This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Anatomy
[{'content': 'Initial investigation of choice for biliary obstruction \nSelect and explain. \nA. CT abdomen, B. ERCP, C. MRCP, D. USG', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ultrasonography Initial imaging modality of choice in obstructive jaundice It is operator dependent and may be suboptimal due to excessive body fat and intraluminal bowel gas USG can demonstrate Biliary calculi Size of GB and CBD Thickness of GB wall Presence of inflammation around GB Occasionally, presence of stones within the biliary tree Ref: Sabiston 20th edition Pgno : 1487', 'role': 'assistant'}]