Before about 1970, physicians had few techniques with which to examine the internal structure of the living human body. X rays, discovered by Wilhelm Conrad Röntgen in 1895, had been utilized for decades, but could only show bones (which absorb x rays) and some soft tissue around them. Viewing other organs was difficult.

In the early 1970s the field of medical informatics was developed by Robert Ledley and others, in which computers and other information technologies aid physicians in diagnosis. South African physicist Allan M. Cormack and British engineer Sir Godfrey Hounsfield independently developed the field of x-ray computed tomography, referred to as simply CT, or CAT. Computed tomography uses the fact that different tissues absorb varying amounts of x-ray energy--the denser the tissue, the more energy absorbed.

An x-ray beam sent through tissue will therefore exit with a reduced energy, depending on what...