<prompt> A patient with a history of choledocholithiasis presents with elevated conjugated bilirubin. Ultrasound reveals a dilated biliary system up to the terminal pa. In case of suspicion of an ampullary obstructive calculus which of the following investigations would be most sensitive?PTCMRCPX-ray abdomenEndoscopic USG  <response>: Endoscopic USG - Most sensitive method to detect ampullary stones. EUS sensitivity of 93.7 to detect choledocholithiasis. Magnetic resonance cholangiopancreatography MRCP is also highly sensitive 90 with an almost 100 specificity for the diagnosis of common duct stones.Advantages of EUS is it can be followed up with ERCP immediately.An advantage of MRCP is completely non-invasiveSabiston 20th edition pg 1521 