With the advances in computer technology during the 1960s several authors, including Cormack, Kuhl and Edwards, began to discuss the possibility of improving the quality of ordinary x-ray tomography using exact mathematical reconstruction techniques. The basic method is to measure x-ray attenuation along sets of parallel lines oriented at multiple angles, all contained within a single transverse cross-sectional slice of the body. These measurements can be represented mathematically as linear combinations of the unknown mass attenuation coefficients in the slice. Standard mathematical techniques developed for the solution of simultaneous linear equations can be adopted to "reconstruct" the unknown cross-section distribution from such data. The result can be displayed as a two-dimensional array using computer generated display techniques, and closely resembles the image that could have been obtained if the cross-sectional slice were removed from the body and imaged by conventional projection radiography.