Kuhl & Edwards Produce CT Scan

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In the late 1950s, University of Pennsylvania researchers David Kuhl and Roy Edwards began work on a new way to use tomographic imaging to identify radioactive isotopes in the body. Kuhl was a doctor who had been interested in radiology since high school and spent his spare hours in medical school trying to build a rectilinear scanner using the photorecording method. Edwards ran the university’s engineering shop in the department of radiology.

Their experiments with Geiger-Muller tubes, a technology developed in the late 1940s, created a picture that had similar characteristics to a plane X-radiograph. This insight led them to develop the Mark II scanner, which was fully designed by July 1959, was under construction by September of that year, and used for emission tomography as early as summer 1963.

On 14 May 1965, they generated what was possibly the first CT (computer tomography) scan of a patient ever made. The CT scanner that they built used a computer to analyze x-ray images, taken from many different directions, in order to map objects blocking the x-rays. This device, called the Mark II, used a double-headed scanner to perform a transaxial section tomography of a living body. Unlike later tomography devices, the Mark II used an optical integrator rather than a digital computer to actually capture the images. In their linear movements, these detectors recorded a simple back projection. Despite this advance, diagnosticians considered these images too blurry to use for most medical purposes, although they could help doctors and scientists understand the orientation and geometry of the scanned subject.

In 1971, British scientist Godfrey Hounsfield would perform the first scan of a human patient with a computer that could create a composite image using input from x-rays. Although Hounsfield, who would later share the 1979 Nobel Prize for this invention, was apparently unaware of Kuhl and Edwards’ experiments in tomography, his contemporaries noted the similarities. “It is the confinement of the scan lines to the single plane,” argues a historian of radiological tomography, Steve Webb, “that enables us to regard Kuhl and Edwards’ experiment as an important precursor of emission CT.” (Webb 1990, p. 179)

Kuhl and Edwards’ team followed up this experiment by developing a series of SPECT (single photon emission computer tomography) devices that could produce a clearer image more quickly: the Mark III, completed in 1968, and the Mark IV, completed in 1975. Their techniques became the basic approach that the developers of PET scanners would use in their devices.

Further Reading

Steven Webb, From the Watching of Shadows: The Origins of Radiological Tomography (CRC Press, 1990), pp. 177-184.