Bile duct cancer. Coloured angiogram (X-ray) of a patient's common bile duct (green, centre right) that has been blocked by cancer. The cancer (not seen) has caused a narrowing, or stricture, of the duct. A stent (fine mesh tube, lower frame) has been permanently inserted into the duct to correct the stricture. A tube (catheter) inside the stent will be removed when fluid has drained from the duct. Bile fluid, secreted by the liver cells, emulsifies ingested fats. It drains into the small intestine through the common bile duct when food enters the intestine. A contrast medium injected into the duct makes it visible on X-ray.