Use of [18F] Fluoroethyl-L-tyrosine PET/MRI for Identifying Small Functional Pituitary Adenomas

Inclusion Criteria: * Patients 18 to 75 years of age with biochemically proven CD, Acromegaly, or tumor hyperprolactinemia as per current Endocrinology guidelines. * Clinical DCE-MRI protocol that is negative or equivocal for identifiable tumor. * Patient willing to have surgery if lesion found, or already scheduled for surgery and lesion identification would be helpful. * Able to provide informed consent and be capable of completing the imaging protocols. * Female subjects of childbearing potential (women of childbearing potential \[WOCBP\]) must have a negative urine pregnancy test ≤48 hours prior to the 18F-FET injection. Exclusion Criteria: * Patients with contraindications to MRI or PET scans. * Patients with known allergies to contrast agents or other imaging-related materials. * Patients with severe medical conditions that preclude participation in the study (e.g. inability to lie supine for 30-60 minutes). * Patients with successful MRI localization of the adenoma.