X-ray CT device, correction method and device, and measurement method and device thereof

Abstract

The present invention relates to an X-ray CT apparatus and its correction method and apparatus, and a measurement method and apparatus. CT scanning is performed with a spherical correction jig (30) of known dimensions in contact with a subject (W) to generate volume data. The contour of the surface shape of the subject (W) in the volume data is acquired, and the boundary surface of the spherical correction jig (30) is calculated based on the center coordinates of the spherical correction jig (30). A correction value is obtained for aligning the boundary surface of the subject W obtained based on the slope of the contour with the boundary surface of the spherical correction jig (30). The boundary surface of the subject (W) is corrected using the correction value, and the shape of the subject (W) is determined using the corrected boundary surface. Thus, high-precision X-ray CT for measurement is achieved by highly accurately detecting the boundary surface of the subject.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The disclosure of Japanese Patent Application No. 2019-172253 filed on September 20, 2019 including the specification, drawings, and claims is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a calibration method and apparatus, a measurement method and apparatus, and a measuring X-ray CT apparatus for a measuring X-ray CT apparatus, and in particular to a calibration method and apparatus, a measurement method and apparatus, and a measuring X-ray CT apparatus for a measuring X-ray CT apparatus capable of achieving high precision by detecting a boundary surface of an object with high precision. Background Art

[0004] Medical X-ray CT systems came into practical use in the 1970s, and based on this technology, X-ray CT systems for industrial products began to appear in the early 1980s. Since then, industrial X-ray CT systems have been used to observe and inspect issues difficult to detect visually, such as pores in castings, poor soldering in welded parts, and defects in the circuit patterns of electronic components. Meanwhile, with the recent proliferation of 3D printers, the need for not only observing and inspecting the interiors of 3D-printed products but also measuring and achieving high-precision 3D dimensions of internal structures has also increased.

[0005] In response to the aforementioned technological trends, measurement X-ray CT systems have become increasingly common, primarily in Germany (see Japanese Patent Application Publication Nos. 2002-71345 and 2004-12407). These measurement X-ray CT systems place the object being measured at the center of a rotating table, and irradiate the object with X-rays while rotating it.

[0006] exist Figure 1 2 shows the structure of a typical X-ray CT apparatus 1 used for measurement. Within a housing 10 that blocks X-rays, there are an X-ray source 12 that radiates cone-beam X-rays 13, an X-ray detector 14 that detects X-rays 13, a rotational table 16 on which a subject W is placed and rotated for CT imaging, and an XYZ movement mechanism 18 for adjusting the position and magnification of the subject W as it enters the X-ray detector 14. Furthermore, the apparatus includes a controller 20 for controlling these components and a control PC 22 that provides instructions to the controller 20 through user operations.

[0007] The control PC 22 has a function of displaying a projection image of the subject W captured by the X-ray detector 14 and a function of reconstructing a tomographic image from a plurality of projection images of the subject W, in addition to controlling each device.

[0008] like Figure 2 As shown, X-rays 13 emitted from an X-ray source 12 pass through a subject W on a rotating table 16 and reach an X-ray detector 14. While the subject W is rotating, the X-ray detector 14 obtains transmission images (projection images) of the subject W in all directions. These images are reconstructed using a reconstruction algorithm such as back projection or successive approximation, thereby generating a tomographic image of the subject W.

[0009] By controlling the XYZ axes of the XYZ moving mechanism 18 and the θ axis of the rotating stage 16 , the position of the subject W can be moved, and the imaging range (position, magnification) and imaging angle of the subject W can be adjusted.

[0010] In order to obtain a tomographic image or volume data (a collection of stereoscopic images or tomographic images of the subject W in the Z-axis direction) of the subject W, which is the final target of the X-ray CT apparatus 1 , a CT scan of the subject W is performed.

[0011] CT scanning includes two processes: obtaining projection images of the subject W and CT reconstruction. In the projection image obtaining process, the rotating table 16 on which the subject W is placed is rotated continuously at a fixed speed or intermittently at a fixed step length during X-ray irradiation to obtain projection images of the subject W in the entire circumference (fixed interval). CT reconstruction algorithms such as back projection method and successive approximation method are used. Figure 3 By performing CT reconstruction on the obtained projection images in the entire circumferential direction (at fixed intervals) as illustrated, a tomographic image or volume data of the subject W is obtained.

[0012] When measuring a subject using a survey X-ray CT apparatus, as described above, a CT scan is first performed to acquire volume data of the subject, the surface shape of the volume data is detected, and then various measurements of the surface shape are performed. Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, the above process has a problem in that it is difficult to accurately detect the boundaries of the surface shape due to the characteristics of the X-ray source and the X-ray detector, which greatly affects the measurement accuracy.

[0015] The present invention is made to solve the above-mentioned conventional problems, and therefore aims to achieve higher accuracy of measurement X-ray CT by simultaneously measuring the subject and a spherical correction jig of known dimensions to detect the boundary surface of the subject with high precision.

[0016] Solutions for solving problems

[0017] The contour of the surface shape (boundary surface) of the volume data is as follows Figure 4 With such a wide curved shape, it is difficult to detect a boundary surface close to the true value based on the contour.

[0018] However, if Figure 5 In the volume data of a sphere (perfect sphere) 30 made of a single material (if X-ray-related correction has been applied), the contour of the sphere's surface shape is roughly the same at all locations, so the center coordinates of the sphere can be calculated with approximately high accuracy regardless of the position of the contour used as the boundary surface.

[0019] Therefore, in the present invention, a sphere made of a single material with known dimensions (hereinafter referred to as a spherical correction jig) is brought into contact with the subject to perform CT scanning, and the boundary surface of the subject is detected with high precision by obtaining volume data thereof.

[0020] As described above, the center coordinates of the spherical correction jig can be obtained with high accuracy. In addition, since the dimensions of the spherical correction jig are known, the boundary surface of the spherical correction jig can also be obtained with high accuracy.

[0021] In order to detect the boundary surface of the object W with high precision, it is necessary to Figure 6 In order to accurately determine the contact point between the object W and the spherical correction jig 30 as shown, it is necessary to determine the contact direction.

[0022] In the detection of the boundary surface, the user selects which boundary surface to detect, for example, based on the material of the object W. When making this selection, the approximate direction of the boundary surface to be detected can be determined, and this information can be used to determine the contact direction (in Figure 6 ( ) When the approximate direction determined by the user's boundary surface selection is set as the search reference direction, the contour is checked while gradually deviating from the search reference direction to determine whether there is contact.

[0023] For example, Figure 7 As shown, if vectors A, B, and C are defined as vectors extending in a direction slightly deviated from the search reference direction, originating from the center coordinates of the spherical correction jig 30, the resulting contour displays components in the order of the spherical correction jig 30, the air layer, and the subject W. The vectors that do not include an air layer between the spherical correction jig 30 and the subject W are considered to be in contact, confirming the absence of an air layer around the boundary surface of the spherical correction jig 30. The air layer is more permeable to X-rays than the spherical correction jig 30 and the subject W, and therefore displays a lower component in the contour. Therefore, in the contours of each of the vectors A, B, and C, the vector with the highest component near the boundary surface of the spherical correction jig 30 is close to the contact direction.

[0024] In this way, the search is performed with the search reference direction as the center to obtain the desired contour, and a highly accurate search direction is obtained to calculate the contact points.

[0025] In order to use the contact points obtained by the above method to obtain the boundary surface of the object W with high accuracy, as shown in FIG. Figure 8 As shown, the boundary surface determined from the slope of the contour, etc., is utilized. The difference between the contact point determined by the spherical calibration jig 30 and the contact point determined from the slope of the contour can be used as a correction value. The correction value determined from the contour of the contact direction (contact point) can be applied to the entire or partial boundary surface of the same subject (same material) at that time.

[0026] The spherical correction jig 30 is made of resin, aluminum, iron, or other materials, and can be appropriately selected according to X-ray measurement conditions (tube voltage, tube current, etc.) during CT scanning and the material of the object W.

[0027] The present invention, which has been completed based on the above findings, solves the above-mentioned problems by providing a calibration method for a measuring X-ray CT apparatus. The calibration method for a measuring X-ray CT apparatus is characterized in that the measuring X-ray CT apparatus irradiates a subject disposed on a rotating table with X-rays while rotating the subject, reconstructing projection images of the subject to generate tomographic images of the subject. When calibrating the measuring X-ray CT apparatus, a CT scan is performed with a spherical calibration jig of known dimensions in contact with the subject to generate volume data. The contour of the subject's surface shape is acquired from the volume data, and a boundary surface of the spherical calibration jig is calculated based on the center coordinates of the spherical calibration jig. A calibration value is then determined to make the boundary surface of the subject, which is determined based on the slope of the contour, coincide with the boundary surface of the spherical calibration jig.

[0028] Here, the material of the spherical correction jig can be the same as that of the object under inspection.

[0029] The present invention also relates to a calibration device for a measuring X-ray CT apparatus that irradiates an object placed on a rotating table while rotating the object, reconstructs a projection image of the object, and generates a tomographic image of the object. The calibration device for the measuring X-ray CT apparatus comprises:

[0030] A unit for generating volume data by performing CT scanning with a spherical correction jig of known dimensions in contact with a subject;

[0031] A unit for acquiring the outline of the surface shape of the subject in the volume data and calculating the boundary surface of the spherical correction jig based on the center coordinates of the spherical correction jig; and

[0032] a means for obtaining a correction value for making the boundary surface of the object obtained from the slope of the contour coincide with the boundary surface of the spherical correction jig;

[0033] This solves the above-mentioned problem in the same manner.

[0034] In the present invention, a measuring X-ray CT apparatus irradiates a subject, which is placed on a rotating table, with X-rays while rotating it, and reconstructs projection images of the subject to generate tomographic images of the subject. When performing measurements using the measuring X-ray CT apparatus, CT scanning is performed with a spherical correction jig of known dimensions in contact with the subject to generate volume data. The correction values obtained by the method described above are used to determine the boundary surface of the subject, and the shape of the subject is determined using this boundary surface, thereby similarly solving the above-mentioned problem.

[0035] Here, a correction value can be calculated in advance for each normal direction of the measurement surface of the test object, and a database can be created for each combination of correction value and material. When measuring the test object, the correction value corresponding to the normal direction of the measurement surface is read from the database for measurement.

[0036] The present invention also relates to a measuring device of a measuring X-ray CT apparatus, which irradiates an object placed on a rotating table while rotating the object, reconstructs a projection image of the object, and generates a tomographic image of the object, the measuring device comprising:

[0037] A unit for generating volume data by performing CT scanning with a spherical correction jig of known dimensions in contact with a subject;

[0038] a unit for finding a boundary surface of a subject using the correction value found by the apparatus; and

[0039] A unit for finding the shape of the object using this boundary surface,

[0040] This can similarly solve the above-mentioned problems.

[0041] Here, you can also have:

[0042] a database obtained by calculating a correction value for each normal direction of a measurement surface of the object and created for each combination of the correction value and the material; and

[0043] When measuring the subject, a correction value corresponding to the normal direction of the measurement surface is read from a database for use in the measurement.

[0044] In the present invention, a subject and a spherical correction jig of known dimensions are placed in a box that transmits X-rays. CT scanning is performed within the box with the spherical correction jig in contact with the subject to generate volume data. The correction values obtained by the above method are used to determine the boundary surface of the subject, and the shape of the subject is determined using this boundary surface, thereby similarly solving the above-mentioned problem.

[0045] The present invention also has:

[0046] A spherical calibration jig with pre-known dimensions;

[0047] a box body for housing the spherical correction jig, through which X-rays pass;

[0048] A unit for generating volume data by performing CT scanning in a state where the spherical correction jig is in contact with the subject within the housing; and

[0049] a unit for determining a boundary surface of a subject using the correction value determined by the apparatus described above; and

[0050] A unit for finding the shape of the object using this boundary surface,

[0051] This can similarly solve the above-mentioned problems.

[0052] The present invention further provides a measuring X-ray CT apparatus, characterized by comprising:

[0053] A spherical correction jig, the dimensions of which are known in advance;

[0054] a unit for generating volume data by performing CT scanning with the spherical correction jig in contact with the subject;

[0055] a unit for acquiring a contour of a surface shape of a subject in the volume data;

[0056] Calculating a unit of a boundary surface of the spherical correction jig in the volume data according to the center coordinates of the spherical correction jig;

[0057] a unit for correcting a boundary surface of the object using the correction value obtained by the apparatus; and

[0058] A means for obtaining the shape of the subject using the corrected boundary surface.

[0059] Here, a box may be further provided for accommodating the subject and the spherical correction jig, wherein X-rays pass through the box and the spherical correction jig is brought into contact with the subject within the box.

[0060] Effects of the Invention

[0061] According to the present invention, by simultaneously measuring the object and a spherical calibration jig of known dimensions, the surface shape of the object can be accurately detected, thereby achieving higher precision in X-ray CT measurement. This allows high-precision X-ray CT measurement without the use of specialized measuring equipment such as a three-dimensional coordinate measuring machine (CMM).

[0062] These and other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The preferred embodiments are described with reference to the accompanying drawings, wherein like elements are designated by like reference numerals throughout the drawings, and wherein:

[0064] Figure 1 It is a cross-sectional view showing the overall structure of a conventional X-ray CT apparatus used for measurement.

[0065] Figure 2 It is a perspective view showing the arrangement of main parts of a conventional X-ray CT apparatus used for measurement.

[0066] Figure 3 FIG. 1 is a diagram showing a state of CT reconstruction in the conventional art.

[0067] Figure 4 This is a line diagram for explaining problems of the conventional technology.

[0068] Figure 5 This is a perspective view for explaining the principle of the present invention, showing a case where the amount of change in the center coordinates of the detection position based on the boundary surface is small.

[0069] Figure 6 This is a diagram showing the contact state between the spherical correction jig and the object to be inspected, for explaining the principle of the present invention.

[0070] Figure 7 This is a diagram for explaining the principle of the present invention, showing a case where a vector extends in a direction slightly deviated from a search reference direction.

[0071] Figure 8 This is a line graph showing an example of the relationship between the boundary surface of the spherical correction jig and the boundary surface of the subject obtained from the slope of the contour, for explaining the principle of the present invention.

[0072] Figure 9 This is a flowchart showing the processing procedure of the first embodiment of the present invention.

[0073] Figure 10 This is a flowchart showing the processing procedure of the second embodiment of the present invention.

[0074] Figure 11 This is a perspective view showing a state in which a subject and a spherical correction jig are placed in a box made of a material that easily transmits X-rays in the second embodiment.

[0075] Figure 12 This is a diagram showing an example of the relationship between the volume data of the spherical correction jig in contact with the subject and the volume data of the subject in the second embodiment. DETAILED DESCRIPTION

[0076] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The present invention is not limited to the contents described in the following embodiments and examples. Furthermore, the constituent elements in the embodiments and examples described below include constituent elements that can be easily imagined by a person skilled in the art, substantially the same constituent elements, and so-called equivalent constituent elements. Furthermore, the constituent elements disclosed in the embodiments and examples described below may be appropriately combined for use or appropriately selected for use.

[0077] In a first embodiment of the present invention, Figure 9 As shown, first, in step 110, the subject W is brought into contact with the spherical correction jig 30 to perform CT scanning, and a CT scan is generated as shown in FIG. Figure 6 or Figure 7 Volume data as shown in the example.

[0078] Next, in step 120 , the center coordinates of the spherical correction jig 30 are calculated on the volume data.

[0079] Next, in step 130 , the boundary surface of the object W to be found is designated, and a search reference direction is calculated.

[0080] Next, in step 140 , the contact direction is searched to obtain the contact point and the correction value.

[0081] Next, in step 150 , the boundary surface of the object W obtained from the slope of the contour is corrected.

[0082] By bringing the object W into contact with the spherical correction jig 30, the boundary surface of the contact portion can be corrected based on the aforementioned principle. By using the corrected boundary surface, for example, the distance of the object W can be calculated.

[0083] In addition, it is also possible to calculate a correction value for each normal direction of the measurement surface of the test object W. For example, a database can be created for each combination of correction value and material. When measuring the test object W, the correction value corresponding to the normal direction of the measurement surface is read from the database for measurement.

[0084] Next, refer to Figure 10A second embodiment of the present invention will be described.

[0085] In this embodiment, first, in step 200, a box 40 made of a material that is easy to transmit X-rays is prepared. Figure 11 As shown in the example, the box 40 is filled with the object W and a plurality of spherical correction jigs 30 .

[0086] The same steps 110 to 150 as those in the first embodiment are then performed. In steps 110 and 120 , there are multiple spherical correction jigs 30 .

[0087] In this embodiment, Figure 12 As illustrated, by using the corrected boundary surface, for example, the distance calculation of the subject W can be performed.

[0088] The present invention can be applied to methods other than the second embodiment as long as the arrangement allows the subject W to come into contact with the spherical correction jig 30 .

[0089] It is easier to acquire an image if the material of the spherical correction jig 30 is the same as that of the subject W. Alternatively, the material may be changed, and for example, brass, aluminum, iron, or ceramics may be used.

[0090] It is obvious to those skilled in the art that the above-described embodiments are merely illustrative and represent the application of the principles of the present invention, and that those skilled in the art can easily devise various other embodiments without departing from the spirit and scope of the present invention.

Claims

1. A calibration method for a measurement X-ray CT device, characterized in that: The measuring X-ray CT apparatus irradiates an object placed on a rotating table while rotating the object, reconstructs a projection image of the object, and generates a tomographic image of the object. When calibrating the measuring X-ray CT apparatus, A spherical calibration jig of known dimensions is placed in contact with the subject to perform CT scanning to generate volume data. Acquire the contour of the surface shape of the subject in the volume data, and calculate the boundary surface of the spherical correction jig according to the center coordinates of the spherical correction jig, A correction value is obtained for aligning the boundary surface of the object obtained from the slope of the contour with the boundary surface of the spherical correction jig.

2. A calibration device for a measuring X-ray CT apparatus that irradiates an object placed on a rotating table while rotating the object, reconstructs projection images of the object, and generates tomographic images of the object, the calibration device comprising the following means: A unit for generating volume data by performing CT scanning with a spherical correction jig of known dimensions in contact with a subject; A unit for acquiring the outline of the surface shape of the subject in the volume data and calculating the boundary surface of the spherical correction jig based on the center coordinates of the spherical correction jig; and A means for obtaining a correction value for making the boundary surface of the test object obtained from the slope of the contour coincide with the boundary surface of the spherical correction jig.

3. A measuring method for an X-ray CT device, characterized in that: The measuring X-ray CT apparatus irradiates an object placed on a rotating table while rotating it, reconstructs a projection image of the object, and generates a tomographic image of the object. When measuring using the measuring X-ray CT apparatus, A spherical calibration jig of known dimensions is placed in contact with the subject to perform CT scanning to generate volume data. Correcting the boundary surface of the subject using the correction value obtained by the method according to claim 1, The shape of the object is determined using the corrected boundary surface.

4. The measuring method of the X-ray CT apparatus for measurement according to claim 3, characterized in that: A correction value is calculated in advance for each normal direction of the measurement surface of the object, and a database is created for each combination of correction value and material. When measuring the object, the correction value corresponding to the normal direction of the measurement surface is read from the database for measurement.

5. A measuring device of a measuring X-ray CT apparatus, wherein the measuring X-ray CT apparatus irradiates an object placed on a rotating table while rotating the object, reconstructs a projection image of the object, and generates a tomographic image of the object, the measuring device comprising: A unit for generating volume data by performing CT scanning with a spherical correction jig of known dimensions in contact with a subject; means for correcting a boundary surface of the subject using the correction value obtained by the apparatus according to claim 2; and A unit for obtaining the shape of the subject using the corrected boundary surface.

6. The measuring device of the X-ray CT apparatus for measurement according to claim 5, characterized in that: Also features: a database obtained by calculating a correction value for each normal direction of a measurement surface of the object and created for each combination of the correction value and the material; and When measuring the subject, a correction value corresponding to the normal direction of the measurement surface is read from a database for use in the measurement.

7. A measuring method for an X-ray CT device, characterized in that: The specimen and a spherical calibration jig of known dimensions are placed in a box that allows X-rays to pass through. Performing CT scanning in the housing with the spherical correction jig in contact with the subject to generate volume data, Correcting the boundary surface of the subject using the correction value obtained by the method according to claim 1, The shape of the object is determined using the corrected boundary surface.

8. A measuring device for an X-ray CT device for measurement, characterized in that: have: A spherical correction jig, the dimensions of which are known in advance; a box body, which is used to accommodate the spherical correction jig and the object to be inspected, and through which X-rays pass; a unit for generating volume data by performing CT scanning in the housing while the spherical correction jig is in contact with the subject; as well as means for correcting a boundary surface of the subject using the correction value obtained by the apparatus according to claim 2; and A unit for obtaining the shape of the subject using the corrected boundary surface.

9. A measuring X-ray CT device, characterized in that: have: A spherical correction jig, the dimensions of which are known in advance; a unit for generating volume data by performing CT scanning with the spherical correction jig in contact with a subject; a unit for acquiring a contour of a surface shape of the subject in the volume data; Calculating a unit of a boundary surface of the spherical correction jig in the volume data according to the center coordinates of the spherical correction jig; a unit for correcting a boundary surface of the object using the method according to claim 1; and A means for obtaining the shape of the subject using the corrected boundary surface.

10. The measuring X-ray CT apparatus according to claim 9, characterized in that: A box is further provided for accommodating the object and the spherical correction jig, wherein X-rays pass through the box and the spherical correction jig is brought into contact with the object within the box.

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