Cormack, Allan MacLeod

▪ 1999

      South African-born American physicist (b. Feb. 23, 1924, Johannesburg, S.Af.—d. May 7, 1998, Winchester, Mass.), formulated the mathematical algorithms that made possible the development of the cross-sectional X-ray imaging process known as computerized axial tomography (CAT) scanning, for which he was awarded a share of the 1979 Nobel Prize for Physiology or Medicine. A lecturer in physics at the University of Cape Town, Cormack was hired for a part-time job at Cape Town's Groote Schuur Hospital in 1955 because of a regulation requiring that trained physicists calculate radiation doses for cancer therapy, even though he had no medical training and knew nothing about medical diagnostics. Cormack observed the inadequacies of X-ray technology, whose imprecise images made diagnosis haphazard. He determined that much greater precision could be achieved by taking many X-ray images of the same body part from different perspectives and then integrating the data to produce a single image. Recognizing that the problem was fundamentally mathematical, Cormack published the results of his work in two papers in 1963 and 1964, documenting a technique that represented a vast improvement over conventional X-ray imaging methods and permitted a much more precise differentiation of soft tissues. Cormack never attempted to build a working tomographic scanner that would demonstrate the technique he had formulated, and his papers attracted little notice. His work was reproduced independently in the early 1970s by the British engineer Godfrey Newbold Hounsfield, whose CAT scanning machine gained worldwide attention, and with whom Cormack shared the Nobel Prize. After his tenure (1950-56) at the University of Cape Town, Cormack held a one-year research fellowship at Harvard University, then moved to Tufts University, Medford, Mass., where he remained until his retirement in 1980, studying the interaction of subatomic particles and refining the mathematics of tomographic imaging methods. Cormack became a member of the American Academy of Arts and Sciences in 1980.

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▪ American physicist

born Feb. 23, 1924, Johannesburg, S.Af.

died May 7, 1998, Winchester, Mass., U.S.

 South African-born American physicist who, with Godfrey Hounsfield, was awarded the 1979 Nobel Prize for Physiology or Medicine for his work in developing the powerful new diagnostic technique of computerized axial tomography (CAT). Cormack was unusual in the field of Nobel laureates because he never earned a doctorate degree in medicine or any other field of science.

      After graduating from the University of Cape Town in 1944 Cormack pursued advanced studies there and at the University of Cambridge. He was a lecturer at Cape Town from 1950 to 1956 and then, after a year's research fellowship at Harvard University, became assistant professor of physics at Tufts University. His main research at Tufts centred on the interaction of subatomic particles. He advanced to full professor in 1964, was chairman of the department from 1968 to 1976, and retired in 1980. He became a U.S. citizen in 1966.

      A part-time position as physicist for a hospital radiology department first aroused Cormack's interest in the problem of X-ray imaging of soft tissues or layers of tissue of differing densities. The two-dimensional representations of conventional X-ray plates were often unable to distinguish between such tissues. More information could be gained if X rays of the body were taken from several different directions, but conventional X-ray techniques made this procedure problematic. In the early 1960s Cormack showed how details of a flat section of soft tissues could be calculated from measurements of the attenuation of X rays passing through it from many different angles. He thus provided the mathematical technique for the CAT scan, in which an X-ray source and electronic detectors are rotated about the body and the resulting data is analyzed by a computer to produce a sharp map of the tissues within a cross section of the body. Cormack became a member of the American Academy of Arts and Sciences in 1980.

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