Imaging of CB1 Receptors Using (11C)SD5024

Background: \- The cannabinoid type 1 (CB1) receptor is a protein found on some brain cells. It may play a role in obesity or some psychiatric disorders such as schizophrenia. Imaging studies like positron emission tomography (PET) can show where CB1 receptors are located. A new radioactive chemical, 11C-SD5024, may be able to show these receptors more clearly than previous radioactive chemicals. Better images of CB1 receptors in the brain may help improve our understanding of obesity and psychiatric disorders. This information may lead to better treatments. Objectives: \- To test how well a new radioactive chemical, 11C-SD5024, is taken up by the brain during imaging studies. Eligibility: \- Healthy volunteers between 18 and 50 years of age who are able to have positron emission tomography scans. Design: * All participants will be screened with a physical exam, medical history, and blood tests. * Participants will be in one of three groups for the study. Each group will receive 11C-SD5024 and have a different set of imaging studies. * Group 1 will have a magnetic resonance imaging (MRI) scan and PET scan of the brain. They will also have blood and urine tests. * Group 2 will have a whole-body PET scan, as well as blood and urine tests. * Group 3 will have an MRI scan of the brain, followed by two PET scans of the brain. They will also have blood and urine tests. The two PET scans can happen on the same day or on two different days.