Preoperative imaging identification and localization of adrenocorticotropin hormone (ACTH)-secreting pituitary adenomas is critical for the accurate diagnosis and the successful surgical treatment of Cushing s disease (CD). Unfortunately, over 40 percent of CD patients do not have a visible pituitary adenoma on magnetic resonance (MR)-imaging (the most sensitive imaging modality for ACTH-positive adenoma detection and localization). Lack of MR-imaging for diagnosis and to guide surgical resection results in significantly higher rates of surgical failure compared to cases associated with adenomas visible on MR-imaging. Because ACTH-adenomas are metabolically active compared to the surrounding pituitary gland, (18)F-fludeoxyglucose ((18)F-FDG) positron emission tomography (PET)-imaging in CD patients could be used to detect adenomas not detectable on MR-imaging. Moreover, corticotropin-releasing hormone (CRH) can be given to selectively increase the metabolic activity of ACTH-secreting pituitary adenomas to increase the likelihood of their detection and localization by (18)F-FDG PET-imaging. To determine the effect of CRH stimulation on (18)F-FDG uptake using PET-imaging in CD, we will perform (18)F-FDG high-resolution PET-imaging (with and without CRH stimulation) in CD patients.