A Doppler ultrasound is a test that uses high-frequency sound waves to measure the amount of blood flow through your arteries and veins, usually those that supply blood to your arms and legs. This test can detect abnormal flow within an artery or blood vessel and can help to diagnose and treat a variety of conditions, including blood clots and poor circulation. If you show signs of decreased blood flow in the arteries or veins of your legs, arms, or neck, your doctor may suggest use to take this test.