A total of 7,000 Medicare beneficiaries meeting the study's eligibility criteria will be consented and enrolled over 30 months at sites throughout the United States. To ensure diversity, the study will enroll at least 2,000 Blacks/African Americans, at least 2,000 Latinos/Hispanics, and up to 3,000 additional participants from other racial and ethnic backgrounds. Based on disease stage prior to PET, all participants will be classified as having MCI or dementia as their disease stage. Based on their clinical presentation prior to PET, all participants will be classified as having "typical" (i.e. progressive amnestic) or "atypical" clinical presentations of AD as the potential cause of dementia or MCI.

Dementia specialists will team with PET facilities that have trained radiologists/nuclear medicine physicians and access to perform amyloid PET. All participating physicians and study staff will complete comprehensive training to ensure adherence of data requirements and study timelines. Amyloid PET will be performed and interpreted at each facility with results provided to the ordering dementia specialist for support in further decision making. The dementia specialists will record their diagnosis and intended management plan based on the current clinical and diagnostic information, and assuming no future access to amyloid PET at the "Pre-PET visit." This represents a "thought experiment" documenting the management plan that would be recommended by the specialist if the participant were not enrolling in New IDEAS and thus had no access to amyloid PET. PET results will be disclosed to patients and any consequent changes in management (if any) will be recommended at the "PET disclosure visit." Patients will return 90 ± 30 days following PET for an in person "Post-PET visit." At this final visit, the dementia specialists will record the diagnosis and implemented management plan, incorporating amyloid PET into clinical decision making. Medicare claims data will be collected directly from CMS for 12 months prior to the PET imaging and 12 months after the PET imaging, for each participant.

Aim 1 utilizes Medicare claims data to compare 12-month claims-derived outcomes in amyloid PET-positive versus amyloid PET-negative individuals with MCI and dementia across the entire cohort. Aims 2 and 3 investigate these associations in sub-groups of study participants based on self-identified race and ethnicity (Aim 2) and clinical presentation (Aim 3). Aims 2 and 3 additionally evaluate changes in management between the pre- and post-PET visits in the relevant sub-groups, to test whether benefits in health outcomes are mediated by changes in clinical management. The investigator's over-arching hypothesis, supported by preliminary data from the first IDEAS study, is that amyloid PET results will be associated with changes in clinical management, which in turn will translate into improved health outcomes in patients with amyloid PET-positive scans in comparison with patients with amyloid PET-negative scans. We further hypothesize that these effects will be seen across patients of different ethnoracial backgrounds, clinical presentations and disease stages (MCI and dementia).

Optional components of the study include the collection and archival of participant's amyloid PET images, and blood plasma. These repositories will serve as a resource to the field, enabling the testing and validation of emerging genetic and blood biomarkers. Separate consent will be obtained for participation in these components.