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What is Doppler effect results from the change in and explain in detail?
An ultrasound beam insonating a blood vessel is paially reflected by red blood cells. If these are moving, there is a change in the frequency of the reflected pulse: an increase in frequency if the flow is towards the probe and a decrease if it is away from it. This is the Doppler effect and the changes in frequency referred to as the Doppler shift. (Ref: Grainger and Allison&;s diagnostic radiology 6th edition, page 63)