This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Brain Imaging: Anatomy, Trauma, and Tumors, Subject name: Radiology
[{'content': 'Investigation of choice for acute SAH is? \nSelect and explain. \nA. DSA, B. X ray, C. CT scan, D. MRI', 'role': 'user'}, {'content': 'Answer: C \nExplanation: ANSWER: (C) CT scan REF: Sutton 7th ed p. 1779See APPENDIX-66 for "INVESTIGATION OF CHOICE"SUBARACHNOID HEMORRHAGEInvestigation of choice : non contrast CT scanIf scan fails : lumbar puncture to establish blood in CSFMost sensitive investigation for evaluating etiology : DSA of four vessels (carotids and vertebrals)Most common intracranial lesion after head injury: sub dural hematomaMost common cause of sub arachnoid hemorrhage: head traumaMost common cause of spontaneous SAH: ruptured aneurysmHEMATOMA ON CT SCAN:Epidural hematoma: biconvex or lens shaped, hyperdense (acute 2/3), hypodense ( chronic 1/3)Subdural hematoma: crescent, hyperdense (< 2 weeks), isodense (2-4 weeks ), hypodense (> 4 weeks)', 'role': 'assistant'}]