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?

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