Noninvasive quantification of brain edema and the space-occupying effect in rat stroke models using magnetic resonance imaging.

BACKGROUND AND PURPOSE Brain edema is a life-threatening consequence of stroke and leads to an extension of the affected tissue. The space-occupying effect due to brain edema can be quantified in rat stroke models with the use of MRI. The present study was performed to test 2 hypotheses: (1) Can quantification of the space-occupying effect due to brain edema serve as a noninvasive measure for brain water content? (2) Does morphometric assessment of brain swelling allow determination of true infarct size on MRI after correction for the space-occupying effect of edema? METHODS Thirty rats were subjected to permanent suture middle cerebral artery occlusion. MRI was performed after 6 or 24 hours, and hemispheric swelling was assessed morphometrically. Interobserver and intraobserver agreements were determined for MRI measurements. In study I, the space-occupying effect due to brain edema was correlated with the absolute brain water content by the wet/dry method. In study II, lesion volumes corrected and uncorrected for edema were calculated on MRI and on TTC staining and compared. RESULTS Interobserver and intraobserver agreements for MRI measurements were excellent (r>or=0.97). Brain water content and hemispheric swelling correlated well after 6 and 24 hours (r>or=0.95). Corrected lesion volumes correlated with r=0.78 between TTC staining and MRI. Without edema correction, lesion volumes were overestimated by 20.3% after 6 hours and by 29.6% after 24 hours of ischemia. CONCLUSIONS Morphometric assessment of hemispheric swelling on MRI can determine the increase in absolute brain water content noninvasively and can also provide ischemic lesion volumes corrected for brain edema.