Compartmental Modeling of Iodine-123-Iodobenzofuran Binding to Dopamine D2 Receptors in Healthy Subjects

Iodine-123-labeled iodobenzofuran ([123I]IBF) is a potent dopamine D2 antagonist that provides good visualization of D2 receptors in primates. The feasibility of measuring dopamine D2 binding potential with [123I]IBF in humans was evaluated in eight healthy subjects. Following [123I]IBF injection (6 mCi), scans were acquired every 10 min for 160 min with the brain-dedicated CERASPECT camera. Arterial activities were obtained at various intervals and corrected for the presence of metabolites by extraction followed by reverse-phase high-performance liquid chromatography. Reconstructed images exhibited adequate basal ganglia-to-occipital ratios (from 1.96 +/- 0.34 at 30 min to 3.54 +/- 0.71 at 150 min, mean +/- s.d.). Time-activity curves demonstrated reversibility, with peak basal ganglia uptake at 50 +/- 25 min. Regional time-activity curves were analyzed with kinetic three-compartment modeling and graphic analysis. In all subjects, D2 binding potential values, as derived by both methods, were in excellent agreement (mean +/- s.d. D2 binding potential = 129 +/- 51). An empiric count ratio method that does not require measurement of arterial tracer concentrations was evaluated and found to be in reasonable agreement with the model-derived binding potential. Iodine-131-IBF is a suitable ligand for quantitative studies of D2 receptor density with SPECT in humans.