Real time software processing and audio reproduction of directional Doppler signals

In ultrasound Doppler systems, directional signals are typically obtained by processing quadrature demodulated data with dedicated analog or digital circuits. In this paper, a software approach is proposed, that allows fully exploiting the reproduction and recording capabilities of low-cost personal computer sound cards and/or embedded chips. Forward/reverse signals are separated through a wideband Hilbert filter. No limitations are imposed on the input signal sample rate, which is matched to the standard output format of sound cards through a band-limited interpolation filter controlled in a feedback loop. The digital audio streaming is performed in real-time in a Windows®-based application. The processed data are in a standard format compatible with real-time recording in waveform or compressed files, as requested in many research applications. Simulations and in vivo tests show a typical cross talk of -50 dB between forward and reverse components, with low latency time (39 ms) and central processing unit load compatible to currently available personal computers.