ACHE and Alzheimer disease: A recent PET study demonstrated that intravenously administered [11C]-donepezil, an acetyl-cholinesterase (AChE) inhibitor used in AD therapy, rapidly enters the brain and mainly distributes to the striatum, thalamus, and cerebellum, which are known to contain high densities of AChE compared with the cerebral cortex and hippocampus (Okamura et al., 2008).