Conventional contrast-enhanced magnetic resonance imaging is typically performed with extracellular gadolinium chelates, which is often limited in patients with CKD owing to the risk of nephrogenic systemic fibrosis. Ferumoxytol, a novel contrast medium, can be used as an "off-label" contrast agent for magnetic resonance imaging. During the last decade, ferumoxytol has gained appeal as an MRI contrast agent in patients with estimated glomerular filtration rates <30mL/min and there are reports in the literature for its safe use and utility in both adult and pediatric patients with CKD. The study is designed to evaluate the diagnostic performance of ferumoxytol-enhanced magnetic resonance imaging in patients suspected of renal artery stenosis, investigate the correlation between renal cortical T2*(T2*=1/R2*) and renal function, and develop an automatic algorithms for renal vessel segmentation.

This study is a single-center, prospective, controlled and diagnostic clinical trial to evaluate renal vasculature and renal function with ferumoxytol-enhanced magnetic resonance imaging using domestic polysaccharide superparamagnetic iron oxide injection as the contrast agent. This study will enroll 40 patients with or without renal impairment that are expected to undergo renal artery angiography in China. The investigators will record the baseline data of patients after admission. Patients will receive enhanced renal magnetic resonance imaging with polysaccharide superparamagnetic iron oxide nanoparticle to assess renal vasculature and renal function. The related laboratory indices will be reviewed at 24-72 h after magnetic resonance imaging, and then patients will receive renal angiography. The indices will be reexamined at 1 month and 3 months after magnetic resonance imaging. In order to evaluate the safety of polysaccharide superparamagnetic iron oxide nanoparticle, patients will detect iron levels in peripheral and tissue before and after the examination. The results of MR imaging including image quality, degree of vascular stenosis, and quantitative T2* values of the renal cortex will be evaluated independently by two experienced radiologists. The degree of stenosis of the same vessels assessed by Quantitative Coronary Analysis (QCA) will be used for comparison with MR results. All clinical adverse events will be recorded by investigators.

Inclusion Criteria:

• Age ≧ 18 years, < 75 years;
• Patients who planned renal angiography (hypertension 、renal failure、atherosclerosis）;
• Patients with normal renal function or CKD stage 1-5(Patients diagnosed with CKD as defined in the KDIGO Clinical Practice Guidelines for the Evaluation and Management of Chronic Kidney Disease 2012 Edition);
• Patients themselves or authorized families to sign informed consent voluntarily.

Exclusion Criteria:

• Patients who were allergic to iodine contrast agent or had allergic history or allergic constitution to iron and dextran;
• Patients who can't accept magnetic resonance examination because of psychological ( such as Claustrophobia ) or physical reasons ( such as metal retention in the body );
• Malignancies or other comorbid conditions with life expectancy less than 1 year;
• Pregnant or lactating women;
• Hearing impaired persons;
• Cardiac function grade III-IV;
• Patients who were taking other iron agents orally or intravenously;
• Patients with hemosiderin deposition or hemochromatosis;
• Patients with acute coronary syndromes;
• Any other patients that researcher deems it's unsuitable to be admitted.