J Am Med Inform Assoc 13:465-469 doi:10.1197/jamia.M2127
  • The Practice of Informatics
  • Historical perspective

The Story Behind the Development of the First Whole-body Computerized Tomography Scanner as Told by Robert S. Ledley

  1. Dean F Sittig,
  2. Joan S Ash,
  3. Robert S Ledley
  1. Affiliations of the authors: Department of Medical Informatics (DFS), Kaiser Permanente, Northwest, Portland, OR; Department of Medical Informatics and Clinical Epidemiology (DFS, JSA), Oregon Health & Science University, Portland, OR
  1. Correspondence and reprints: Dr. D.F. Sittig, Northwest Permanente, PC, 3800 N. Interstate Ave., Portland, OR 97227e-mail:<Dean.F.Sittig{at}>
  • Received 12 April 2006
  • Accepted 6 June 2006

“The army called me down to New York [in 1950]. I was with New York University (NYU)—and the colonel said to me, ‘Well, if you volunteer to be in the army, then you'll become a lieutenant, an officer. But if you don't volunteer, you'll be drafted anyway, and sent to boot camp. So I volunteered. And they sent me to medical field service school in Fort Sam Houston, Texas. And that was kind of interesting. And then, I guess my card dropped out, they wanted a dentist who was a physicist. And that was me.”

Robert S. Ledley


Dr. Robert S. Ledley is credited with “sowing the seeds” for the field of medical informatics [Ledley 1959],1 initiating the development of computerized medical image analysis [Ledley 1964],2 and for being the principal investigator of the Protein Information Resource (PIR) for 20 years [Dayhoff 1965].3 Dr. Ledley is best known for developing the first whole-body computerized tomography (CT or CAT) scanner in 1973 (Patent No. 3,922,552), which revolutionized diagnostic medicine. Dr. Ledley's first CT scanner [which he called the Automatic Computerized Transverse Axial, or ACTA, scanner; [Ledley 1974a, 1974b]2 4 is now owned by the Smithsonian Institution's Museum of American History [Kondratas 2005].5 Using his scanner, he was the first to perform three-dimensional reconstructions [Huang 1975],6 the first to use CT in radiation therapy planning for cancer patients [Scheer 1977],7 and the creator of many other “firsts” in the application of CT in medicine. The following story describes his efforts to develop this scanner.

How Did You Become a Dentist and a Physicist?

I always liked physics. I started at Columbia [University in 1942]. Once you're in the college, you can take any course in the whole university. In those days they only gave one year of college physics, and everything else was graduate …

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