FIRST-PASS EXTRACTION FRACTION OF I-123 LABELED PERFUSION TRACERS IN LIVING PRIMATE BRAIN

The cerebral extraction and retention of three radioiodinated SPECT pe rfusion tracers were measured using residue detection in a baboon. A p ermeability-surface area product PS' with special relevance to SPECT w as calculated from the retention of tracer in the brain after 10 min. PS' differs from the traditional PS value, which is calculated from th e tracer clearance curve at 2 min. The PS' values ranged from 50 to 95 mL/min/100 g, decreased in the order [I-123]IMP > [I-123]iodoperidol approximate to [I-123]HIPDM and did not differ for specific activities of 10 MBq/mmol to 74 TBq/mmol. These radioiodinated compounds exhibit ed extraction characteristics superior to these of [Tc-99m]HMPAO but u nderestimated cerebral blood flow when flows were above 20-30 mL/min/1 00 g, underscoring the need for development of a more ideal SPECT perf usion tracer.