ObjectiveBoth ischemic stroke and traumatic brain injury are common and main causes for brain injury, and brain edema, which succeeds after the two causes, is closely related to the patient's state of severity and his prognosis. In order to observe the changes of edema at these two pathological states and seek a non-invasive method for measuring brain edema appropriate for the two types of brain injury, this study uses the models of intraluminal occlusion of the rat's middle cerebral artery (MCAO) and of impact-acceleration brain injury, and by analyzing the correlation between regional brain water content and MRI parameters, it observes the occurrence and development ofbrain edema at the two pathological states, and meanwhile seeks the index in vivo for measuring brain water content of tissue.MethodsBrain water content of parietal cortex and striatum tissues are measured with specific gravity (SG). By comparing SG changes of both frozen tissue samples and fresh samples it is to determine the sampling methods' effect on measurement of specific gravity of tissue. By mock-up the control group of the two models it is to establish the equation of transformation from SGt to BWC so as to prepare for the successive experiment.MCAO model is set up with middle cerebral artery occlusion by intraluminal block. Rats are randomly divided into 4 groups: control group, acute ischemic group, intra-magnetic field control group and intra-magnetic field ischemic group. By observing physiological parameters and changes of BWC of the 4 groups it is to analyze the possible effect of rats' body posture, head-mounting and high field MR on thoseparameters. TI and ADC during two hours' cerebral ischemia are observed with horizontal 7 Tesla magnet equipped a 200 mT/m gradient coil, and BWC is measured after 2 hours' ischemia in vitro and the correlation between TI and BWC is analyzed.The traumatic brain injury model is created by impact-acceleration. Rats are randomized into four groups: control group, TBI 8-hours group, TBI 24-hours group and TBI 8-hours group with the measurement of MRI. The changes of BWC in the first three groups are dynamically observed. The correlation between TI and BWC is analyzed by continuously measuring TI and ADC during 8 hours after TBI, and measuring BWC at the end of 8 hours after TBI. Rat's endothelial barrier antigen (EBA) and Collagen-type IV at the different states of edema is examined with immunohistochemistry with double markers and staining with fluorescence. HE staining is conducted and histology's changes are observed.ResultsIt is found that post-freezing sampling may cause net increase 0.34% of BWC by comparing the fresh brain tissue, measured with SG. In comparison with the method of wet-to-dry weight ratio in the same model of TBI, the method of SG decreases the diversity of BWC results by 50%.Rats' body posture, head-mounting and high field MR within two hours have no significant effect on rats' physiological parameters and BWC. Permanent ischemia significantly lengthens TI after one hour and ADC apparently decreases after one hour and three quarters. The length of TI after two hours' permanent ischemia has correlation in height with the increase of BWC.The rat at first has no evident changes of physiological parameters after TBI, and has a slight edema at the end of 24 hours after TBI; however the rat with hypotension has evident edema at 8 hours post-trauma and its increase of BWC has a correlation with the lengthen of TI. The result of immunohistochemistry shows that the densities of EBA and of Collagen IV in the rat with severe brain injury have decreased significantly compared with the rat with slight edema.Conclusions1 , The specific gravity in vitro for measurement of BWC is characteristic of requirement of small sample size and high sensitivity. It also has a definite advantage of measuring BWC in different zone of brain and with different pathological changes.2, Rats' body posture, head-mounting and high field MR within two hours have no significant effec