The vast majority of patients with clinical concern of biliary colic will have a preceeding ultrasound.   The distal duct is often very difficult to observe well due to obscuration from bowel gas, as is the cystic duct.

In this case a proximal CBD stone and dilated CBD were observed on ultrasound.  MRCP prior to treatment with ERCP revealed a whole lot more than a single CBD stone and demonstrates the exquisite detail offered by MRCP, especially with a 3D volume sequence.