84 Chapter 4 Tests on which lower scores indicated better performance (TMT-A and -B, Stroop Colour Word test I, II and III) were inverted. Domain scores were only calculated if two or more tests within a domain were available. Statistical analyses To assess the correlations between [18F]flortaucipir BP ND and R1, with age, sex, education and Fazekas score, a correlation matrix was created using Spearman correlations. A p value below 0.05 was considered statistically significant. To examine the regional associations between [18F]flortaucipir BP ND and R1, linear regression analyses, adjusted for age and sex, were performed. To assess the contribution of white matter damage in these associations, analyses were additionally adjusted for Fazekas score. To assess voxel-wise associations between [18F]flortaucipir BP ND or R1 and cognition, voxel-wise regression analyses using SPM12 were performed. Analyses were adjusted for age, sex and education. A p value below 0.001 (uncorrected) was considered statistically significant for voxel-wise analyses. Additionally, a more conservative family-wise error (FWE) correction at p < 0.05 was applied. To investigate regional associations between [18F]flortaucipir BP ND or R1 and cognition (dependent variables), linear regression analyses, adjusted for age, sex and education (model 1), were used. Subsequently, we entered [18F]flortaucipir BP ND and R1 simultaneously in the model to assess their independent associations with cognition (model 2). For all regional analyses, we report the level of significance both with and without correction for multiple comparisons using the Benjamini-Hochberg procedure with a false discovery rate (FDR) Q value of 5%. A p value below 0.05 was considered statistically significant. All regional and voxel-wise analyses were repeated with partial volume-corrected data. RESULTS Participants A total of 71 subjects (MCI due to AD: n = 10, and AD dementia: n = 61) with a mean age of 66 ± 8 years and MMSE score of 23 ± 4 were included (Table 1). By study design, all subjects had abnormal amyloid biomarkers. [18F]Flortaucipir BP ND values were highest in parietal (0.55 ± 0.43) regions and R1 values were lowest in medial temporal regions (0.68 ± 0.06) (Table 1). [18F]Flortaucipir BP ND and/or R1 showed statistically significant correlations with age and education (Table 2), but not with sex.
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