This study will compare the results of a clinically ordered abdominal CT angiography to a research non-contrast MR angiogram (MRA). CTA is a "gold-standard" for identifying blockages in the kidney arteries or other blood vessel problems. CTA requires radiation and contrast to obtain useful images. Conversely, the MR abdomen technique being used for the study uses no radiation or contrast and is felt to be a safer option for individuals who have kidney problems. there is benefit to establishing non-contrast MRA as a clinically accurate test.

REACT is a prospective, minimal-risk, and multi-center international trial. The purpose of the study is to evaluate the safety and efficacy of non-contrast magnetic resonance angiography (MRA) for the diagnosis of renal artery stenosis (RAS).

The current "gold standards" for diagnosing RAS are non-invasive 3D angiography with contrast-enhanced CTA/MRA or invasive X-ray angiography. All of these techniques require the use of an intravenous injection of either iodinated contrast material or gadolinium based agents.

Iodinated contrast agents are contraindicated in patients with renal dysfunction and have increased risk of allergic reaction. Contrast-enhanced magnetic resonance angiography (MRA) with gadolinium has fewer risks associated with it, however, is currently contraindicated in patients with severe renal insufficiency because of concerns about developing a rare but often fatal condition termed nephrogenic systemic fibrosis (NSF).

Non-contrast MRA techniques are felt to provide an avenue for safer, effective vascular imaging in patients both with and without kidney dysfunction. In this trial we propose to validate the contrast-free MRA technique, T-SLIP (time-spatial labeling inversion pulse), for diagnosing RAS. This study will compare T-SLIP to the reference standard of contrast-enhanced CTA and is designed to test its efficacy, reproducibility, reliability, and safety.

Inclusion Criteria:

• The abdominal CTA evaluation form has been completed and confirmed to fit criteria for study enrollment
• The research MRA will be completed within 3 months of abdominal CTA
• Subject signed and dated the informed consent form
• Subject agrees to a "research" abdominal MRA
• Subject is able to follow breathing and scanning instructions
• Subject is at least 18 years of age

Exclusion Criteria:

• Subject has had a significant change in clinical condition between the time of abdominal CTA and abdominal MRA (e.g. worsening renal function, renal vascular intervention)
• Subject has renal stents, or other known material that may affect MR image quality
• Subject has a contraindication to an MRI
• Subject had intravenous gadolinium media within the previous 24 hours
• Subject has a baseline heart rate >90 beats per minute or respiratory rate >25 breaths/minute

Patients who have had an abdominal CT for any reason will be considered for the REACT study. They may be referred from private practice or imaging center.