Abstract
1062
Aim: In the last years, hybrid PET/MRI has become a promising tool to image multiple aspects of Alzheimer’s disease (AD). In this study, we used the new-generation tau radiotracer [18F]PI-2620 to evaluate tau pathology together with structural and functional brain parameters in different AD phenotype variants.
Methods: 14 patients (7 female, 71±14 years old, MMSE score=20±8) with different AD dementia phenotypes and with positive amyloid biomarker constellation were so far included into this study. These were 8 patients with classical AD, 3 patients with visual-variant (posterior cortical atrophy, PCA), 2 patients with language-variant (logopenic aphasia, LPA), and 1 patient with genetic variant (autosomal-dominant AD, ADAD) of AD. The patients underwent 0-60min p.i. [18F]PI-2620 tau PET/MRI (Siemens Biograph mMR). The AD data were compared with those of respective healthy control groups (n=10). Kinetic modeling (MRTM2, reference region=lower cerebellum) of the dynamic PET data resulted in [18F]PI-2620 BPND (tau load) and R1 (blood flow) maps, while voxel-based MR morphometry yielded atrophy and resting-state fMRI (default mode network (DMN), seed=posterior cingulate cortex) yielded functional connectivity readouts.
Results: In classical AD, [18F]PI-2620 BPNDs were increased in the typical Braak histopathology regions, while [18F]PI-2620 R1s were mainly decreased in temporoparietal and posterior cingulate/precuneus regions. Atrophy was most pronounced in mesial temporal and temporoparietal areas, while functional connectivity of the DMN was generally reduced. Different to classical AD, the PCA cases showed additional [18F]PI-2620 BPND increases in occipital areas, with concomitant atrophy/[18F]PI-2620 R1 reduction and lowered DMN activity. The LPA cases revealed left-hemispherical predominance of all finding together with partial co-involvement of frontal areas. The ADAD case showed a multi-parameter constellation similar to that of the classical AD cases. Conclusion: These preliminary data point to multi-parametric [18F]PI-2620 PET/MRI being able to provide a range of different brain state readouts which show characteristic patterns for different AD phenotype variants. Larger studies are thus justified to investigate the potential of this approach for AD subtype differential diagnosis.