18F-AV-1451 PET Imaging in Participants Enrolled in the LEARN Study

Participants should meet inclusion and exclusion criteria for the LEARN study, and in addition: Inclusion Criteria: * Male or female that have consented and are currently enrolled in the LEARN protocol; * Participants who sign an IRB approved informed consent form prior to any study procedure; and * Participants who in the opinion of the investigator can tolerate the PET scan procedures. Exclusion Criteria: * Has any condition that, in the investigator's opinion, could increase risk to the participant, limit the participant's ability to tolerate the experimental procedures, or interfere with analysis of the data. (For example, participants with chronic back pain might not be able to lie still during the scanning procedures.); * Has abnormal findings on physical examination or laboratory screening tests that suggest the participant might have a condition that could, in the opinion of the investigator, affect his or her response to the radiopharmaceutical and related testing procedures; * Is deemed likely to be unable to perform all of the imaging procedures for any reason; * Has a history of risk factors for torsades de pointes, including clinically significant findings on ECG, or is taking medications known to prolong QT interval such as citalopram ≥ 40 mg/day, disopyramide, dofetilide, ibutilide, procainamide, quinidine, sotalol, or bepridil; A list of restricted medications will be provided. * Are females of childbearing potential (extremely unlikely in the LEARN eligible population ages 65 to 85) who are not surgically sterile, not refraining from sexual activity or not using reliable methods of contraception. Females of childbearing potential must not be pregnant (negative serum or urine β-hCG at the time of screening and negative serum or urine β-hCG on imaging day) or breastfeeding at screening. Females must agree to avoid becoming pregnant, and both females and males must agree to refrain from sexual activity or to use reliable contraceptive methods for 24 hours following administration of 18F-AV-1451 Injection; Males with female partners who are pregnant or of childbearing potential must agree to refrain from sexual activity for 24 hours following administration of 18F-AV-1451 Injection. Additionally, males must agree not to donate sperm for 24 hours following administration of 18F-AV-1451 Injection; * Has hypersensitivity to 18F-AV-1451 or any of its excipients.