Since the invention of the X-ray machine, it has been apparent to physicians that an efficient and precise method for viewing patients' internal structures was essential. Fluoroscopes could outline bone structure and help locate foreign objects, but were not sensitive enough to show in detail organs such as the brain. During the late 1960s, Alan Cormack (1924-), an American, and Godfrey Hounsfield (1919-), an Englishman, independently developed a method called computerized axial tomography (CAT) scanning by which the internal structure of the body could be seen by assembling X-ray cross-sections, taken along a body axis, into a three-dimensional picture.

Cormack was the first to construct a tomographic device. His initial model used a thin beam of X-rays aimed at one section of the body but repeated from many different angles. This method allowed him to combine the many X-ray pictures into one complete view...