Test-retest reproducibility of dopamine D2/3 receptor binding in human brain measured by PET with [11C]MNPA and [11C]raclopride.

Dopamine D receptors (DRs) have two affinity states for endogenous dopamine, referred to as high-affinity state (D ), which has a high affinity for endogenous dopamine, and low-affinity state (D ). The density of D can be measured with (R)-2-CHO-N-n-propylnorapomorphine ([C]MNPA), while total density of D and D (DRs) can be measured with [C]raclopride using positron emission tomography (PET). Thus, the ratio of the binding potential (BP) of [C]MNPA to that of [C]raclopride ([C]MNPA/[C]raclopride) may reflect the proportion of the density of D to that of DRs. In the caudate and putamen, [C]MNPA/[C]raclopride reflects the proportion of the density of D to that of DRs. To evaluate the reliability of the PET paradigm with [C]MNPA and [C]raclopride, we investigated the test-retest reproducibility of non-displaceable BP (BP ) measured with [C]MNPA and of [C]MNPA/[C]raclopride in healthy humans. Eleven healthy male volunteers underwent two sets of PET studies on separate days that each included [C]MNPA and [C]raclopride scans. BP values in the caudate and putamen were calculated. Test-retest reproducibility of BP of [C]MNPA and [C]MNPA/[C]raclopride was assessed by intra-subject variability (absolute variability) and test-retest reliability (intraclass correlation coefficient: ICC). The absolute variability of [C]MNPA BP was 5.30 ± 3.96 % and 12.3 ± 7.95 % and the ICC values of [C]MNPA BP were 0.72 and 0.82 in the caudate and putamen, respectively. The absolute variability of [C]MNPA/[C]raclopride was 6.11 ± 3.68 % and 11.60 ± 5.70 % and the ICC values of [C]MNPA/[C]raclopride were 0.79 and 0.80 in the caudate and putamen, respectively. In the present preliminary study, the test-retest reproducibility of BP of [C]MNPA and of [C]MNPA/[C]raclopride was reliable in the caudate and putamen.