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Medical News & Perspectives |

Improved Stroke Imaging Techniques

Pat Phillips
JAMA. 1999;281(22):2073-2074. doi:10.1001/jama.281.22.2073.
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Venice—Neuroimaging is beginning to come into its own for the precise diagnosis of stroke and, potentially, for determining and monitoring stroke therapy.

The integrated diffusion-perfusion MRI examination provides metabolic and hemodynamic information during the first critical hours after a stroke. A 24-second DWI protocol using high-speed echo-planar MRI sequences acquired 4 hours after onset of symptoms in a 64-year-old man (lying on his side) shows no clear lesion on the T2-weighted (nondiffusion-weighted) MRI scans. The corresponding diffusion-weighted and apparent diffusion coefficient (ADC) images clearly highlight the location and extent of the lesion. The hallmark of cerebral ischemia is the lower-than-normal ADC value, indicating slower-than-normal water proton diffusion within the acute lesion resulting from decreased metabolism and impaired cellular pumps. The 80-second perfusion-weighted (contrast bolus-tracking) protocol yields relative cerebral blood volume (rCBV), mean transit time (rMTT), and blood flow (rCBF) parametric maps that depict a large hemispheric increase in contrast bolus transit and a decrease in blood flow, indicative of a diffusion-perfusion "mismatch" and a potential worsening of the attack, as more of the perfusion deficit is recruited by the lesion. (Photo credit: Michael E. Moseley, PhD, Stanford University School of Medicine)

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The integrated diffusion-perfusion MRI examination provides metabolic and hemodynamic information during the first critical hours after a stroke. A 24-second DWI protocol using high-speed echo-planar MRI sequences acquired 4 hours after onset of symptoms in a 64-year-old man (lying on his side) shows no clear lesion on the T2-weighted (nondiffusion-weighted) MRI scans. The corresponding diffusion-weighted and apparent diffusion coefficient (ADC) images clearly highlight the location and extent of the lesion. The hallmark of cerebral ischemia is the lower-than-normal ADC value, indicating slower-than-normal water proton diffusion within the acute lesion resulting from decreased metabolism and impaired cellular pumps. The 80-second perfusion-weighted (contrast bolus-tracking) protocol yields relative cerebral blood volume (rCBV), mean transit time (rMTT), and blood flow (rCBF) parametric maps that depict a large hemispheric increase in contrast bolus transit and a decrease in blood flow, indicative of a diffusion-perfusion "mismatch" and a potential worsening of the attack, as more of the perfusion deficit is recruited by the lesion. (Photo credit: Michael E. Moseley, PhD, Stanford University School of Medicine)

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