Beta Amyloid PET Imaging for Alzheimer Disease With [18F]-Fluselenamyl

Inclusion Criteria: * Male or Female, any race * Age ≥ 18 years * Healthy volunteers or volunteers with Alzheimer's disease Exclusion Criteria: * Has hypersensitivity to 18F-Fluselenamyl or any of its excipients ; * Has hypersensitivity to 11C-PIB or any of its excipients ; * Incapable of providing written informed consent or lacking a legally authorized representative (LAR) to provide informed consent ; * Unwilling or unable to undergo PET scans tracer injections ; * Unwilling or unable to undergo MRI (Aim 2 and Aim 3) * Any condition that, in the Investigator's opinion, could increase the risk to the participant, limit the participant's ability to tolerate the research procedures, or interfere with the collection/analysis of the data (e.g., renal or liver failure, advanced cancer); * Women who are currently pregnant or breast-feeding; * Current or recent (within 12 months prior to screening) participation in research studies involving radioactive agents such that the total research-related radiation dose to the participant in any given year would exceed the limits set forth in the U.S. Code of Federal Regulations (CFR) Title 21 Section 361.1.