In late middle age, cognitively normal subjects who are homozygous for the epsilon 4 allele for apolipoprotein E have reduced glucose metabolism in the same regions of the brain as in patients with probable Alzheimer's disease. These findings provide preclinical evidence that the presence of the epsilon 4 allele is a risk factor for Alzheimer's disease. PET may offer a relatively rapid way of testing future treatments to prevent Alzheimer's disease.

Positron emission tomography (PET) of brain amyloid b is a technology that is becoming more available, but its clinical utility in medical practice requires careful definition. To provide guidance to dementia care practitioners, patients, and caregivers, the Alzheimer's Association and the Society of Nuclear Medicine and Molecular Imaging convened the Amyloid Imaging Taskforce (AIT). The AIT considered a broad range of specific clinical scenarios in which amyloid PET could potentially be used appropriately. Peer-reviewed, published literature was searched to ascertain available evidence relevant to these scenarios, and the AIT developed a consensus of expert opinion. Although empirical evidence of impact on clinical outcomes is not yet available, a set of specific appropriate use criteria (AUC) were agreed on that define the types of patients and clinical circumstances in which amyloid PET could be used. Both appropriate and inappropriate uses were considered and formulated, and are reported and discussed here. Because both dementia care and amyloid PET technology are in active development, these AUC will require periodic reassessment. Future research directions are also outlined, including diagnostic utility and patient-centered outcomes.

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