This study will examine the use of a new radioactive tracer called [18F]FECNT in positron emission tomography (PET) scanning for measuring dopamine transporter (DAT) in the brain. DAT is found in brain neurons (nerve cells) that release the chemical messenger dopamine. By taking pictures of the DAT, scientists hope to learn more about the function of these neurons.

Normal, healthy volunteers between 18 and 65 years of age may be eligible for this study. Candidates are screened with a medical history and physical examination, psychological assessment, and blood and urine tests.

Subjects enrolled in the study participate in one of the following procedures:

Brain Imaging Study: Part 1

Two catheters (small plastic tubes) are placed into veins in the subject's arms for injecting [18F]FECNT and for collecting blood samples during the scan. A third catheter is placed into a wrist artery to obtain arterial blood during the scan. With the catheters in place, the subject lies down on the scanner bed with his or her head placed in a special mask that limits movement during the brain scan. The scan begins with an initial x-ray like picture for about 10 minutes, after which the [18F]FECNT is injected and the actual PET scan starts. The entire procedure takes about 6 hours, including 2 hours of continuous scanning sessions, during which the subject is required to lie still. Subjects can relax out of the scanner between scans. They are monitored throughout the procedure. Vital signs are measured and electrocardiogram is taken once before and twice after injection of the tracer. At the end of the scanning, additional blood and urine samples are collected. Subjects are asked to urinate every 2 hours to lessen the radioactivity in the body.

Whole Body Imaging Study: Part 2

For this procedure, a catheter is placed in a vein for injecting the [18F]FECNT tracer. A total of five scans are taken, each one spanning from head to upper thigh. During the course of the scans, x-ray like pictures are obtained. The first scan takes about 100 minutes. Four additional 1-hour scans are done every 100 minutes. The total time for the scans is about 6 hours, and the total time for the entire procedure is about 9 hours. About 2 tablespoons of blood are drawn by needle stick at one time during the imaging. Subjects can leave the PET scanner between scans. They are asked to urinate every 2 hours for 6 hours from the time of tracer injection and to collect all the urine so that radioactivity can be measured.

Brain Imaging Study: Part 3

Part 3 of the study is the same as Part 1, except that two PET procedures are done on separate days, the second within 4 weeks of the first. In addition, participants may also under magnetic resonance imaging (MRI) scanning, a test that uses magnetic fields and radio waves to obtain pictures of the brain.