FMultifunctional magnetic resonance imaging for the assessment of renal pathological alterations in IgA nephropathy

We aimed to evaluate the application value of multiparametric diffusion weighted magnetic resonance imaging (MRI) for the assessment and risk stratification of renal histopathological injuries in patients with IgA nephropathy (IgAN), as an exploratory study.

95 patients were prospectively enrolled, intravoxel incoherent motion (IVIM), diffusion tensor imaging (DTI), and diffusion kurtosis imaging (DKI) were performed, and a renal biopsy was performed within 3 days after MRI examination. Finally, 31 patients with pathologically confirmed IgAN were selected for analysis, and glomerulosclerosis index (GSI) and tubulointerstitial fibrosis index (TBI) were assessed by two experienced pathologists who were blinded to the clinical and multiparametric diffusion weighted imaging MRI data.

Correlation analysis showed that eGFR was negatively correlated with age, GSI, and TBI. Both GSI and TBI were negatively correlated with the true diffusion coefficient (D, cortex), mean diffusivity (MD, cortex and medulla), fractional anisotropy (FA, medulla), and axial diffusivity (Da, cortex and medulla), and positively correlated with the mean kurtosis (MK, cortex) and axial kurtosis (Ka, cortex and medulla). Compared with the normal control group, the moderate-to-severe GSI/TBI groups showed significant decreases in most diffusion parameters and increases in kurtosis parameters, while there was no significant difference in all MRI parameters between the mild injury groups and the control group. Multivariate regression and model validation showed that medullary FA was the independent imaging predictor of moderate-to-severe GSI in the DTI-based model (p = 0.013), and the clinical+DTI combined model had a high diagnostic efficacy (AUC = 0.932, optimism-corrected AUC = 0.858); eGFR was the only significant predictor in the DKI-based model (p = 0.023), with the clinical+DKI combined model AUC reaching 0.891 (optimism-corrected AUC = 0.801).

As a preliminary exploratory study,DTI and DKI may provide useful non-invasive information for assessing renal histopathological alterations in IgAN patients. Medullary FA is a promising imaging biomarker for glomerulosclerosis, and its combination with clinical variables shows potential for identifying patients with moderate-to-severe disease. The originally hypothesized superiority of DKI-derived MK was not clearly demonstrated. These findings warrant further validation in larger cohorts.

This study was registered at the Chinese Clinical Trial registry with the registration number was ChiCTR1800020390.