IMPROVING THE RADIONUCLIDIC PURITY OF TC-94M FOR PET IMAGING

The production of Tc-94m as pertechnetate, a t(1/2) = 53 min positron emitter, was studied with small and medium energy cyclotrons. At a proton energy of 11 MeV, the irradiation of natural molybdenum provides adequate saturated yields (3 mCi/mu A) with tolerable radionuclidic purity for radiopharmaceutical investigations in man. The longer lived Tc-95, Tc-95m and Tc-96 isotopes can be virtually eliminated by irradiating an isotopically-enriched (MoO3)-Mo-94 target. In a study of alternative entrance channels leading to Tc-94m, natural niobium and molybdenum targets were irradiated with He-3 and He-4 beams. The goal was to reach pure Tc-94m through the Ru-94/Tc-94m generator system, bypassing contamination by the Tc-94g ground state.