Tomogram Reconstruction Using an Opticophotographic Method

The new principle of tomography that first gained practical application with the design of the EMI scanner constitutes one of the most important advances in the field of diagnostic radiology. The wide interest that this method has aroused since the first machine was constructed in 1972 is perhaps reflected in the variety of labels by which it has been designated. Most of the apparatuses employed rely on computer techniques, and efforts have been made to design algorithms for the 'reconstruction' of the images that can be handled with the large data volumes required. Notwithstanding the remarkably good results achieved with this technique it still has a number of disadvantages, including high cost, the need for digitalizing data and images, and low resolution. These shortcomings are avoided by using opticophotographic techniques for the reconstruction of the tomogram in accordance with similar principles but without the aid of computers (PETERS 1973, GORDON & BARRETT 1975, EDHOLM & JACOBSON 1975). One such technique is described in this article. Before describing this system a few related methods will be mentioned. In 1940 FRANK patented a technique for producing transverse tomograms, where the projecting rays were parallel to the layer. TAKAHASHI (1957) described various techniques for producing transverse tomograms based on the same principle of projection. The Takahashi principle is of particular interest. The rays were generated in a roentgen tube and collimated by passing through a lead slit giving a thin and wide 'fan beam'.