Calibration method and apparatus for measurement X-ray CT apparatus, measurement method and apparatus using the same, and measurement X-ray CT apparatus

Abstract

Volume data is generated by performing a CT scan with a spherical calibration jig having known dimensions in contact with an object. A profile of the surface shape of the object in the volume data is obtained, and a boundary surface of the spherical calibration jig is calculated from the center coordinates of the spherical calibration jig. A correction value for adjusting a boundary surface of the object determined from the gradient of the profile to the boundary surface of the spherical calibration jig is determined, and the boundary surface of the object is corrected by using the correction value. The shape of the object is determined by using the corrected boundary surface. The precision of measurement X-ray CT can thus be increased by accurately detecting the boundary surface of the object.

Claims

1. A calibration method for a measurement X-ray CT apparatus configured to irradiate an object placed on a rotating table with X-rays while rotating the object, and reconstruct a projection image of the object to generate a tomographic image of the object, the method being implemented by at least a controller including a processor and operably connected to the X-ray CT apparatus, the method comprising: performing a CT scan, using an X-ray CT scanner, with a spherical calibration jig having a known dimension and in contact with the object, generating, with the processor, volume data from the CT scan with the spherical calibration jig in contact with the object; obtaining, with the processor, a profile of a surface shape of the object in the volume data, and calculating a boundary surface of the spherical calibration jig from center coordinates of the spherical calibration jig; and determining, with the processor, a correction value for adjusting a boundary surface of the object determined from a gradient of the profile to the boundary surface of the spherical calibration jig.

2. The calibration method for a measurement X-ray CT apparatus according to claim 1, wherein the spherical calibration jig is made of the same material as that of the object.

3. A measurement method using a measurement X-ray CT apparatus configured to irradiate an object placed on a rotating table with X-rays while rotating the object, and reconstruct a projection image of the object to generate a tomographic image of the object, the method being implemented by at least the controller including the processor, the method comprising: generating, with the processor, volume data from the CT scan with the spherical calibration jig in contact with the object; determining, with the processor, a boundary surface of the object by using the correction value determined by the method according to claim 1; and determining, with the processor, a shape of the object by using the boundary surface.

4. The measurement method using a measurement X-ray CT apparatus according to claim 3, wherein a database is generated for each combination of the correction value and a material, the correction value being determined for each normal direction of a measurement surface of the object, and in measuring the object, the correction value corresponding to the normal direction of the measurement surface is read from the database and used for the measurement.

5. A measurement method using a measurement X-ray CT apparatus, the method being implemented by at least a controller including a processor, the method comprising: putting an object and a spherical calibration jig having a known dimension in a box transmitting X-rays; generating, with the processor, volume data from the CT scan with the spherical calibration jig being in contact with the object in the box; determining, with the processor, a boundary surface of the object by using the correction value determined by the method according to claim 1; and determining, with the processor, a shape of the object by using the boundary surface.

6. A calibration apparatus for a measurement X-ray CT apparatus configured to irradiate an object placed on a rotating table with X-rays while rotating the object, and reconstruct a projection image of the object to generate a tomographic image of the object, the apparatus comprising an X-ray CT scanner, including a controller with a processor, configured to: generate volume data by performing a CT scan with a spherical calibration jig having a known dimension and in contact with the object; obtain a profile of a surface shape of the object in the volume data, and calculate a boundary surface of the spherical calibration jig from center coordinates of the spherical calibration jig; and determine a correction value for adjusting a boundary surface of the object determined from a gradient of the profile to the boundary surface of the spherical calibration jig.

7. The calibration apparatus for a measurement X-ray CT apparatus according to claim 6, wherein the spherical calibration jig is made of the same material as that of the object.

8. A measurement apparatus using a measurement X-ray CT apparatus configured to irradiate an object placed on a rotating table with X-rays while rotating the object, and reconstruct a projection image of the object to generate a tomographic image of the object, the measurement apparatus comprising the X-ray CT scanner, including the controller including the processor, configured to: generate volume data by performing a CT scan with a spherical calibration jig having a known dimension and in contact with the object; determine a boundary surface of the object by using the collection value determined by the apparatus according to claim 6; and determine a shape of the object by using the boundary surface.

9. The measurement apparatus using a measurement X-ray CT apparatus according to claim 8, further comprising: a database generated for each combination of the correction value and a material, the correction value being determined for each normal direction of a measurement surface of the object, wherein the X-ray CT scanner, including the controller including the processor, is further configured to read the correction value corresponding to the normal direction of the measurement surface from the database and using the correction value for measurement in measuring the object.

10. A measurement apparatus using a measurement X-ray CT apparatus, comprising: a spherical calibration jig having a known dimension; a box that accommodates the spherical calibration jig and transmits X-rays; the X-ray CT scanner, including the controller including the processor, further configured to: generate volume data by performing a CT scan with the spherical calibration jig being in contact with the object in the box; determine a boundary surface of the object by using the correction value determined by the apparatus according to claim 6; and determine a shape of the object by using the boundary surface.

11. A measurement X-ray CT apparatus comprising: a spherical calibration jig having a known dimension; and the X-ray CT scanner, including the controller including the processor, further configured to: generate volume data by performing a CT scan with the spherical calibration jig being in contact with an object; obtain a profile of a surface shape of the object in the volume data; calculate a boundary surface of the spherical calibration jig in the volume data from center coordinates of the spherical calibration jig; correct a boundary surface of the object by using the correction value determined by the apparatus according to claim 6; and determine a shape of the object by using the corrected boundary surface.

12. The measurement X-ray CT apparatus according to claim 11, further comprising a box that accommodates the object and the spherical calibration jig and transmits the X-rays, and wherein the spherical calibration jig is brought into contact with the object in the box.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The preferred embodiments will be described with reference to the drawings, wherein like elements have been denoted throughout the figures with like reference numerals, and wherein;

(2) FIG. 1 is a sectional view showing an overall configuration of a typical X-ray CT apparatus used for measurement;

(3) FIG. 2 is a perspective view showing an arrangement of essential parts of the same;

(4) FIG. 3 is a diagram showing how CT reconstruction is performed;

(5) FIG. 4 is a diagram for describing a conventional problem;

(6) FIG. 5 is a perspective view for describing the principle of the present invention, showing that center coordinates do not change much depending on the detection position of a boundary surface;

(7) FIG. 6 is a diagram for the same purpose, showing a state of contact between a spherical calibration jig and an object;

(8) FIG. 7 is a diagram for the same purpose, showing a state where vectors extend in directions slightly shifted from a search reference position;

(9) FIG. 8 is a chart for the same purpose, showing an example of a relationship between a boundary surface of the spherical calibration jig and a boundary surface of the object determined from the gradient of a profile;

(10) FIG. 9 is a flowchart showing a processing procedure according to a first embodiment of the present invention;

(11) FIG. 10 is a flowchart showing a processing procedure according to a second embodiment of the present invention;

(12) FIG. 11 is a perspective view showing a state where an object and spherical calibration jigs are put in a box made of a material that easily transmits X-rays according to the second embodiment; and

(13) FIG. 12 is a diagram showing an example of a relationship between volume data on spherical calibration jigs being in contact with an object and volume data on the object according to the second embodiment.

DESCRIPTION OF EMBODIMENTS

(14) Embodiments of the present invention will be described in detail below with reference to the drawings. It should be noted that the present invention is not limited to the contents described in the following embodiments and practical examples. The components of the embodiments and practical examples described below may include ones easily conceivable by those skilled in the art, substantially identical ones, and ones within the range of equivalency. The components disclosed in the embodiments and practical examples described below may be combined as appropriate, and may be selected and used as appropriate.

(15) In a first embodiment of the present invention, as shown in FIG. 9, a CT scan is initially performed in step 110 with an object W being in contact with a spherical calibration jig 30. Volume data such as illustrated in FIG. 6 or 7 is thereby generated.

(16) In step 120, the center coordinates of the spherical calibration jig 30 are calculated on the volume data.

(17) In step 130, a boundary surface of the object W to be determined is specified, and a search reference direction is calculated.

(18) In step 140, a contact direction is searched for, and a contact point and a correction value are determined.

(19) In step 150, the boundary surface of the object W determined from the gradient of a profile is corrected.

(20) Since the object W is in contact with the spherical calibration jig 30, the boundary surface of the contact portion can be corrected by the foregoing principle. The corrected boundary surface can be used to calculate the distance of the object W, for example.

(21) Correction values may be determined for respective normal directions of measurement surfaces of the object W, and a database may be generated for each combination of a correction value and a material, for example. In measuring the object W, a correction value corresponding to the normal direction of the measurement surface can be read from the database and used for measurement.

(22) Next, a second embodiment of the present invention will be described with reference to FIG. 10.

(23) In the present embodiment, in step 200, a box 40 made of a material that easily transmits X-rays is initially prepared. As shown in FIG. 11, an object W is put into the box 40 and a plurality of spherical calibration jigs 30 are spread out inside.

(24) Steps 110 to 150 similar to those of the first embodiment are then performed. Note that the number of spherical calibration jigs 30 in steps 110 and 120 is plural.

(25) In the present embodiment, as illustrated in FIG. 12, the corrected boundary surfaces can be used to calculate a distance of the object W, for example.

(26) The present invention is also applicable to methods other than that of the second embodiment as long as the object W and the spherical calibration jigs 30 can be arranged in contact with each other.

(27) Images can be obtained more easily if the spherical calibration jigs 30 are made of the same material as that of the object W. Different materials, such as brass, aluminum, iron, and ceramic, may be used.

(28) It should be apparent to those skilled in the art that the above-described embodiments are merely illustrative which represent the application of the principles of the present invention. Numerous and varied other arrangements can be readily devised by those skilled in the art without departing from the spirit and the scope of the present invention.