This study will test dihydrotetrabenazine, or 11C-DTBZ, a radioactive tracer, as an imaging agent in positron emission tomography (PET). That tracer may have the ability to noninvasively measure beta cell, that is, -cell mass (BCM) in humans. For researchers hoping to develop new treatments for diabetes mellitus, a method of measuring BCM is very important. In this study, researchers will determine if patients with Type 1 diabetes mellitus, who have almost no BCM, have much less pancreatic uptake of the tracer than do patients without diabetes. Patients ages 18 and older may be eligible for this study. Three groups will be studied: Participants who have Type 1 diabetes, those without diabetes, and those who have been successfully treated with a transplant of the pancreas or pancreas and kidney

The study involves three sets of tests that can be done as an outpatient or after being admitted to the hospital. Patients will undergo a medical history and procedures including collection of blood (about 4 teaspoons), pregnancy test for women of childbearing age, magnetic resonance imaging (MRI) scan, PET scan, and tests involving arginine and glucose. Arginine is a substance that stimulates insulin release from the -cells. During the procedure, two intravenous (IV) lines are placed into the arms, one to administer arginine and the other to draw blood (about eight samples during 10 minutes). For the glucose test, patients will drink a solution of dextrose, a sugar, and blood samples will be taken over 2 hours from the IV lines. Some patients experience nausea after drinking the solution. Within 48 hours of either test or both, patients will be placed in the PET scan machine and given an injection of the radioactive material through an IV line. Blood samples of about one-half teaspoon will be drawn before the procedure starts and again every 10 seconds for the first 2 minutes and at several intervals, up to 60 minutes. Finally, patients will also an MRI scan, 30 to 60 minutes long, of the abdomen. This test will be down within two weeks of the PET scan. MRI uses a strong magnetic field and radio waves to obtain images of body organs and tissues. During the scan, patients will be asked to lie still on a table that slides into the tunnel of the scanner. They will be given earplugs, for the machine can be noisy. Patients who have metal within their body that is not compatible with the MRI machine will be withdrawn from the study.