anti-3-[18F]FACBC is an amino acid based PET radiotracer which has shown utility in detecting a variety of tumors. In cell culture experiments, anti-3-[18F]FACBC has shown uptake in parathyroid cells greater than thyroid cells. Therefore, the investigators think that this radiotracer may be able to help us identify parathyroid adenomas better than 99mTc sestamibi.