OPTICAL COMPUTERS FOR RECONSTRUCTING OBJECTS FROM THEIR X-RAY PROJECTIONS.

The current generation of transaxial tomograhy scanners uses digital processing to compute the distribution of the x-ray attenuation coefficient in a section of a body from projection data of that section. However, the operations required to reconstruct this distribution from the projection data also appertain to the domain of optical processing. Among the reconstruction algorithms that can be implemented optically are filtered and unfiltered back projection, one-dimensional convolution, circular harmonic transform, and Fourier synthesis. These approaches to transaxial tomography are functionally quite distinct, although mathematically equivalent. A review is presented of research efforts in this area with special emphasis on the practical realization of these diverse formulations.