Carotid Duplex Scans are tests done using a handheld device (transducer) applied to the neck area, where the carotid arteries (the arteries that supply blood to the brain) are located. Sound waves are used to produce a visual image of the artery and to measure the blood flow through the artery. This may be done on one side of the neck, or on both sides. The scan can detect the severity and location of any blockages in these arteries. Your provider uses this information to determine the best course of treatment for you, if any is needed.