Final answer:
In postoperative cholangiography, the superior end of the T-tube is placed into the common bile duct, where it meets the main pancreatic duct at the hepatopancreatic ampulla (ampulla of Vater), regulated by the sphincter of Oddi.
Step-by-step explanation:
The superior end of the T-tube is placed into the common bile duct during postoperative cholangiography to assess the ductal structures after gallbladder surgery. This imaging technique involves the introduction of a dye that helps visualize the bile and pancreatic ducts for any abnormalities. The common bile duct, which transports bile from the liver to the duodenum, meets the main pancreatic duct at the hepatopancreatic ampulla (ampulla of Vater), located within the duodenal wall. This important anatomical site is regulated by the sphincter of Oddi, which controls the flow of bile into the duodenum.