# US 9,750,479 B2 · Three-dimensional x-ray CT calibration and verification apparatus and method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,750,479 B2 - Document ID: US9750479B2 - Status: Granted - Kind: B2 - Application number: 14/317,432 - Filed: 2014-06-27 - Published: 2015-12-31 - Granted: 2017-09-05 - Earliest claimed: 2014-06-27 - Assignees: Hexagon Metrology, Inc. - Applicants: Hexagon Metrology, Inc. - Inventors: Gurpreet Singh - Web page: https://patentgrep.com/patent/US9750479B2 ## CPC - A61B 6/582: {Calibration} - A61B 6/03: Computed tomography [CT] - A61B 6/035: {Mechanical aspects of CT} - A61B 6/583: {using calibration phantoms} - G01N 23/046: using tomography, e.g. computed tomography [CT] - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract An apparatus for calibrating an x-ray computed tomography device has a plurality of objects formed from a material that is visible to x-rays. The plurality of objects are configured to receive x-rays without changing shape, and have substantially the same shape. The objects each have an object attenuation value to x-rays and a center point such that they are symmetrically shaped relative to their respective center points. The apparatus also has a base at least in part fixedly supporting the plurality of objects so that each of the plurality of objects contacts at least one of the other objects. Like other physical objects, such as the objects, the base has a base attenuation value to x-rays, and that value is greater than the base attenuation value. The center points of the plurality of objects together form a three-dimensional volume. ## Claims ### Claim 1 An apparatus for calibrating an x-ray computed tomography device, the apparatus comprising: first, second, and third spheres formed from a material that is visible to x-rays, the three spheres being configured to receive x-rays without changing shape, each of the three spheres having a sphere attenuation value to x-rays; and a base at least in part supporting the three spheres so that each of the spheres contacts at least one of the other spheres, the base having a base attenuation value to x-rays, the sphere attenuation value being greater than the base attenuation value, each of the spheres being locked in place on the base in a manner that prevents sphere translational movement, the second sphere contacting the first and third spheres, the first sphere having a first center, the second sphere having a second center, the third sphere having a third center, the first and second centers forming a first line, the first and third centers forming a second line, the first and second lines diverging, the first, second and third spheres being kinematically locked together. ### Claim 2 (depends on 1) The apparatus as defined by claim 1 further comprising a fourth sphere contacting the first, second and third spheres. ### Claim 3 (depends on 2) The apparatus as defined by claim 2 wherein the fourth sphere has a fourth center forming a third line with the first center, the first line and the third line forming a plane that intersects the second line. ### Claim 4 (depends on 1) The apparatus as defined by claim 1 wherein the base includes an orientation mark. ### Claim 5 (depends on 1) The apparatus as defined by claim 1 further comprising a fourth sphere in contact with the first and second spheres, the fourth sphere being not in contact with the third sphere. ### Claim 6 (depends on 1) The apparatus as defined by claim 1 wherein the first sphere contacts the third sphere. ### Claim 7 (depends on 1) The apparatus as defined by claim 1 wherein the first, second, and third spheres are dimensionally identical and each have a precision to at least 0.01 millimeters. ### Claim 8 (depends on 1) The apparatus as defined by claim 1 wherein the first, second, and third spheres comprise at least one of sapphire and ruby material. ### Claim 9 (depends on 1) The apparatus as defined by claim 1 wherein an adhesive secures the first sphere to the second sphere. ### Claim 10 (depends on 1) The apparatus as defined by claim 1 wherein the first, second, and third spheres are precision ground or lapped spheres. ### Claim 11 (depends on 1) The apparatus as defined by claim 1 wherein each of the first, second, and third spheres includes a certification of at least one of its dimensional properties. ### Claim 12 (depends on 1) The apparatus as defined by claim 1 wherein each of the first, second, and third spheres is a free-standing sphere. ### Claim 13 (depends on 1) The apparatus as defined by claim 1 wherein the base is configured to expose the first, second, and third spheres to the environment. ### Claim 14 An apparatus for calibrating an x-ray computed tomography device, the apparatus comprising: a plurality of objects formed from a material that is visible to x-rays, the plurality of objects being configured to receive x-rays without changing shape, each of the plurality of objects having substantially the same shape, the objects each having an object attenuation value to x-rays, each of the plurality of objects having a center point and being symmetrically shaped relative to its center point; and a base at least in part fixedly supporting the plurality of objects so that each of the plurality of objects contacts at least one of the other objects, the base having a base attenuation value to x-rays, the object attenuation value being greater than the base attenuation value, the center points of the plurality of objects together forming a three-dimensional volume, the plurality of objects being kinematically locked together. ### Claim 15 (depends on 14) The apparatus as defined by claim 14 wherein the plurality of objects comprises a sphere. ### Claim 16 (depends on 14) The apparatus as defined by claim 14 wherein the plurality of objects are oriented in a pyramidal form. ### Claim 17 (depends on 14) The apparatus as defined by claim 14 wherein the base includes a stem with an orientation mark. ### Claim 18 (depends on 14) The apparatus as defined by claim 14 wherein the plurality of objects comprises four objects. ### Claim 19 (depends on 14) The apparatus as defined by claim 14 wherein the plurality of objects comprises at least one of sapphire and ruby material. ### Claim 20 (depends on 14) The apparatus as defined by claim 14 wherein an adhesive secures at least one object to the base. ### Claim 21 A method of calibrating or verifying the dimensional accuracy of an x-ray computed tomography machine, the method comprising: providing an x-ray computed tomography machine having calibration settings; using the x-ray computed tomography machine to image a gauge to produce a gauge reconstruction, the gauge comprising first, second, and third spheres visible to x-rays, each sphere in contact with at least one other sphere, the first, second and third spheres being kinematically locked together, the centers of the first and second spheres forming a first line, the centers of the first and third spheres forming a second line, the first line diverging from the second line; measuring, in the gauge reconstruction, the distance between at least two of the spheres to produce measured center distance values; comparing the measured center distance values against known center distance values; and using the comparison to determine if there is a distance error in the gauge reconstruction. ### Claim 22 (depends on 21) The method as defined by claim 21 further comprising: modifying the calibration settings of the x-ray computed tomography machine if the comparison determines that there is a distance error in the gauge reconstruction. ### Claim 23 (depends on 22) The method as defined by claim 22 further comprising: determining the difference between each measured center distance value and the relevant known center distance value, modifying the calibration settings being a function of each difference. ### Claim 24 (depends on 21) The method as defined by claim 21 wherein using the x-ray comprises: producing a reconstruction of the gauge from a plurality of different projections, the method further comparing the measured center distance values of the spheres in each of the reconstruction against the respective known center distance values for calibrating the computed tomography machine. ### Claim 25 (depends on 21) The method as defined by claim 21 wherein measuring comprises measuring a 3D model of the gauge. ### Claim 26 (depends on 21) The method as defined by claim 21 wherein each of the spheres is identically sized. ### Claim 27 (depends on 21) The method as defined by claim 21 wherein the three or more of the spheres each have a precision to at least 0.01 millimeters. ### Claim 28 (depends on 21) The method as defined by claim 21 wherein measuring comprises measuring in at least two dimensions.