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

Purpose: Moderate-to-high correlations have been reported between the [C-11]PiB PET-derived relative tracer delivery rate R-1 and relative CBF as measured using [O-15]H2O 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 [C-11]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 [C-11]PiB R-1 suggests suitable applicability for cross-sectional and longitudinal studies.