An MRA, or magnetic resonance angiography, is an imaging scan that produces detailed pictures of your blood vessels without surgery or radiation. It uses the same technology as a standard MRI (magnetic fields and radio waves) but is specifically designed to visualize arteries and veins. The scan typically takes 20 to 60 minutes and is one of the primary tools doctors use to check for blockages, aneurysms, and other vascular problems throughout the body.
How an MRA Creates Images of Blood Vessels
A standard MRI creates images of organs, muscles, and other soft tissues. An MRA narrows the focus to blood vessels specifically, using techniques that highlight flowing blood while suppressing the signal from surrounding stationary tissue.
The most common non-contrast technique is called time-of-flight imaging. It works by repeatedly pulsing radio waves at a specific area of the body, which saturates the tissue there and essentially silences its signal. Blood flowing into that area hasn’t been exposed to those pulses yet, so it produces a much stronger signal. The result is a bright image of the blood vessels against a dark background. A second technique, called phase-contrast imaging, measures the speed of blood moving through a vessel, which can be useful for evaluating flow direction and velocity.
Some MRAs use a contrast dye (a gadolinium-based agent) injected through an IV. The dye shortens the time needed for the scan and produces sharper images, especially in areas where blood flow is slow or travels in directions that the non-contrast technique struggles to capture. In stroke imaging, for example, contrast-enhanced MRA matches the accuracy of the gold-standard catheter angiography for pinpointing vessel blockages, while the non-contrast version can sometimes misidentify where an occlusion is located.
What Conditions an MRA Can Detect
Doctors order MRAs to evaluate a wide range of vascular problems. Common reasons include:
- Aneurysms: weak spots in artery walls that balloon outward, particularly in the brain or aorta
- Arterial narrowing or blockage: reduced blood flow in the neck, brain, arms, or legs, often from atherosclerosis (hardening of the arteries)
- Aortic dissection: a tear in the wall of the aorta that allows blood to leak between layers
- Stroke evaluation: identifying which vessel is blocked and assessing collateral blood flow
- Renal artery stenosis: narrowing of the blood vessels in the kidneys, which can cause high blood pressure and kidney damage
- Arterial dissection in the neck: tears in the carotid or vertebral arteries, which can cause stroke in younger adults
MRA vs. CT Angiography
CT angiography (CTA) is the other major option for imaging blood vessels. It’s faster and widely available, but it uses X-ray radiation, which is a concern when patients need repeated follow-up scans or are relatively young. MRA avoids radiation entirely.
MRA also has an edge in soft tissue detail. It can detect signs of acute stroke using diffusion-weighted imaging, something CT can’t do as effectively. For suspected artery tears in the neck, MRA can reveal the blood clot forming inside the vessel wall (a finding called the crescent sign on specific imaging sequences) that helps confirm the diagnosis. CTA, on the other hand, is generally faster to perform and better tolerated by patients who are claustrophobic or unable to lie still for extended periods.
What the Scan Feels Like
You’ll lie on a narrow table that slides into a large tube-shaped magnet. The machine is loud, producing repetitive knocking and buzzing sounds, so you’ll be given earplugs or headphones. The scan itself is painless. The only physical sensation, aside from the noise, is the IV insertion if contrast dye is being used. Some people notice a brief metallic taste in their mouth when the dye is injected.
You’ll need to stay still during the scan to avoid blurring the images. Depending on which blood vessels are being examined and whether contrast is used, the whole process takes anywhere from 20 minutes to an hour.
Who Cannot Have an MRA
Because an MRA uses a powerful magnet, anything metallic in or on your body is a potential safety issue. Before the scan, you’ll go through a screening process to identify any implants or foreign objects.
Certain devices are not safe in the scanner. These include most pacemakers and implantable defibrillators (which can malfunction, overheat, or deliver inappropriate shocks), cochlear implants, implantable drug infusion pumps, and neurostimulation devices. Metallic foreign bodies, particularly metal fragments near the eyes, are also dangerous because the magnetic field can cause them to move. Cerebral aneurysm clips, certain dental implants, and retained shrapnel or bullet fragments are additional concerns.
Some implants fall into a gray area. Coronary stents, joint replacements, IUDs, and surgical clips may be safe depending on the specific make and model. Your imaging team will verify compatibility before proceeding. Newer “MRI-conditional” pacemakers exist that can be scanned under specific protocols, but this requires coordination between your cardiologist and the imaging center.
Risks of Contrast Dye
Non-contrast MRAs carry essentially no known biological risks beyond the standard MRI safety concerns listed above. When contrast dye is used, the main consideration is kidney function. Gadolinium-based contrast agents were historically linked to a serious condition called nephrogenic systemic fibrosis (NSF) in people with severe kidney disease. This caused thickening and hardening of the skin and connective tissues.
Newer formulations of gadolinium have largely eliminated this risk. A large review of patients with advanced kidney disease (stage 4 or 5, meaning severely reduced kidney function) found that the pooled risk of NSF with current contrast agents was 0%, with the upper statistical bound below 0.1% for most formulations. Still, if you have known kidney problems, your doctor will check your kidney function before ordering a contrast-enhanced MRA and may opt for a non-contrast technique instead.
How to Prepare
Preparation is minimal for most MRAs. You’ll be asked to remove all jewelry, watches, hair clips, and clothing with metal fasteners. Some facilities provide a gown. You’ll fill out a detailed questionnaire about any implants, prior surgeries, or possible metal exposure (such as working with metal grinding tools). If contrast dye is planned and you have a history of kidney disease, a blood test to check kidney function is standard. Some facilities ask you to avoid eating for a few hours before the scan, particularly if sedation is being used for claustrophobia.