Computer-assisted location of reference points in three dimensions for radiographic cephalometry.

A major obstacle to the derivation of three-dimensional data from lateral and coronal radiographs of the head has been the lack of precision in locating the same landmarks on each of the biplanar images. The method described herein uses radiographic equations based on the geometry of a biplanar system to predict the location of a reference point on one film from its location on the other. This technique, which differs from previously described systems, allows a pair of cephalometric films to be digitized by an on-line procedure controlled by a personal computer. Three-dimensional coordinates of reference points are calculated and stored for subsequent retrieval when they can be used for metric analysis or for the display of simple wire-frame models of the skull. Computing algorithms are provided to aid software development.