Objective To evaluate the feasibility of MR PWI in judging maturity and variability of tumor vasculature in gliomas in rats.Methods Twenty male SD rats were randomly assigned to tumor group and control group.Four weeks after implantation of C6 glioma cells in the brains of tumor group and injection of saline in the brains of control group,all rats were examined using MR PWI before and after inhalation of a mixture of 10% CO2 and 90%air.PaCO2 and blood pH values of rats were monitored.Relative cerebral blood volume(rCBV)and relative cerebral blood flow(rCBF)values of tumors and normal brain tissue were measured.Brain sample were examined histologically using HE and immunohistochemical staining for smooth muscle actin(SMA).The histological features of gliomas were observed and SMA positively stained vessels of each tumor were counted manually using a light microscope.Perfusion data and pathological findings were analyzed statistically with SPSS for Windows.Results PaCO2 increased significantly[from(4.69±0.62)kPa to(7.62±0.81)kPa in tumor group and from(4.67±0.51)kPa to(7.63±0.78)kPa in control group,P＜0.05)after inhalation of the mixed gas.The rCBV and rCBF values of tumor core were remarkably greater than those of normal contralateral brain tissue.The increasing rate of rCBV and rCBF values in gliomas[(26±17)%and(26±18)%respectively]were significantly less than those in normal brain tissue[(90±32)%and(45±14)%repectively](t=5.05 and 2.355,P＜0.05)Immunohistochemical staining of 10 tumors as well as contralateral brain tissue all demonstrated positive SMA expression in the smooth muscles of the vessels.The vascular walls of positive SMA labeled vessels within tumors were thinner and their vascular lumen wider than those within normal brain tissues.The number of SMA(+)vessels in tumors[(6.7±2.8)/HP]was statistically less than that in contralateral brain tissue[(12.7±2.8)/HP](t=1.86,P＜0.01).Changing rate of rCBV,rCBF of the tumor cores and number of the positive SMA labeled vessels showed no correlation(r=0.504 and 0.607,P＞0.05),while changing rate of rCBV,rCBF in normal brain tissue correlated well with number of positive SMA labeled vessels(r=0.721 and 0.525,P＜0.05).Conclusion PWI can detect the hemodynamic change induced by PaCO2 increase in the normal brain and in the tumor.It may be a useful technique to measure maturity of tumor vessels.