The performance characteristics and diagnostic efficacy of the Aβ ligands when used alone, and more recently when used with other imaging modalities (e.g., structural MRI and fluorodeoxyglucose PET) [e.g., [42,61] or in conjunction with the assessment of the well known AD risk variant of apolipoprotein E (ε4 allele) [e.g., [62], have been described in over a decade of literature. The gene discussed is APOE; the disease is Alzheimer disease.