الفهرس 
VASCULAR ANATOMY OF THE BRAINOnly 14 pages are availabe for public view
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Abstract
Multi–detector CT of the brain has revolutionized the evaluation of acute ischemic stroke patients. 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.
There are 2 methods of CTP performance: (1) the slow-Infusion/Whole-brain technique, where the entire brain parenchyma can be imaged for the determination of CBV only. MTT and CBF cannot be determined with this method, the actual level of ischemia and distinction between reversible and irreversible ischemia may not be possible with this method. (2) First-Pass Bolus-Tracking methodology, based on monitoring the first pass of a contrast agent bolus through the cerebral vasculature. Contrast agent time-concentration curves are generated. CBF, CBV and MTT are calculated from the changes in the time-concentration curves using a complex mathematical process, then PCT maps are generated.
Using the First-Pass Bolus-Tracking methodology, a limited amount of the brain can be imaged covering 2 to 8 cm of the brain, the whole-brain coverage will be possible in the next few years. The physician should decide what parts of the brain should be scanned and whether one or more than one region should be studied
There are 2 strategies: the common strategy is to study a single anatomic level (slice or slab) at the level of the basal ganglia. Another strategy is to scan more than one anatomic level, based on either clinical findings or prior imaging studies. Each level studied requires a separate infusion of contrast medium usually 40–50 ml of iodinated contrast medium. Total infusion volume should not be greater than 200 ml of iodinated contrast.
For selection of vascular ROI placement, there are 3 available CTP analysis software: the first requires manual placement of vascular input ROIs, the second is fully automated software, the third method combines manual and computer selection and offers advantages of both methods. The physician chooses the arterial input ROI; an initial analysis is done using an artery unaffected by stroke, to help the investigator visually locate areas of hemodynamic disturbance for subsequent study using the obstructed artery.
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.
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.
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 autoregulation. 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.
CTP can provide information about using a new selection criteria of stroke patients for acute treatment: the extent of the infarct core, and the relative extent of penumbra and infarct core. CTP help to exclude patients who have nothing to gain from acute reperfusion therapy, with large infarct core, even in the 0–3 hour.
CTP can assess the microvascular permeability, help in differentiation between infarcts that will develop HT and those that will not, in patients treated with tissue plasminogen activator within 3 hours after symptom onset. PS measurement can be a guide in emergent stroke management.