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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

Stroke and Brain Parenchyma

Nima Aghaebrahim

August 28, 2008

  • 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
goals of acute stroke imaging
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
it is all about the penumbra
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.
imaging options
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…
diffusion weighted mr
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
  • 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
perfusion weighted imaging
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)
comparison of pwi and dwi
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
significance of pwi dwi mismatch
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
acute stroke in a 67 year old woman with acute left hemiplegia 2 hours after carotid endarterectomy
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.

ct perfusion iodine injection
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
the future
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
  • 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


Thank you