This imaging method is used to ensure that no gallstones remain in the bile duct after a cholecystectomy, the surgical removal of the gallbladder. During the surgery, a T-shaped rubber tube is placed into the bile duct and left there. About a week later, a contrast medium is injected into the tube, followed by X-ray imaging. If no gallstones are found, the tube is removed. If stones are present, they can either be extracted via ERCP or dissolved through a solvent administered through the tube.