Vascular ultrasound provides pictures of the body’s veins and arteries. Doppler ultrasound is a special ultrasound technique that evaluates blood flow through a blood vessel, including the body’s major arteries and veins in the abdomen, arms, legs and neck. Doppler ultrasound measures the direction and speed of blood cells as they move through vessels. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). A computer collects and processes the sounds and creates graphs or color pictures that represent the flow of blood through the blood vessels.