PET imaging of noradrenaline transporters in Parkinson's disease: focus on scan time

ObjectiveIn subjects with idiopathic Parkinson's disease (PD) the functional state of the locus coeruleus and the subtle derangements in the finely tuned dopamine-noradrenaline interplay are largely unknown. The PET ligand (S,S)-[C-11]-O-methylreboxetine (C-11 MRB) has been described to reliably bind noradrenaline transporters but long scanning protocols might hamper its use, especially in patients with PD. We aimed to assess the feasibility of reducing C-11 MRB scans to 30min.MethodsTen patients with idiopathic PD underwent dynamic C-11 MRB PET (120min duration) and brain magnetic resonance imaging. Model-based (i.e., simplified and multilinear reference tissue model 2) non-displaceable binding potentials (BP) of selected brain regions were analyzed for a 90min scan protocol and compared with BP derived from static 30-min data with different starting times (30, 40, 50 and 60min) after C-11 MRB injection. Intraclass correlation coefficient and linear regression analysis were used to explore the association between BP of different scan durations. Spearman's served to describe the correlation of BP with demographic and clinical parameters.ResultsWith respect to kinetic models, BP50-80 and BP60-90 showed the best correlation in several brain areas (R-2 range 0.95-98; p<0.001). The thalamus showed the highest BP on average. No correlation between BP, clinical and demographic characteristics was observed.ConclusionsAn acquisition time of 30min, starting 50 or 60min after C-11 MRB injection, allows a reliable estimation of noradrenaline transporter binding values in Parkinsonian people. A short acquisition time can significantly reduce the discomfort of Parkinsonian patients and facilitate PET studies, especially in the medication-off-state.