Basic Physical and “Technical Principles Doppler” and Duplex Sonography

This will be explained below Regarding the basic techniques of ultrasound dopler:

Continuous-wave (CW) Doppler:
>Principle: Twopiezoelectriccrystalsareused,oneforthecontinuous transmission of ultrasound pulses (continuous wave) and one for the reception of reflected ultrasound signals.
Signal display: The frequency spectra of returning echoes are displayed acoustic all yand also visually if desired.The frequency shift scan beused to calculate the direction and velocity of blood flow. This technique does not, however, provide information on the depth or range of the echo source.
Pulsed Doppler: Principle: histechniqueemploysonepiezoelectriccrystalthatfunctionsalternately as a transmitter and receiver (pulsed wave).
Signaldisplay: Echosignalsarerecordedfromadesignatedsamplevolumeduring the receiving phase of the scan. This makes it possible to determi ne the
depth and width of the sample volume and investigate blood flow within a circumscribed area.
Duplex sonography:
Principle: CW or pulsed Doppler is combined with B-mode imaging, providing visual feedback for positioning the Doppler beam and the sample volume.
Power Doppler: This technique demonstrates the spatial distribution of blood flow but cannot determine flow direction. It is most useful in establishing the presence or absence of vascularity and evaluating the quantity of blood flow.
Power Doppler is excellent for detecting increased vascularity due to inflammation, for example.
Spectral Doppler: The spectral analysis of blood flow patterns is used to  determine the time course and velocity distribution of the flow, ,its mean and maximum velocities. This is of key importance in the diagnosis of vascular stenosis.

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