The carotid ultrasound is most frequently performed to detect narrowing of the carotid artery, a condition that substantially increases the risk of stroke. Ultrasound is a safe and painless technique that produces pictures of the inside of the body using sound waves. It uses a small probe called a transducer and gel placed directly on the skin. High-frequency sound waves travel from the probe through the gel into the body. The probe then collects the sounds that bounce back and a computer uses those sound waves to create an image. Ultrasound exams do not use radiation (as used in x-rays). Because images are captured in real-time, they can show the structure and movement of the body's internal organs. They can also show blood flowing through the body's two carotid arteries and provides detailed pictures of these blood vessels and information about the blood flowing through them. The images help the physician diagnose and treat medical conditions of the arteries in the neck.