99mTc is the work horse of every nuclear medicine department. It is obtained by the elution of a 99Molybdenum-99mTechnetium (99Mo-99mTc) generator. Molybdenum-99 (t1/2 = 66 h) decays by beta emission to 99mTc (87%) and 99Tc (13%), emitting photons of 740 and 778 keV.1 Ideally, 99mTc eluates contain no  radionuclide impurity. However, as a consequence of generator aging or possible occurrence of a mechanical defect, 99Mo may also be extracted from the column during this elution process (Molybdenum breakthrough), becoming a contaminant in the eluate to be administered to the patient.

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