99mTc

99mTc, or technetium-99m, is a metastable nuclear isomer of technetium-99. It has a half-life of about 6.01 hours and decays to the ground state 99Tc by isomeric transition, emitting a 140 keV gamma photon in the majority of decays. The combination of suitable gamma energy and a short half-life makes it ideal for diagnostic imaging with gamma cameras and SPECT.

99mTc is produced from molybdenum-99 in a Mo-99/Tc-99m generator. Mo-99, produced in reactors, decays to Tc-99m with a half-life of about 66 hours. The generator allows clinical sites to elute Tc-99m on site, providing a readily available supply for imaging procedures and reducing the need for on-site reactor production.

In medicine, Tc-99m is used with a variety of radiopharmaceuticals depending on the target organ or process. Examples include sodium pertechnetate for thyroid imaging, Tc-99m MDP for bone scans, MAG3 and DTPA for renal imaging, sestamibi for myocardial perfusion imaging, and HMPAO (exametazime) for brain perfusion imaging. SPECT imaging with Tc-99m compounds is widely employed across medical specialties for diagnostic assessments.

Safety and regulation govern the handling, preparation, and disposal of Tc-99m radiopharmaceuticals. The short half-life minimizes long-term radiation exposure, and strict quality controls ensure appropriate radiochemical purity and patient safety.