Answer
Answer
Magnetic resonance angiography (MRA) is very sensitive to flow and is based on the difference in signal between moving blood and stationary brain tissue; angiographic-like images of the cervicocranial vasculature are produced.
MRA images are a useful tool in identifying dissections, in that the true and false lumen of the involved artery can be observed on the source images. Following is a brief description of the 2 basic techniques.
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Media Gallery
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Magnetic resonance imaging in acute stroke. Left: Diffusion-weighted MRI in acute ischemic stroke performed 35 minutes after symptom onset. Right: Apparent diffusion coefficient (ADC) map obtained from the same patient at the same time.
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Magnetic resonance imaging in acute stroke. Left: Perfusion-weighted MRI of a patient who presented 1 hour after onset of stroke symptoms. Right: Mean transfer time (MTT) map of the same patient.
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Magnetic resonance imaging in acute stroke. Diffusion-perfusion mismatch in acute ischemic stroke. The perfusion abnormality (right) is larger than the diffusion abnormality (left), indicating the ischemic penumbra, which is at risk of infarction.
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The diffusion-weighted MRI reveals a region of hypointensity in the distribution of the right middle cerebral artery. Flanking the anterior and posterior regions of this abnormality are regions of hyperintensities, which represent regions of new infarct. The contiguity of these regions suggests that they are extensions of the old infarct.
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