Longitudinal multi-b-value diffusion-weighted imaging in renal transplant recipients: diagnostic efficacy and prognostic value for allograft dysfunction.

Background: Early estimation and monitoring of renal function is important to guiding clinical intervention and reducing complications. Our previous research confirmed that diffusion-weighted imaging (DWI) can evaluate the varying degrees of transplanted kidney function; however, its value in conducting follow-up and predicting long-term prognosis has not yet been assessed. This study aimed to evaluate the ability of multi-b-value DWI to evaluate and monitor the function of transplanted kidneys in follow-up and to determine the predictive value for allograft dysfunction during follow-up.

Methods: The data of 66 patients who underwent kidney transplantation at our hospital from February 2019 to October 2022 were prospectively collected. Multi-b-value DWI was performed at 14, 30, 90 days after transplantation, and the estimated glomerular filtration rate (eGFR) at each time point and at 1 year after were recorded in the cohort study. Based on the eGFR, recipients were divided into three groups: group A (allograft function stable), group B (allograft function decreased), and group C (allograft function impaired). Additionally, 20 healthy volunteers were recruited as a control group. The intraclass correlation coefficient (ICC) was used to evaluate the consistency of the measurements. The Fisher exact test, one-way analysis of variance (ANOVA), and the Kruskal-Wallis test were used to compare the differences. Generalized estimation equations (GEEs) were used to compare the changes in parameters during follow-up period. Binary logistic regression was used to analyze the value of parameters at 14 days after transplantation in predicting allograft dysfunction at 1 year. Spearman correlation analysis was used to evaluate the correlation between magnetic resonance imaging (MRI) parameters and eGFR. Receiver operating characteristic (ROC) curve analysis was applied to assess the diagnostic efficacy of parameters in diagnosing and predicting allograft dysfunction; meanwhile, the areas under the curve were compared with the DeLong test.

Results: Except for the f-value, all MRI parameters at 14 days showed statistically significant differences between the groups. The differences in cortical mean kurtosis (MK), medullary MK, and apparent diffusion coefficient (ADC) values between group A and B were statistically significant. However, there were no significant differences in cortical and medullary D, MK, or ADC during the follow-up period. For patients with good renal function at 14 days after transplantation, the independent protective factors for allograft dysfunction within 1 year were 14-day medullary MK [odds ratio (OR) =1.062; P=0.020] and 14-day eGFR (OR =0.878; P=0.011).

Conclusions: Multi-b-value DWI provides a useful tool for the noninvasive longitudinal follow-up allograft function and may be incorporated into routine posttransplant monitoring protocols to provide early indicators of renal allograft dysfunction.