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': 'Optium phase for cardiac and coronary vessel imaging are \nSelect and explain. \nA. Early systole, B. Mid-diastole, C. Early diastole, D. Late diastole', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Optimum phase for cardiac and coronary vessel image is\xa0\n\nMid-diastole at low or intermediate heart rates.\nLate-systole - at high heart rates.', 'role': 'assistant'}]