Multiparametric renal MRI assessments in adults for evaluation of chronic unilateral obstructive uropathy: Arterial spin labeling as the robust functional biomarker

Chronic unilateral urinary obstruction leads to progressive renal impairment. Isotope diuretic renography, the accepted functional reference standard, carries limitations including radiation exposure, limited availability, and poor anatomical resolution.To prospectively evaluate the diagnostic value of functional MRI 3 Tesla comprising apparent diffusion coefficient (ADC), intravoxel incoherent motion (IVIM), diffusion kurtosis (DK), and arterial spin labeling (ASL) for discriminating chronic unilateral urinary obstruction from healthy kidneys, using isotope glomerular filtration rate (GFR) as the reference standard. Sixty participants: 30 adults confirmed chronic unilateral upper urinary tract obstruction (mean age 40.1 +/- 12.6years; 19 male) and 30 matched healthy volunteers (mean age 36.4 +/- 11.2 years; 18 male). Cortical ADC, medullary ADC, IVIM true diffusion coefficient (D), pseudo-diffusion coefficient (D*), and perfusion fraction (f), diffusion kurtosis, and ASL renal blood flow were measured independently by two radiologists and correlated with isotope-derived GFR. ASL demonstrated the strongest correlation with GFR (rho = 0.68, p = 0.001) and the highest discriminatory performance (AUC 0.91; 95% CI 0.88–0.94). Cortical ADC and IVIM D* also achieved significant between group separation (AUC 0.62 and 0.70, respectively). A model combining all three yielded an AUC of 0.93 (95% CI 0.90–0.96; optimism-corrected AUC 0.91), and confirmed clinical utility on decision curve analysis. ASL is the most robust MRI biomarker for renal assessment in chronic unilateral urinary obstruction. Its combination with cortical ADC and IVIM D* in a multivariable model marginally improves the performance.