99mTclabeled

99mTc-labeled radiopharmaceuticals are compounds in which the radioactive isotope technetium-99m (99mTc) is bound to a biologically active ligand. 99mTc is a metastable isomer with a half-life of about 6 hours and emits 140 keV gamma photons, which are well suited for gamma camera imaging. These properties enable high-contrast single-photon emission computed tomography (SPECT) studies while keeping radiation exposure relatively low. Most 99mTc labeling uses a Mo-99/Tc-99m generator, which provides pertechnetate (TcO4−) that is reduced, typically with stannous ions, to form a Tc complex with the chosen ligand. Many kits enable convenient, kit-based radiolabeling with stringent quality control to ensure radiochemical purity.

Applications of 99mTc-labeled compounds cover a wide range of diagnostic imaging. 99mTc-labeled phosphates and diphosphonates (for example, MDP) are widely used for bone scanning to detect metastases, fractures, and infections. Myocardial perfusion imaging often uses 99mTc-labeled agents such as sestamibi or tetrofosmin. Renal imaging employs 99mTc MAG3 for tubular function and 99mTc DMSA for renal cortical anatomy. Hepatobiliary imaging uses 99mTc-labeled iminodiacetic acid derivatives to evaluate liver and biliary tract function. Brain perfusion studies have used 99mTc-labeled radiopharmaceuticals like Exametazime (HMPAO) or later tracers. 99mTc-labeled colloids are used for lymphoscintigraphy and spleen/liver imaging as well.

Imaging is typically performed with SPECT, often combined with CT for anatomical correlation. Safety considerations include radiation dose from the administered activity, which varies by study but is generally low due to the short half-life. 99mTc-labeled radiopharmaceuticals remain a mainstay of diagnostic nuclear medicine due to versatility, accessibility, and favorable imaging characteristics.