An on-line synthesis of [15O]N2O: new blood-flow tracer for PET imaging

This paper describes a recently developed on-line synthesis of a new blood-flow tracer, O-15-labeled nitrous oxide. The tracer was produced by catalytic oxidation of anhydrous ammonia in a gas mixture containing O-15-labeled molecular oxygen. (The oxygen-15 was produced by a 14N(d,n)15O reaction.) Anhydrous ammonia was mixed with the gas containing [15O]O2, and after preheating to about 200 degrees C was carried through an oven containing a Pt catalyst kept at about 310 degrees C. Labeled gas was purified in H3PO4 and KOH traps. O-15-labeled nitrous oxide was identified by gas radiochromatography and by various chemical reactions. Radiochemical purity of the O-15-labeled nitrous oxide exceeded 98%, radiochemical yield corrected for radioactioactive decay was 15-20%, and specific activity at the end of synthesis was about 50 mCi/mmole.