Distribution of Tc-99m administered as labeled microspheres for lung imaging

We have measured the distribution of Tc-99m in 36 patients receiving labeled microspheres for routine lung imaging studies. Quantitative organ measurements were made by conjugate counting with an Anger camera at various times for 24 hours. Initial uptake was all in lung as expected. Removal of Tc-99m from lung was principally by elution of activity as TcO4- rather than by breakup of the microspheres. Calculated radiation doses in mrad/mCi were as follows: lung, 229; kidney, 138; stomach, 72; thyroid, 72; and bladder wall, 40. Doses to other tissues were all below 40 mrads/mCi