Carotid ultrasonography is an ultrasound-based diagnostic imaging technique to reveal structural details of the carotid arteries, so as to look for blood clots, atherosclerotic plaque buildup, and other blood flow problems. Carotid ultrasonography is an ultrasound-based diagnostic imaging technique to reveal structural details of the carotid arteries, so as to look for blood clots, atherosclerotic plaque buildup, and other blood flow problems. A carotid duplex is a carotid ultrasonography carried out by duplex ultrasonography. A duplex carotid ultrasound may include a Doppler ultrasound, a special test able to reveal the movement of blood cells through the carotid arteries.