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(Stroke. 2001;32:958.)
© 2001 American Heart Association, Inc.

Original Contributions

Correlation of Cerebral Hypoxic-Ischemic T2 Changes With Tissue Alterations in Water Content and Protein Extravasation

Min Qiao, MD; Krisztina L. Malisza, PhD; Marc R. Del Bigio, MD, PhD Ursula I. Tuor, PhD

From the Institute for Biodiagnostics, National Research Council Canada (M.Q., K.L.M., U.I.T.), and Department of Pathology, University of Manitoba (M.R. Del B.), Winnipeg, Manitoba, Canada.

Correspondence to Ursula I. Tuor, PhD, Institute for Biodiagnostics, National Research Council, 435 Ellice Ave, Winnipeg, Manitoba, Canada, R3B 1Y6. E-mail Ursula.Tuor{at}nrc.ca

Background and Purpose—Age-dependent changes in T2-weighted MR images have been reported in cerebral hypoxia-ischemia. However, the biophysical mechanisms responsible for the image changes remain poorly defined. We investigated whether cerebral hypoxia-ischemia–induced T2 changes correlate with alterations in either water content or protein extravasation.

Methods—One- and 4-week-old rats were subjected to unilateral carotid artery occlusion plus hypoxia in 8% oxygen. T2 images were acquired before, during, and 1 or 24 hours after hypoxia-ischemia. Blood-brain barrier disruption and brain edema were evaluated by immunohistological detection of IgG extravasation and measurement of water content by dry-wet weight and specific gravity methods.

Results—In 1-week-old rats, T2 values, areas of hyperintensity on T2-weighted images, and water content in the ipsilateral hemisphere increased during hypoxia-ischemia, recovered at 1 hour after hypoxia-ischemia, and increased again at 24 hours after hypoxia-ischemia. Extravasation of IgG occurred during hypoxia-ischemia and remained detectable 24 hours after hypoxia-ischemia. In 4-week-old rats, an increase in T2 or extravasation of IgG did not occur until 24 hours after hypoxia-ischemia despite a comparable elevation in water content during and soon after hypoxia-ischemia.

Conclusions—T2 imaging appears reliable for detecting edema associated with disruption of the blood-brain barrier but not necessarily an increase in cerebral water or plasma proteins alone. The different hypoxic-ischemic changes in T2 in immature and older brain are associated with differences in alterations in water content plus extravasation of protein, consistent with age-dependent differences in hypoxic-ischemic alterations in vascular permeability.

Key Words: blood-brain barrier • brain edema • cerebral ischemia • hypoxia • magnetic resonance imaging

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