Doppler ultrasound

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Doppler ultrasound (dop-ler) n. a diagnostic technique utilizing the fact that the frequency of sound or light waves changes when they are reflected from a moving surface. It is used to study the flow in blood vessels and the movement of blood in the heart. The frequency detector may be part of the ultrasound imaging probe, which displays an image of the anatomy on a monitor. Simultaneously, the Doppler signal from a particular point on the image can be displayed next to the anatomical position using a split screen (duplex imaging). Direction and velocity of blood flow can each be allocated different colours and displayed on a colour monitor over the anatomical image (colour flow ultrasound imaging). [ C. J. Doppler (1803–53), Austrian physicist]