<prompt> IOC for sub-arachnoid hemorrhageCT scanMRILumbar punctureMRA  <response>: Ans. a CT scanRef.: Harrison 19th ed. 1786 The diagnosis of subarachnoid hemorrhage SAH usually depends on a high index of clinical suspicion combined with radiologic confirmation via urgent computed tomography CT scan without contrast. Traditionally, a negative CT scan is followed with lumbar puncture LP. However, non-contrast CT followed by CT angiography CTA of the brain can rule out SAH with greater than 99 sensitivity. 