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Aliasing is an artifact that lowers the frequency components when the PRF is less than 2 times the highest frequency of a Doppler signal
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Beat frequency, for CW Doppler, is the Doppler shift
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Doppler shift is the change in the perceived frequency relative to the transmitted frequency. Doppler shift frequency: fD = fr - f0 = 2f0v/c
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Doppler shift frequency with incident angle: fD = 2f0v/c cos q
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Ensemble length -packet size, shots per line- is the number of pulses per scan line. In color Doppler, each line of sight most be pulsed several times
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FFT. Fast Fourier Transform analyzer is a common device that performs spectral analysis in ultrasound instruments. In this case, it displays different quadrature Doppler frequencies, or reflector velocities when a sample volume cursor is used (Doppler frequency is proportional to reflector velocity) along time
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High pass filter is the wall filter
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Nyquist Frequency is the maximum frequency that can be sampled without aliasing. NF = PRF/2 (PRF stands for Pulse Repetition Frequency)
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Quadrature detection is a signal processing method for directional Doppler in which the signal reference frequency for two channels differ in phase by 1/4 period. The output Doppler signal phase for both channels also depends on the Doppler shift, whether positive or negative
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Spectral analysis is the quantitative analysis to display the distribution of frequencies
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Variance is the variation of Doppler frequencies within each pixel during a pulse packet, efective to detect turbulence with color Doppler