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': 'Investigation of choice for a pregnant lady with upper abdominal mass \nSelect and explain. \nA. Barium meal, B. MRI, C. CT scan, D. DSA', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. MRI', 'role': 'assistant'}]