Evaluation of Tau Protein in the Brain of Participants With Alzheimer's Disease Compared to Healthy Participants

Inclusion Criteria: All Participants * Female participants must be documented by medical records or physician's note to be either surgically sterile (by means of hysterectomy, bilateral oophorectomy, or tubal ligation) or post-menopausal for at least 1 year. Male participants and their partners of childbearing potential must commit to the use of two methods of contraception, one of which is a barrier method for male participants for the study duration * Male participants must not donate sperm during the study and for 3 months after completion Healthy Participants * Males and females aged greater than or equal 50 years. Healthy with no clinically relevant finding on physical examination at screening and upon reporting for the \[18F\]molecular neuroimaging (MNI)-1020 imaging visit * Have screening \[18F\]florbetapir positron emission tomography (PET) imaging demonstrating no significant amyloid binding based on qualitative analysis (visual read) Alzheimer Disease - Have screening \[18F\]florbetapir or prior amyloid (in the last 12 months) PET imaging demonstrating amyloid binding based on qualitative (visual read) Exclusion Criteria: All Participants * Prior participation in other research protocols or clinical care in the last year in addition to the radiation exposure expected from participation in this clinical study, such that radiation exposure exceeds the effective dose of 50 millisievert (mSv), which would be above the acceptable annual limit established by the United States Federal Guidelines * Unsuitable veins for repeated venipuncture * Magnetic resonance imaging exclusion criteria include: evidence of cerebrovascular disease (more than two lacunar infarcts, any territorial infarct greater than 1 centimeter 3, or deep white matter abnormality corresponding to an overall Fazekas scale of 3 with at least one confluent hyperintense lesion on the FLAIR sequence that is greater than or equal to 20 millimeter (mm) in any dimension), infectious disease, space-occupying lesions, normal pressure hydrocephalus or any other abnormalities associated with central nervous system disease * Implants such as implanted cardiac pacemakers or defibrillators, insulin pumps, cochlear implants, metallic ocular foreign body, implanted neural stimulators, central nervous system aneurysm clips and other medical implants that have not been certified for MRI, or history of claustrophobia in Magnetic Resonance Imaging (MRI) Alzheimer Disease \- Has received treatment that targeted amyloid beta or tau within the last 3 months