(18F)FCWAY and the Blood-Brain Barrier

Background: \- The blood-brain barrier helps protect the brain from infections and toxins in the blood stream. But it can also prevent certain drugs from reaching the brain to treat diseases or other problems. Researchers are interested in chemicals that will help show how the barrier works. One possible chemical, (18F)FCWAY, may be useful for studying the barrier. More tests are needed to determine how effective it is. Objectives: \- To test whether (18F)FCWAY can be used to help study the blood-brain barrier. Eligibility: \- Healthy volunteers between 18 and 50 years of age. Design: * This study requires a screening visit and two scanning visits. * Participants will be screened with a physical exam and medical history. They will also have blood and urine tests. * At the first scanning visit, participants will have a magnetic resonance imaging scan to provide baseline images of the brain. * Before the second visit, some participants will stay overnight in the hospital. They will receive the drug tariquidar, which may help the (18F)FCWAY show the blood-brain barrier more clearly. * At the second scanning visit, all participants will have a positron emission tomography scan with (18F)FCWAY to see how well the drug shows the blood-brain barrier on the scan.