Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na⁺,K⁺ -ATPase Activity

Abstract

Summary: Diffusion-weighted magnetic resonance (MR) images from rats during acute cerebral ischemia induced by middle cerebral artery occlusion were analyzed for correspondence with changes in brain water, cation con centrations , and Na + ,K + -ATPase activity measured in vitro after 30 or 60 min of ischemia. In the ischemic hemi sphere, signal intensity was increased at 30 min (p < 0.05 vs contralateral hemisphere) and further increased at 60 min. Na + ,K + -ATPase activity was 34% lower in isch emic cortex and 40% lower in ischemic basal ganglia after 30 min (p < 0.05), but water content and Na + and K + concentrations were not significantly different between Diffusion-weighted magnetic resonance (MR) im aging can detect less severe and potentially revers ible cerebral ischemia much earlier than conven tional T2-weighted MR imaging (Moseley et aI., 1990; Mintorovitch et aI., 1991; Minematsu et aI., 1992; van Bruggen et aI., 1992 Abbreviations used: ADC, apparent diffusion coefficient; ANOV A, analysis of variance; MCA, middle cerebral artery; MR, magnetic resonance; TE, echo time; TR, repetition time. 332hemispheres. After 60 min , water content and Na + con centration were increased , and both Na + ,K + -ATPase activity and K + concentration were decreased in the ischemic hemisphere (p < 0.05). These findings are con sistent with the hypothesis that the early onset of signal hyperintensity in diffusion-weighted MR images may re flect cellular edema associated with impaired membrane pump function. Early in vivo detection and localization of potentially reversible ischemic cerebral edema may have important research and clinical applications.

Correlation of early reduction in the apparent diffusion coefficient of water with blood flow reduction during middle cerebral artery occlusion in rats

“…The size of the ADC 15 area corresponded best to the size of the CBF 25 area, as indicated by the mean square difference results in Table 1. Comparisons between the ADC 15 areas and the CBF 15 , CBF 25 , and CBF 50 areas are shown in the graphs of Fig.…”

“…2. The ADC 15 area and the area of substantially reduced blood flow showed close anatomical correspondence in all rats examined. In most rats subjected to 30 min of ischemia, the ADC 15 areas were limited to the basal ganglia; a large region of reduced ADC, occupying the entire MCA distribution as in the image on the right, was observed in only two rats.…”

“…CBF rates were estimated with a method that corrects for the "wash-out" volume of blood in the arterial and venous catheters (25). The percent of ischemic hemisphere with CBF rates less than 15,20,25,30,35,40, and 50 m1/100 g/min (CBF 15 , CBF 20 , CBF 25 , CBF 30 , CBF 35 , CBF 40 , and CBF 50 ) was determined for three sections from within the 2-mm thick slice of the MR images. Reported results are the mean of the three measurements.…”

“…Second, intracerebral administration of ouabain to induce focal ATPdependent sodium-potassium pump failure resulted in hyperintensity on D-MR images (7). Third, hyperintense regions on D-MR images had higher total sodium and tissue water content and lower Na + /K + ATPase activity (15). Acute cellular energy failure during ischemia in rats occurs when cerebral blood flow (CBF) is below approximately 20 m1/100 g/min (16).…”

Evolution of lesion volume in acute stroke treated by intravenous t‐PA

“…Both animal (1,12) and human studies (2,13,14) have highlighted its ability to detect early the ischemic lesion with better sensitivity than other conventional MRI techniques (15,16). Even without a complete understanding of the biophysical background, it is certain that an acute increase of DWI signal intensity during ischemia is due to a failure of ion pumps and anoxic cell membrane depolarization with a subsequent water shift from the extracellular to the intracellular space, which, in turn, causes cell swelling (17). This so-called "cytotoxic edema," with containment in the intracellular space, induces a translational movement of water particles that decrease, with a reduced apparent diffusion coefficient (ADC) (18,19).…”