The Comparative Study Of Acute Radiation Microvascular Injury In The Rat Submandibular Gland: Diagnostic Performance Of Intravoxel Incoherent Motion

Objective A model of acute radiation injury in rats was established.To evaluate the diagnostic value of intravoxel incoherent motion（IVIM）in acute radiation microvascular injury of submandibular gland in rats.Methods Twenty female SD rats were randomly divided into control group（n=4）and irradiation group（n=16）.A compound anesthetic agent configured by ketamine hydrochloride combined with midazolam was used to administer intramuscular anesthesia using the medial thigh muscle of the right lower limb of the rat as the injection point.Then the two groups of rats were placed under an electron linear accelerator.The irradiation dose of the bilateral submandibular glands in the irradiation group was 15 Gy,while the control group was not irradiated.The control group underwent routine MR and IVIM scans immediately after the radiotherapy examination.The irradiation group was randomly divided into 4 groups,each 4 rats as a group,and each group was named 2h after irradiation,6h after irradiation,12h after irradiation,and 24h after irradiation.Routine magnetic resonance（MR）and IVIM scans were performed at 4h,6h,12h,and 24h after irradiation in irradiation group respectively.Both submandibular gland specimens were taken from the rats immediately after the end of the MRI examination.Submandibular gland tissues are processed in the following order:fixation,dehydration,transparency,paraffin embedding,and sectioning.Immunohistochemical staining of the prepared sections,and then counting the microvessel density（MVD）under the microscope.The statistical methods of analysis of variance and Pearson correlation were used to analyze and compare the differences of IVIM parameters（D value,D*value and f value）and MVD between the submandibular glands of each group,and analyze the correlation between MVD and IVIM parameters.Results（1）Comparison of MVD between the irradiation group and the control group:The MVD value of the group 2h after irradiation of the submandibular gland in rats was slightly higher than that of the control group,but the difference was not statistically significant（P=0.473）;The MVD value of the group 6h after irradiation was significantly reduced compared with the control group,the difference was statistically significant（P<0.001）,and it was the lowest among the five groups;The MVD value of the groups 12h and 24h after irradiation were lower than of the control group(P_12h=0.004,P_24h=0.004),the difference were statistically significant.（2）Comparison of IVIM parameters（D values,D*values and f values）between the irradiation group and the control group:The D value of the irradiation group was lower than that of the control group(P_2h=0.043,P_6h=0.035,P_12h<0.001,P_24h<0.001).In other words,the D value began to decrease at 2h after irradiation,and the D value of the groups 6h,12h,and 24h after irradiation continued to decrease.There were no significant differences in the D*value and f value of the submandibular glands in the five groups of rats（P=0.266 and P=0.111,respectively）.（3）Correlation analysis between MVD and IVIM parameters:MVD has positive correlation with D value（r=0.345,P=0.046）.MVD has no correlation with D*value（r=-0.153,P=0.386）.MVD has no correlation with f value（r=-0.205,P=0.244）.Conclusion（1）The change of MVD in the submandibular glands of rats with acute radiation injury has certain regularity.The D value in the imaging parameters of IVIM has a statistical correlation with the change of MVD in the submandibular glands of rats with acute radiation injury.Therefore,the D value in the IVIM imaging parameters can be used as a monitoring and evaluation index for acute radiation injury of the submandibular gland in rats.（2）IVIM imaging technology is expected to become an effective technique for noninvasive,quantitative,and dynamic evaluation of acute submandibular gland injury in rats.