The Correlative Study Of Perfusion MR Imaging And Pathology In Radiation-induced Brain Injury

Objective:To research the change regulation of Magnetic resonance perfusion weighted imaging (MR-PWI) and pathology in different stages of radiation-induced brain injury and to investigate the correlation between the relative cerebral blood volume (rCBV) ratios and vascular endothelial growth factor (VEGF)Material and Methods:Thirty maturity rats were randomly divided into two groups: control and radiation group. The control group was not to be irradiated. The radiation group were irradiated the whole brain by6Mev electron beam at a single dose of20Gy. The control group rats were performed with MRI and MR-PWI examination at first. The irradiation group rats were performed with MRI, MR-PWI at1,3,6,9,12month respectively after radiation. The brains were removed immediately after the MRI examination to make paraffin section, HE staining-. immunohistochemical staining of vascular endothelial growth factor (VEGF) and electron microscopy were performed. MR-PWI examination mainly measure the relative cerebral blood volume (rCBV)^mean transit time (MTT)、time to peak (TTP) of the white matter surrounding the bilateral cerebral ventricle. We observed the absorbance of VEGF in immunohistochemical staining, the changes of vascular morphology、structure and density in HE staining and the changes of tiny structures of vessel in electron microscopy, including the vascular cavity、basement membrane.Results:①The rCBV ratios and the absorbance of VEGF in the irradiation area decreased gradually after irradiation, but the MTT and TTP ratios increased gradually.②The rCBV、MTT and TTP ratios at the first month after irradiation showed no significant statistical difference compared with control group. The rCBV ratios began to decrease, while the MTT and TTP ratios increase in other radiation groups from the third month. Compared with control group, their differences was statistical meaning.③The absorbance of VEGF at the first month after irradiation showed no significant statistical difference compared with control group. From the third month, the absorbance of VEGF began to decrease gradually in other radiation groups. Compared with control group, the differences of VEGF was statistical meaning.④The rCBV positively correlated with the VEGF (r=0.94), the differences was statistical meaning.Conclusion:MR-PWI examination can directly reflect the pathophysiological changes of brain tissue after the irradiation. But the VEGF can indirectly reflect its pathophy-siological changes. The rCBV positively correlated with the VEGF. The decreased expression of VEGF results in the reduction of the microvascular network. The decreased microvascular network further results in the hypoperfusion. The hypoperfusion named the rCBV ratios decreased. The decreased expression of VEGF plays a critical role in the pathogenesis of radiation-induced brain injury.