Obituary: Professor Allan Cormack

ALLAN CORMACK, Nobel Laureate in Medicine and Physiology, was famous as one of the developers of CAT scanning, an advance in X-ray diagnosis which allows information on the entire three-dimensional region scanned by an X-ray beam to be imaged rather than the traditional two-dimension flat image of everything squeezed together on the X-ray film.

Cormack was born in South Africa in 1924 and attended the University of Cape Town. After graduation, he spent four years of postgraduate study at St John's College, Cambridge, working with Otto Frisch on the properties of Helium 6 before returning to be a lecturer in the Cape Town Physics Department. While at Cambridge, he met his future wife, Barbara Seavey.

As the only qualified nuclear physicist in Cape Town, he was asked to spend part of the week at Groote Schur Hospital (later famous for heart transplant surgery) to deal with radioactive materials, and in particular, to find a way to measure X-ray absorption by different parts of the body.

It was there, for the first time, that he began to think about the X- ray imaging problem and how most of the information in an X-ray was being wasted. In 1956, Cormack went to Harvard University on sabbatical, where he began completely different work with the physicists Norman Ramsey and Richard Wilson on the scattering of protons.

While at Harvard, he was invited to join the Physics Department at Tufts University by the then Chairman, Julian Knipp. He continued the nuclear physics work for many years at the Harvard cyclotron.

When Cormack realized that tomography, used in mapping in diverse fields such as astronomy and oceanography, could be applied to the X-ray analysis problem, he was surprised that he was unable to find a solution in the existing scientific literature. He decided to work out the problem himself, first with a mathematical analysis and then with crude (by today's standards) experimental set-ups.

After confirming his calculations with experiments on objects as diverse as a penny and a pork chop, he published his results in a series of papers in the Journal of Applied Physics in the mid-Sixties with the unpresumptuous titles "Representation of a Function by its Line Integrals", with "Some Radiological Applications, I" and "II".

Having solved the basic problem, Cormack had little interest in the engineering aspects and the first commercial CAT scanner was patented by the Englishman Godfrey Hounsfield in 1968. Hounsfield applied fast computers to the mathematical analysis of the tomographic X-ray data and succeeded in obtaining images of the inside of the body. The two men shared the Nobel Prize in 1979, meeting for the first time in Stockholm.

Cormack was a modest man who enjoyed the academic routine at Tufts, teaching undergraduates and graduate students and serving on university committees. In fact, when word of the Nobel Prize reached him in the early autumn of 1979, his teaching duty was lecturing to (mainly) freshmen engineering students in Introductory Physics. In the excitement and confusion surrounding the award's announcement, he said at the time that, having lived in an "ivory tower" all his life, he was hoping to return to it as soon as possible.

After the prize, he continued his normal duties at Tufts, taking his turn at teaching several of the regular courses in mechanics, optics and modern physics with the other faculty until his retirement in 1995. After retirement, Allan Cormack continued to use his office in the Tufts Physics Department and maintained many of his professional activities.

David Weaver

Allan MacLeod Cormack, physicist: born Johannesburg, South Africa 23 February 1924; Junior Lecturer, University of Cape Town 1946-47, Lecturer 1950-56; Research Fellow, Harvard University 1956-57; Assistant Professor of Physics, Tufts University 1957-60, Associate Professor 1960-64, Professor 1964-80, University Professor 1980-94 (Emeritus); Nobel Prize in Medicine and Physiology 1979; married 1950 Barbara Seavey (one son, two daughters); died Winchester, Massachusetts 7 May 1998.