Radiation-induced Parotid Injury Evaluated By Magnetic Resonance Imaging In Minipigs

Part 1 Build the radiation-induced parotid injury model with minipigsObjective: Build the radiation-induced parotid injury model with minipigs, and evaluate the chanes of general condition and parotid glands structure in minipig.Methods: 9 minipigs were randomly divided into control group(3) and radiotherapy group(6). Radiotherapy group minipigs were subjected 20 Gy to one parotid gland with a linear accelerator。Observe the general condition of minipigs, and compare the parotid gland structure of control groupand radiotherapy group.Results: Radiotherapy group minipigs were shown diet decline and weight loss. Irradiated parotid glands showed reduction of acinarsize and number, inflammatory cell infiltration, an increase in adipose tissue, and interstitial fibrosis, indicating atrophy and degeneration of parenchymal cells. And the radiated side was more seriously.Coclusion: Sigle does irradiatin to parotid gland would induce injury which shown an obviously pathologic change. Non-radiated side would be damaged at the same time.Part 2 The role of MRI evaluation of radiationinduce parotid injury in the minipigsThesis 1 MRI 3D reconstruction and volume measurement in evaluating radiation-induce parotid injuryObjective: MRI 3D reconstruction and volume measurement were performed through mimics software, and explore the change of parotid volume after radiotheraphy.Methods: Control group and radiotheraphy group minipigs were performed MRI scan pre-irradiation, 2 weeks and 4 weeks postirradiation. Using mimics software for parotid gland T2 WI images 3D reconstruction and volume measurement, and compare the changes of the parotid volume at different time points.Results: Radiated side and non-radiated side of parotid volume in radiotheraphy group minipigs were shrinked(t were-6.642 and-6.880, and P were 0.007 and 0.006, respectively) at 2 weeks after radiotherapy. The shrinkage of radiated side was more than non-radiated side(47.13±7.10 ml VS 25.55±7.43 ml, t=4.563,P=0.02). Radiotheraphy group protid volume at 4weeks post-irradiation have no significant difference with ones at 2weeks post-irradiation(t were-1.030 and-1.956, and P were 0.379 and 0.145, respectively). There was no obvious volume change in control group.Conclusion: Mimics software can evaluate parotid gland volume change simply and quickly. Parotid shrinkage was occurred mainly in 2 weeks after radiotherapy, and it is does-related.Thesis 2 Intravoxel incoherent motion diffusion weighted imaging in evaluating radiation-induce parotid injuryObjective: Explore the feasibility of Intravoxel incoherent motion diffusion weighted imaging(IVIM-DWI) in evaluating pathologic change in of radiation-induce parotid injury.Methods: Control group and radiotheraphy group minipigs were performed IVIM-DWI scan at pre-irradiation, 2 weeks and 4 weeks post-irradiation. Compare the changes of the D, D* and f at different time points. And compare the correlations between acinar cell density and D, MVD and D*, MVD and f.Results: Pearson correlation analysis results show that the acinar cell density and the D value showed a negative correlation(r = 0.567, P = 0.014), microvascular density values were positively correlated with the D*(r = 0.846, P = 0.000). However, the microvascular density was not related with f values. D values of both side of adiotheraphy group minipigs were increased gradually, and D* values were decreased gradually.Conclusion: IVIM-DWI evaluates pathologic change in of radiationinduce parotid injury is feasible, D can reflect Acinar cell damage, and D* can reflect the vascular endothelial injury.Thesis 3 The feasibility of IDEAL-IQ quantitative evaluation of chanes of fat fraction content in radiation-induce parotid injuryObjective: Explore the feasibility of IDEAL-IQ quantitative evaluation of chanes of fat fraction content in radiation-induce parotid injury.Methods: Control group and radiotheraphy group minipigs were performed IDEAL-IQ scan at pre-irradiation, 2 weeks and 4 weeks post-irradiation. Compare the changes of the fat fraction at different time points. And compare the correlations between the amount of fat cells and fat fraction.Results: Pearson correlation analysis results show that the the amount of fat cells and fat fraction showed a positive correlation(r = 0.567, P = 0.014. Fat fractions of both side of radiotheraphy group minipigs were increased gradually, the fat fractions at 2 weeks post-irradiation were similar with ones pre-irradiation. Fat fractions of radiotheraphy group at 4 weeks post-irradiation were higher than the ones preirradiation and 2 weeks post-irradiation(Radiated side: t=3.397,P=0.019 and t=2.750,P=0.040; non-radiated side: 3.380,P=0.020 and t=3.404,P=0.019).Conclusion: The IDEAL- IQ sequence can reflect the change of parotid gland fat after radiation injury. According to the change of fat fraction, it is implied that parotid gland hyperplasia of fat mainly after 2 weeks post-irradiation.Thesis 4 The role of SWAN evaluation of vascular injury in parotid post-irradiationObjective: Explore the role of SWAN evaluation of vascular injury in parotid post-irradiation.Methods: Control group and radiotheraphy group minipigs were performed SWAN scan at pre-irradiation, 2 weeks and 4 weeks postirradiation. Compare the changes of intraparotid susceptibility signal intensity(IPSS) and the largest diameter of veins at different time points. And compare the correlations between MVD and IPSS.Results: Pearson correlation analysis results show that MVD and IPSS showed a positive correlation(r=0.643,P<0.01). IPSS of both side of radiotheraphy group minipigs were decreased gradually, the ones at 4 weeks post-irradiation were lower than the ones preirradiation(Radiated side: t=-2.714,P=0.042;non-radiated:t=-2.982, P=0.031). There is no obvious change in the largest diameter of veins.Conclusion: SWAN can reflect the change of the microvascular density, and evaluatie parotid gland vascular endothelial damage after radiotherapy.