In 1972, at a meeting of the British Institute of Radiology, Godfrey Hounsfield reported on a machine he had developed at EMI for creating images of the brain, a task for which conventional X-ray radiography was unsuitable. His invention of the computed tomography scanner, known as the CT (or CAT) scanner, was the birth of a new industry that would save countless lives.

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Godfrey Newbold Hounsfield, engineer and inventor: born Sutton on Trent, Nottinghamshire 28 August 1919; Head of Medical Systems Section, Thorn EMI Central Research Laboratories (later Central Research Laboratories of EMI Group) 1972-76, Chief Staff Scientist 1976-77, Senior Staff Scientist 1977-85, Consultant to Laboratories 1986-2004; FRS 1975; CBE 1976; Nobel prize in Physiology or Medicine (jointly with Allan M. Cormack) 1979; Kt 1981; died Kingston upon Thames, Surrey 12 August 2004.

In 1972, at a meeting of the British Institute of Radiology, Godfrey Hounsfield reported on a machine he had developed at EMI for creating images of the brain, a task for which conventional X-ray radiography was unsuitable. His invention of the computed tomography scanner, known as the CT (or CAT) scanner, was the birth of a new industry that would save countless lives.

Twenty-five years later, when the annual meeting of the British radiological community, Radiology '97, celebrated a quarter century of CT scanning, the event had become a massive gathering held at the International Convention Centre, Birmingham. There was an academic programme with dozens of research papers, professional development seminars for practitioners, and a trade fair with over a hundred exhibitors. As Hounsfield (by then Sir Godfrey - and a Nobel prize-winner) took in the scene, it was impossible not to imagine what was going through the mind of this "mild-mannered genius."

Godfrey Newbold Hounsfield was born in 1919 near Sutton on Trent, near Newark in Nottinghamshire, the youngest of five children of a steel-worker turned farmer. He recalled that his childhood was idyllic. It gave him a lifelong passion for the outdoor life, and the opportunity to explore electrical and mechanical farm machinery. He eventually rigged up a projector for the village cinema.

He attended Magnus Grammar School, Newark, but was not strong academically, and he left to work for a local builder. On the outbreak of war in 1939 he volunteered for the RAF, which was to be his making. He was encouraged to study radio mechanics, and passed his first examination with such flying colours that he spent the rest of the war as an instructor, first at the Royal College of Science, London, and then at the Cranwell Radar School. He received a Certificate of Merit for experimental work, and after the war he was awarded a scholarship to study for a diploma at the Faraday House Electrical Engineering College in London.

In 1951 he joined EMI, in Hayes, Middlesex, where he initially worked on radar and guided weapons. He became interested in computers and in 1958 led the development of the Emidec 1100, Britain's first all-transistor computer. The computer was not a commercial success, however, and EMI sold off its computer division in 1962. Hounsfield then transferred to EMI's Central Research Laboratory, where he first worked on computer memories. In 1967, however, EMI was flush with funds from the unanticipated success of the Beatles recordings, and he was given a free rein to pursue product research of his own choosing.

It was on a long country ramble that he decided to work on a practical CT scanner, a method of examining body organs by scanning them with X-rays and using a computer to construct a series of cross- sectional scans along a single axis. At that time computed tomography was in the air, and several researchers were working on the problem, including Allan M. Cormack at the Groote Schuur Hospital in Cape Town (and then at Tufts University in Massachusetts), with whom he would later share a Nobel prize. However, Hounsfield's unique contribution was to turn these ideas into a product.

Scanning was different to conventional radiography, where a flood of X-rays passed though the patient's body to expose a photographic plate. The resulting image was satisfactory for injuries such as fractures, because bones were relatively opaque, but they were much less use for diagnosing diseases in areas such as the brain and kidneys, because cancers or tumours were only slightly more opaque than the surrounding soft tissue.

A CT scanner (also known as a CAT scanner: computed axial tomography or computer- assisted tomography) worked by firing a narrow beam of radiation through the affected region in thousands of different directions, and detecting the slight attenuation of each beam after it passed through the subject. A computer was then used to reconstruct the image from these thousands of measurements. Hounsfield's first experimental system successfully scanned a pig's brain in 1968. The scanning process took nine days and required two and a half hours to process the resulting 28,000 measurements on a high-speed computer.

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In 1968, EMI patented the invention, and secured further development funds from the Medical Research Council in exchange for a share of the profits. Thereafter, the development took place largely in secret. The scanning mechanism was improved, faster data processing algorithms were developed, and advantage was taken of the rapid price-performance improvements of computers in the early 1970s. In October 1971, the first individual to benefit from the prototype machine was a woman with a suspected brain lesion, a patient of the neurosurgeon James Ambrose at Atkinson Morley's Hospital, Wimbledon.

The EMI scanner, costing about £100,000, was announced in 1972. It could perform a scan in four minutes and render a computerised image in three seconds. Six machines were sold, two to the United States. Thereafter, scanning technology improved very rapidly, both by EMI, which produced two improved models, and by several American competitors, who paid EMI handsomely for use of its patents. Full-body scanners were placed on the market, and by the end of the 1970s the blurry images of the first scanners had been transformed into high-resolution cross-sections of stunning fidelity.

EMI's hard-nosed commercialism in the development of the scanner led to tensions with the medical community and a surge of patenting activity by its competitors. However, an American historian of the industry later concluded:

It is hard to imagine how the instrument would have gone into production without the support of a company like EMI. The combination of the Beatles' success with the British system of research subsidies and the genius of one engineer broke the cash barrier and changed the face of modern medicine.

By 1976 the cost of staying in the CT-scanning business had escalated with the entry of major players such as General Electric and Siemens, and EMI sold out. Now in his late fifties, Hounsfield remained as a Senior Staff Scientist with EMI's Central Research Laboratory for the remainder of his career. During this time, as well as sharing the Nobel prize for physiology and medicine in 1979, he received dozens of honorary degrees and international scientific honours. He was elected to the Royal Society in 1975, and knighted in 1981. In 1986, following his retirement, he became a part-time consultant to EMI and to several hospitals. In his seventies he was still spending a day a week at the Royal Brompton Hospital.

A life-long bachelor - he was nearly 60 before he had a permanent residence - he confessed that scientific and experimental work was the centre of his life. Characteristically, he used some of his Nobel prize money to set up a small laboratory in his home. His other consuming interests were mountain walking and leading country rambles.

Martin Campbell-Kelly