Carotid duplex is a procedure that uses ultrasound to look for plaques, blood clots, or other blood flow problems in the carotid arteries. The carotid arteries, located in the neck, supply blood to the brain.It may be performed if a patient has high blood pressure or a carotid bruit - an abnormal sound in the neck that is heard with the stethoscope. Other risk factors calling for a carotid ultrasound are advanced age, diabetes, elevated blood cholesterol, and a family history of stroke or heart disease. A water-soluble gel is placed on the skin where the transducer (a handheld device that directs the high-frequency sound waves to the arteries being tested) is to be placed. The gel helps transmit the sound to the skin surface where images of the carotid arteries and pulse wave forms are obtained. The test assesses blood flow and is used to detect the conditions involving stenosis (narrowing and hardening), thrombosis (clotting), and other causes of obstruction in the carotid arteries.