Transporter with SPECT After Bolus and Bolus/Infusion

The aim of the present study was to describe a method com- bining easy implementation in a clinical setting with accuracy and precision in quantification of 123I-labeled N-(3-iodoprop- (2E)-enyl)-2-carboxymethoxy-3-(4-methylphenyl)nortropane (PE2I) binding to brain dopamine transporter. Methods: Five healthy subjects (mean age, 50 y; range, 40-68 y) were studied twice. In the first experiment, dynamic SPECT data and arterial plasma input curves obtained after 123I-PE2I bolus injection were assessed using Logan, kinetic, transient equilibrium, and peak equilibrium analyses. Accurate and precise determination of BP1 (binding potential times the free fraction in the metabo- lite-corrected plasma compartment) and BP2 (binding potential times the free fraction in the intracerebral nonspecifically bound compartment) was achieved using Logan analysis and kinetic analysis, with a total study time of 90 min. In the second exper- iment, 123I-PE2I was administrated as a combined bolus and constant infusion. The bolus was equivalent to 2.7 h of constant infusion. Results: The bolus-to-infusion ratio of 2.7 h was based on the average terminal clearance rate from plasma in the bolus experiments. Steady state was attained in brain and plasma within 2 h, and time-activity curves remained constant for an- other 2 h. Even when an average bolus-to-infusion ratio was used, the striatal BP1 and BP2 values calculated with kinetic analysis (BP1 21.1 1.1; BP2 4.1 0.4) did not significantly differ from those calculated with bolus/infusion analysis (BP1 21.0 1.2; BP2 4.3 0.3). Computer simulations confirmed that a 2-fold difference in terminal clearance rate from plasma translates into only a 10% difference in BP1 and BP2 calculated from 120 to 180 min after tracer administration. Conclusion: The bolus/infusion approach allows accurate and precise quan- tification of 123I-PE2I binding to dopamine transporter and is