Comparison of Early-Phase 11C-Deuterium-L-Deprenyl and 11C-PiB PET for Assessing Brain Perfusion in Alzheimer's Disease.

The PET tracer ¹¹C-deuterium-L-deprenyl (¹¹C-DED) has been used to visualize activated astrocytes in vivo in patients with Alzheimer's disease (AD). In this multitracer PET study, early-phase ¹¹C-DED and ¹¹C-Pittsburgh compound-B (¹¹C-PiB) (eDED and ePiB, respectively) were compared as surrogate markers of brain perfusion, and the extent to which ¹¹C-DED binding is influenced by brain perfusion was investigated.

METHODS: ¹¹C-DED, ¹¹C-PiB and ¹⁸F-fluorodeoxyglucose (FDG) dynamic PET scans were performed in age-matched groups comprising AD patients (n = 8), patients with mild cognitive impairment (MCI, n = 17), and healthy controls (HC, n = 16). A modified-reference Patlak model was used to quantify ¹¹C-DED binding. A Simplified Reference Tissue Model was applied to both ¹¹C-DED and ¹¹C-PiB to measure brain perfusion relative to the cerebellar gray matter (GM) (R₁) and binding potentials. ¹¹C-PiB retention and ¹⁸F-FDG uptake were also quantified as target-to-pons standardized uptake value ratios in 12 regions of interest (ROIs).

RESULTS: The strongest within-subject correlations with the corresponding R₁ values (R_1,DED and R_1,PiB, respectively) and with ¹⁸F-FDG uptake were obtained when the eDED and ePiB PET data were measured 1-4 min post-injection. The optimum eDED/ePiB intervals also showed strong, significant ROI-based inter-subject Pearson's correlations with R_1,DED/R_1,PiB and with ¹⁸F-FDG uptake, while ¹¹C-DED binding was largely independent of brain perfusion, as measured by eDED. Corresponding voxelwise correlations confirmed the ROI-based results. Temporo-parietal eDED or ePiB brain perfusion measurements were highly discriminative between patient and control groups, with discriminative ability statistically comparable to that of temporo-parietal ¹⁸F-FDG glucose metabolism. Hypometabolism extended over wider regions than hypoperfusion in patient groups compared to controls.

CONCLUSION: The 1-4 min early-frame intervals of ¹¹C-DED or ¹¹C-PiB are suitable surrogate measures for brain perfusion. ¹¹C-DED binding is independent of brain perfusion and thus ¹¹C-DED PET can provide information on both functional (brain perfusion) and pathological (astrocytosis) aspects from a single PET scan. In comparison with glucose metabolism, early-phase ¹¹C-DED and ¹¹C-PiB perfusion appear to provide complementary rather than redundant information.