- Previous or current evidence on screening MRI, computed tomography (CT), or other biomarker studies that suggests an alternate etiology (other than probable AD in patients with AD) for cognitive deficit; or in the case of non-AD controls any evidence on screening MRI, CT, or other biomarker studies that suggests the presence of AD pathology. Brain amyloid-β peptides (Aβ) on Amyloid imaging/PET imaging, however, is expected in many non-AD/DS and all AD/DS subjects, and will not be grounds for exclusion.