 The IDEAS Study is an observational, open-label, longitudinal cohort study designed to assess the impact of amyloid PET on patient-oriented outcomes in Medicare beneficiaries with mild cognitive impairment MCI or dementia of uncertain etiology. The study falls under the Centers for Medicare Medicaid Services CMS Coverage with Evidence Development CED policy. A total of 18,488 Medicare beneficiaries meeting Appropriate Use Criteria AUC for amyloid PET will be enrolled over 24 months at sites throughout the United States. Dementia specialists will team with PET facilities able to perform amyloid PET and with trained radiologistsnuclear medicine physicians, all of whom will consent to completing the data requirements and timelines for the study. Amyloid PET will be performed and interpreted at each facility with results provided to the ordering physician for support in further clinical decision making, which will be captured for the study. 