X-ray computed tomography device calibration and verification apparatus
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, 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. Each one of the plurality of objects: 1) is configured to receive x-rays without changing shape, 2) has substantially the same shape and size as the other objects, 3) has an attenuation value to x-rays (“object attenuation value”), and 4) is symmetrically shaped relative to its center point. Like the objects, the base also has an attenuation value to x-rays (the “base attenuation value”). The object attenuation value is greater than the base attenuation. Each of the plurality of objects is kinematically locked in place on the base.
1. 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;
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; and
a securing member applying a force to the plurality of objects, the securing member cooperating with the base to fixedly secure the plurality of objects to be substantially unmovable,
the object attenuation value being greater than the base attenuation value, each of the plurality of objects being kinematically locked in place on the base.
2. The apparatus as defined by claim 1 wherein each of the plurality of objects comprises at least one of sapphire and ruby material.
3. The apparatus as defined by claim 1 wherein the base comprises ceramic.
4. The apparatus as defined by claim 1 wherein the plurality of objects have a spherical shape with a precision of at least 0.01 millimeters.
5. The apparatus as defined by claim 1 wherein the plurality of objects and the base have a coefficient of thermal expansion that is no greater than the coefficient of thermal expansion of steel.
6. The apparatus as defined by claim 1 wherein the plurality of objects are oriented in a straight line.
7. The apparatus as defined by claim 1 wherein each object is kinematically locked without any external locking components between the objects.
8. The apparatus as defined by claim 1 wherein each object is minimally constrained with no more than four contact points with other objects and the base.
9. The apparatus as defined by claim 1 wherein the base comprises a groove having substantially straight and flat surfaces.
10. The apparatus as defined by claim 9 wherein the groove forms a V-shape having an angle of between about 60 and 120 degrees.
11. The apparatus as defined by claim 1 wherein each of the plurality of objects has a maximum dimension of no greater than about 10 millimeters, each of the plurality of objects having the same maximum dimension.
12. The apparatus as defined by claim 1 wherein the plurality of objects are precision ground or lapped objects.
13. The apparatus as defined by claim 1 wherein each of the plurality of objects includes a certification of at least one of its dimensional properties.
14. The apparatus as defined by claim 1 wherein each of the plurality of objects is a free-standing object.
15. The apparatus as defined by claim 1 comprising three or more objects.
16. An apparatus for calibrating an x-ray computed tomography device, the apparatus comprising:
at least three objects formed from a material that is visible to x-rays, the at least three objects being configured to receive x-rays without changing shape, each of the at least three objects having an object attenuation value to x-rays, each of the at least three objects having an identifiable region;
a base at least in part fixedly supporting the at least three objects so that each of the objects contacts at least one of the other objects, the base having a base attenuation value to x-rays, the identifiable regions of the at least three objects forming a substantially straight line on the base,
the object attenuation value being greater than the base attenuation value, each of the objects being locked in place on the base in a manner that prevents object translational movement,
wherein the objects comprise first, second, and third spheres, the second sphere contacting the first and third spheres.
17. The apparatus as defined by claim 16 wherein the first and third spheres apply equal and opposite force vectors to the second sphere along the same longitudinal axis.
18. The apparatus as defined by claim 17 wherein the base contacts the second sphere at two points to produce an effective single force vector that is normal to the force vectors the first and third spheres apply to the second sphere.
19. The apparatus as defined by claim 16 wherein the first, second, and third spheres are dimensionally identical and each have a precision to at least 0.01 millimeters.
20. The apparatus as defined by claim 19 wherein the first, second, and third spheres are dimensionally identical and each have a precision to 0.0001 millimeters.
21. The apparatus as defined by claim 16 wherein the first, second, and third spheres each have a precision to at least 0.01 millimeters.
22. The apparatus as defined by claim 16 wherein the at least three objects are free standing objects and locked in place on the base in a manner that permits the objects to rotate relative to the base.
23. The apparatus as defined by claim 16 wherein the at least three objects each are symmetrically shaped relative to a center point, the identifiable region of each object being the center point.