Diffusion‐weighted MR images were compared with T2‐weighted MR images and correlated with 1H spin‐echo and 31P MR Spectroscopy for 6‐8 h following a unilateral middle cerebral and bilateral carotid artery occlusion in eight cats. Diffusion‐weighted images using strong gradient strengths (b values of 1413 s/mm2) displayed a significant relative hyperintensity in ischemic regions as early as 45 min after onset of ischemia whereas T2‐weighted spin‐echo images failed to clearly demonstrate brain injury up to 2‐3 h postocclusion. Signal intensity ratios (SIR) of ischemic to normal tissues were greater in the diffusion‐weighted images at all times than in either TE 80 or TE 160 ms T2‐weighted MR images. Diffusion‐ and T2‐weighted SIR did not correlate for the first 1‐2 h postocclusion. Good correlation was found between diffusion‐weighted SIR and ischemic disturbances of energy metabolism as detected by 31P and 1H MR Spectroscopy. Diffusion‐weighted hyperintensity in ischemic tissues may be temperature‐related, due to rapid accumulation of diffusion‐restricted water in the intracellular space (cytotoxic edema) resulting from the breakdown of the transmembrane pump and/or to microscopic brain pulsations. © 1990 Academic Press, Inc.
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