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A Doppler ultrasound is a non-invasive test that can depict blood flow by bouncing high-frequency sound waves off of red blood cells to create images of blood vessels, tissues, and organs. Faintness or absence of sound may indicate an obstruction in the blood flow.
The amount of blood pumped with each beat is an indication of the size of a vessel's opening. Also, Doppler ultrasound can detect abnormal blood flow within a vessel, which can indicate a blockage caused by a blood clot, a plaque, or inflammation.