A Doppler test is a type of exam that uses sound waves to see how blood flows through a blood vessel, states WebMD. During a Doppler test, sound waves are sent into an area that then bounce off solid objects, such as blood cells, and return to the transceiver.
The movement of blood cells in a blood vessel causes the transceiver's pitch to change in a fashion that mirrors the Doppler effect, according to WebMD. Computers can then interpret the varying pitch or create visual representations of one's blood flow. If there is no blood flow present, the pitch doesn't change.
Usually, Doppler tests are performed to find blood clots or narrowed blood vessels, states WebMD. It can also be used to check a patient's blood flow after a stroke and map veins that can be used for blood vessel grafts. Sometimes, the test is used to check for plaque that develops in blood vessels or to check the health of a fetus by checking blood flow through the umbilical cord.
There are three types of Doppler tests, according to WebMD. The first, called continuous-wave Doppler is used to help doctors evaluate blood flow by sound alone. The second, called duplex Doppler, creates a picture of blood vessels and surrounding organs. Finally, color Doppler is used to create images of blood vessels by converting sound into color.