Early detection of regional cerebral ischemia in cats: Comparison of diffusion‐ and T2‐weighted MRI and spectroscopy

Abstract

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.

Acute changes in extracellular volume fraction in skeletal muscle monitored by23Na NMR spectroscopy

“…Numerous NMR techniques have been proposed for measuring cell volume fraction including water diffusion and T 2 weighted sequences (Moseley et al. 1990) or using an extracellular contrast agent like Gd‐DTPA (Mulkern et al. 1989).…”

Late stimulation of the sphenopalatine‐ganglion in ischemic rats: Improvement in N‐acetyl‐aspartate levels and diffusion weighted imaging characteristics as seen by MR

“…MRI and MR spectroscopy (MRS) are widely used for investigating, in vivo, neurological disorders in general, and ischemic stroke in particular (17)(18)(19). The versatility of the MR technique enables noninvasive studying of not only the progression of neurological pathology during longitudinal follow-up, but also the evaluation of the pathophysiologic state of the studied tissue, without the need of animal sacrificing.…”

“…Apparent diffusion coefficient (ADC) maps, calculated from DWI, may be used to evaluate infarct size as well as tissue condition, and were found to correlate with infarct sizes evaluated from histology (20,21). The acute stage of the ischemic stroke is characterized, inter alia, by cellular swelling (cytotoxic edema) and increase in the extracellular tortuosity that reduces the ADC of the water molecules in the ischemic region (17,18). In the chronic stage of ischemic stroke, high ADC values (compared with the contralateral regions) are observed for the infarct area as a result of the necrotic process that includes cells death and membrane loss (22).…”

Identification of Collaterally Perfused Areas following Focal Cerebral Ischemia in the Rat by Comparison of Gradient Echo and Diffusion-Weighted MRI

“…, 1994). After 24 h this area constitutes the region destined to necrosis (Moseley et al, 1990;Minematsu et al, 1992), i. e. , the isch emic focus.…”