Wilhelm Röntgen discovered x-rays, earning the first Nobel Prize in Physics in 1901, "in recognition of the extraordinary services he has rendered by the discovery of the remarkable rays (or x-rays)," and invented radiography. Christiaan Barnard performed the first heart transplant Ian Donald pioneered the use of the ultrasound scan, which led to its use as a diagnostic tool. Sir Godfrey Hounsfield invented the computed tomography (CT) scanner, sharing the 1979 Nobel Prize in Physiology or Medicine with Allan M. Cormack, "for the development of computer assisted tomography."