A Doppler ultrasound is performed by passing the Doppler over the skin and measuring the waves that come back, as stated by WebMD. The aim is to identify how blood is flowing through a vessel. Doctors usually perform a continuous wave Doppler, duplex Doppler or color Doppler.
During the ultrasound, the doctor identifies the blood vessels for investigation and passes the Doppler over the skin. The sound waves the Doppler emits bounce off blood cells and feed a signal back to the ultrasound machine, allowing the physician to identify conditions. During a continuous wave Doppler, the doctor listens for sounds that indicate underlying pathologies. This is a bedside procedure.
Duplex Doppler's are performed in the same manner, but they produce an image in the form of a graph. Using this information, doctors can determine how the blood is flowing, including the speed and direction. Color Doppler's also examine the speed and direction, but they produce color images to identify how the blood moves through organs.
Doctors may use a Doppler ultrasound for a number of conditions. This includes looking for blood clots, examining varicose veins, evaluating atherosclerosis or examining the brain after a stroke. Patients preparing for ultrasounds should avoid smoking up to 2 hours before the test to avoid false results.