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
Best test to determine etiology of SAH – 
Select and explain. 
A. Enhanced CT, B. Unenhanced CT, C. Intra arterial digital substraction angiography, D. MRI
C: Intra arterial digital substraction angiography
Answer: C: Intra arterial digital substraction angiography 
Explanation: Investigation of choice to know the etiology of SAH is four vessels digital substraction angiography.