What is carotid Doppler ultrasound?
Carotid Doppler ultrasound (also called carotid duplex) is a test that uses reflected sound waves—the same used to see the fetus during pregnancy to create detailed images of the inside of the carotid arteries in the neck. The test does not require entering the body (it is noninvasive). Carotid Doppler ultrasound is used to check for blood flow problems caused by blood clots or fatty deposits (plaque) on the walls of the arteries. The test can also detect tears in the carotid artery or a hematoma (a mass of clotted blood), which can interfere with blood flow.
Carotid Doppler ultrasound is usually the first imaging test used to diagnose carotid artery disease caused by plaque (atherosclerosis), which can cause a blocked-vessel (ischemic) stroke.
A. Illustration showing the device placed on the side of the neck during a carotid Doppler ultrasound. B. Color ultrasound image showing the flow of blood inside the carotid artery on the side of your neck. C. Waveform image showing the sound of flowing blood in the carotid artery. Source: National Heart, Lung, and Blood Institute
How does carotid Doppler ultrasound work?
The carotid Doppler ultrasound test evaluates the flow of blood through the carotid arteries and detects any blockages caused by blood clots or atherosclerosis. A small hand-held device (called a probe) that looks like a microphone is placed lightly on your neck. The device gives off high-frequency sound waves that pass into the body and bounce off the arteries and the red blood cells moving through them, like an echo. The echoes are picked up by the device and sent to a computer, which converts them into moving images of the inside of the carotid arteries and measurements of the speed and direction of the blood flow.
Who might have a carotid Doppler ultrasound?
If you have never had a stroke but have very high blood pressure and your doctor suspects or has heard an abnormal whooshing sound in your neck (carotid bruit) with a stethoscope, a carotid Doppler ultrasound may be done to see if there are blockages or narrowing in your carotid artery. A carotid bruit is a sign that plaque is interfering with the blood flow in your carotid artery and you may be at risk for stroke. Routine screening for stroke is not recommended if you do not have any symptoms.
A carotid Doppler ultrasound is also the first screening test to determine if you are eligible for treatment to prevent a first or repeat stroke.3 If you have recently had a stroke, an ultrasound to evaluate your risk of another stroke will only be performed after your first stroke has been diagnosed (with CT or MRI) and treated (with tPA, if you are eligible). If the test shows signs of severe narrowing (70% or more) you will usually undergo a more sensitive test such as angiography to determine if you would benefit from treatments such as carotid endarterectomy and carotid stenting. In some hospitals a carotid Doppler ultrasound is the only imaging test used to screen patients for carotid endarterectomy.
The test may also be used after you undergo one of these procedures to make sure the treatment was successful and blood is flowing normally through the artery.
Should carotid Doppler ultrasound be used for stroke screening in healthy people?
Recently, some companies have started to offer stroke screenings for healthy people using the carotid Doppler ultrasound test. Screening for stroke refers to tests given to people who have no signs or symptoms of artery blockage or stroke. Many people have a “better safe than sorry” viewpoint, reasoning that peace of mind is worth the price of the test. However, in 2007 the US Preventive Services Task Force issued a statement saying that neither carotid ultrasound nor any other imaging test should be used as a screening test for stroke in the general population.
At first glance, a test like ultrasound might seem harmless, but there are hidden risks when it is used in people who are not at high risk for stroke (click here to find out your stroke risk). There is a chance of a false positive with this test, meaning that it could detect a blockage that is not there. When this happens, an angiogram is usually used to try to confirm the results of the ultrasound; the angiogram test requires inserting a catheter into your arteries, which can cause serious complications such as stroke or even death.
If you are generally healthy but are concerned about your stroke risk, the best thing you can do is have regular tests for stroke risk factors like high blood pressure, high cholesterol, and diabetes, and work to control any risk factors you do have.