This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'Radiation is not used in: \nSelect and explain. \nA. CAT scan, B. NMR, C. Digital substraction imaging, D. Thyroid scan', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. NMR', 'role': 'assistant'}]