A Preliminary Study On The Value Of Intravoxel Incoherent Motion Of MRI In Evaluating The Injury Of Submandibular Giand Radiotherapy In Mini-pigs

Objective To establish a model of radiation damage of submandibular glands of mini-pigs,explore the correlation between the MR-IVIM parameters and pathology to Evaluat the value of intravoxel incoherent motion in radiotherapy of submandibular glands of minipigs.Methods Nine Guangxi Bama minipigs were randomly divided into radiotherapy group A,B and control group respectively,each group had 3minipigs.Before the Magnetic resonance examination and irradiation,all minipigs were anesthetized by ketamine hydrochloride and midazolam.The intramuscular injection site was an insertion point about 2cm from the midline of the back of the small pig's left ear,and the intramuscular anesthesia was used.Before irradiation,all minipigs were examined with MRI-IVIM,then bilateral submandibular glands were irradiated with a corresponding beam dose using a linear accelerator,then observe the general signs of the minipigs within four weeks after irradiation.On the fourth weekend after irradiation,all minipigs were scanned by MRI-IVIM again.The parameters of IVIM(D,D~*and f)of three groups of miniature pig submandibular glands at different time points were statistically analyzed.At the end of the examination,the above-mentioned minipigs were subjected to air embolization via the ear vein and the minipig's submandibular gland tissue was removed for pathological HE staining and immunohistochemical staining.The difference was compared between the experimental groups and the control group.Finally the correlation between D and percentage of acinar area,D*and the microvessel density(MVD),f and the microvessel density(MVD)were analyzed.Results IVIM parameter analysis,The D and f of group A and group B were higher than those in control group,but D~*were lower than those in control group,the differences among the three groups by single-factor analysis of variance were statistically significant(P<0.05);The f-values has statistical difference between group A and group B(P<0.05).Pathological HE staining revealed that the serous cells in the submandibular glands of the irradiated group were atrophied,the glandular volume became smaller,the eosinophilic cytoplasm of the acinar cells changed,and the nucleus was pyknosis;the changes of the mucinous glands were small;the interstitial fibrous tissue was hyperplastic,Lymphocyte infiltration.The structure of the submandibular gland in the control group showed completeness.Pathological parameter analysis,compared with the control group,the percentage of acinar area and microvessel density in the irradiated group A and B were statistically different,and the acinar area of the irradiated group A and the irradiated group B also had statistically significant differences,the reduction of the percentage of the acini area was more than 10%compared with the control group.Spearman rank correlation analysis showed negative correlation between the D and the percentage of acinar area(r=-0.639,P=0.004).The D~*was positively correlated with the microvessel density(MVD)(r=0.767,P<0.000).The f was negative correlated with the microvessel density(MVD)(r=-0.631,P=0.005).Conclusions It is feasible to establish the radiotherapy injury model of submandibular gland by small pigs.Ketamine hydrochloride combined with midazolam injection anesthesia,can meet the needs of the experiment.The submandibular glands of minipigs were irradiated with high-dose radiation at a single time.In the irradiation group,minipigs submandibular glands all exhibited varying degrees of radiation injury.The MR-IVIM can reflect the pathological changes of submandibular gland radiation damage to some extent.