The easiest way to confirm the presence of gallstones is by performing a fasting ultrasound examination of the gallbladder. The patient refrains from eating for 6 hours to ensure the gallbladder is well distended and there is little shadowing from overlying bowel gas. The examination may also identify bile duct dilation and the presence of cholecystitis. Magnetic resonance cholangiopancreatography (MRCP) is another way to image the gallbladder and biliary tree. MRCP uses fluid present in the bile ducts and in the pancreatic duct as a contrast agent to show stones as well as filling defects within the gallbladder and intrahepatic or extrahepatic bile ducts. It can demonstrate strictures in the biliary tree and can also be used to visualize liver and pancreatic anatomy (Fig. 4.118).