Hounsfield Introduces the CAT Scan Summary

  • Last updated on November 10, 2022

The advent of more comprehensive and more informative methods than plain X rays for seeing inside the living human body revolutionized diagnostic medicine in the 1970’s. Among the most useful is computerized axial tomography scanning, which creates cross-sectional images of both hard and soft tissue by reassembling mathematical data from a series of X-ray photographs taken at various angles.

Summary of Event

Computerized axial tomography (CAT) scanning, or computed tomography (CT), was separately and gradually invented by four scientists, William H. Oldendorf, David Edmund Kuhl, Allan M. Cormack, and Godfrey Newbold Hounsfield, and three mathematicians, Hendrik Antoon Lorentz, Johann Radon, and Ronald Bracewell. They remained mostly ignorant of one another’s work until Hounsfield’s CAT technology became well established in the mid-1970’s. Their story is an example of insufficient communication within the scientific and mathematical community. CAT scanning Computerized axial tomography scanning X-ray technology[X ray technology] Radiology [kw]Hounsfield Introduces the CAT Scan (Apr. 19, 1972) [kw]CAT Scan, Hounsfield Introduces the (Apr. 19, 1972) CAT scanning Computerized axial tomography scanning X-ray technology[X ray technology] Radiology [g]Europe;Apr. 19, 1972: Hounsfield Introduces the CAT Scan[00710] [g]United Kingdom;Apr. 19, 1972: Hounsfield Introduces the CAT Scan[00710] [g]England;Apr. 19, 1972: Hounsfield Introduces the CAT Scan[00710] [c]Health and medicine;Apr. 19, 1972: Hounsfield Introduces the CAT Scan[00710] [c]Inventions;Apr. 19, 1972: Hounsfield Introduces the CAT Scan[00710] [c]Science and technology;Apr. 19, 1972: Hounsfield Introduces the CAT Scan[00710] Hounsfield, Godfrey Newbold Cormack, Allan M. Radon, Johann Oldendorf, William H. Kuhl, David Edmund Edwards, Roy Q. Ambrose, James Kreel, Louis Bracewell, Ronald Lorentz, Hendrik Antoon Bull, James William Douglas

Around 1904, Lorentz discovered equations for reconstructing three-dimensional objects as two-dimensional. In 1917, Radon published what came to be known as the Radon transform, a mathematical formula for representing three-dimensional objects as an infinite series of two-dimensional cross sections. Both Lorentz’s and Radon’s work in this area remained generally unknown and unused until the 1970’s. Only a few scientists recognized any practical need to show an opaque three-dimensional object as a flat cross section. Even metallurgists, geologists, and physicians remained oblivious to the great benefit that such technology would eventually give to their respective professions.

The first practical use of such mathematics was Bracewell’s two-dimensional reconstruction of the Sun in 1956. He was unaware of Radon’s formula but developed a similar algorithm on his own. Correlation among his, Radon’s, and Lorentz’s results was not noticed until the 1970’s.

In 1961, Oldendorf, unaware of Radon, Lorentz, and Bracewell, patented the world’s first apparatus that used X rays to create cross sections of three-dimensional objects. Because his machine, although successful, had minimal mathematical foundations, he could not convince any manufacturers to underwrite its further development.

Kuhl and his colleague at the University of Pennsylvania, Roy Q. Edwards, built several radionuclide scanning machines between 1954 and 1966 that anticipated CAT and two other basic medical imaging techniques, positron emission tomography Positron emission tomography scanning PET scanning (PET) and single photon emission computed tomography (SPECT). On August 21, 1959, Kuhl and Edwards created the first tomographic image of the human body.

A patient undergoes a CT scan.

(Digital Stock)

Cormack was not familiar with any of these predecessors in 1963 when he independently solved Radon’s problem and began applying this formula toward creating computerized composite medical images. He did not hear of Radon until 1972.

Hounsfield was unaware of any of this previous work when, on behalf of his employer, the Central Research Laboratories (CRL) of Electrical and Musical Industries (EMI) in London, he began applying his computer engineering skills to problems of medical tomography in 1967. He had long studied the mathematics of pattern recognition. As early as 1957, he had conjectured that practical two-dimensional slices of three-dimensional objects might be constructed mathematically from X-ray photographs.

His first scanner required nine days of gathering data by passing gamma rays through a cadaver skull and two hours of mainframe computer time to obtain just one cross section of the brain. Substituting a standard X-ray tube for the gamma radiation source reduced his data-gathering time to nine hours, still much too slow for clinical use. In 1969, having improved both the mathematical and the mechanical aspects of his designs, Hounsfield enlisted the help of several physicians, including James Ambrose and Louis Kreel of Atkinson Morley’s Hospital in Wimbledon.

Hounsfield, Ambrose, and Kreel refined Hounsfield’s tomography to reduce the scanning time, increase the contrast between white and gray matter in the brain, and refine the quality of the computer printouts. They experimented with dead cattle and pigs as well as human cadavers. By early 1971, the three believed that they had progressed sufficiently to expand their research into clinical settings with real patients.

Although EMI generously funded Hounsfield’s research, it was unwilling to commit money to manufacture clinical medical equipment. Ambrose successfully applied to the British Department of Health and Social Security (DHSS) for funds to build a prototype and three additional scanners. With this government support, Hounsfield and Ambrose oversaw the construction and installation of the prototype, the EMI Mark I head scanner, at Atkinson Morley’s. On October 1, 1971, Ambrose used the scanner to perform the first scan of a living patient. This trial detected a cystic brain tumor, thus effectively overcoming the skull as an obstacle to noninvasive diagnosis. On April 19, 1972, the team announced its discovery to the world by presenting its findings at a meeting of the British Institute of Radiology.

James William Douglas Bull demonstrated CAT in New York in May, 1972. Ambrose and Hounsfield published their landmark articles, “Computerized Transverse Axial Tomography” and “Computerized Transverse Axial Scanning (Tomography)” in the February and December, 1973, issues of the British Journal of Radiology. The first two CAT scanners in the United States were installed in 1973 at the Mayo Clinic in Rochester, Minnesota, and the Massachusetts General Hospital in Boston. The DHSS installed its other three scanners in Manchester, Glasgow, and London. Only after this initial success did Hounsfield learn of Radon, Cormack, and the others.


Medical technicians study CT scan results.


Promoted strongly by Ambrose, Kreel, and many American physicians, CAT scanning became the most important new diagnostic tool of the 1970’s. Early CAT scanners required a water tank for the patient and were only effective for the head. By 1975, Hounsfield had solved these problems, thus making the pneumoencephalograph obsolete and enabling CAT scanning for any part of the body. He and other researchers reduced scanning time to under four minutes, made the process more convenient and comfortable for the patient, decreased the thickness of each scan in the series, and enabled scans to be shown at high resolution in several media, including computer printouts, television displays, and Polaroid photographs.

Even after these developments, the most common use of CAT in the 1970’s was for brain scans, but soon its value for studying other diseased or injured parts of the body became equally obvious. Kreel’s research focused on the chest. In 1976, he became the first physician to diagnose pulmonary lesions with CAT.

Hounsfield shared the 1979 Nobel Prize in Physiology or Medicine Nobel Prize in Physiology or Medicine;Godfrey Newbold Hounsfield[Hounsfield] Nobel Prize in Physiology or Medicine;Allan M. Cormack[Cormack] with Cormack. The Karolinska Institute divided the award this way despite the facts that Hounsfield had not used Cormack’s results in his research and that Cormack’s invention did not achieve the prevalence of Hounsfield’s. Some historians and scientists questioned the justice of this decision, charging that Oldendorf, Kuhl, and Ambrose each deserved a share of Hounsfield’s Nobel Prize as much as Cormack did. Agreeing that Hounsfield was primarily responsible yet asserting that he was just one among many, they reasoned that the Nobel Prize should have been given either to him alone, to him and Ambrose, or to all five. CAT scanning Computerized axial tomography scanning X-ray technology[X ray technology] Radiology

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Bushong, Stewart C. Computed Tomography. New York: McGraw-Hill, 2000. Written for health care professionals, but on a level accessible to the general public. Contains clear historical and technical information and useful illustrations.
  • citation-type="booksimple"

    xlink:type="simple">Gedeon, Andras. Science and Technology in Medicine: An Illustrated Account Based on Ninety-Nine Landmark Publications from Five Centuries. New York: Springer, 2006. Contains a biographical sketch of Hounsfield and illustrated excerpts from his 1973 articles.
  • citation-type="booksimple"

    xlink:type="simple">Guy, Chris, and Dominic Ffytche. Introduction to the Principles of Medical Imaging. London: Imperial College Press, 2005. Not highly technical, but written for college undergraduates with a basic knowledge of science.
  • citation-type="booksimple"

    xlink:type="simple">Oldendorf, William H. The Quest for an Image of the Brain. New York: Raven Press, 1980. Historical account by one of the founders of neurological imaging.
  • citation-type="booksimple"

    xlink:type="simple">Potchen, E. James. “Reflections on the Early Years of Nuclear Medicine.” Radiology 214 (2000): 623-629. Gives details and personal testimonies from several researchers, including David Kuhl, on the American precursors of CAT scanning.
  • citation-type="booksimple"

    xlink:type="simple">Simmons, John Galbraith. Doctors and Discoveries: Lives That Created Today’s Medicine. Boston: Houghton Mifflin, 2002. Brief biographical introduction that contains a chapter each on most of the major biomedical innovators since the Renaissance, including one on Hounsfield.
  • citation-type="booksimple"

    xlink:type="simple">Wolbarst, Anthony Brinton. Looking Within: How X-Ray, CT, MRI, Ultrasound, and Other Medical Images Are Created, and How They Help Physicians Save Lives. Berkeley: University of California Press, 1999. Readable historical and technological introduction to modern processes of medical imaging and their clinical applications. Written for laypeople.
  • citation-type="booksimple"

    xlink:type="simple">Wolpert, Samuel M. “Neuroradiology Classics.” American Journal of Neuroradiology 21 (2000): 605-606. Sketches the whole history of computed tomography from the original mathematics in 1905 to the Nobel Prize in 1979.

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