A flow-through detector for nano-Curie activities encountered in HPLC analysis of PET tracer metabolites

The need for a flow-through detector with high efficiency and vanishingly low background arises in HPLC (high-pressure liquid chromatography) analysis of PET (positron emission tomography) tracer metabolites, where the free drug input function must be separated from the total circulating activity in sequential blood samples. Subnanocurie activities of positron emitters in 100 mu l plasma samples are chemically resolved, and then assayed by a triple coincidence beta - gamma - gamma -detector. Multiple coincidence logic between a BC-400 plastic scintillator flow-cell, sandwiched between two large NaI(Tl) gamma detectors, reduces the background event rate to 10/sup -3/ to 10/sup -6/ counts per second, with an overall efficiency of 25% for /sup 18/F-labeled eluates. Careful attention is paid to the construction of the beta cell, maintaining the chemical resolution of the HPLC system while optically transporting the few beta scintillation photons to multiple photomultipliers without losing the solid angle to the surrounding mantle of gamma detectors.<>