The technical advances in computed tomography (CT) and magnetic resonance (MR) have increased the utilization of noninvasive studies for both diagnosis and treatment assessment of numerous central nervous system (CNS) lesions amenable to endovascular therapy. Multidetector CT (MDCT) scanners with real-time workstations have enabled computed tomography angiography (CTA) to become the preferred initial diagnostic study to evaluate for suspected aneurysms in the setting of acute subarachnoid hemorrhage (SAH) with excellent delineation of aneurysm morphology and follow-up of related complications. In the setting of acute ischemia, noninvasive imaging using CT or MR play critical roles in the initial assessment of the ischemic tissue and help in the appropriate selection for inclusion or exclusion of patients for more aggressive intervention. The chapter discusses about the role of CT and MR in the diagnosis of carotid artery disease, acute arterial infarctions, subarachnoid hemorrhage, arteriovenous malformations, and dural arteriovenous fistula.