Sensitive measurement of positron emitters eluted from HPLC

For sensitive analysis of the radioactive-metabolite in human PET, a radio-HPLC system coupled to a newly designed positron detector was constructed. The detector had the advantages of low noise level (1.7 +/- 1.0 cpm) and high sensitivity (32 +/- 1%) due to coincidence counting and large BGO crystals. Furthermore, the detector was easy to move, since a pair of the BGO housings coupled to photomultipliers was effectively arranged in parallel and a HPLC cell with different volume could be inserted between the BGO housing. This radio-HPLC system was useful for analyzing samples with low radioactivity. It was applied to the measurement of [11C]FLB457 in plasma, having high affinity and high selectivity with dopamine D2 receptors. Extremely low radioactivity of [11C]FLB457 (2500 dpm) could be analyzed by using the radio-HPLC system. The performance of this detector was compared with those of commercially available systems that had been used as sensitive detectors for HPLC.