Assessment of motion and model bias on the detection of dopamine response to behavioral challenge.

Compartmental modeling analysis of C-raclopride (RAC) PET data can be used to measure the dopaminergic response to intra-scan behavioral tasks. Bias in estimates of binding potential (BP) and its dynamic changes (ΔBP) can arise both when head motion is present and when the compartmental model used for parameter estimation deviates from the underlying biology. The purpose of this study was to characterize the effects of motion and model bias within the context of a behavioral task challenge, examining the impacts of different mitigation strategies. Seventy healthy adults were administered bolus plus constant infusion RAC during a simultaneous PET/magnetic resonance (MR) scan with a reward task experiment. BP and ΔBP were estimated using an extension of the Multilinear Reference Tissue Model (E-MRTM2) and a new method (DE-MRTM2) was proposed to selectively discount the contribution of the initial uptake period. Motion was effectively corrected with a standard frame-based approach, which performed equivalently to a more complex reconstruction-based approach. DE-MRTM2 produced estimates of ΔBP in putamen and nucleus accumbens that were significantly different from those estimated from E-MRTM2, while also decoupling ΔBP values from first-pass k' estimation and removing skew in the spatial bias distribution of parametric ΔBP estimates within the striatum.