detector so that the transmission image of the calibration phantom is projected to a place other than the pipe projection region, and the angle of the calibration phantom with respect to the detector is adjusted (step 802). . In addition, the calibration phantom is attached so that the vertical and horizontal fine wires of the calibration phantom are perpendicular and horizontal to the detector, respectively.

  After the calibration phantom is attached to the detector, the X-ray source 201 starts X-ray irradiation on the piping and the calibration phantom. The detector control unit 208 acquires imaging data of the inspection object 230 such as a calibration phantom and piping (step 803). The central control unit 209 derives the geometric arrangement of the X-ray source 201 and the detector 203 from the imaging data of the calibration phantom. Further, a feature value of the pipe transmission image is extracted based on the imaging data of the pipe, and this feature value is set as an initial value (procedure 804).

  While moving the X-ray source and the detector in parallel, the detector acquires imaging data of the piping and the calibration phantom at regular time intervals (step 805). In step 805, imaging data of the piping and the calibration phantom is acquired at each imaging time point. Based on the imaging data of the calibration phantom, the geometric arrangement of the X-ray source 201 and the detector 203 at each imaging time is calculated by the same method as in the procedure 804. Also, the amount of change in the piping position with respect to the X-ray source 201 and the detector 203 at each imaging time point is derived based on the amount of change in the piping feature amount. As described above, the relative positions of the X-ray source 201, the detector 203, and the pipe 230 are determined for each imaging time point based on the geometric arrangement of the X-ray source and the detector and the amount of change in the pipe position with respect to the X-ray source and the detector. Derived (procedure 806). At each imaging time point, the imaging data of the pipe is corrected from the relative position information, and corrected transmission data is created (step 807). Image reconstruction is performed from the corrected transmission data, and a pipe tomogram is obtained (procedure 808).

  Next, a method for calculating the geometric arrangement of the X-ray source and the detector at each imaging time point based on the imaging data of the calibration phantom will be described. FIG. 3 is a view showing a transmission image of the vertical thin line 102. Since the detector 203 of this embodiment has a two-dimensional detection surface, the detector 203 detects a planar transmission image. FIG. 3 shows a case where there are four vertical thin wires 102. The X-ray source 201 has a minute size of less than 1 mm and radiates X-rays radially. Therefore, the transmission image 401 of the vertical thin line 102 is projected on the opposite side of the direction in which the X-ray source 201 is viewed from the vertical thin line 102. Therefore, as shown in FIG. 3, an intersection 403 of line segments 402a, 402b, 402c, and 402d obtained by extending the transmission images 401a, 401b, 401c, and 401d of the respective vertical thin lines 102 indicates a planar position of the X-ray source 201. . The X-ray source 201 is located above the intersection point 403.

  If there are at least two vertical thin lines 102, the position of the X-ray source 201 can be derived. However, in the case of two, it is a necessary condition that the X-ray source 201 is not located on a line segment connecting the two vertical thin wires 102. Further, since the position of the X-ray source 201 is derived from the transmission image, the error can be reduced if the width of the image is as narrow as possible. The width of the transmission image is desirably about the element of the detector 203. Therefore, it is desirable that the diameter of the vertical thin wire 102 is also approximately the same as the element size of the detector 203. Increasing the number of vertical thin wires 102 improves the positional accuracy of the X-ray source. When the number of thin lines is n, the statistical error decreases by 1 / √n.

  FIG. 4 shows the relationship between the fine line of the calibration phantom 101 and the inspection object 230. It is desirable that the fine line be installed at a position that does not overlap with an X-ray path that passes through an object having a large X-ray attenuation rate such as a pipe. In the detector 203, the transmission image of the fine line does not overlap with the pipe, and the transmission image of the fine line can be detected with high accuracy.

  FIG. 5 is a conceptual diagram for deriving the distance between the X-ray source 201 and the detector 203 by the vertical wiring 102. Two arbitrary vertical thin lines 102 are selected, and the distance between the lower ends of the thin lines is L1, and the distance between the upper ends is L2. The height of the fine line is D. These three numerical values can be precisely controlled when the calibration phantom is manufactured. Further, the distance from the X-ray source 201 to the lower end of the vertical thin line 102 is Z1, the distance to the upper end is Z2, and the distance from the X-ray source 201 to the detection surface of the detector 203 is H. These three numbers are unknown. Further, in the transmission image of the vertical thin line obtained by the detector 203, the distance of the lower end transmission image is L1 ′, and the distance of the upper end transmission image is L2 ′.

  When the enlargement ratio of the transmission image is r1 at the lower end and r2 at the upper end, they are respectively expressed by the following equations.

  When these are transformed,

Because the fine wire height D is the difference between Z1 and Z2.

Thereby, the distance H between the X-ray source 201 and the detection surface of the detector 203 is derived from known numerical values.

  FIG. 6A is a conceptual diagram for deriving the distance between the X-ray source 201 and the detector 203 using the horizontal thin lines 103a and 103b. As shown in FIG. 6B, when L1 ′ and L2 ′ are derived from the transmission image intervals of the thin lines arranged in parallel, the numerical values derived from a plurality of parallel lines are averaged to calculate L1 ′ and L2 ′. it can. Therefore, the error between L1 ′ and L2 ′ is reduced.

  The transmission image (X-ray attenuation amount) has blur. This is derived from the X-ray transmission distance and the size of the X-ray source. In the case of a vertical thin line, since a transmission image at the end of the thin line is used, the attenuation curve of the imaging data changes suddenly and non-uniformly. For this reason, it is difficult to derive L1 ′ and L2 ′ with high accuracy using the vertical thin wire. On the other hand, in the case of the horizontal thin wires 103a and 103b, blur appears in the thin wire diameter direction. The X-ray attenuation continuously decreases from the center of the thin line toward the edge, and the X-ray attenuation changes smoothly (FIG. 7). Therefore, the central portion of the fine line of the transmission image can be derived with high accuracy, and the parallel intervals L1 ′ and L2 ′ of the fine transmission image can be derived with high accuracy. The distance H can be obtained by applying these L1 'and L2' to the above equations (1) to (5).

  As described above, the distance between the X-ray source and the detector can be obtained by the vertical thin line or horizontal thin line of the calibration phantom, the geometric arrangement of each detector element of the detector and the X-ray source, and the initial X A line transmission path can be determined.

  Next, a method for correcting the imaging data of the inspection object based on the transmission image of the inspection object and the calibration phantom will be described. FIG. 8 shows a transmission image of the inspection object. In step 804, a feature amount is extracted from the transmission image shape of the inspection object, and this feature amount is set as an initial value. In this embodiment, the feature amount is the pipe width. On the other hand, in step 806, the inspection object is imaged at regular time intervals, the feature amount of the transmission image at each imaging time is extracted, and compared with the initial value. When the feature amount is the pipe width, when the amount of change in the width becomes positive, it indicates that the pipe 230 has moved to the X-ray source 201 side. Further, when the amount of change in the pipe width is negative, it indicates that the pipe 230 has moved to the detector 203 side. The change rate of the pipe width is proportional to the ratio of the distance H between the X-ray source 201 and the detector 203 and the distance M between the X-ray source 201 and the pipe. Furthermore, since the procedure 806 also captures the calibration phantom at each imaging time, the arrangement of the X-ray source 201 and the detector 230 at each imaging time is also known. Therefore, relative position information of the X-ray source 201, the detector 203, and the pipe 230 can be calculated at each imaging time point.

  Specifically, at each imaging time, when the distance H between the X-ray source 201 derived from the above equations (1) to (5) and the detection surface of the detector 203 is H (t), the X-ray source 201 The ratio of the distance H between the detector 203 and the distance M between the X-ray source 201 and the pipe is H (t) / M, which is equal to the magnification of the transmission image of the pipe. Here, the enlargement ratio means the ratio of the transmission image pipe width to the actual pipe width. When the enlargement ratio at a certain time t1 increases by 10% with respect to the initial enlargement ratio, the ratio of the distance M between the X-ray source 201 and the pipe to H (t) is reduced by 10%. Yes. Thereby, the distance H (t) between the X-ray source 201 and the detector 203 at each time and the distance M between the X-ray source 201 and the pipe 230 are determined, and the relative positions thereof are determined. Based on this relative position, pipe coordinates in the image reconstruction area are sequentially set to perform image reconstruction.

  As described above, in an inspection apparatus having an X-ray source and a detector, an inspection object is based on a calibration phantom installed in an X-ray region irradiated by the X-ray source, and transmission images of the inspection object and the calibration phantom. Correct imaging data of objects. Further, since the imaging data of the inspection object and the calibration phantom are acquired in synchronization, the imaging data can be corrected even if the position of the apparatus is shifted due to vibration during the inspection. By performing image reconstruction based on the corrected imaging data, the image reconstruction can be made more accurate.

  FIG. 10 shows a method for manufacturing a calibration phantom. The structural member for holding the fine wire is divided, and a slit is provided at a place where the fine wire is to be installed, and the fine wire is installed in the slit. After installing the thin wire, the structural members are joined to form a phantom. By doing so, the position accuracy and angle accuracy of the thin line can be maintained.

  FIG. 11 shows an apparatus configuration of the third embodiment. The cover member 220 is not attached to the top of the detector 203. In this case, L1 = L1 ′, and equation (5) becomes

It is expressed.

  FIG. 12 shows an apparatus configuration of the fourth embodiment, and shows a case where a calibration phantom is installed in front of the X-ray source 201. In this case, the calibration phantom becomes compact and can be permanently installed in the X-ray source 201, so that the apparatus installation time can be shortened.

  The present invention can be used for a pipe inspection apparatus using radiation, and can be used for pipe thinning inspection and three-dimensional shape data acquisition in a plant.

101 Calibration Phantom 201 X-ray Source 203 Detector 209 Central Control Unit

Claims (3)

X-ray inspection having an X-ray source for irradiating an inspection object with X-rays, a detector for detecting X-rays transmitted through the inspection object, and a control unit for processing imaging data output by the detector In the device
A calibration phantom installed in an X-ray irradiation area irradiated by the X-ray source;
An X-ray inspection apparatus comprising: correction means for correcting the imaging data of the inspection object based on the inspection object and a transmission image of the calibration phantom.   2. The X-ray inspection apparatus according to claim 1, wherein the fine line of the calibration phantom is installed at a position that does not overlap an X-ray path that passes through the inspection object. X-ray inspection having an X-ray source for irradiating an inspection object with X-rays, a detector for detecting X-rays transmitted through the inspection object, and a control unit for processing imaging data output by the detector In the inspection method of the device,
With the X-rays irradiated from the X-ray source, the calibration phantom and the inspection object are imaged, and imaging data of the calibration phantom and the inspection object are acquired,
Based on the imaging data of the calibration phantom, calculate the geometric arrangement of the X-ray source and the detector,
Based on the imaging data of the inspection object, to calculate a position change amount of the inspection object,
Based on the geometric arrangement and the position change amount, the relative position information of the X-ray source, the detector, and the inspection object for each imaging time point is calculated.
Based on the relative position information, the imaging data is corrected,
An inspection method for an X-ray inspection apparatus, wherein image reconstruction is performed based on the corrected imaging data.

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