Another new technique, dual-energy CTA, has diag- nostic image quality at a lower radiation dose than digital subtraction CTA and high diagnostic accuracy compared with 3-dimensional DSA (but not 2-dimensional DSA) in the detection of intracranial aneurysms.113 Cerebral angiography is still widely used in the investiga- tion of aSAH and the characterization of ruptured cerebral aneurysms. Although CTA is sometimes considered suffi- cient on its own when an aneurysm will be treated with surgical clipping,114 substantial controversy remains about the ability of CTA to determine whether or not an aneurysm is amenable to endovascular therapy.115 120 In 1 series,115 95.7% of patients with aSAH were referred for treatment on the basis of CTA. In 4.4% of patients, CTA did not provide enough information to determine the best treatment, and those patients required DSA; 61.4% of patients were referred to endovascular treatment on the basis of CTA; and successful coiling was achieved in 92.6%. The authors concluded that CTA with a 64-slice scanner is an accurate tool for detecting and characterizing aneurysms in acute aSAH and that CTA is useful in deciding whether to coil or clip an aneurysm.115 Partial volume averaging phenomena may artificially widen the aneurysmal neck and may lead to the erroneous conclu- sion that an aneurysm cannot be treated by endovascular coiling. This controversy is likely caused by the different technological specifications (16- versus 64-detector rows), slice thickness, and data processing algorithms of various CT systems, which have different spatial resolutions. 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. 