Evaluation of a bolus/infusion protocol for 11C-ABP688, a PET tracer for mGluR5

C-11-ABP-688 is a selective tracer for the mGluR5 receptor. Its kinetics is fast and thus favourable for an equilibrium approach to determine receptor-related parameters. The purpose of this study was to test the hypothesis that the pattern of the C-11-ABP688 uptake using a bolus-plus-infusion (BA) protocol at early time points corresponds to the perfusion and at a later time point to the total distribution volume. Methods: A bolus and a B/I study (1 h each) was performed in five healthy male volunteers. With the B/I protocol, early and late scans were normalized to gray matter, cerebellum and white matter. The same normalization was done on the maps of the total distribution volume (Vt) and K-1 which were calculated in the study with bolus only injection and the Logan method (Vt) and a two-tissue compartment model (K-1). Results: There was an excellent correlation close to the identity line between the pattern of the late uptake in the B/I study and Vt of the bolus-only study for all three normalizations. The pattern of the early uptake in the B/I study correlated well with the K-1 maps, but only when normalized to gray matter and cerebellum, not to white matter. Conclusion: It is demonstrated that with a B/I protocol the C-11-ABP688 distribution in late scans reflects the pattern of the total distribution volume and is therefore a measure for the density pattern of mGluR5. The early scans following injection are related to blood flow, although not in a fully quantitative manner. The advantage of the B/I protocol is that no arterial blood sampling is required, which is advantageous in clinical studies. (C) 2010 Elsevier Inc. All rights reserved.