Single-Channel Digital Demodulation of Ultrasound Bandpass Signals for Flow -Imaging Applications
Operation of ultrasound Pulsed Wave (PW) f1owmeters is based on the emission of a burst of acoustic energy at a rate PRF1. Typically, the Radio-Frequency (RF) received echoes are synchronously demodulated on two quadrature channels, so that, for each depth of interest, a couple (I and Q) of samples are selected. The continuous Doppler signal can be reconstructed through Low-Pass Filters (LPF’s) which are also useful to minimize the noise bandwidth. Finally, suitable High-Pass Filters (HPF’s) can be used to reject the unavoidable high-level low-frequency components (“clutter”), originated from vessel wall slow movements. For a correct detection of Doppler frequencies, careful amplitude and phase match between the two channels must be ensured.
KeywordsExpense Autocorrelation Cross Correlation Acoustics
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