Apparent diffusion coefficient of kidneys with non-contrast magnetic resonance angiography for functional and anatomical assessment in renal artery stenosis

BACKGROUND Renal artery stenosis (RAS) is a vascular disorder linked to secondary hypertension, chronic kidney disease, and renal failure due to interstitial fibrosis. Early diagnosis is crucial as RAS-induced hypertension responds well to angioplasty. Non-invasive imaging techniques, including non-contrast magnetic resonance angiography (NC-MRA), help assess RAS without contrast-related risks. Diffusion-weighted MR imaging (DW-MRI) has emerged as a promising method for evaluating kidney function by measuring the apparent diffusion coefficient (ADC), which correlates with renal pathology. AIM To compare ADC values in hypertensive, RAS, and healthy kidneys, assess the correlation between ADC and stenosis severity, and evaluate its relationship with split glomerular filtration rate (GFR). METHODS This prospective observational study which included 86 patients with suspected RAS and twenty normal healthy controls underwent NC-MRA on a 3T-MR-Scanner followed by DW-MRI at b values of 0 and 1000 seconds/mm2 in the transverse plane. ADC maps were created using Functool. ADC values were measured in the cortex and medulla of each kidney's upper, middle, and lower pole, and the average ADC (ADCavg) for cortex and medulla calculated. In patients with RAS, degree of stenosis (DOS) was calculated on NC-MRA. The ADC of 212 kidneys was compared, and the relationship between DOS and ADC was established. In addition, split GFR was calculated in 30 kidneys using 99mTc-DTPA, and correlated with ADC value. The ADC values of kidneys with and without RAS were compared using the Student’s t -test. The correlation between ADC and stenosis severity was assessed by Spearman’s test, while the relationship between ADC and split GFR was evaluated using Pearson’s test. A P value < 0.05 was considered statistically significant. RESULTS RAS was detected in 58 of 86 (67.44%) hypertensive patients (81 of 172 kidneys), and the ADCavg (P = 0.044) was significantly lower in RAS kidneys than in kidneys with normal arteries and essential hypertension and healthy controls. CONCLUSION DW-MRI can be a useful non-invasive technique to estimate the kidney’s functional status in RAS patients. It can be used as a complementary assessment tool with NC-MRA to triage patients in need of interventional management.