In work initiated at the University of Cape Town and Groote Schuur Hospital in early 1956, and continued briefly in mid-1957, South African-born American physicist Allen M. Cormack showed that changes in tissue density could be computed from x-ray data. His results were subsequently published in two papers:
"Representation of a Function by its Line Integrals, with Some Radiological Applications," Journal of Applied Physics 34 (1963) 2722-27; "Representation of a Function by its Line Integrals, with Some Radiological Applications. II," Journal of Applied Physics 35 (1964) 2908-13.
Because of limitations in computing power no machine was constructed during the 1960s. Cormack's papers generated little interest until Godfrey Hounsfield and colleagues invented computed tomography, and built the first CT scanner in 1971, creating a real application of Cormack's theories.