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': 'Best test to determine etiology of SAH \nSelect and explain. \nA. Enhanced CT, B. Unenhanced CT, C. Intra aerial digital Substraction Angiography, D. MRI', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Intra aerial digital Substraction Once dx is done by CT Scan; digital substraction angiography (DSA) is done to determine etiology. DSA is most sensitive & best inv. for determining etiologyQ. Now DSA is being replaced by noninvasive methods as MRA (MRI - angiography) & CTA (CT - Angiography).', 'role': 'assistant'}]