Preparation of 99mTc-Pertechnetate Free from Evaporation Residue for Concentration before Use

It has been proved that 99mTc can be obtained from the generator in a solution free from evaporation residue by the following procedure: (1) elution with aqueous NaNO2 solution instead of physiological saline, (2) leading of the effluent into a column of cation exchange resin in NH4- form for Na+ to NH4+ exchange, (3) collection of 99mTc-containing portion of the effluent, and its heating for complete decomposition of NH4NO2 into N2 and H2O. The resultant solution can be evaporated to dryness, leaving the 99mTc without any visible residue. Necessity and usefulness of this procedure are discussed and exemplified by the preparation of 99mTc-labeled carbon aerosols.