The Study Of Radiation-Induced Brain And Optic Nerve Injury By Functional Magnetic Resonance Imaging

Objective:Acute radiation injury is serious that requires prompt and accurate diagnosis and assessment.Currently,there is no effective imaging method to evaluate acute radiation injury in the early stage.We used multi-modal MRI to evaluate acute radiation-induced brain injury.Methods:Different extents of brain injury were created by exposing SD rats to different radiation doses,namely,0,10,20,30 and 40 Gy.DCE-MRI,IVIM-MRI and MRS were performed on the 5th day after irradiation.The parameters Ktrans,Ve,Vp,and iAUC from DCE-MRI,S0,f,and D*from IVIM-MRI,and the parameters NAA/Cho,NAA/Cr and Cho/Cr from MRS were measured.The correlation between quantitative parameters and radiation dose levels was analyzed using the Spearman's rank correlation.The area under the receiver operating characteristic curve(ROC)was used to test the diagnostic value of each quantitative parameter to determine the degree of radiation damage.Immunohistochemistry,Western blot and electron microscopy were used to determine histopathological changes in neurons and glial cells.Results:For DCE,as the radiation dose increased,Ktrans,Ve,Vp,and iAUC increased significantly.For IVIM,as the radiation dose increased,SO,f,and D*also increased significantly.The values of Ktrans,Ve,iAUC in DCE,and S0,f,D*in IVIM in the 30 Gy group were significantly higher than those in the other groups(P<0.05).The Ktrans,Ve,and iAUC values in DCE and the S0,f and D*values in IVIM showed significant positive correlations with radiation injury grade.In particular,Ktrans,iAUC and S0 showed very good correlations with injury grade(r>0.5,P<0.05),and the values in the 30 Gy group were significantly higher than those in the other groups(P<0.05).MRS showed that the NAA/Cr ratio in the 30 Gy group was significantly lower than those in the other groups(P<0.05),and the NAA/Cho ratio was significantly decreased(P<0.05);the Cho/Cr ratios of the 20 Gy and 30 Gy groups were higher than 0 Gy and 10 Gy group(P<0.05).Western blot showed that as the irradiation dose increased from 10 Gy to 30 Gy,the expression of VEGF in the cerebral cortex increased,which was more pronounced in the 20 Gy and 30 Gy groups(P<0.05),and the expression of caspase-3 was increased,which was more obvious in the 30 Gy group(P<0.05).Immunohistochemical staining with GFAP showed a significant increase in the number of astrocytes in the 20 Gy and 30 Gy groups(P<0.05).MBP staining showed no significant difference between the control group and each irradiation group(P>0.05).Electron microscopy showed that mild myelinated vacuoles were observed in the 10 Gy group,exacerbations of myelinated vacuoles and cytoplasmic edema were observed in the 20 Gy group,and neuronal morphology was significantly abnormal in the 30 Gy group,with nuclear condensation and mitochondrial atrophy.ROC analysis demonstrated that the quantitative parameters of DCE,IVIM,and MRS were more effective for diagnosing the 30 Gy group than it was for the 10 Gy and 20 Gy groupsConclusion:Multi-modal MRI can noninvasively evaluate acute radiation-induced brain injury in the early stage,particularly high-dose radiation exposure.Objective:Radiation brain damage in craniocerebral tumors could induce radiation brain damage.When the hippocampus is damaged,it will lead to the decline of the neurocognitive function of the patients,which seriously affects the patient's quality of life and is more serious for young children.In this study,the radiation-induced brain injury in juvenile rats was used as a model to investigate the changes of inflammasomes,pyroptosis and apoptosis in the hippocampus during the acute and early delayed phases of radiation injury.And we used manganese-enhanced magnetic resonance imaging(MEMRI)to assess hese changes.Methods:Sixty 4-week-old male SD rats were divided into a control group(0 Gy)and two experimental groups(15 Gy and 25 Gy).The experimental group received a single dose of 15 Gy and 25 Gy whole brain irradiation.MEMRI and MRS examinations were performed 4 days and 8 weeks after the irradiation,respectively.The manganese enhanced signal intensity(SI)and metabolite changes in hippocampaus were measured.After MRI examination,the expression of inflammasomes AIM2,GSDMD,NLRP1 and NLRP3 and apoptotic proteins cleaved caspase-1 and cleaved caspase-3 in hippocampal tissue were detected by Western blot.ELISA was used to detect the expression of inflammatory factors IL-1? and IL-18 in hippocampus.Transmission electron microscopy was used to observe the ultrastracture of apoptosis.Results:In both the 15 Gy and 25 Gy groups,inflammasomes including AIM2,GSDMD,NLRP1 and NLRP3 showed no significant changes at 4 days or 8 weeks after radiation injury(P>0.05).The expression levels of inflammatory cytokines interleukin-1?(IL-1? and interleukin-18(IL-18)were not significantly different among the groups(P>0.05).The expression levels of cleaved caspase-1 and-3,indicators of apoptosis,were significantly higher in the irradiation groups than in the control group at 4 days post irradiation,especially cleaved caspase-3(P<0.05).The expressions of cleaved caspase-1 and cleaved caspase-3 decreased at 8 weeks after irradiation,but cleaved caspase-3 was still significantly higher than that of the control group(P<0.05).MEMRI showed no significant difference in SI between the left hippocampus and the right hippocampus of the rats in each group(P>0.05).Four days post irradiation,the SI decreased significantly,especially in the 25 Gy group(P<0.05).Eight weeks after radiation injury,the SI of the 15 Gy group and the 25 Gy group recovered by different degrees,but the SI of the 25 Gy group was still significantly lower than that of the control group(P<0.05).On day 4 post irradiation,the metabolic ratio of NAA/Cr in the 15 Gy group and the 25 Gy group was significantly lower than that in the control group(P<0.05).The NAA/Cr ratio in the 15 Gy group recovered to control levels at 8 weeks(P>0.05),but the NAA/Cr ratio in the 25 Gy group remained significantly lower than that in the control group(P<0.05).Electron microscopy results showed that the number of apoptotic neurons in the 25 Gy group was more than that in the 15 Gy group at 4 and 8 weeks after irradiation.Apoptosis at 4 days after irradiation was more obvious than that at 8 weeks after irradiation,and pyroptosis was observed at neither time point.Conclusion:Radiation-induced brain injury is associated with apoptosis but not inflammasomes or pyroptosis,and the change in neuropathy can be detected by MEMRI.Objective:Radiation-induced optic neuropathy(RION)is a serious complication after radiation therapy of tumor in the vicinity of optic nerve,yet knowledge of its mechanism and imaging performance are poorly understood.In this study,we employed manganese-enhanced MRI(MEMRI)to assess optic nerve axonal transport in tree shrews and rats after irradiation.Methods:Study 1:Comparison of the optic pathway between tree shrews and rats by MEMRI.The eyeballs,lens,retinal thickness,optic nerve width,vitreous cavity volume,and superior colliculus area of normal adult tree shrews and rats were measured on MEMRI.Study 2:Longitudinal MEMRI of optic nerve axonal transport after radiation injury.To evaluate MEMRI as a tool for monitoring radiation-induced optic nerve axonal transport impairment,tree shrews and rats were monitored by longitudinal MEMRI for 5,10,20 or 30 weeks after receiving 20 Gy(10 Gy each time,5 days interval)irradiation.Contrast noise ratio(CNR)was used to the enhancement of optic nerve and the superior colliculus.Study 3:Longitudinal changes in 1H MRS in the thalamus near the optic chiasm after radiation injury.The detection time of 1H MRS is consistent with the time of MEMRI.Twenty-four before each MRI examination,2 ?1 of a 30 mmol/L manganese chloride(MnCl2·4H2O)solution was slowly injected into the vitreous cavity of one eye of the animal.Visual evoked potentials(VEP)were used to detect visual function in rats at the end of the observation.At the end of observation,motor proteins(Kinesin-1,Kinesin-2,Cytoplasm dynein,and Tau)on axonal transport were detected by western blot and axon cytoskeleton(?-tubulin,?-tubulin,SMI-31,MBP,and MAP-2)was assessed by immunofluorescence.Retinal ganglion cells(RGCs)were retrogradely labeled with fluorescent gold and the number of RGCs were counted.The transmission electron microscope was used to observe the ultrastructure of tree shrews and rat optic nerve.Results:The eyeballs,lens size,vitreous volume,optic nerve and superior colliculus of tree shrews were significantly larger than those of the rats in MEMRI(P<0.05),but there was no significant difference in retinal thickness(P>0.05).After radiation optic nerve injury,the CNR of the optic nerve and superior colliculus in the tree shrew group gradually decreased from 5 to 30 weeks.The enhancement of the optic nerve and SC in rats is similar to that of tree shrews.The CNR of the ON and SC gradually decreased from 5 to 30 weeks,especially from 20 to 30 weeks(P<0.05).The CNR between 5 weeks and 30 weeks for the ON and SC in the irradiated groups decreased by 44.29%and 65.29%in the tree shrew group and 48.07%and 71.53%in the rat group,respectively.1H MRS showed that from 10 to 30 weeks after irradiation,the metabolic rate of NAA/Cr gradually decreased,especially at 30 weeks(P<0.05 in tree shrew group,P<0.05 in rat group).The VEP results showed that there was no significant difference in N1 value between the irradiation group and the control group(P>0.05).The Nl-P1 amplitude of the irradiation group decreased,and there was a significant difference between the control group(P<0.05).Western Blot results showed that Cytoplasm dynein,Kinesin-1,and Kinesin-2 protein levels were significantly reduced in the irradiated group compared with the control group(all P<0.05).The Tau protein in the irradiation group increased slightly,and there was no significant difference compared with the control group(P>0.05).Immunofluorescence results showed that there was no significant difference in ?-tubulin,?-tubulin,SMI-31,MBP and MAP-2 between the experimental group and the control group(all P>0.05).There was no significant difference in RGCs count between the irradiation group and the control group(t=0.053,P=0.958).Electron microscopy results showed that the density of axons decreased,the axons expanded abnormally and swelled,and a large number of vacuoles,demyelinating,and myelin separation occurred.Conclusion:Tree shrews show great advantages in visual neuroscience of MEMRI research.The main cause of the decline in axonal transport in RION is an insufficient level of motor protein rather than damage to the axonal cytoskeletal structure.Longitudinal MEMRI can be used to noninvasively detect changes in axonal transport function and to observe the relatively intact axon structure from the early to late stages after radiation administration.