Technetium-99m

Technetium-99m (99mTc) is a <a href="/facts/Metastable/H72SMWof">metastable</a> <a href="/facts/Nuclear_isomer/L8DHcqnk">nuclear isomer</a> of <a href="/facts/Technetium-99/0w2EE0G2">technetium-99</a> (itself an isotope of <a href="/facts/Technetium/MGYWNI5d">technetium</a>), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used <a href="/facts/Radiopharmacology/EArnJn3N">medical radioisotope</a> in the world.
Technetium-99m is used as a <a href="/facts/Radioactive_tracer/0210Jncn">radioactive tracer</a> and can be detected in the body by medical equipment (<a href="/facts/Gamma_camera/coGxuajk">gamma cameras</a>). It is well suited to the role, because it emits readily detectable <a href="/facts/Gamma_ray/5Drf913J">gamma rays</a> with a <a href="/facts/Photon_energy/Gy4zEAaE">photon energy</a> of 140 <a href="/facts/Kiloelectronvolt/YMT1fqX9">keV</a> (these 8.8 <a href="/facts/Picometre/Cb54mVBX">pm</a> <a href="/facts/Photon/mFNhAEzA">photons</a> are about the same wavelength as emitted by conventional X-ray diagnostic equipment) and its <a href="/facts/Half-life/kGVH8BAB">half-life</a> for gamma emission is 6.0058 hours (meaning 93.7% of it decays to 99Tc in 24 hours). The relatively "short" physical <a href="/facts/Half-life/kGVH8BAB">half-life</a> of the isotope and its <a href="/facts/Biological_half-life/7nB2JtMr">biological half-life</a> of 1 day (in terms of human activity and metabolism) allows for scanning procedures which collect data rapidly but keep total patient radiation exposure low. The same characteristics make the isotope unsuitable for therapeutic use.
Technetium-99m was discovered as a product of <a href="/facts/Cyclotron/Q8APwhWm">cyclotron</a> bombardment of <a href="/facts/Molybdenum/RX6vp2bF">molybdenum</a>. This procedure produced <a href="/facts/Molybdenum-99/gpYnY3bx">molybdenum-99</a>, a radionuclide with a longer half-life (2.75 days), which decays to 99mTc. This longer decay time allows for 99Mo to be shipped to medical facilities, where 99mTc is extracted from the sample as it is produced. In turn, 99Mo is usually created commercially by fission of <a href="/facts/Highly_enriched_uranium/vSb2Tcsb">highly enriched uranium</a> in a small number of research and material testing nuclear reactors in several countries.

Technetium-99m open-in-new

Technetium-99m