Carotid Artery Ultrasound (Duplex)

What it is

The question this test answers is how narrow the carotid arteries have become, because narrowing there is a direct route to a stroke — either by choking off flow or by shedding debris that travels up into the brain. Duplex refers to doing two things at once. The grey-scale picture shows the wall of the vessel and any plaque built up along it. The Doppler part measures how fast blood is moving at each point, and speed is what converts an image into a number: blood forced through a tighter opening accelerates, so the peak velocity is used to estimate the degree of narrowing. That estimate, more than the picture, is what a vascular surgeon acts on.

Why it is done

• To assess the carotid arteries after a stroke or a transient ischemic attack, the brief episode sometimes called a mini-stroke
• To investigate a bruit, the whooshing sound a doctor may hear over the neck with a stethoscope
• To follow known narrowing over time and see whether it is progressing
• To check the arteries before certain major operations
• To examine the arteries after a procedure to open or bypass them

What to expect

There is nothing to prepare. Patients lie on their back with the head turned slightly to one side, and a collar or high neckline is removed so the neck is accessible. Warm gel is applied and the probe is moved along each side of the neck in turn. The Doppler portion produces a pulsing, whooshing sound from the machine, which is the sound of blood flow, not a sign of a problem. The exam is painless and typically takes something like fifteen to thirty minutes for both sides. The images and measurements go to a physician for interpretation, so results are not usually given during the appointment.

Questions worth asking

• This code is the complete bilateral study. A limited or follow-up study is a different code at a lower price — ask which one was ordered.
• Carotid screening in someone with no symptoms is frequently not a covered benefit. If this is being done as a screen rather than for a symptom, ask the insurer before the appointment, not after.
• Ask whether the reading physician bills separately from the vascular lab, and whether both are in network.
• Be careful with heavily advertised low-cost vascular screening events; ask what code is billed and whether a physician interpretation is included.
• If a CT or MR angiogram of the neck is likely to follow to confirm the finding, ask what that would cost, since the ultrasound is often the first of two tests rather than the last.