Value of Diffusion Kurtosis Imaging in Assessing IgG4 Kidney Disease: A Feasibility Study

Background: Immunoglobulin G4 (IgG4)-related kidney disease (IgG4-RKD) is pathologically featured by interstitial IgG4+ plasma cell infiltration and interstitial fibrosis, and often leads to chronic kidney dysfunction. Our study aims to explore the use of invasive diffusion kurtosis imaging (DKI) in assessing IgG4-RKD and to evaluate the potential of DKI-based quantitative parameters in the clinical assessment of IgG4-RKD. Methods: A prospective study was conducted on 23 IgG4-RKD patients who underwent bilateral renal MRI with T1WI, T2WI, and DKI sequences. Two radiologists evaluated the MR images and determined the distribution pattern and signal intensity of the renal lesions. The mean kurtosis (MK), mean diffusivity (MD), and apparent diffusion coefficient (ADC) of the renal parenchyma, cortex, and medulla were measured. Correlation analysis with clinical indicators such as creatinine, estimated glomerular filtration rate (eGFR), IgG4, IgG, complement, and erythrocyte sedimentation rate (ESR) was performed, and interclass correlation coefficient (ICC) was used to evaluate consistency of measurement. Results: IgG4-RKD showed bilateral (90.91%), multiple (95.24%) and wedge- or round-shaped renal parenchymal lesions (90.91%) with iso-signal on T1WI (80.96%), low signal on T2WI (85.71%) and high-signal on DKI (95.24%). MK, MD, and ADC did not differ between the left and right kidneys. There were no significant differences in MK and ADC in the renal parenchyma, renal cortex, and renal medulla, but MD was higher in the renal cortex. There was a strong negative correlation between eGFR and renal cortical MK (r = 0.66, p = 0.002), as well as a weak positive correlation between serum IgG4/IgG and parenchymal ADC (r=0.37, p=0.038). The C4 was positively correlated with MD-P (r=0.51, p=0.118), and ESR was positively correlated with renal parenchymal MK (r=0.58, p=0.005). The agreement of DKI parameters was moderate to good, except for bilateral renal medullary MD. Conclusion: DKI images can be used to assess IgG4-RKD renal imaging alterations, and the quantitative parameter MK obtained on the basis of DKI correlates with serum creatinine, eGFR and IgG4/IgG ratio. DKI images have the potential to assess IgG4-RKD clinical condition.