Boxplots of β-amyloid burden by clinical classification . β-amyloid (Aβ) burden in the Alzheimer's disease (AD) group was significantly higher (+) compared with the mild cognitive impairment (MCI) and healthy control (HC) groups. Aβ burden was high in 83% of the amnestic single-domain MCI (asMCI) participants and significantly higher than in HC (†). Only one nonamnestic MCI (naMCI) subject presented with high 18F-florbetaben retention. Dotted line, threshold between high and low Aβ burden. amMCI, amnestic multidomain MCI; SUVR, standard uptake value ratio.