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 speficity. Functional renal MRI techniques (mpMRI), 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. 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 renal mpMRI. 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. 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 functional MRI parameter might detect renal alterations in AAV that precede clinical changes. Therefore, mpMRI might offer novel opportunities for non-invasive detection of disease-associated changes.