Comparison of zero crossing counter to FFT spectrum of ultrasound Doppler

Doppler data were obtained from a normal carotid, popliteal, and radial artery. It was found that the results of a digital zero-crossing counter-mean frequency estimate and the first moment of the FFT (fast-Fourier-transform)-generated spectra were comparable for high signal-to-noise ratio (SNR), as in the case of the carotid arterial waveform. However, the digital zero-crossing with thresholding was a more accurate representation of the expected velocity-vs.-time waveforms in the case of low-SNR Doppler obtained from the popliteal and radial arteries.