Technetium-99m

Metastable nuclear isomer of technetium-99

Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical radioisotope in the world. Technetium-99m is used as a radioactive tracer and can be detected in the body by medical equipment (gamma cameras). It is well suited to the role, because it emits readily detectable gamma rays with a photon energy of 140.5 keV (within the range emitted by conventional X-ray diagnostic equipment) and its half-life is 6.0066 hours (meaning 93.7% of it decays to 99Tc in 24 hours).

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