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What is a carotid artery duplex scan?

A carotid artery duplex scan is a type of vascular ultrasound study done to assess the blood flow of the arteries that supply blood from the heart through the neck to the brain. There are six carotid arteries -- the right and left common carotid arteries, which divide and form the right and left internal carotid arteries and the right and left external carotid arteries. One pair (external and internal) is located on each side of the neck.

A carotid artery duplex scan is a noninvasive (the skin is not pierced) procedure. The term "duplex" refers to the fact that two modes of ultrasound are used -- Doppler and B-mode. The B-mode transducer (like a microphone) obtains an image of the carotid artery being studied. The Doppler probe within the transducer evaluates the velocity and direction of blood flow in the vessel.

A transducer sends out ultrasonic sound waves at a frequency too high to be heard. When the transducer is placed on the carotid arteries at certain locations and angles, the ultrasonic sound waves move through the skin and other body tissues to the blood vessels, where the waves echo off of the blood cells. The transducer picks up the reflected waves and sends them to an amplifier, which makes the ultrasonic sound waves audible. Absence or faintness of these sounds may indicate an obstruction to the blood flow.

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