Answer
Answer
Two-dimensional (2D) TOF MRA also depends on the relative contrast between flowing blood and stationary tissue; it provides better images than 3D TOF in slow-flow regions. 2D TOF images correlate well with carotid angiography images in depicting cervical bifurcation disease. Their disadvantages, however, are the significant artifacts (eg, stepladder) that often occur, which may obscure vessel details, and the longer scanning time.
The modified TOF MRA technique, which uses multiple overlapping thin slab acquisitions (MOTSA), combines the advantages of 2D and 3D TOF techniques. It is very helpful in demonstrating severe stenosis, although the degree of stenosis might be slightly overestimated.
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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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