About an MR angiogram of the leg
An MR angiogram (MRA) is a type of MRI scan that focuses on blood vessels. It uses a strong magnetic field, radio waves and a computer to make detailed pictures of the arteries without X-rays, and without the need to pass a tube (catheter) into an artery as in a traditional angiogram.
An MRA of the leg is most often used to look at the arteries of people with peripheral arterial disease (PAD). PAD happens when fatty deposits build up in the leg arteries, narrowing them and reducing blood flow. A common symptom is pain in the legs when walking that eases after a few minutes’ rest (intermittent claudication). Smoking, diabetes, high blood pressure, high cholesterol and older age all increase the risk.
In the UK, NICE guidance recommends a duplex ultrasound scan as the first imaging test when treatment to restore blood flow is being considered, followed by a contrast-enhanced MR angiogram if more detail is needed. Left and right legs are separate scans, so choose the side you need when you book.
Referral needed: this scan requires a referral from a specialist, such as a vascular surgeon. You can upload the referral when you book.
What happens during the scan
You lie on your back on the scanner bed with a coil placed over your legs. The scanner is loud, so you will wear ear plugs or headphones, and the radiographer can see, hear and talk to you throughout. You will need to keep your legs very still, as even small movements can blur the pictures of the blood vessels.
Most MR angiograms use an injection of contrast dye (gadolinium) through a small cannula in a vein, usually in your arm or hand, so the blood vessels show up clearly. Gadolinium is less likely to cause an allergic reaction than the iodine-based dye used for CT. Some vessels can also be imaged without contrast. If you have contrast, you may be asked to wait for up to 30 minutes afterwards. Where contrast is needed, it is charged separately.
Because the leg arteries are long, the bed may move in stages during the scan so that pictures can be taken from the top of the leg down to the foot.
What the scan can show
An MR angiogram of the leg can help to look at:
- narrowing (stenosis) or blockage of the leg arteries, as in peripheral arterial disease
- where and how long any narrowing is, to help plan angioplasty, a stent or bypass surgery
- swelling of an artery (aneurysm), for example behind the knee
- abnormal connections between arteries and veins (vascular malformations)
- damage to blood vessels after an injury
- how well a stent or bypass graft is working after treatment
MRA does not show calcium in the artery walls, and the smallest vessels in the foot can be harder to see. Your specialist will advise whether MRA, ultrasound or a CT angiogram is best for you.
Sudden symptoms? If your leg or foot suddenly becomes painful, pale, cold or numb, get urgent medical help straight away rather than waiting for a scan.
Preparing for your scan
No special preparation is usually needed. Because a leg MR angiogram normally uses contrast dye, let us know when you book if you have kidney problems or have had a reaction to contrast before. If you have diabetes, tell us when booking.
You can usually eat, drink and take your normal medicines unless the scanning centre tells you otherwise. Wear loose, comfortable clothing without metal zips or buttons, and leave jewellery at home. You will be asked to remove metal items such as hair clips, hearing aids, coins and keys, and you may be asked to change into a gown.
Before the scan you will complete a safety questionnaire. Tell the team if you have a pacemaker, any metal implant, surgical clips or other device, if you have kidney problems or allergies, or if you are, or might be, pregnant or breastfeeding. If you feel anxious in enclosed spaces, let us know when you book. Some centres can offer a relaxant, and if you take one you will need someone to take you home and must not drive for 24 hours.
Frequently asked questions
Do I need a referral for an MR angiogram of the leg?
Yes. This scan requires a referral from a specialist, such as a vascular surgeon. Please upload your referral when you book so the scanning centre can check that the right scan is arranged.
What is peripheral arterial disease?
Peripheral arterial disease (PAD) is narrowing of the arteries in the legs caused by a build-up of fatty deposits. It can cause leg pain when walking that eases with rest, although many people have no symptoms. An MR angiogram can show where the arteries are narrowed or blocked.
Is MRA better than ultrasound for leg arteries?
They are used together. Ultrasound is usually the first test. A contrast-enhanced MR angiogram gives a more complete map of the arteries and is often used when treatment such as angioplasty or surgery is being planned.
Will I need a contrast injection?
Usually, yes. Contrast dye helps the arteries show up clearly. It is given through a small cannula in your arm and is charged separately where it is needed.
Sources
- RadiologyInfo.org – Magnetic Resonance Angiography (MRA)
- NHS – Peripheral arterial disease (PAD)
- NICE CG147 – Peripheral arterial disease: diagnosis and management
- NHS – MRI scan
The information on this page has been gathered from various sources and is provided for general information only. It is not medical advice. TOP MRI is not liable for the accuracy or completeness of this information. Please speak to your doctor or the scanning centre about your own situation.