On this day in 1971 Dr. Allan M. Cormack and Geoffrey Hounsfield were awarded the Nobel Prize in medicine for developing the com - puted axial tomography scan, or CAT scan. The scan uses computers to generate a three-dimensional image from two-dimensional X-rays. To do this, the computer takes pictures of one “slice” of an organ from all directions—the X-ray machine moves 360 degrees around the organ to take depth and volume measurements, which are important in determining the size and shape of the problem at hand. The CAT scan has become integral in pinpointing and diagnosing problems in organs such as the brain, liver, stomach, and lungs.