Production of radiopharmaceuticals with high specific activity

Various radioisotopes and labeled compounds have been applied and used. The present report reviews studies on the production of radiopharmaceuticals with high specific activity. Short-lived positron emitters such as 11C, 13N, 15O and 18F are very important in the field of nuclear medicine and biochemistry since they can be easily produced with a commercially available cyclotron. Their practically attainable specific activities are much lower than the theoretical ones due to isotopic dilution in the course of target preparation, irradiation, labelling procedure, etc. [11C]CH3I is the most widely used precursor for 11C-labeling since it can be synthesized easily and rapidly from [11C]CO2. A production method of [11C]Ro15-1788 is presented as an example of producing radiotracers with high specific activity. The report also discusses major problems associated with high specific activity and describes some attempts to achieve higher specific activity. (N.K.)