Stability of 11C-labeled PET radiopharmaceuticals

The stability of widely used 11C-radiopharmaceuticals was investigated. The purity of many 11C-radiopharmaceuticals was found to be low even at the end of synthesis and to lower with time by radiolysis. Examinations of the effects of radical scavengers showed that the radiopharmaceuticals were classified into four groups: Group 1 showing excellent stability; Group 2 showing suppressed radiolysis in the presence of a selective scavenger of hydroxyl radicals; Group 3 showing suppression in the presence of a selective scavenger of hydrated electrons; Group 4 showing suppression in the presence of both scavengers. Using appropriate additives according to these classes, 11C-radiopharmaceuticals were prepared with excellent radiochemical purity even with high levels of radioactivity and specific activity.