This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gallbladder, Subject name: Surgery
Investigation of choice in suspected gallbladder stone is: 
Select and explain. 
A. Ultrasound, B. X-ray, C. Barium study, D. Oral cholecystography
A: Ultrasound
Answer: A: Ultrasound 
Explanation: USG is IOC for acute calculous cholecyctitis, chronic cholecystitis and cholilithiasis 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.