Patent US 4,630,203

A method and apparatus for reconstructing the three-dimensional coordinates of an identifiable contour on an object without relying on markers or pre-existing knowledge of the geometry of the object is described. The technique is defined as Contour Radiography. In the preferred embodiment two X-ray sources irradiate an object possessing a radiographically identifiable contour and then the two images of the contour are projected onto an X-ray film at spaced locations on the film plane. These images are digitized by the tracing of the image curves with a cursor or some other means thereby establishing the coordinates of an arbitrary number of image points. The digital data thus obtained is processed in accordance with a Contour Radiography (CONRAD) algorithm to identify corresponding points on the two curves which originate from the same point on the physical contour. The spatial coordinates of the X-ray sources are determined using a special calibration system. Then the coordinates of each corresponding point pair are processed with the spatial coordinates of the X-ray source to determine the three-dimensional coordinates of their originating space-point on the contour. In this way the three-dimensional coordinates of the contour are determined. The three-dimensional coordinates are then processed in a commercially available graphics system to visually display the reconstructed contour. The technique has particular application in medicine for determining the undistorted shape, position, size and orientation of selected internal organs, such as bone, which have a radiographically identifiable contour.