Three- dimensional cerebral angiography is more sensitive for de- tecting aneurysms than 2-dimensional angiography.121,122 The combination of 3- and 2-dimensional cerebral angiography usually provides the best morphological depiction of aneu- rysm anatomy with high spatial resolution, and it is, of course, always used in preparation for endovascular therapy. Flat-panel volumetric CT is a relatively recent develop- ment that allows the generation of CT-like images from a rotational 3-dimensional spin of the x-ray gantry in the angiography room. For the moment, it has no substantial role in the initial diagnosis of aSAH because its spatial and contrast resolutions are not high enough123; however, this technology can be used intraprocedurally during emboliza- tions to rule out hydrocephalus.124 Recently, radiation dose has emerged as an important and worrisome consideration for patients with SAH.125,126 The combination of noncontrast head CT for the diagnosis of aSAH, confirmation of ventric- ulostomy placement, investigation of neurological changes, CTA for aneurysmal diagnosis, CTA and CT perfusion for recognition of vasospasm, and catheter cerebral angiography for aneurysm embolization and then for endovascular therapy of vasospasm can result in substantial radiation doses to the head, with possible risk of radiation injury, such as scalp erythema and alopecia. Although some or all of these radio- logical examinations are often necessary, efforts need to be made to reduce the amount of radiation exposure in patients with aSAH whenever possible. Clinical Manifestations and Diagnosis of aSAH: Recommendations 1. aSAH is a medical emergency that is frequently misdiagnosed. A high level of suspicion for aSAH should exist in patients with acute onset of severe headache (Class I; Level of Evidence B). 2. Acute diagnostic workup should include noncontrast head CT, which, if nondiagnostic, should be followed by lumbar puncture (Class I; Level of Evidence B). 3. 