Preparation and Quality Control of [N-Methyl-11C]choline for Routine PET Application

The goal of this study was to optimize the synthesis of [N-methyl-¹¹C]choline, a radiopharmaceutical used in the diagnosis of brain tumors and prostate cancer with positron emission tomography (PET). The synthetic method is based on methylation with [¹¹C]CH₃I of N,N-dimethylaminoethanol (DMAE) immobilized on the surface of a tC18 solid support (Waters). The optimal amounts of DMAE (25 l in 50 l of ethanol) and tC18 (0.1 g) were found, providing a high radiochemical yield of the labeled choline (85%, corrected for radioactive decay) and radiochemical purity of more than 99.5%. After purification on the Sep-Pak Light cation-exchange cartridge (Accell Plus CM, Waters), the concentration of DMAE in the final product was 1.6 g ml^-1. For monitoring of DMAE in the final product, a simple and convenient HPLC method with an indirect UV detection providing sufficient sensitivity was proposed.