Doppler Ultrasound

A Doppler ultrasound test uses reflected sound waves to evaluate blood as it flows through a blood vessel. It helps doctors evaluate blood flow through the major arteries and veins of the arms, legs, and neck. It can show blocked or reduced blood flow through narrowing in the major arteries of the neck that could cause a stroke. It also can reveal blood clots in leg veins (deep vein thrombosis, or DVT) that could break loose and block blood flow to the lungs (pulmonary embolism). See an illustration of a stroke and an embolus . During pregnancy, Doppler ultrasound may be used to look at blood flow in an unborn baby (fetus) to check the health of the fetus.

During Doppler ultrasound, a handheld instrument (transducer) is passed lightly over the skin above a blood vessel. The transducer sends and receives sound waves that are amplified through a microphone. The sound waves bounce off solid objects, including blood cells. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). If there is no blood flow, the pitch does not change. Information from the reflected sound waves can be processed by a computer to provide graphs or pictures that represent the flow of blood through the blood vessels. These graphs or pictures can be saved for future review or evaluation. See an illustration of a Doppler ultrasound .