143 Cerebral blood flow, amyloid burden and cognition Relationship between BPND and R1 Next, we investigated the relationship between BPND and R1. We first investigated the effect of BPND on R1 (Table 3). Somewhat counterintuitively, higher baseline values for occipital BPND were associated with higher baseline values for occipital R1 (Table 3). There were no cross-sectional associations in other regions. By contrast, longitudinally, in all regions higher baseline BPND was associated with steeper decrease in R1 in those same regions. Figure 2 visualizes the association between baseline BPND and R1 over time. Next, we investigated the effect of R1 on BPND (Table 4). Again, we found higher baseline values for occipital R1 to be associated with higher concurrent values for occipital BPND, but no cross-sectional associations in other regions. Longitudinally, baseline R1 values in frontal, temporal and composite regions were inversely associated with change in BPND over time in those same regions. This means a lower baseline R1 was associated with an increase in BPND over time. After correction for multiple testing, baseline R1 remained associated with longitudinal BPND in frontal and composite regions. Figure 3 visualizes the association between baseline R1 and BPND over time. Table 3. Associations with cross-sectional and longitudinal R1 Region Concurrent Longitudinal Model 1 Frontal 0.08 (0.07) -0.08 (0.03)* Temporal -0.07 (0.07) -0.12 (0.03)* Parietal -0.03 (0.07) -0.09 (0.03)* Occipital 0.14 (0.08) -0.12 (0.04)* Composite -0.07 (0.07) -0.11 (0.03)* Model 2 Frontal 0.08 (0.07) -0.09 (0.03)* Temporal 0.01 (0.07) -0.12 (0.03)* Parietal 0.03 (0.07) -0.10 (0.03)* Occipital 0.15 (0.08) -0.14 (0.04)* Composite 0.00 (0.07) -0.11 (0.03)* Notes: Results shown are beta (SE) as estimated by linear mixed models, outcome is R1. In model 1, the predictors are BPND, time between PET scans in years and the interaction BPND*time. Model 2 is additionally corrected for age, sex and PET and MRI scanner type. Values given represent betas associated with BPND (concurrent) and BPND*time (longitudinal). Models included a random intercept. R1 and BPND are z-transformed. Bold P value < 0.05. * FDR corrected P value < 0.05. 6
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