technet99m

Technetium-99m, often written Tc-99m, is a metastable nuclear isomer of technetium-99. It emits gamma radiation with a predominant energy of about 140 keV and has a half-life of roughly 6.01 hours, properties that make it well suited to diagnostic imaging with conventional gamma cameras and single-photon emission computed tomography (SPECT). Tc-99m is produced in a Mo-99/Tc-99m generator, where the parent isotope molybdenum-99 decays to Tc-99m. The eluate is typically received as sodium pertechnetate (TcO4−) and then incorporated into radiopharmaceuticals for imaging.

A key feature of Tc-99m is its ability to be labeled to a variety of molecules, producing targeted radiopharmaceuticals. Common forms include Tc-99m sestamibi or tetrofosmin for myocardial perfusion imaging, Tc-99m exametazime (HMPAO) for brain imaging and lymphoscintigraphy, Tc-99m MAG3 or DTPA for renal imaging, Tc-99m sulfur colloid for liver-spleen imaging, and Tc-99m-labeled macroaggregated albumin (MAA) for lung perfusion scans.

Tc-99m radiopharmaceuticals provide high-contrast images with relatively low radiation doses and enable rapid imaging protocols. The technology underpins routine diagnostic procedures in cardiology, oncology, neurology, and hepatobiliary imaging, among others, and is generally used for diagnosis rather than therapy.

Safety and regulation: handling requires specialized facilities, and radiopharmaceuticals are administered in controlled doses under regulatory oversight. Supply chains can be sensitive to reactor outages affecting Mo-99 production, so quality controls and reliable production are essential components of Tc-99m imaging programs.

History: Since the 1960s, Tc-99m has become the most widely used medical radioisotope for diagnostic imaging due to its favorable physical properties and chemistry.