Evaluation of [11C]RO6924963, [11C]RO6931643, and [18F]RO6958948 as Tracers for Positron Emission Tomography (PET) Imaging of Tau in Healthy and Alzheimer's Disease (AD) Participants
Evaluation of [11C]RO6924963, [11C]RO6931643, and [18F]RO6958948 as Tracers for Positron Emission Tomography (PET) Imaging of Tau in Healthy and Alzheimer's Disease (AD) Participants
This study is designed to obtain basic information on three PET imaging tracers developed to
 detect tau pathology in the brain. In this study, healthy control participants and
 participants with AD will be studied. Information collected will include brain and plasma
 kinetics, tissue distribution (in the brain), radiation dosimetry, and test-retest
 variability of the signal in the brain. The study will consist of Part 1, Part 2A, and Part
 2B. During Part 1, imaging data will be assessed on an ongoing basis and based on data, one
 tracer will be prioritized over the other two tracers. The tracer selected will be further
 investigated in Part 2A and Part 2B.
Inclusion Criteria:

 Inclusion Criteria for All Participants

 -  Agreement to use highly effective contraception measures

 -  If participants are on any concomitant medication, the indication and dosage of these
 medicines should be stable for at least 4 weeks prior to study start with the
 expectation that no relevant changes in use or dose will occur throughout the study

 -  Body mass index (BMI) between 18 and 32 kilograms per square meter (kg/m^2)

 -  Weight less than or equal to (</=) 300 pounds (lb)

 Inclusion Criteria for Healthy Control Participants

 -  Healthy "young" control participants aged 25-40 years or healthy "elderly" control
 participants aged greater than or equal to (>/=) 50 years

 -  Normal cognitive function, including a normal Mini Mental State Examination (MMSE)
 score as judged by the investigator

 -  Healthy control participants who participate in Part 2B: must be less than (<) 195
 centimeter (cm) (6 feet, 5 inches) tall in order to accommodate the whole body
 scanning

 Inclusion Criteria for Participants with a Diagnosis of Probable AD

 -  Diagnosis of probable AD, according to the National Institute of Neurological and
 Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders
 Association criteria

 -  Participants aged >/= 50 years

 -  A study partner able to accompany the participant to all visits and answer questions
 about the participant

 -  MMSE score between 16 and 26, inclusive

 Exclusion Criteria:

 Exclusion Criteria for All Participants

 -  History or presence of a neurological diagnosis other than AD that may influence the
 outcome or analysis of the scan results; examples include but are not limited to
 stroke, traumatic brain injury, space occupying lesions, non-Alzheimer's tauopathies,
 and Parkinson's disease

 -  Participants with a medical history that includes known autosomal dominant AD
 mutations in amyloid precursor protein (APP) or presenilin (PS1, PS2) or mutations in
 genes that cause other types of autosomal dominant familial dementia

 -  History or presence of any clinically relevant hematological, hepatic, respiratory,
 cardiovascular, renal, metabolic, endocrine, or central nervous system disease or
 other medical conditions that are not well controlled, may put the participant at
 risk, could interfere with the objectives of the study, or make the participant
 unsuitable for participation in the study for any other reason in the opinion of the
 principal investigator

 -  Clinically relevant pathological findings in physical examination, electrocardiogram,
 or laboratory values at the screening assessment that could interfere with the
 objectives of the study

 -  Known history of clinically significant infectious disease including acquired
 immunodeficiency syndrome (AIDS) or serological indication of acute/chronic hepatitis
 B or C or human immunodeficiency virus infection

 -  Pregnancy or lactation

 -  Unsuitable veins for repeated venipuncture

 -  Current symptoms of allergy and/or severe allergy to drugs in medical history

 -  Alcohol consumption that averages >3 drinks daily or regular smoker (>10 cigarettes,
 >3 pipefuls, or >3 cigars per day)

 -  Coffee (or tea) consumption >10 cups per day or methylxanthine-containing drinks >1.5
 liters per day (L/day)

 -  Have received an investigational medication within the last 3 months or 5 times (x)
 the elimination half-life, whichever is longer, prior to Day 1 (i.e., enrollment)

 Exclusion Criteria Related to Trial Procedures

 -  Presence of pacemakers; aneurysm clips; artificial heart valves; ear implants; foreign
 metal objects in the eyes, skin, or body, or any other circumstance (e.g.
 claustrophobia) that would contraindicate a magnetic resonance imaging (MRI) scan

 -  For participants of Part 1 and Part 2A, any contraindications to arterial cannulation

 Exclusion Criterion for Participants with Probable Alzheimer's Disease

 -  Has received treatment that targeted amyloid-beta or tau within the last 24 months