technetium99m

Technetium-99m (Tc-99m) is a metastable nuclear isomer of technetium-99. It emits gamma rays with an energy of about 140 keV and has a half-life of 6.01 hours, properties that make it highly suitable for diagnostic nuclear medicine imaging using gamma cameras and SPECT.

Tc-99m is produced from molybdenum-99 in a generator system, commonly referred to as a Mo-99/Tc-99m generator. Molybdenum-99 decays to Tc-99m, which is eluted as sodium pertechnetate (TcO4−) and then incorporated into various radiopharmaceuticals through coordination chemistry.

Applications: It is the most widely used radionuclide in diagnostic imaging. Common Tc-99m radiopharmaceuticals include Tc-99m sestamibi for myocardial perfusion imaging, Tc-99m MDP (or HDP) for bone scanning, Tc-99m sulfur colloid for liver/spleen and lymphoscintigraphy, and Tc-99m DMSA for renal cortex imaging. These and other compounds enable imaging of bone, heart, kidneys, liver, thyroid, brain, and sentinel lymph nodes.

Safety and regulation: The short half-life limits radiation exposure, and the 140 keV gamma emission is well matched to gamma cameras. Production depends on reactor-generated Mo-99, though alternative methods are explored. Radiopharmaceuticals are subject to strict quality control and regulatory oversight to ensure purity, sterility, and accurate dosimetry.

History: Tc-99m became widely used in the 1960s and 1970s after the development of the Mo-99/Tc-99m generator, establishing Tc-99m as the standard radionuclide for diagnostic imaging due to its favorable imaging characteristics and chemistry.