This is an investigational study. Gas insufflation and glucagon are FDA approved for use with CT colonography (colonoscopy that uses CT scanning), which is typically used to screen for colon cancer. PET/CT scanning is FDA approved for use in checking the status of mantle cell lymphoma. Using PET/CT scanning to detect mantle cell lymphoma in the colon, however, is investigational. For this purpose, at this time PET/CT scanning is being used in research only.