The Value Of Intravoxel Incoherent Motion Imaging And T1-Mapping In The Evaluation Of Long-term Survived Of Transplanted Kidney

Objective To appraise the functional status of long-term survived transplanted kidneys by using certain parameters of intravoxel incoherent motion(IVIM)and T1-mapping,and to analyze changes in these IVIM-derived parameters as well as T1 values.To discover the diagnostic value of parameters mentioned above for renal graft function.Method 35 patients(30 males,5 females)with allograft renal transplantation,who met the inclusion criteria,were prospectively recruited in this study from June 2020 to October 2020 at Qilu Hospital of Shandong University.6 healthy volunteers(3 males,3 females)were also incorporated.According to the current staging standard for chronic renal insufficiency,all patients were divided into 2 groups:20 patients were classified into Group A,namely the good transplant function group(Scr<133μmol/L)and the rest 15 were classified into Group B,namely the moderately-impaired transplant function group(133 μmol/L<Scr<442μmol/L).IVIM-DWI and T1-Mapping imagingwere performed at a 3T MRI scanner(MAGNETOM Prisma,Siemens Healthcare,Erlangen,Germany)with an 18-channel body phased-array coil among all subjects.IVIM and T1-Mapping images of all 41 subjects were processed and analyzed in Siemens Healthcare Syngo.via Workstation.Several regions of interest(ROIs)were placed respectively on the superior,medium and inferior pole of each kidney within both cortex and medulla by two seasoned radiologists.The quantitative parameters derived from IVIM and T1-Mapping,namely D、D~*、f and T1 values,were measured in all ROIs from three groups of subjects.Statistical analyses were performed in IBM SPSS software(Version 21;Armonk,NY,USA).Measurement data,if satisfying the normal distribution,were shown in the form of mean ±standard deviation(x±s).If not,the data were shown in the form of the median(M)and interquartile range(Q1,Q3).Enumeration data were shown in the form of numbers and the percentage.The intraclass correlation coefficient(ICC)was used to evaluate the consistency of measurement results between two observers.The normal distribution of these 4 quantitative parameters in Group A,Group B and normal kidney control group(Group C)was determined by the Kolmogorov-Smirnov test.According to test results,the two independent samples t-test(Student’s t-test)was used for comparing D、D~*、f and T1 values of the cortex and those of medulla in each group.The receiver operating characteristic curve(ROC)analysis was used to evaluate the efficacy of certain parameters in differentiating Group A and B,Group B and C,Group A and C,respectively.For parameters with significant differences,areas under ROC curve(AUCs)were calculated.The threshold,sensitivity and specificity of certain parameters were determined by the maximum Youden index.Statistical significance was defined as P<0.05.Result ① Significant differences were demonstrated among the 3 groups in the Scr level,but not in the age and gender.In terms of the consistency of measurement results between two observers,the D,f and T1 values of both cortex and medulla among 3 groups were in good consistency,the D~*values of cortex among 3 groups were in moderate consistency,and the D~*values of medulla were also in good consistency.② There were no significant intra-group differences in D and D~*between cortex and medulla in(t=0.306,P=0.760;t=-1.030,P=0.306;t=0.257,P=0.798 for D values in Group A,B and C,respectively;t=1.483,P=0.139;t=0.233,P=0.816;t=0.234,P=0.815 for D~*values in Group A,B and C,respectively).While intra-group differences were found in f and T1 values between cortex and medulla(t=5.786,P<0.001;t=4.032,P<0.001;t=4.940,P<0.001 for f values in Group A,B and C,respectively;t=-30.09,P<0.001;t=-22.61,P<0.001;t=-22.80,P<0.001 for T1 values in Group A,B and C,respectively).③ The inter-group difference of D and f values in both cortex and medulla as well as that of T1 value in the cortex were significant(F=12.071,P<0.001 and F=13.926,P<0.001 for D value in cortex and medulla,respectively;F=10.774,P<0.001 and F=8.185,P<0.001 for f value in cortex and medulla,respectively;F=78.80,P<0.001 for T1 value in the cortex).There were no significant inter-group differences of D~*value in both cortex and medulla,with no significant inter-group differences of T1 value in the medulla(F=0.405,P=0.667 and F=0.607,P=0.546 for D~*value in cortex and medulla,respectively;F=2.505,P=0.083 for T1 value in the medulla).④ The AUC of T1 value was the largest in differentiating Group A from B,Group A from C,and Group B from C.The AUC and its 95%CI of T1 value for distinguishing the good transplant function group(Group A)and the impaired transplant function group(Group B)were 0.721(0.652～0.790),larger than that of D value(0.685[95%CI:0.611～0.759]for cortex and 0.668[95%CI:0.892～0.743]for medulla)and f value(0.658[95%CI:0.582～0.734]for cortex and 0.666[95%CI:0.590～0.741]for medulla),with the sensitivity of 81.1%and specificity of 60%.The AUC and its 95%CI of T1 value for distinguishing the good transplant function group(Group A)and the normal kidney group(Group C)were 0.776(0.708～0.844),larger than that of D value(0.649[95%CI:0.569～0.729]for cortex and 0.697[95%CI:0.623～0.771]for medulla)and f value(0.530[95%CI:0.437～0.624]for cortex and 0.569[95%CI:0.482～0.655]for medulla),with the sensitivity of 70.8%and specificity of 73.3%.The AUC and its 95%CI of T1 value for distinguishing the impaired transplant function group(Group B)and the normal kidney group(Group C)were 0.923(0.879～0.967),larger than that of D value(0.548[95%CI:0.458～0.638]for cortex and 0.522[95%CI:0.431～0.613]for medulla)and f value(0.639[95%CI:0.549～0.729]for cortex and 0.592[95%CI:0.503～0.681]for medulla),with the sensitivity of 85.6%and specificity of 86.1%.Conclusion D and f values of IVIM imaging and T1 value of TI-mapping may serve as promising indicators for evaluating the function of long-term survived transplanted kidneys,among which the T1 value shows the supreme diagnostic efficacy.Therefore,IVIM and T1-mapping imaging can provide much more biological information in the aspect of function assessment for long-term survived renal grafts.As a non-invasive examination,T1-mapping also shows broad prospects in the clinical application.