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Stroke and Brain Parenchyma

Stroke and Brain Parenchyma. Nima Aghaebrahim August 28, 2008. Stroke. Third leading cause of death and leading cause of disability in the U.S. Incidence: 700,000 per year and increasing about one stroke every minute Every 3.3 minutes, someone dies of a stroke Goal of imaging:

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Stroke and Brain Parenchyma

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  1. Stroke and Brain Parenchyma Nima Aghaebrahim August 28, 2008

  2. Stroke • Third leading cause of death and leading cause of disability in the U.S. • Incidence: 700,000 per year and increasing • about one stroke every minute • Every 3.3 minutes, someone dies of a stroke • Goal of imaging: • Establish diagnosis fast • Obtain accurate information regarding intracranial vasculature and brain perfusion • Appropriate therapy

  3. Goals of Acute Stroke Imaging • 4 Ps • Parenchyma: • Assess early sign of acute stroke, rule out hemorrhage (unenhanced CT) • Pipes: • Assess extracranial circulation (carotid and vertebral arteries of the neck) • Assess intracranial circulation for evidence of intravascular thrombus • Perfusion: • Assess Cerebral blood volume, cerebral blood flow, and mean transit time • Penumbra: • assess tissue at risk of dying if ischemia continues without recanalization of intravaslular thrombus

  4. It is all about the Penumbra! • When a cerebral artery is occluded, a core of brain tissue dies rapidly (irreversible) • Surrounding this infarct core is an area of brain that is hypoperfused but does not die quickly, because of collateral blood flow, • This surrounding area is penumbra (salvageable) • Its fate depend on the reperfusion of the ischemic brain • Will also die unless early recanalization is present • Thrombolysis via tPA, thrombus removal, etc.

  5. Imaging options • Unenhanced CT: rule out hemorrhage • Not very good to detect ischemia • T1 or T2 weighted MRI • Good for detecting ischemia • Cannot differentiate between acute versus chronic ischemia • So we have…

  6. Diffusion-weighted MR • More sensitive for detection of hyperacutre ischemia • becomes abnormal within 30 minutes • Distinguish b/w old and new stroke • New stroke: bright on DWI • Old stroke: Low SI on DWI • It detects irreversible infarcted tissue

  7. Physiology • Ischemia  shortage of metabolites • Na+/K+ channel failure in the cell • Cause cytotoxic edema: shift of water into intracellular compartment • Leads to a narrowing of the extracellular matrix • Restricted diffusion of water within the cell • Increase signal which can be measured with DWI

  8. MRIOLD –VS- NEW ISCHEMIC INFARCT T1 T2 DIFFUSION

  9. Perfusion-Weighted imaging • Allows the measurement of capillary perfusion of the brain • Uses a MR contrast agent • The contrast bolus passage causes a nonlinear signal decrease in proportion to the perfusion cerebral blood volume • Meaning, it can identify areas of hypoperfusion, the reversible ischemia, as well (unlike DWI)

  10. Comparison of PWI and DWI • DWI  irreversibly damaged infarct • PWI  reflects the complete area of hypoperfusion • The volume difference between these two, the PWI/DWI mismatch would be the PENUMBRA! • If there is no difference in PWI and DWI, no penumbra is present

  11. Significance of PWI/DWI mismatch • IV thrombolytic treatment is not typically administered to patients with acute stroke beyond 3-hrs period • Risk of hemorrhage • However, recent studies have shown that IV thrombolytic therapy may benefit patients who are carefully selected according to PWI/DWI mismatch, beyond 3-hrs window

  12. Acute stroke in a 67-year-old woman with acuteleft hemiplegia 2 hours after carotidendarterectomy. (a) Diffusion- weighted MR image shows an area of mildly increased signal intensity in the right parietal lobe (arrows). The ADC values in this region were decreased. (b) Perfusion-weighted MR image shows a larger area with increased time to peak enhancement (arrows) in the right cerebral hemisphere. The mismatch between the perfusion and diffusion images is indicative of a large penumbra.

  13. CT PERFUSIONIodine Injection • CT angiography (CTA) and Perfusion CT (PCT) also provide information regarding vessel patency and the hemodynamic repercussions of a possible vessel occlusion • More widely available • Lower cost

  14. The Future • More effective selection of patient for thrombolytic therapy • PWI/DWI mismatch rather than time of onset as sole determinant of selection • MR permeability imaging: based on dynamic contrast-enhanced imaging • Allows quantization of defects in the blood-brain barrier, who have increased risk of hemorrhagic transformation with thrombolytic therapy

  15. Conclusion • Current imaging techniques can be used to identify hyperacutre stroke and guide therapy • PWI/DWI mismatch would be a good tool to identify a target group who would benefit from early reperfusion • Both CT and MR imaging are useful for the comprehensive evaluation of acute stroke

  16. Questions? Thank you

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