Neck MRA (blood vessel MRI, without contrast)

What it is

A great many strokes do not begin in the brain. They begin in the neck, where plaque built up in a carotid artery either narrows it or sheds a fragment that travels upward and lodges in a brain vessel. Finding that out changes what happens next, because a narrowed neck artery is something that can be treated directly. This study is the search for it: a map of the two carotid arteries and the two vertebral arteries along their course from the chest to the base of the skull.

The unenhanced version relies on flowing blood producing its own signal, so no needle is involved. In the neck this is a reasonable but imperfect technique — the vessels are long, they curve, and flow through a tight narrowing becomes turbulent, which can make a stenosis look worse than it is. Radiologists know this and read accordingly, and it is why a contrast-enhanced neck MRA exists as a separate, more expensive code.

Why it is done

• To look for narrowing of a carotid artery after a stroke or a transient ischemic attack
• To investigate a bruit — a whooshing sound a clinician hears over the neck artery with a stethoscope
• To look for a tear in the wall of a carotid or vertebral artery, which can follow a neck injury and is a recognized cause of stroke in younger adults
• To follow a narrowing that is known about and being watched rather than operated on
• To check the neck vessels in someone who cannot have iodinated contrast for a CT angiogram

What to expect

There is no fasting, no needle and no preparation beyond the metal questionnaire, which is detailed because the magnet is always on. You lie on your back with a coil placed around the neck, head first in the tube. Stillness is the whole requirement, and in the neck that includes swallowing: repeated swallowing blurs a sequence and gets it repeated. Scanning takes roughly fifteen to thirty minutes for the neck alone, though many appointments are longer because a brain study is booked alongside it. Hearing protection is provided. You leave and carry on with your day.

Questions worth asking

• Head and neck are separate codes. Ask whether the order covers the neck only, or the neck plus the head, and get an estimate for each line.
• Ask whether a carotid ultrasound would answer the same question here. It is a far cheaper study and is often the first test for carotid narrowing.
• Confirm that this is the unenhanced code. The contrast-enhanced neck MRA is a different and higher-priced code, and orders are sometimes changed at the scanner.
• Ask whether the reading radiologist bills separately from the imaging facility, and whether both are in your network.
• If you are being scanned in a hospital outpatient department, ask what the same code costs at the system's freestanding imaging centre.