Effect of small amounts of 131I on 99mTc detection by the scintillation camera

A patient who had recently received a therapeutic dose of Na131I showed no 99mTc activity on the scintillation camera when a pertechnetate brain scan was attempted. Subsequent experiments showed that, when even small amounts of 131I are present in the field of view of a scintillation camera equipped with a collimator designed for low-energy photons, counting rates from 99mTc are markedly affected.