Evaluating infusion methods and simplified quantification of synaptic density in vivo with [ 11 C]UCB-J and [ 18 F]SynVesT-1 PET.

For some positron emission tomography studies, radiotracer is administered as bolus plus continuous infusion (B/I) to achieve a state of equilibrium. This approach can reduce scanning time and simplify data analysis; however, the method must be validated and optimized for each tracer. This study aimed to validate a B/I method for in vivo quantification of synaptic density using radiotracers which target the synaptic vesicle glycoprotein 2 A: [ 11 C]UCB-J and [ 18 F]SynVesT-1. Observed mean standardized uptake values (SUV) in target tissue relative to that in plasma ( C T / C P ) or a reference tissue (SUVR-1) were calculated for 30-minute intervals across 120 or 150-minute dynamic scans and compared against one-tissue compartment (1TC) model estimates of volume of distribution ( V T ) and binding potential ( BP ND ), respectively. We were unable to reliably achieve a state of equilibrium with [ 11 C]UCB-J, and all 30-minute windows yielded overly large bias and/or variability for C T / C P and SUVR-1. With [ 18 F]SynVesT-1, a 30-minute scan 90-120 minutes post-injection yielded C T / C P and SUVR-1 values that estimated their respective kinetic parameter with sufficient accuracy and precision (within 7 ± 6%) . This B/I approach allows a clinically feasible scan at equilibrium with potentially better accuracy than a static scan SUVR following a bolus injection.