Tomographic systems are able to produce cross sectional planar images of three dimensional volumes because of the relative motion of the source, film and the volume under examination. Analysis shows that the image produced is a result of a three dimensional linear filtering process where the filter characteristics are determined by the scan geometry (3). If, instead of integrating continuously on a single film, a set of N radiographs are recorded, each corresponding to a point along the scan trajectory, then a simple filter can be defined to reconstruct the entire three dimensional structure from this data. In this case, the transfer function exhibits repetitive peaks whose spacing is determined by N and whose width is determined by the total scan length. The number of views required to produce the same “blurring” as the continuous case can then be determined by the Nyquist criteria(3).

An optical projection system based on circular geometry for producing three dimensional medical images has been fabricated and tested. The technique can be generalized to any geometry and to all x-ray applications where plane-by-plane examination of a structure would prove beneficial.