Carotid Ultrasound and Transcranial Doppler: Non-Invasive Tests for Stroke Risk

Your brain depends on a constant supply of blood delivered through the arteries in your neck and inside your skull. When those arteries become narrowed or blocked, the risk of stroke rises. The good news is that the condition of these vessels can be checked quickly and painlessly with ultrasound. Two of the most useful tests are the carotid duplex ultrasound and the transcranial Doppler (TCD).

Carotid and transcranial testing is available in our Westwood, NJ office. This article explains what each test examines, who should have it, what the experience involves and how the results influence treatment.

The Arteries That Supply the Brain

Blood reaches the brain through two pairs of arteries in the neck. The two carotid arteries run up the front of the neck, one on each side, and supply most of the front and middle of the brain. The two vertebral arteries travel along the spine and supply the back of the brain, brainstem and cerebellum. Inside the skull these arteries connect and branch into a network of smaller vessels.

Over time, fatty deposits called plaque can build up in artery walls, a process known as atherosclerosis. Plaque can narrow the artery (stenosis) and reduce blood flow. Even more importantly, pieces of plaque or small blood clots can break off and travel into the brain, causing a stroke or a transient ischemic attack (TIA).

Carotid Duplex Ultrasound

A carotid duplex ultrasound combines two kinds of ultrasound:

• Imaging ultrasound, which creates a picture of the artery wall and any plaque inside it.
• Doppler ultrasound, which measures the speed and direction of blood flow. Blood speeds up as it squeezes through a narrowed segment, so flow velocities are used to estimate how severe a narrowing is.

The test also checks the vertebral arteries, including the direction of blood flow, which can reveal problems further down in the circulation.

What to expect

You lie on your back with your head turned slightly to one side. A clear warm gel is applied to your neck, and a handheld probe is moved gently along the artery. You may hear whooshing sounds, which are the blood flow signals. The test usually takes 20 to 40 minutes. There are no needles, no contrast dye and no radiation.

Transcranial Doppler (TCD)

The skull blocks most ultrasound, but there are thinner areas, called "windows," where sound waves can pass through. Transcranial Doppler uses a probe placed over the temples, the back of the head and sometimes the closed eyelid to measure blood flow in the major arteries inside the skull.

TCD can help:

• Detect narrowing of arteries inside the head (intracranial stenosis).
• Assess how well blood flow is compensating around a blocked artery in the neck.
• Detect tiny particles (microemboli) passing through brain arteries, which can signal an active source of clots.
• Screen for a right-to-left shunt, such as a patent foramen ovale (a small opening between the chambers of the heart), using a "bubble study" in which agitated saline is injected into an arm vein.
• Monitor blood vessel spasm after bleeding in the brain, usually in the hospital.

Like carotid ultrasound, TCD is painless and radiation-free. A standard study often takes 30 to 45 minutes; specialized monitoring studies take longer.

Who Should Be Tested?

Your neurologist may recommend carotid and/or transcranial testing if you:

• Have had a stroke or TIA, including brief episodes of weakness, numbness, trouble speaking or temporary loss of vision in one eye.
• Have a carotid bruit, an abnormal sound heard through a stethoscope over the neck.
• Have known atherosclerosis elsewhere, such as coronary artery disease or peripheral artery disease.
• Have dizziness or vertigo episodes that raise concern about blood flow to the back of the brain.
• Need monitoring of a previously detected narrowing or follow-up after carotid surgery or stenting.

Routine screening of people without symptoms is not recommended for everyone. Your doctor will weigh your risk factors, such as high blood pressure, high cholesterol, diabetes, smoking and family history, to decide whether testing will change your care.

How to Prepare

• Wear a top with an open neckline and avoid necklaces or high collars.
• You can eat and take your medications normally.
• For TCD, avoid heavy hair products on the day of the test, since gel needs to contact the skin of the temples.
• If a bubble study is planned, a small IV line will be placed in your arm.
• Bring prior imaging reports, especially previous ultrasound, CT angiography or MRI angiography results, for comparison.

Understanding the Results

Carotid narrowing is usually reported as a percentage range, such as less than 50 percent, 50 to 69 percent, or 70 percent or more. The significance of a narrowing depends heavily on whether it has caused symptoms.

• Mild to moderate narrowing is typically managed with medical therapy: antiplatelet medication when appropriate, a statin, blood pressure and diabetes control, exercise and stopping smoking.
• Severe narrowing in an artery that has caused a stroke or TIA may benefit from a procedure to clear or open the artery, such as carotid endarterectomy or stenting, often performed soon after the event. Your neurologist would coordinate referral to a vascular specialist.
• Severe narrowing without symptoms requires an individual discussion of risks and benefits.

Ultrasound findings are sometimes confirmed with additional imaging, such as CT angiography or MR angiography, especially before a procedure.

Reducing Your Stroke Risk

Whatever your results, the same habits protect your arteries: keep blood pressure and cholesterol in your target range, manage diabetes, avoid tobacco, stay physically active, maintain a healthy weight and follow a diet rich in vegetables, fruit, whole grains and healthy fats. If you have an irregular heart rhythm such as atrial fibrillation, appropriate treatment is essential. And everyone should know the warning signs of stroke. Review them in our guide to stroke warning signs and TIA.

Neurovascular Testing in Westwood, NJ

Dr. David D. Van Slooten is board certified in Neurosonology, the specialty focused on ultrasound of the blood vessels of the brain, and lists carotid and transcranial ultrasound among his specialized interests. Stroke is also a clinical interest of Dr. Lorraine S. Lira.

To learn more, review our neurology services, or find directions and visit information on our contact page.

This article is for general education and does not replace advice from your own physician. If you think you are having a medical emergency, call 911.