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Medical Definition of Technetium-99m
1. A radioisotope of technetium which decays by isomeric transition, emitting an essentially monoenergetic gamma ray of 142 keV with a half-life of 6.01 hr. 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. 99mTc diphosphonate, a radionuclide complex used for bone scans. 99mTc-DPTA, a radionuclide chelate complex used for renal imaging and function testing. 99mTc sulfur colloid, a particulate radionuclide complex taken up by the reticuloendothelial system; used for imaging the liver and spleen. (05 Mar 2000)