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a chemical element, atomic number 43, atomic weight 99, symbol Tc. (See Appendix 6.)
technetium 99m the most frequently used radioisotope in nuclear medicine, a gamma emitter having a half-life of 6.01 hours.
tech·ne·ti·um 99m (99mTc),(tek-nē'shē-ŭm),
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.