Have you know what is Doppler Measurement?

The Doppler Effect describes the shift in wave length frequency or pitch that result when sound or light from any portion of the electromagnetic spectrum are influenced by the distance and directional movement of the object. Both ultrasound and laser Doppler techniques rely on this physical principle to make the skin blood flow measurement.
A continuous wave Doppler ultrasound emits a high frequency sound wave from which reflected or echo sounds can be used to calculate the direction of flow and velocity of moving objects (circulating blood cells).When ultrasound equipment

is pulsated, the depth of the circulatory flow vessel can be identified.
The blood flow is assessed in Doppler units or volts and can be continuously monitored over a small surface area. Similar measurements can be made with the laser Doppler technique, but neither technique is able to yield quantitative blood flow values except through reference data obtained by VOP.
TheDoppler ultrasound signal is the reflection of an ultrasonic beam due to moving red blood cells and provides information regarding blood vessels and heart chambers. Doppler ultrasound(ultrasound machine) signals in patients with narrowing of the aortic valve were analyzed using the spectrogram by Cloutier et al. [1991]. Guo and colleagues [1994] examined and compared the application of five different time–frequency representations (the spectrogram, short-time AR model, CWD, RID, and Bessel distributions) with simulated Doppler ultrasound signals of the femoral artery. Promising results were obtained fromthe Bessel distribution, the CWD, and the short-time AR model.
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