An elderly patient presented with sudden onset of headache and altered sensorium, is diagnosed to have Subarachnoid hemorrhage. What is the best investigation of choice in this case?

(A) CT Scan # Subarachnoid hemorrhage (SAH) implies the presence of blood within the subarachnoid space from some pathologic process.> Initial study of choice is an urgent CT scan without contrast CT also can detect intracerebral hemorrhage, mass effect, and hydrocephalus. A falsely negative CT scan can result from severe anemia or small-volume SAH.> Cerebral angiography is performed once the SAH diagnosis is made.> This study assesses the following: Vascular anatomy Current bleeding site Presence of other aneurysms> Magnetic resonance imaging (MRI) is performed if no lesion is found on angiography.