APOE and Alzheimer disease: Once we set the relation between Aβ units and the standard uptake value ratio (SUVR) of amyloid imaging in the next section, we then simulate the outcome of two clinical experiments: the effect of scopolamine on cognition in MCI subjects with and without Aβ load [18]; and the effect of APOE genotype on cognitive trajectory in placebo-treated AD patients [19, 32].