Sodium Time Course Using 23Na MRI in Reversible Focal Brain Ischemia in the Monkey

Purpose: To demonstrate the use of sodium MRI for measuring the time course of tissue sodium concentration (TSC) in a nonhuman primate model of reversible focal brain ischemia. Materials and Methods: Reversible endovascular focal brain ischemia was induced in nonhuman primates (n = 4), and sodium MRI was performed on a 3 Tesla scanner for monitoring changes in TSC during both the middle cerebral artery (MCA) occlusion and MCA reperfusion portions of the experiment. Results: The TSC increased linearly in the ischemic tissue during MCA occlusion (ranging from a mean TSC increase of 5.44%/h to 7.15%/h across the four subjects), and then there was a statistically significant change from a positive TSC slope during MCA occlusion to a TSC slope after MCA reperfusion that was not statistically different from zero. The linear increase in sodium MRI during brain ischemia was used to estimate the stroke onset time to within 0.45 h in each of the four subjects (with a maximum 95% confidence interval of +/- 1.147 h). Conclusion: The data indicate that sodium MRI increases linearly during brain ischemia, and that this increase is stopped by tissue reperfusion within 5.4 h after stroke onset.