Test-Retest Variability of Relative Tracer Delivery Rate as Measured by [ 11 C]PiB

Purpose Moderate-to-high correlations have been reported between the [ 11 C]PiB PET-derived relative tracer delivery rate R 1 and relative CBF as measured using [ 15 O]H 2 O PET, supporting its use as a proxy of relative CBF. As longitudinal PET studies become more common for measuring treatment efficacy or disease progression, it is important to know the intrinsic variability of R 1 . The purpose of the present study was to determine this through a retrospective data analysis. Procedures Test-retest data belonging to twelve participants, who underwent two 90 min [ 11 C]PiB PET scans, were retrospectively included. The voxel-based implementation of the two-step simplified reference tissue model with cerebellar grey matter as reference tissue was used to compute R 1 images. Next, test-retest variability was calculated, and test and retest R 1 measures were compared using linear mixed effect models and a Bland-Altman analysis. Results Test-retest variability was low across regions (max. 5.8 %), and test and retest measures showed high, significant correlations ( R 2 =0.92, slope=0.98) and a negligible bias (0.69±3.07 %). Conclusions In conclusion, the high precision of [ 11 C]PiB R 1 suggests suitable applicability for cross-sectional and longitudinal studies.