Technetium (Tc, element 43) is a radioactive metallic element that does not occur naturally either in its pure form or as compounds; it is produced during nuclear fission. A fission product of molybdenum (Mo, element 42), Tc can also occur as a fission product of uranium (U, element 92). It was the first element to be made artificially in 1937 when it was isolated and extracted by Carlo Perrier (1886–1948) and Emilio Segrè (1905–1989).

Technetium has found significant application in diagnostic imaging and nuclear medicine. Ingested soluble technetium compounds tend to concentrate in the liver and are valuable in labeling and in radiological examination of that organ. Also, by technetium labeling of blood serum components, diseases involving the circulatory system can be explored.