Quantification of nicotinic acetylcholine receptors in the human brain with PET: Bolus plus infusion administration of 2-[18F]F-A85380

Quantitative analysis of most positron emission tomography (PET) data requires arterial blood sampling and dynamic scanning when the radioligand is administered as a bolus injection. Less invasive studies can be accomplished if the radioligand is administered as a bolus plus constant infusion (B/I). The purpose of the current study was to evaluate a B/I paradigm for quantifying high affinity nicotinic acetylcholine receptors (nAChRs) with PET and 2-[18F]F-A85380 (2FA). Seven volunteers underwent a study in which 2FA was administered as a bolus injection and another study in which the 2FA was administered by B/I (Kbolus = 500 min). We evaluated the feasibility of using scans of a 2 h duration starting 6 h after the start of the 2FA administration and data from venous blood. Radioactivity in the brain and in arterial and venous plasma reached steady state by 6 h. Volumes of distribution (VT) calculated from the ratio of radioactivity in the brain areas of interest to the radioactivity corresponding to unbound, unmetabolized 2FA in venous plasma at steady state in the B/I studies were very similar to those calculated from time activity curves of unbound, unmetabolized 2FA in arterial plasma and regional brain radioactivity from 8-h dynamic scans after bolus administration of 2FA. The results of repeated PET studies with 2FA showed a high reproducibility of VT measurements. We conclude that B/I methodology will be useful for clinical and research studies of brain nAChRs.