A radioisotope of technetium that decays by isomeric transition, emitting an essentially monoenergetic gamma ray of 142 keV with a half-life of 6.01 hours. It is usually obtained from a radionuclide generator of molybdenum-99 and is used to prepare radiopharmaceuticals for scanning the brain, parotid, thyroid, lungs, blood pool, liver, heart, spleen, kidney, lacrimal drainage apparatus, bone, and bone marrow.