Doppler Ultrasound Doppler ultrasound is a noninvasive test that uses sound waves to take a close look inside your blood vessels and measure blood flow. While a regular ultrasound can create pictures of the vessels, a Doppler ultrasound estimates how fast blood is flowing flows by measuring the rate of change in its pitch (frequency). Your doctor may recommend a Doppler ultrasound to diagnose a blood clot, venous insufficiency, a blocked artery, or an aneurysm. During the test, a technician presses a small wand (transducer) firmly against your skin. It typically takes 30 minutes, and you’ll be able to return home after the test.