The purpose of this study is to determine the effectiveness of fluorodeoxyglucose (FDG) as a direct means of detecting patients with acute cholecystitis. FDG is an imaging agent that has previously been shown to accumulate in areas of infection and/or inflammation. The location and intensity of FDG accumulation in the body can be detected with a camera system called a "positron emission tomography" (PET) camera. In theory, this test should be effective in detecting acute infection and/or inflammation of the gallbladder.