الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Cerebro vascular disease is so prevalent as to be the leading cause of neurological disability. Its diverse manifestation are largely accounted for by the anatomical distribution of the stems and branches of the cerebral & brain stem vessels. Because interpretation of the symptoms produced by cerebro vascular accidents requires prior knowledge of brain function. The brain is absolutely dependent on a continuous supply of oxygenated blood. It controls the delivery of blood by sensing the momentary pressure changes in its main arteries of supply ”the internal carotids”. It controls the arterial oxygen tension by monitoring respiratory gas levels in the internal carotid artery and in the CSF beside the medulla oblongata. The control systems used by the brain are equisitely. Sophisticated but they can be brought to nothing if a distributing artery ruptures spontenously or is rammed shut by an embolus. Stroke is defined as the abrupt onset of new neurological abnormalities due to lack of blood flow (ischemia) or bleeding (hemorrhage) in the brain. Approximately 85% of all strokes are ischemic infarction is often caused by diseases of the cerebral blood vessels also can result from primary diseases of the heart or other parts of the body. Classification of infarction: 1. Transient ischemic attacks (TIA’s). Neurologic symptoms or deficits clearing < 24 h. 2. Progressing stroke: Unstable : Progressing neurologic deficits. 3. Completed stroke. Non progressing neurologic deficit. 4. Lacunar infarction: caused by hyaline thickening of small penetrating arteries in subcortical brain and commonly associated with hypertension. An ischemic stroke is caused by occlusion of a blood vessel either within the brain or leading into the brain. The three most common causes of ischemic stroke are athero sclerosis, embolism, hypoperfusion. Other causes of ischemic stroke are lipohyalinolysis, vasculopathies, aypercoagulable states, hemoglobinpathies. The brain normally dervies its energyfrom the oxidative metabolism of glucose. Because there are negligible stores of glucose in the brain, when CBF falls below 20 ml/100g brain/mm, the oxygen extraction fraction becomes maximal and CMRO begins to fall (i.e ischemia). Transient ischemia implies reperfusion. This is the most commonly encountered in embolic cases, when an embolus blocks a vessel, then is lysed with re-establishment of flow. Reperfusion is beneficial if it occurs before CBF levels fall to 10ml/100g/min. Reperfusion can be also beneficial before endothelial cell injury, 3-6 hours post ictus, re-establishes CBF to normal levels, and resolves cytotoxic edema in 3-7 days. Because stroke is common and in the differential diagnosis of most acute neurologic events, diffusion weighted MR imaging should be considered an essential sequence which provides potentially unique information on the viability of brain tissue. It provides image contrast that is dependent on the molecular motion of water, which is substantially altered by disease. Diffusion magnetic resonance imaging provides unique information on the state of living tissue because it gives image contrast that is dependent on the molecular motion of water. Diffusion MRI is the most reliable method for detecting acute ischemia and has assumed an essential role in the detection of acute ischemic brain infarction and in differentiating acute infarction from other disease process. For acute stroke studies, DWI images, expotential images, ADC maps & T2 weighted images should be reviewed. In lesions such as acute ischemic stroke, the T2 & diffusion effects both cause increased signal on the DWI and we identify regions of decreased diffusion best on DWI. The EXP image and ADC maps are used to exclude (T2 shine through) as the cause of increased signal on DWI. Truly decreased diffusion will be hypointense on ADC & hyper intense on expotential images. The EXP image & ADC map are also useful for detecting areas of increased diffusion that may be masked by T2 effects on the DWI. On DWI, regions with elevated diffusion may be slightly hypointense, isointense, or slightly hyperintense, dependending on the strength of the diffusion and T2 components. Regions with elevated diffusion are hyperintense on ADC map & hypointense on EXP image.