Contrast-free functional MRI for assessing renal involvement in patients with ANCA-associated vasculitis

BACKGROUND: Early detection of renal involvement in ANCA-associated vasculitis (AAV) is crucial, as functional changes often precede anatomical damage. Current diagnostic standards, such as the measurement of serum creatinine, renal biopsy and urinary analyses have limitations due to delayed detection and lack of specifity. Functional renal MRI (fMRI) techniques, including diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), arterial spin labeling (ASL) and blood oxygenation level dependent (BOLD) offer promising non-invasive alternatives for assessing renal function in AAV. The aim of this study was to evaluate the feasibility of non-invasive assessment of renal changes associated with AAV using mpMRI (multiparametric MRI). METHODS: This study evaluated 7 patients and 10 healthy controls: patients with rapidly progressive glomerulonephritis (RPGN) due to AAV (n = 3), AAV patients without clinical signs of renal involvement (n = 4), and healthy controls (n = 10). All participants underwent functional renal MRI. Key parameters, including the apparent diffusion coefficient (ADC), fractional anisotropy (FA), and ASL-based renal perfusion and T2* parameter maps, were acquired and analyzed. RESULTS: The following differences in renal imaging parameters were observed between RPGN patients and healthy controls: RPGN patients showed reduced ADC values in the renal medulla and increased FA values compared to controls. Additionally, ASL values in the renal cortex were lower in RPGN patients. T2* values were lower in RPGN patients compared to the healthy control group in the cortex, and higher in the medulla. Patients with AAV without confirmed renal involvement also showed alterations in ADC, T2* and FA values compared to healthy controls. CONCLUSION: Our findings indicate that mpMRI parameter might detect renal changes in AAV. Therefore, mpMRI might offer novel opportunities for non-invasive detection of disease-associated changes.