DRD1 and juvenile Huntington disease: Our aim in this study was to compare different non-invasive pharmacokinetic models and assess test–retest reproducibility of the radioligand [11C]SCH23390 for the quantification of dopamine D1-like receptor (D1R) in both wild-type (WT) mice and heterozygous (HET) Q175DN mice as Huntington’s disease (HD) model.