Patent ID: 7330026

Claim:
Apparatus for use in measuring distortion in imaging system, the apparatus comprising a three-dimensional structure having a plurality of boundary surface portions, the structure defining a plurality of control points thereon which are of constant spatial relationship to each other, each of the control points being definable by reference to three orthogonal planes, each of which is identifiable by reference to one or more of the boundary surface portions of the structure, wherein in an image of the apparatus produced by the imaging system, the position of each of said planes for each control point is determinable by detecting in the image an interfacial boundary between the respective boundary surface portion(s) and a medium surrounding the structure, wherein the control points are distributed uniformly over substantially the entire volume of the three-dimensional structure such that geometric distortion can be mapped for the entire volume with a single three dimensional image scan, wherein the structure comprises a plurality of spaced parallel planar grids, each grid having opposed planar boundary surface portions, wherein each planar grid comprises a plurality of spaced parallel first slat-like portions and a plurality of spaced parallel second slat-like portions orientated orthogonally to the first slat-like portions and intersecting therewith, each of the slat-like portions having opposed boundary surface portions orthogonal to the plane of the grid, wherein each control point is located on a boundary surface portion of a said planar grid at the intersection of a respective one of the first slat-like portions with a respective one of the second slat-like portions, and further wherein each control point is defined by reference to the intersection of: (a) the plane of the boundary surface portion of the grid on which it is located, (b) a plane in the middle of the opposed boundary surface portions of the respective first slat-like portion, and (c) a plane in the middle of the opposed boundary surface portions of the respective second slat-like portion.