Introduction
Magnetic resonance angiography (MRA) is a radiology test to study blood vessels, particularly those in the head, neck, lungs, kidneys and legs. An MRA is really a variation of a magnetic resonance imaging (MRI) but with the use of a contrast agent such as gadolinium. Without the gadolinium, it is not possible to distinguish the blood vessels from the surrounding tissue.
Compared to Conventional Angiography
The most accurate way to look at blood vessels is to perform conventional angiography. This is an invasive procedure that requires placing a large tube into the blood vessels and injecting a contrast dye containing iodine. This is not without risks, particularly for bleeding, infection, blood vessel spasm, allergic reactions and kidney failure.
MRA of the Kidney
MRA is not as accurate as conventional angiography (the quality is improving fast) but it is easy to obtain and gnereally safer. It is particularly useful for assessing if narrowing of the kidney or renal arteries as the cause of high blood pressure or kidney failure. In order to get good pictures, enough of a contrast agent must be given. Fortunately, we can use a gadolinium-based contrast agent, which does not cause the kidney failure and allergic reactions seen with iodine agents.
Gadolinium Poses Risk to Kidney Failure Patients
Although MRA with gadolinium can be safer than receiving traditional contrast dyes, this may not be true in advanced kidney failure. Gadolinium has been linked to a nephrogenic fibrosing dermopathy (NFD) in people with advanced chronic kidney disease (Stage 4 or 5 CKD). NFD is a very serious disease involving scarring of the skin, deeper tissues and even internal organs. As a result, MRA with gadolinium is generally restricted in advanced kidney failure unless absolutely necessary. Also, follow-up hemodialysis may be performed to remove the gadolinium if appropriate.
Sources:
Hartman et al. “Evaluation of renal causes of hypertension”. Radiologic Clinics of North America 41 (2003): 917-18.