Optimal duration of PET studies with ¹⁸F-fluoroethyl- diprenorphine

The tracer 6-O-(2-¹⁸F-fluoroethyl)-6-O-desmethyldiprenorphine (¹⁸F-FDPN) provides enhanced flexibility to PET studies of the opioidergic system because the label has a longer half-life than the label of ¹¹C-diprenorphine. Here we evaluated the ideal length of PET studies with ¹⁸F-FDPN. Methods: ¹⁸F-FDPN binding kinetics were quantified with protocols of different lengths by use of a 1-tissue or a 2-tissue compartment model for different volumes of interest. Furthermore, the effects of scanning duration were assessed by parametric analyses. Results: A 90-min protocol resulted in less than 10% bias in distribution volume (DV) relative to the full-length protocol. Correlation analyses of the DV estimates for the full-length protocol and the shortened protocols showed good replication of DV estimates for regions with both low and high levels of binding at schedules of up to 90 min. Conclusion: Data sampling in dynamic ¹⁸F-FDPN PET acquisitions should not be shorter than 90 min to maintain reliable estimates of DV.