| Part Ⅰ Quantitative evaluation of renal ischemia-reperfusion injury by three imaging techniques R2 mapping,R2*mapping and R2’ mapping:an experimental studyPurpose:To compare the ability of three quantitative imaging techniques including R2 mapping,R2*mapping and R2’ mapping in evaluating the feasibility of renal oxygen changes during renal ischemia-reperfusion injury(IRI)in rabbits.Methods:Thirty-two New Zealand white rabbits were selected and assigned according to the principle of random allocation.Among them,twenty-seven rabbits were used as the IRI group and five rabbits were used as the control group.MRI scans were performed at the IRIpre,IRI1h,IRI12h,IRI24h,and IRI48h time points(including axial T2WI image,axial T2 mapping,and T2*mapping).Every three animals were sacrificed for pathological examinations at the first four time points.The remaining fifteen animals were sacrificed to obtain specimen after the MRI examination,and the pathological sections were stained with HE,PAS and immunofluorescence.T2 mapping and T2*mapping and R2’ mapping were performed in the AW4.6 post-processing workstation.Mapping is reconstructed to obtain R2 map,R2*map and R2’ map images,and the margin of the cortex,inner medulla and outer medulla was manually outlined to obtain quantitative values.Repeated measurement variance was used to analyze the differences at each time point,and Spearman correlation analysis was used to compare the correlation between the R2 values,R2*values and R2’ values at the IRI48h time point and the pathological hypoxia fluorescence staining score.Results:The outer medullary R2 values in the IRI group were statistically different between the IRIpre timepoint and IRI1h timepoints(P<0.05).There were no statistically significant differences in the inner medulla or cortex R2 values.The inner and outer medulla R2*values and R2’ values in the IRI group were statistically different at each time point(all P values<0.05).There was no statistical difference in the cortical R2 values in the IRI group.The R2 value,R2*value and R2’ value were not statistically different at each time point in the control group.Pathologically,with the prolongation of IRI time,the reperfusion injury was gradually obvious,and immunofluorescence staining showed that the staining intensity and area in the outer medullary zone gradually increased.At the IRI48h timepoint,the outer medulla R2*values and R2’ values were positively correlated with the pathologically hypoxia score(R2=0.50,0.90,r=0.71,0.95,P<0.05),while the outer medullary R2 value was not significantly correlated with the pathological score.Conclusion:R2*mapping and R2’ mapping can be used as imaging indicators for quantitative evaluation of renal oxygen changes in the process of renal IRI injury,and R2’mapping is superior to the other two methods.R2 mapping can be used as an indicator for evaluating the injury of kidney,but it cannot be used as an indicator for evaluating renal oxygen.Part Ⅱ To evaluate the effect of diuretics on renal ischemia-reperfusion injury with R2’ mappingPurpose:To explore whether R2’ mapping can evaluate the changes of renal oxygen level in renal ischemia-reperfusion injury(ERI)in rabbit after diuretic treatment.Methods:Forty rabbits were randomly divided into four groups according to the clamped time:the sham group;the mild,moderate and severe groups(the clamped time was 45min,60min,and 75min,seperately,with n=10 each group).Intravenous furosemide(FU)was administered 24 hours after IRI.All rabbits underwent MR scanning at 5 timepoints(IRIpre,IRI24h,FUsmin,FU12min and FU24min,seperately).The R2’ values and the hypoxic scores were then recorded.The repeated measurement analysis of variance and Spearman correlation analysis was used for statistical analysis.Spearman correlation analysis was used to compare the correlation between the medulla R2’ values,the R2’decreased values(the difference between the R2’ values at the IRI24h timepoint and the R2’value at the FUsmin timepoints before intravenous FU injection)and the hypoxia score.Results:Compared to the baseline,the medullary R2’ values significantly increased 24 hours after IRI(baseline R2’ values:19.31±1.21 s-1;mild group:20.05±1.26 s-1;moderate group:25.38±1.38 s-1;severe group:25.79±1.10 s-1,each P<0.001).Furosemide led to a significant decrease of the medullary R2’ value(sham group:11.17±4.33 s-1,mild group:7.80±0.74 s-1,moderate group:3.92±0.28 s-1 and severe group:3.82±0.23 s-1,each P<0.05).Quantitative hypoxic scores revealed significant differences among the four groups in the outer medulla(each P<0.001).The medullary R2’ values at FU24min timepoint and the R2’ decreased values(before and after intravenous furosemide)were significantly correlated with the hypoxic scores,respectively,(P<0.001).Conclusion:R2’ mapping is helpful in evaluating renal hypoxia in the procession of IRI in rabbits and might serve as a quantitative biomarker for IRI.Part Ⅲ Evaluating the protective effect of AMPK receptor agonists on renal ischemia-reperfusion injury with R2’ mapping:an experiment studyPurpose:To explore the feasibility of R2’ mapping technique in evaluating the protection of AMPK receptor agonist(AICAR)pretreatment on mild,moderate and severe renal IRI.Methods:48 New Zealand white rabbits were chosen,according to the length of clamped time of renal pedicle,and divided into mild,moderate and severe IRI group(clamped time was 45min,60min and 75min,respectively),and the control group was set up.Each group was subdivided into AICAR subgroup and saline subgroup(the same amount of AICAR and 0.9%saline were injected intramuscularly before the IRI operation),there were six rabbits in each group.MRI scans(including axial T2WI images,axial T2 mapping and T2*mapping sequences)were performed at the IRIpre,IRI1h,IRI12h,IRI24h and IRI48h time points.HE staining,PAS staining and hypoxia fluorescence staining were performed after the MRI examination.The R2’ values were generated by manually outlining the margin of the outer medulla.Multivariate repeated measurement variance was used to analyze the differences at the five time points,and variance analysis was used to compare the differences of hypoxia scores in each group.Results:The AICAR subgroups and the saline subgroup in the mild,moderate and severe IRI groups had statistically different R2’ values at the 5 time points including IRIpre,IRI1h,IRI12h,IRI24h and IRI48h(P<0.05).The outer medulla R2’ value showed the regular trend.The R2’ value at the IRI1h timepoint was the lowest,and gradually increased as time progressed.The AICAR subgroups of the mild,moderate and severe IRI groups had lower R2’ values than the saline subgroup in the outer medulla,and there was a statistical difference between the R2’ values of two subgrops.The results of pathological scores showed that the hypoxia scores gradually increased from that in control group to the mild IRI,moderate IRI and severe IRI groups.The pathological scores of the mild and moderate IRI group were statistically different between the AICAR subgroup and the saline subgroup.Conclusion:R2’ mapping can detect the hypoxic changes in the different IRI models after pretreatment with AMPK receptor agonists.The R2’ value of the outer medulla can be used as an imaging index of assessing the therapeutic effect of renal IRI. |
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