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What does Doppler ultrasound do?
- Detects the pressence, velocity, and properties and direction of blood flow.
- Velocity is both speed and direction.
What is Doppler Effect?
An apparent change in frequency of sound observed if there is relative motion bwn sound source and the receiver of the sound (or listener).
When Whistler moving toward listener:
- Shorter Wavelength
- Higher Frequency
- Positive Doppler Effect
When Whistler moving away from listener:
- Longer Wavelength
- Low Frequency
- Negative Doppler Effect
What is Doppler Shift?
- the difference bwn the received txd frequency and the sent txd frequency.
- Doppler Shift (Hz)= Reflected Frequency - Transmitted Frequency.
- Fd =Fr-Ft
What is Doppler Equation?
Range of Doppler shifted frequency
- Between 20Hz and 20000 Hz (20kHz)
- This is audible range.
Effects of beam angle on Dopple shift:
- Doppler angle and doppler shift are inversely proportional.
- Increase Doppler angle, Decrease Dopple shift
- Increase Doppler angle, Decrease Cosine of angle