Godfrey Newbold Hounsfield

English electrical engineer

• Born: August 28, 1919
• Birthplace: Newark-on-Trent, Nottinghamshire, England
• Died: August 12, 2004
• Place of death: Kingston upon Thames, England

Hounsfield invented computed tomography, a method of producing detailed images of internal body tissues that provides physicians with much more information than ordinary X rays can supply. Computed tomography inspired the development of other advanced methods of medical imaging in the late twentieth century.

Early Life

Godfrey Newbold Hounsfield (HOWNZ-feeld) was born in Newark, Nottinghamshire, and was raised on a farm in the nearby town of Sutton-on-Trent in a rural area of central England. His father, Thomas Hounsfield, had previously worked as an engineer in the steel industry but had turned to farming after World War I because of failing eyesight. Another relative, Leslie Hounsfield, was a noted inventor who had designed an automobile known as the Trojan in 1910. As the youngest of five children, Hounsfield was often left out of the activities of his older siblings and so found himself free to follow his own inclinations. He amused himself by figuring out how his father’s farm equipment worked and soon revealed a talent for engineering. As an adolescent, he built phonographs, radio sets, and gliders. Bold as well as ingenious, he once nearly blew himself up while trying to see how high he could propel tar barrels filled with water and acetylene to produce a water jet. “During this time,” he later wrote in an autobiographical sketch, “I was learning the hard way many fundamentals in reasoning.”

Hounsfield’s formal education was similarly governed by idiosyncratic interests. He attended the Magnus Grammar School in Newark, where he excelled in science and mathematics but did not do well enough in other subjects to attend a university. Instead, he studied radio communications at City and Guilds College in London. He also worked as a draftsman for a local builder and joined the Voluntary Reserve of the Royal Air Force. When World War II broke out in 1939, Hounsfield was called to active duty. Because of his engineering skills, he was assigned to the Royal College of Science and then to the military’s Cranwell Radar School. Radar, a newly developed technology, was a military secret and vital to the British war effort. Hounsfield did so well as a student at this school, building large-screen oscilloscope and demonstration equipment, that he was soon made an instructor. When the war ended in 1945, he was awarded a Certificate of Merit from the Royal Air Force.

After leaving the military in 1946, Hounsfield, with the help of Air Vice-Marshall J. R. Cassidy, won a government grant to attend Faraday House Electrical Engineering College in London, where he studied electrical and mechanical engineering. After graduating in 1951, Hounsfield began working for Electrical and Musical Instruments Limited (EMI). He spent the rest of his professional life there.

Life’s Work

Because of his experience in the military, Hounsfield began his career at EMI by working on radar and weapons guidance systems. He later started working on computer design. From 1958 to 1959, he led a design team that developed the EMIDEC 1100, the first large British computer to be built with transistors instead of vacuum tubes. Hounsfield’s most important contribution to this project was the use of small magnetic cores within the computer that enabled the transistors to work much more quickly.

Hounsfield next began working on computer memory systems. He developed a method of storing information on large, thin, grooved sheets of copper coated with a magnetic substance. Although Hounsfield was able to prove that this technique was feasible, EMI abandoned the idea as unprofitable. EMI allowed Hounsfield to submit several ideas for his next project. Eventually it was agreed that he would work on the problem of pattern recognition. Hounsfield’s assignment was to develop methods that would allow machines to correctly interpret information presented in the form of characters, such as the letters of the alphabet.

In 1967, during one of the long walks through the countryside that made up his favorite form of recreation, Hounsfield began thinking of ways to combine his experience with radar, computers, and pattern recognition to develop a method for imaging the contents in a box by taking readings at all angles. He quickly realized, however, that such a device would be invaluable for medical imaging. Traditional X-ray photography produced excellent images of bones and good images of air-filled organs such as the lungs but much less information about other tissues.

In the 1920’s and 1930’s, a method known as tomography was developed that allowed X rays to produce a sharply focused image of a thin section of a patient’s body while blurring the image of the tissues surrounding it. This was done by moving the source of the X rays and the photographic film in opposite directions parallel to the patient’s body. Tomography revealed more information about internal organs than ordinary X-ray images, but Hounsfield realized that it could be greatly improved. His basic idea was to project X rays through a patient’s body to a detector. The X-ray source and the detector would then be moved to new positions, and the process would be repeated several times. The data recorded by the detector would then be processed by a computer to produce an image. EMI patented the idea in 1968 and made arrangements with the National Health Service of the British Department of Health and Social Security for Hounsfield to develop a working model. The National Health Service was particularly interested in producing images of the brain, which conventional X-ray photography did very poorly.

Although Hounsfield independently conceived of this method of producing images, which came to be known as computed tomography (CT, also known as the CAT scan), previous researchers had envisioned similar systems. The American physician William Oldendorf built a small model of such a device in 1960 but lacked the computers needed to process the data it produced. The South African-born American physicist Allan Cormack had worked on the mathematical theory of a similar system in the 1950’s and 1960’s but had failed to interest physicians in the possibilities of such a device. Other technology companies had considered the idea but abandoned it as too complex to be practicable.

Hounsfield’s engineering skills, combined with financial support from EMI and the National Health Service, allowed him to build a practical device that could be used on real patients. Although Oldendorf and Cormack would later be honored for their work, Hounsfield is generally considered to be the true inventor of CT. His earliest experiments involved a source of gamma rays and a detector placed on opposite sides of a plastic box filled with water and pieces of metal and plastic. The box, known as a “phantom,” represented a patient’s body. The source and the detector were moved sideways, one-eighth of an inch at a time, across the phantom. The intensity of the gamma rays after they passed through the phantom was recorded at each position. The phantom was then rotated 1 degree, and the process was repeated. After the phantom had been rotated 180 degrees, the resulting measurements were processed by a computer to produce an image. The entire process took nine days of measurements and more than two hours of computer time. The success of this slow but inexpensive demonstration allowed Hounsfield to move on to more powerful X rays instead of gamma rays, reducing the measurement time to nine hours. The X-ray version produced a series of images of two-dimensional slices of the subject, which when stacked together in computer processing turned into a quasi-three-dimensional image.

Instead of phantoms, Hounsfield worked with tissues from freshly slaughtered animals and preserved samples of human tissue. He also imaged the brain in a cow’s head and, for the first live human scan, his own brain. In 1971 a prototype CT machine was installed in Atkinson Morley’s Hospital in Wimbledon, a suburb of London. The first patient to undergo CT was a woman with a suspected brain tumor. After fifteen hours of taking measurements and two days of processing the information, an image of the patient’s brain was produced with the location of the tumor clearly visible, allowing surgeons to remove it. The dramatic success of the first clinical use of CT encouraged EMI to announce the availability of the technology in 1972, which Hounsfield had made capable of producing an image in four and a half minutes. Hospitals in the United Kingdom and the United States soon began installing CT devices despite the fact that each machine cost about $500,000.

Over the next few years, Hounsfield continued to work on improvements in CT. In addition to greatly reducing the time needed to produce an image, in 1975 he changed the way that X-ray sources and detectors moved, which allowed an image of a patient’s entire body to be produced. By 1977 more than one thousand CT units had been installed around the world.

Hounsfield was named head of medical systems at EMI in 1972. He continued to research medical imaging systems for the company, turning his attention to a method known as nuclear magnetic resonance, which used magnetism instead of X rays. He also helped develop a CT scanner fast enough to capture the image of the heart between beats. Hounsfield was promoted to chief staff scientist in 1976 and senior staff scientist in 1977. He retired in 1986 but continued to work as a consultant at EMI’s Central Research Laboratories, near his home in Twickenham. Among the many honors awarded to Hounsfield for his invention were the MacRobert Award, the highest British engineering award, in 1972 and the Lasker Award, a prestigious American award for medical research, which he shared with Oldendorf in 1975. In 1975 he was elected as a fellow to the Royal Society (FSR), a rarity for someone who did not have a university degree, and a year later he was appointed Commander of the British Empire (CBE) and received the Gairdner Foundation’s International Award, given to those who make outstanding contributions to medical sciences. Hounsfield shared the Nobel Prize in Physiology or Medicine with Cormack in 1979 and was knighted in 1981.

Perhaps the greatest tribute scientists can receive, however, is to have a unit of measurement named for them, and such was the case with Hounsfield. The Hounsfield scale measures the radiodensity of a material in Hounsfield units (HU). Air, for example, is -1000 HU, fat -60 to -100 HU, and water 0 HU, while soft tissue, such as muscle, is 40 to 80 HU and bone 400 to 1000 HU.

Although his time was largely devoted to his work, Hounsfield liked to ski and walk in the mountains for recreation. He also enjoyed music and playing the piano. Friends described him as gentle, enthusiastic, and inspiring in conversation, and delightful company all around. His modesty was among his outstanding traits, and he found public interest in his invention embarrassing. On learning that he had been awarded the Nobel Prize, for instance, he advised students not to worry if they do poorly on exams, so long as they feel that they understand the subject: “It’s amazing what you can get by the ability to reason things out by conventional methods, getting down to the basics of what is happening.” In retirement he was a volunteer at the Royal Brompton and Heart hospitals.

Hounsfield died from a longstanding lung disease in a nursing home in Kingston-upon-Thames on August 12, 2004. A lifelong bachelor, he left his estate to the support of engineering research and scholarships.

Significance

The invention of CT was the most important advance in the use of X rays for medical imaging since they were first discovered by the German physicist Wilhelm Conrad Röntgen in 1895. Initially controversial because of the expense involved, CT soon became accepted as a method of diagnosis. The ability of CT to produce detailed images of body tissues made it a valuable tool in the diagnosis of brain diseases, which formerly required difficult and dangerous exploratory surgery. CT proved to be useful in producing images of other soft organs, such as the liver, heart, and kidneys. CT has also been used to produce images of the interiors of ancient artifacts and fossils.

CT went through numerous improvements after Hounsfield’s initial demonstration. The time required to produce an image was reduced from several hours to a few minutes and then to less than one second. In 1989, spiral CT was introduced, producing images that could be viewed from any angle. The success of Hounsfield’s invention paved the way for the development of other methods of medical imaging, including magnetic resonance imaging (MRI) and positron emission tomography (PET). Although MRI and PET do not use X rays, they both use computers to translate complex data into visible images in ways similar to CT.

Bibliography

Bushong, Stewart C. Computed Tomography. New York: McGraw-Hill Medical, 2000. A technically sophisticated, thorough review of the principles and uses of CT scans, with explanatory illustrations.

Fullerton, Gary D., and James A. Zagzebski, eds. Medical Physics of CT and Ultrasound: Tissue Imaging and Characterization. New York: American Institute of Physics, 1980. Two sections of this book are of particular interest. William R. Hendee provides a clear account of the invention of CT and how the technology rapidly advanced in the 1970’s in “History of Computed Tomography.” The history of the theory behind CT is described in “Development of the CT Concept” by Allan Cormack, who shared a Nobel Prize with Hounsfield in 1979.

Hounsfield, Godfrey N. “Computed Medical Imaging.” Science 210 (October 3, 1980): 22-28. This transcription of Hounsfield’s Nobel Prize lecture includes a description of his early experiments with CT and several photographs of the equipment he used and the results he obtained.

Kevles, Bettyann Holtzmann. Naked to the Bone: Medical Imaging in the Twentieth Century. New Brunswick, N.J.: Rutgers University Press, 1997. Kevles provides a detailed history of the technology used to produce images of the interior of the human body. Included in the chapter “The Perfect Slice: The Story of CT Scanning” is an extensive discussion of Hounsfield’s contributions. The book also contains a large bibliography and a useful time line.

“Sir Godfrey Hounsfield.” British Medical Journal 329 (September 18, 2004): 687. This obituary presents a clear, succinct account of Hounsfield’s invention and life, with tributes to his character and genius.

Sochurek, Howard. Medicine’s New Vision. Easton, Pa.: Mack, 1988. This book is intended for a general audience and includes a chapter called “Computed Tomography,” which discusses the advances made in CT technology from the beginning to the 1980’s. Includes numerous colorful photographs illustrating the uses of CT.

Susskind, Charles. “The Invention of Computed Tomography.” In History of Technology Sixth Annual Volume. Edited by A. Rupert Hall and Norman Smith. London: Mansell, 1981. This essay is a lengthy and extremely detailed account of Hounsfield’s invention of CT. Includes extensive information on the inventor, the company he worked for, the device itself, and its influence on the practice of medicine.

Zannos, Susan. Godfrey Hounsfield and the Invention of CAT Scans. Hockessin, Del.: Mitchell Lane, 2002. A spare account of Hounsfield’s life and development of computed tomography up to 1981, intended for young adult readers.