Application Of T2 Mapping In Renal Ischemia-reperfusion Injury

Part Ⅰ Value of T2 mapping in the dynamic evaluation of renal ischemiareperfusion injuryObjective:To explore the value of T2 mapping in the dynamic quantitative evaluation of renal ischemia-reperfusion injury(IRI).Methods:48 healthy New Zealand rabbits were randomly divided into IRI group(n=40)and control group(n=8).Rabbits in the IRI group underwent left renal artery clamping for 60 minutes.The control group underwent laparotomy,but without left renal artery clamping.Rabbits underwent MRI examinations(T2WI and T2 mapping)before and 1 h,12 h,24 h,and 48 h after IRI.The region of interest(ROI)was drawn manually along the outline of the rabbit outer medulla.After MRI examination at each time interval,eight rabbit from IRI group were sacrificed.The rabbits in control group were sacrificed after MRI at all time points up to 48 h after the operation.The left kidney was harvested for paraffin imbedding.The axial sections of the renal hilus,which corresponded to the MRI slices,were chosen for histological analysis and stained with haematoxylin and eosin.Four histopathological features,including tubular epithelial edema,tubular epithelial necrosis,interstitial inflammation,and cast were evaluated.The inter-observer and intra-observer reproducibility of the T2 values were assessed using the intraclass correlation coefficient(ICC)with 95%confidence interval(CI).The repeated measures analysis of variance was used to compare the differences in T2 values of the IRI and control group across the different time points.Differences in the four histopathological features were assessed using the nonparametric Kruskal-Wallis test followed by pairwise comparisons.Correlations between the T2 value of the renal outer medulla and injury scores were assessed by Spearman correlation analysis.Results:Both of the intra-observer(ICC=0.97,95%CI 0.95-0.99)and inter-observer reproducibility(ICC=0.92,95%CI 0.86-0.96)were excellent for T2 values.There were no significant differences in the T2 values of the renal outer medulla in the control group between any pairs of the five different time points(all P>0.05).In IRI group,T2 values of the renal outer medulla were increase at 1 h after IRI(P=0.001)and were decrease from 1 h to 12 h(P=0.002).At 1 h after IRI,the T2 values of the renal outer medulla for the IRI group were higher than those for the control group(P<0.001).There was no significant difference in the T2 values of the renal outer medulla between the control group and IRI group before IRI and at 12 h,24 h,and 48 h after IRI(all P>0.05).The scores for tubular epithelial edema were significantly higher at 1 h,12 h,24 h after IRI than before IRI(P<0.001,P=0.004,P=0.046,respectively).The score for tubular epithelial necrosis was significantly higher at 48 h after IRI than at 1 h and 12 h after IRI(P<0.010 and P=0.019,respectively).The scores for interstitial inflammation and cast were significantly higher at 12 h,24 h,and 48 h after IRI than before IRI(P=0.008,P=0.036;P=0.002,P=0.011;and P<0.001,P<0.001;respectively).The T2 value of the renal outer medulla was moderately positive correlated with tubular epithelial edema(p=0.686,P<0.001).There was no significant correlation between T2 values with tubular epithelial necrosis,interstitial inflammation,and cast(ρ=-0.083,P=0.610;ρ=0.077,P=0.636;ρ=-0.079,P=0.628).Conclusion:T2 mapping can reflect the dynamic changes of renal parenchyma in an animal model of IRI and be used to assess the early renal IRI.Part Ⅱ Value of T2 mapping in evaluating renal reabsorption function after ischemia-reperfusion injuryObjective:To evaluate the renal reabsorption function after ischemia-reperfusion injury(IRI)by T2 mapping imaging.Methods:Twenty-eight healthy New Zealand rabbits were randomly divided into IRI45min group(n=7),IRI-60min group(n=7),IRI-75min group(n=7)and control group(n=7).In IRI group,2 ml furosemide was injected intravenously at the ear margin 24 hours after modeling.The IRI group underwent dynamic MRI(T2WI and T2 mapping)scan before and 24 h after furosemide injection.The control group underwent dynamic MRI scan before furosemide injection and 1,12,24 min after it.The region of interest was drawn manually along the outline of the rabbit outer medulla.All rabbits were killed after dynamic scanning.The left kidney was harvested for paraffin imbedding.The axial sections of the renal hilus,which corresponded to the MRI slices,were chosen for histological analysis and stained with haematoxylin and eosin.The inter-observer and intra-observer reproducibility of the T2 values were assessed using the intraclass correlation coefficient(ICC)with 95%confidence interval(CI).The repeated measures analysis of variance was used to compare the differences in T2 values of the IRI and control groups across the different time points.Results:The inter-observer reproducibility(ICC=0.90,95%CI 0.76-0.96)were excellent for T2 values.There was no significant difference in T2 value between iri-60 min group and IRI-75 min group at different time points(all P>0.05).In IRI-45min group,there were significant differences in T2 values of the outer medulla at 1,12 and 24 min after injection of furosemide and before modeling(P=0.003,P=0.009,P=0.022).In the control group,the T2 values of the outer medulla at 1,12 and 24 min after injection of furosemide were significantly different from those before injection(P=0.003,P=0.003,P=0.013).At 12 min after injection of furosemide,T2 values of outer medulla in IRI-60 min group and control group were significantly higher than those in IRI-75 min group(P=0.02 1,P=0,046).Conclusion:T2 mapping imaging can reflect the changes of renal IRI at different time points after furosemide injection,which is helpful for evaluating renal reabsorption function and monitoring clinical intervention.