Scientists call something “X” when they don’t know what it is. Wilhelm Röntgen, a German, discovered X-rays accidentally in 1895 while doing routine research. He had no idea what he had discovered when he found that rays streaming out of gas bottles, through which he had passed electricity, had the miraculous ability to penetrate dense objects.
In one of the most famous images in science, Röntgen exposed his wife’s hand to the X-rays and produced a perfect image on a photographic plate of the bones in her hand (and her wedding ring).
X-rays were quickly adopted by the medical profession. For the first time, we could look inside a patient’s body without surgery. The basic structure of organs could be determined at the flick of a button. The next challenge, to create a 3D image using X-rays, was addressed by South Africa’s first nuclear physicist, Allan MacLeod Cormack, and a British electrical engineer, Godfrey Hounsfield.
Cormack was born in Cape Town in 1924 and educated at Rondebosch Boys’ High School and UCT, where he studied physics and conducted postgraduate research on X-ray crystallography. Then, he worked at the Cavendish Laboratory at Cambridge University in England, but spent most of his career in the US. He returned briefly to Cape Town where he conducted research at Groote Schuur Hospital on diagnostic radiotherapy.
Cormack worked on the problem of measuring and interpreting the absorption of radiation passing through objects from different directions. He realised that the problem was a mathematical one, found a solution, and was able, in model experiments, to reconstruct an accurate cross-section of an irregularly-shaped object. In 1957, he developed algorithms that used data from X-ray “slices” of a patient’s body to create a 3D image of the whole body. These reconstructions were the first computerised tomograms made – although his “computer” was a simple desktop calculator. He built a simple prototype CATscanner in 1957.
Cormack had difficulty raising interest in his invention, partly because computers did not exist then that could make the necessary calculations quickly enough. Godfrey Hounsfield came to the rescue. He used Cormack’s and other algorithms, and developed a method of his own for computerised tomography. In 1972, he constructed the first practical CATscanner for examination of the head, and provided medical doctors with the first 3D glimpse inside the human body. A whole new field of medical research and diagnostics had been started. CATscanners are now used in every major hospital worldwide.
The invention of the CATscanner has been at the forefront of many significant advances in diagnostic medicine in recent decades, transforming medical intervention from clumsy, painful and sometimes dangerous invasive procedures to precisely targeted, non-invasive techniques. It is the trademark of a great invention that it is initially developed for a narrow application but later finds far wider application.
CATscanners are now also used for non-destructive testing of manufactured objects as well as for investigating internal structures and processes in industrial, biological, environmental, space science and astronomy contexts.
The invention of the CATscanner is also an example of how two scientists, working in different fields and on different continents, can contribute to the development of a single idea that has universal application – the only time that Cormack and Hounsfield met was at the ceremony in Sweden in 1979 where they were jointly awarded the Nobel Prize for Medicine for their co-invention of the CATscanner.
The visualisation of the interior of the human body using a CATscanner is regarded as one of the great medical breakthroughs of the 20th century. Science writer Tim Philbin rated the CATscanner at number 53 in the 100 greatest inventions so far, the only invention from the southern hemisphere to feature in the top 100.
l Mike Bruton was the founding director of the Cape Town Science Centre, and is director of imagineering at MTE Studios (www.mtestudios.com). He authored the book Great South African Inventions, published by Cambridge University Press. - Cape Argus