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.
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.