98 Chapter 4 [18F]flortaucipir currently is the most widely used tracer for tau pathology in AD. Another strength is that both measures were derived from a single dynamic [18F]flortaucipir PET scan, thereby circumventing the need for a dual-tracer study and avoiding bias caused by time-lags between measures of tau pathology and rCBF. Furthermore, analyses were repeated with partial volume-corrected data, and results remained essentially comparable; hence, we feel that our findings are not biased by atrophy to a large extent. This study also has some limitations. The AD patients in this study were relatively young, which might hamper generalizability of results to older patient populations. Also, because our sample included only ten ‘MCI due to AD’ patients, further research is needed to elucidate potential differences in the BPND-R1 relationship between diagnostic groups. Furthermore, it might be difficult to draw firm conclusions about the performance of [18F]flortaucipir R 1 compared to other measures of CBF due to the lack of a golden standard for measuring CBF. At last, this study has a cross-sectional design, which excluded the possibility to investigate whether the associations found between tau pathology, rCBF and cognition in AD represent causality. Therefore, longitudinal designs are required. CONCLUSION This study demonstrates that tau pathology and rCBF derived from a single dynamic [18F]flortaucipir PET scan are associated in a region-specific matter, with high levels of tau pathology being generally present in areas with low levels of rCBF. Lower cognitive scores are associated with higher levels of tau pathology and lower levels of rCBF. A substantial amount of these associations remained present when correcting for the other PET measure, indicating that tau pathology and rCBF (at least in part) independently contribute to cognitive deficits in AD. Besides, this study indicates that the use of dynamic [18F]flortaucipir PET might sometimes be preferable, since accurate quantification of tau pathology and an additional functional measure like rCBF can be derived from a single scan.
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