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': 'IOC for determing the etiology of sub arachnoid hemorrhage \nSelect and explain. \nA. Non - contrast CT, B. CECT, C. Four vessel DSA, D. MRI', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Four vessels (Both carotid and both vertebral) digital subtraction angiography is the IOC for determing the etiology of SAH.', 'role': 'assistant'}]