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 have leg pain or swelling, or if you have had a previous history of deep vein thrombosis (DVT), your doctor may suggest you to take this test.