186 Chapter 7 cognitively impaired (74% in Aβ+ vs 0% in Aβ-; p<0.001) and had lower MMSE scores when compared to Aβ- individuals (26±3 in Aβ+ vs 29±1 in Aβ-; p<0.001). Of the 61 individuals with longitudinal data, Aβ+ individuals had higher BPND values at both baseline and follow-up, whereas cortical thickness and R1 were lower (Table 1). Age, sex and time between scans did not differ between Aβ+ and Aβ- individuals. Table 1. Characteristics of the follow-up sample Total follow-up sample Amyloid positive Amyloid negative Sample, n 61 35 26 Age, y 65.4 ± 7.4 66.3 ± 7.2 63.7 ± 7.7 Female, n 27 15 12 Cognitively impaired, n 26 26*** 0 MMSE (baseline) 27 ± 3 26*** ± 3 29 ± 1 Time between MRI scans, m 25.9 ± 7.2 26.3 ± 5.0 25.3 ± 9.2 Time between PET scans, m 25.2 ± 3.7 25.8 ± 3.4 24.5 ± 4.0 Baseline global tau PET BPND 0.13 ± 0.18 0.22*** ± 0.19 0.02 ± 0.03 Follow-up global tau PET BPND 0.19b ± 0.22 0.30***b ± 0.23 0.04b ± 0.03 Annual change global tau PET BPND 0.02 ± 0.03 0.04*** ± 0.03 0.01 ± 0.01 Baseline global cortical thickness, mm 2.11 ± 0.07 2.08** ± 0.07 2.14 ± 0.07 Follow-up global cortical thickness, mm 2.09a ± 0.09 2.05***b ± 0.08 2.14 ± 0.07 Annual change global cortical thickness -0.01 ± 0.02 -0.02** ± 0.02 0.00 ± 0.02 Baseline global R1 0.90 ± 0.05 0.88* ± 0.05 0.91 ± 0.04 Follow-up global R1 0.90 ± 0.05 0.88** ± 0.05 0.92 ± 0.05 Annual change global R1 -0.00 ± 0.01 -0.00 ± 0.02 0.00 ± 0.01 Amyloid + vs -: *p<0.05, **p<0.01, ***p<0.001; Baseline vs Follow-up: ap<0.01, bp<0.001 Longitudinal change Tau PET BPND significantly increased over time in both Aβ- and Aβ+ individuals, with the largest increases observed in the Aβ+ individuals (Table 1, Figure 2). Cortical thickness decreased over time in Aβ+ individuals only. rCBF, however, did not significantly change over time in either Aβ+ and Aβ- individuals (Table 1, Figure 2). Although LMM results did not show significant (average) change in rCBF on group level, we did observe substantial changes at the individual level (both increases and decreases, potentially canceling each other out when calculating an effect over the
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