الفهرس 
ANATOMY OF THE CEREBRAL VASCULATUREOnly 14 pages are availabe for public view
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Abstract
Stroke imaging and intervention are advancing at a dramatic and revolutionary era. Triage of acute stroke patients and choice of treatment are increasingly driven by advanced imaging findings.
Stroke imaging serves two purposes: First, to diagnose or confirm the occurrence of a stroke and, second, to assess the amount of potentially salvageable brain tissue and irreversibly infarcted tissue; both are necessary, the first for planning management strategy and the second for prognostication.
CT has the advantage of being available 24 hours a day and is the gold standard for hemorrhage. Hemorrhage on MR images can be quite confusing. On CT 60% of infarcts are seen within 3-6 hrs and virtually all are seen in 24 hours. The overall sensitivity of CT to diagnose stroke is 64% and the specificity is 85%.
Currently, multimodal CT indicates the combined use of NCCT, CTP, and CTA techniques in order to image the entire cerebrovascular axis and obtain a complete picture about the extension of ischemic damage in acute stroke patients in around 10 minutes.
NCCT has classically been used as the standard initial imaging examination for acute stroke patients. Unfortunately, NCCT provides solely anatomic, not physiological information and thus has low sensitivity for acute stroke detection during the first few hours of stroke. Also, it is of limited value in terms of showing the extent of cerebral hypoperfusion.
CT perfusion imaging is one of the techniques widely applied for assessing perfusion abnormalities of patients with acute stroke. It is useful for prediction of the initial severity of clinical symptoms, the extent of final infarction, and clinical outcomes.
For diagnosis of acute ischemic stroke, a set of three perfusion parameter maps is required: CBF, CBV and MTT or TTP. The lesion size on CBV maps is always smaller than the perfusion deficit, as shown on the CBF maps due to cerebral auto regulation. This CBF/CBV mismatch is a hallmark of peri-infarct ischemia which indicates the potentially salvageable brain tissue (penumbra). The irreversible infracted core on CTP maps show marked decrease of CBF paralleled by severe reduction of CBV. CTP also can assess the spontaneous recanalization of the occluded artery suggested by marked elevation of CBF and CBV.
CT perfusion combined with CTA are complementary modalities. The role of CTA is to reveal the status of large cervical and intracranial arteries and thereby help define the occlusion site, depict arterial dissection, grade collateral blood flow, and characterize atherosclerotic disease