Proton NMR relaxation times in ischemic brain edema.

The state of water in cerebral ischemia was studied by using the proton nuclear magnetic resonance (1H-NMR) method. Cerebral ischemia was induced experimentally in Mongolian gerbils by unilateral ligation of the common carotid artery. Longitudinal (T1) and transverse (T2) relaxation times of the ischemic brain were measured with a pulse FT-NMR spectrometer and the water content was determined by the wet/dry method. Quantitative analysis of the relaxation times was performed sequentially during the initial 7 hours following ligation and the data were compared with those of brain edema previously reported by S. Naruse in the rat. Characteristic findings in brain ischemia include prolongation of the slow component of T2 and increase in the water content. A quantitative comparison of relaxation rate and water content demonstrates that ischemic brain edema in Mongolian gerbils is different from cytotoxic and vasogenic types of brain edema. When R2 (1/T2) was plotted against the water content, the slope value of ischemia in the gerbil was between the slope values of the TET intoxication and cold injury induced edemas reported previously. From these results, it might be said that ischemic brain edema includes both the cytotoxic and vasogenic types of brain edema. Glycerol was demonstrated to affect brain ischemia by decreasing the water content and by shortening the slow component of T2. By analysis of the relaxation times and water content, we examined the pathophysiological characteristics of water molecules in ischemic brain tissue.