Final answer:
A Cholangiocath is the instrument used to instill contrast media into the biliary system intraoperatively, aiding in the visualization of the bile ducts to diagnose conditions like biliary tree obstructions.
Step-by-step explanation:
The instrument used to instill contrast media into the biliary system intraoperatively is a Cholangiocath. This catheter is specifically designed for accessing the biliary tract to help visualize the structure of the bile ducts during procedures such as endoscopic retrograde cholangiopancreatography (ERCP). ERCP involves placing a tube down the throat, into the stomach, and then into the small intestine, where dye is injected to make the ducts of the gallbladder, liver, and pancreas visible on an X-ray. A Cholangiocath serves a similar purpose intraoperatively by directly injecting the contrast media into the bile ducts. This helps in diagnosing conditions such as biliary tree obstruction, where there is a blockage preventing the excretion of bile pigments.