Endoscopic retrograde cholangiopancreatography (ERCP):  

Endoscopic retrograde cholangiopancreatography (ERCP) is a technique that combines the use of endoscopy and fluoroscopy to diagnose and treat certain problems of the biliary or pancreatic ductal systems. Through the endoscope, the physician can see the inside of the stomach and duodenum, and inject dyes into the ducts in the biliary tree and pancreas so they can be seen on x-rays.
ERCP is used primarily to diagnose and treat conditions of the bile ducts, including gallstones, inflammatory strictures (scars), leaks (from trauma and surgery), and cancer.

The patient is sedated or anaesthetized. Then a flexible camera (endoscope) is inserted through the mouth, down the esophagus, into the stomach, through the pylorus into the duodenum where the ampulla of Vater (the opening of the common bile duct and pancreatic duct) exists. The sphincter of Oddi is a muscular valve that controls the opening of the ampulla. The region can be directly visualized with the endoscopic camera while various procedures are performed. A plastic catheter or cannula is inserted through the ampulla, and radiocontrast is injected into the bile ducts, and/or, pancreatic duct. Fluoroscopy is used to look for blockages, or other lesions such as stones.
When needed, the opening of the ampulla can be enlarged with an electrified wire (sphincterotome) and access into the bile duct obtained so that gallstones may be removed or other therapy performed.
Other procedures associated with ERCP include the trawling of the common bile duct with a basket or balloon to remove gallstones and the insertion of a plastic stent to assist the drainage of bile. Also, the pancreatic duct can be cannulated and stents be inserted. The pancreatic duct requires visualisation in cases of pancreatitis.
In specific cases, a second camera can be inserted through the channel of the first endoscope. This is termed duodenoscope-assisted cholangiopancreatoscopy (DACP) or mother-daughter ERCP. The daughter scope can be used to administer direct electrohydraulic lithotripsy to break up stones, or to help in diagnosis by directly visualizing the duct (as opposed to obtaining X-ray images).