Noninvasive grading of renal interstitial fibrosis and prediction of annual renal function loss in chronic kidney disease: the optimal solution of seven MR diffusion models

To explore the optimal choice of seven diffusion models (DWI, IVIM, DKI, CTRW, FROC, SEM, and sADC) to assess renal interstitial fibrosis (IF) and annual renal function loss in chronic kidney disease (CKD). One hundred thirty-three CKD patients and 30 controls underwent multi-b diffusion sequence scans. Patients were divided into the training, testing, and temporal external validation sets. Least absolute shrinkage and selection operator regression and logistic regression were used to select the optimal metrics for distinguishing the mild from moderate-to-severe IF. The performances of imaging, clinical, and combined models were compared. A linear mixed-effects model calculated estimated glomerular filtration rate (eGFR) slope, and multiple linear regression assessed the association between metrics and 1–3-year eGFR slopes. The training, testing, and temporal external validation sets had 75, 30, and 28 patients, respectively. The combined model incorporating cortical f_IVIM, MK_DKI and eGFR was superior to the clinical model combining the eGFR and 24-hour urinary protein in all sets (net reclassification index [NRI] &gt; 0, <i>p</i> &lt; 0.05). Decision curve analysis showed the combined model provided greater net clinical benefit across most thresholds. Fifty-two, 35, and 16 patients completed 1-, 2-, and 3-year follow-ups. After adjusting for covariates, cortical f_IVIM correlated with the 1-year eGFR slope (β = 30.600, <i>p</i> = 0.001), and cortical α_SEM correlated with the 2- and 3-year eGFR slopes (β = 44.859, <i>p</i> = 0.002; β = 95.631, <i>p</i> = 0.019). A combined model of cortical f_IVIM, MK_DKI and eGFR provides a useful comprehensive tool for grading IF, with cortical f_IVIM and α_SEM as potential biomarkers for CKD progression.