Correlation of cerebral hypoxic-ischemic T2 changes with tissue alterations in water content and protein extravasation.
OBJECTIVE
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.
Qiao
M
M
Institute for Biodiagnostics, National Research Council Canada, Department of Pathology, University of Manitoba, Winnipeg, Manitoba, Canada.
Malisza
K L
KL
Del Bigio
M R
MR
Tuor
U I
UI
D000367:Age Factors; D000375:Aging / Q000378:metabolism; D000818:Animals; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism / Q000473:pathology; D001923:Brain Chemistry; D001929:Brain Edema / Q000378:metabolism; D004195:Disease Models, Animal; D006801:Humans; D020925:Hypoxia-Ischemia, Brain / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D007074:Immunoglobulin G / Q000032:analysis / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D009929:Organ Size; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D013046:Specific Gravity; D014867:Water / Q000032:analysis / Q000378:metabolism*
D007074:Immunoglobulin G; D014867:Water