Godfrey Hounsfield

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Aug. 25, 1973: More Than One Way to Slice a CAT

1973: The CT scan goes into use in the United States. Lives will be saved. Originally known as a CAT scan -- for computed (or computerized) axial tomography, or computer-aided (or assisted) tomography -- the process uses a series of X-rays to create sequential images of virtual slices of body tissue. Those can be integrated into a 3-D X-ray, so doctors know the precise position of diseased or otherwise abnormal tissue. In Medford, Massachusetts, in the 1960s, Tufts University physics professor Allan Cormack's main field was particle physics, but he laid the foundation for computerized tomography in his spare time. He theorized that you could take X-rays from varying angles; account for differences in the density of bone, muscle and organs; and program a computer to assemble 3-D images. Electrical engineer Godfrey Hounsfield was working on a similar line of research at the EMI Central Research Laboratories in England. (Yes, that's the same EMI as the record label, and massive profits from The Beatles' 1960s hits funded development of the CT scanner.) Hounsfield developed a CT machine that could perform brain scans. He began testing it in 1971 -- sometimes carrying bull's brains across London on public transit. His announcement of the invention at a series of British scientific meetings in 1972 created a stir. Hounsfield's prototype took five minutes to make a scan, and two-and-half hours for the computer to process an image. The first production-model EMI-Scanner took four minutes to scan, and its Data General Nova minicomputer needed seven minutes to compute each picture. Meanwhile, back in the United States, dentist-physicist Robert Ledley developed a whole-body scanner at Georgetown University in Washington, D.C., in 1973. It saved its first life while still in development, when a pediatric neurosurgeon used it one weekend while Ledley was off-duty. The Mayo Clinic in Rochester, Minnesota, claims to be the first U.S. medical institution to install the CT, but Massachusetts General Hospital in Boston also began using the CT scanner in August 1973. Hounsfield and Cormack shared the 1979 Nobel Prize in Physiology or Medicine. Ledley was inducted into the National Inventors Hall of Fame in 1990. (Among other achievements, he also devised the image processor and wrote a seminal paper on medical informatics, or computer-aided diagnosis.) CT scanners today are faster -- four to eight images a second -- and more agile. Instead of taking discrete, individual "slices" as images, they use spiral, or helical, tomography, like a virtual Honeybaked ham. That's a lot of progress in 35 years ... which is, after all, 245 in cat years. Source: Various