Diagnosis of Gallbladder and Bile Duct Tumors Ultrasonography (sometimes endoscopic), followed by CT cholangiography or magnetic resonance cholangiopancreatography (MRCP) Sometimes endoscopic retrograde cholangiopancreatography (ERCP) Cholangiocarcinomas and gallbladder carcinomas are suspected when extrahepatic biliary obstruction is unexplained.