We have developed a novel device for the quantification of swelling of cells in acute brain slices. We can also carry out detailed real-time monitoring of hippocampal cells. The device we developed is based on an infrared differential interference contrast microscopy (IR-DIC) and a custom-made real-time computerized image analysis system for the quantification of the morphological dynamics of cells in slice preparations. We applied the coefficient of variation (CV) of light intensity in IR-DIC images to quantify the change in morphological dynamics. There were notable close relationships among the edema formations, the light transmittance, extent of changes in CV, and features of fEPSP during ischemic insult. We also applied this method for the evaluation of neuroprotective effects of mannitol. The dose-dependent improvement on the deteriorated hippocampal slices could be obtained by administration of mannitol (10, 50, and 100 mM) after 10-min ischemia. The present results indicate that CV is a reliable quantification index for edema formation of brain tissue and confirm that applying CV for the analysis in addition to the light transmittance analysis presents additional important information on brain tissue sweling.