الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Cerebral ischemia is interruption of blood flow to a portion of the brain condition in which there is insufficient blood flow to the brain to meet metabolic demand, this leads to poor oxygen supply (cerebral hypoxia), and thus to the death of brain tissue with resulting loss of neurological function.
As thrombolytic therapy with recombinant tissue plasminogen activator (rt-PA) is the treatment of choice for ischaemic stroke presenting within 3hours of clinical onset, early neuroimaging became essential in the diagnosis of cerebral ischemia. Discrimination between infarct core and surrounding potentially salvageable tissue is important so as to better identify patients suitable for treatment.
For imaging of the cerebral parenchyma and exclusion of hemorrhage NCCT, T2* MRI or FLAIR MRI can be used. Detection of cerebral ischemia and exclusion of mimics needs comprehensive CT imaging and DWI. Imaging of cerebral vasculature is done with MRA, CTA, TCD, Carotid duplex, DSA. For imaging of cerebral perfusion and penumbra CT perfusion scan, PWI/DWI, PET, SPECT, and Xenon enhanced CT could be used.
CT is the imaging technique of choice in many institutions for the initial assessment of suspected stroke. Multimodal CT evaluation that combines nonenhanced CT, perfusion CT, and CT angiography has been shown to improve detection of acute infarction, permit assessment of the site of vascular occlusion, the infarct core, salvageable brain tissue.
Multimodal MRI allows estimation of critical parameters essential to manage acute stroke patients. Conventional MR imaging is quite insensitive to the early ischemic change. The FLAIR images are more sensitive to ischemic change than any of the other conventional pulse sequences. Perfusion- and diffusion-weighted MR imaging allow the delineation of the actual ischemic lesion with high sensitivity and specificity. Magnetic resonance angiography (MRA) also allows noninvasive assessment of both the intracranial and extracranial vessels. MRI is the preferred modality for assessment of posterior circulation infarcts.
In acute strokes, TCD can detect arterial occlusion and recanalisation as it is the only diagnostic modality that offers real time monitoring of intracranial vessels. TCD can also provide complementary information to other modalities of imaging. Microemboli detection by TCD may allow identification of the pathophysiological cause of stroke and patients at high risk of further stroke. Carotid ultrasound is a good screening modality for imaging the carotid bifurcation and measuring blood velocities. The main purpose to diagnose carotid artery disease is prevention of stroke in a high risk population. PET is a very useful tool for evaluating the perfusion status of brain tissue, including the hemodynamic and perfusion reserves. PET is used mainly in chronic clinical conditions because it is not possible in the emergency settings. PET/CT systems offers new opportunities for combined imaging approaches for patients with cerebrovascular disease.
SPECT can demonstrate the location, size and extent of the CBF abnormality immediately after the onset of ischemia; however, the detection of the penumbra is difficult because the obtained CBF values are relative perfusion measures in comparison to the contralateral side. Xe CT has been used for quantitative evaluation of CBF in humans. Both need specialized equipment and additional anatomical imaging will be necessary. Competition of those techniques with CT and MR perfusion is likely to remain limited. DSA remains the gold standard against all non-invasive methods of cerebrovascular diseases diagnosis. It is a dynamic study and is a useful tool to visualize slow blood flow through a constricted blood vessel. In addition, cerebral angiography can identify and allow the specialist to treat occluded or narrowed vascular segments.