Supplementary Material for: The effectiveness of lesion detection for IgG4-related kidney diseases by diffusion-weighted imaging

Objectives: To compare the efficacy of magnetic resonance imaging (MRI) with that of plain or contrast-enhanced computed tomography (CT) in the detection of renal parenchymal and pelvic lesions of immunoglobulin G4-related kidney disease (IgG4-RKD).
Methods: Patients with IgG4-RKD and controls, who performed plain, contrast-enhanced CT and MRI around the kidney region in our hospital were enrolled. The diagnosis of IgG4-RKD was made by definite cases of IgG4-RKD diagnostic criteria in 2020. Five blinded observers independently assessed image datasets by confidence scores to assess diagnostic accuracy, sensitivity, specificity, areas under the receiver operating characteristic curve (AUROC), and Cronbach's alpha coefficient.
Results: A total of 31 patients were included in the study. 14 (45.2%) had IgG4-RKD. Five patients with IgG4-RKD had parenchymal lesions, five had renal pelvic lesions, and four had both. In the parenchymal lesions, there was no significant difference in diagnostic performance between contrast-enhanced CT and diffusion-weighted imaging (DWI)-b800. The AUROC and sensitivity were higher in DWI-b800 than in plain CT (P < 0.05). Cronbach's alpha coefficient was 0.44 for plain CT and over 0.80 for contrast-enhanced CT and DWI-b800. In the pelvic lesions, there were fewer differences in the performance among each sequence. Cronbach's alpha coefficient was over 0.80 for plain CT, contrast-enhanced CT, and DWI-b800.
Conclusion: Plain MRI, especially in DWI-b800, can effectively detect renal parenchymal lesions in IgG4-RKD. In difficult cases to use a contrast agent of CT, DWI-b800 can be an alternative for the screening of IgG4-RKD.