This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Medicine
[{'content': "HIDA scan is useful in: \nSelect and explain. \nA. Acute cholecystitis, B. Meckel's diveiculum, C. Colonic angio-dysplasia, D. Diveiculitis", 'role': 'user'}, {'content': 'Answer: A \nExplanation: HIDA Scan: 99mTc hepatobiliary imaging (using iminodiacetic acid compounds), also known as the HIDA scan. is useful in demonstrating an obstructed cystic duct, which is the cause of acute cholecystitis in most patients.', 'role': 'assistant'}]