Coded Spectral Doppler Imaging: from simulation to real-time processing

Transmission of coded pulses and matched receive filtering can improve the ultrasound imaging penetration depth while preserving the axial resolution. This paper shows that the pulse compression technique may be integrated in a low-cost scanner to be profitably used also in spectral Doppler investigations. By operating on beamformed, demodulated and down-sampled data in the frequency domain, a single digital signal processor is proved sufficient to perform both pulse compression and (multigate) spectral Doppler algorithms in real-time. Simulations, phantom and in vivo experiments demonstrate that the transmission of (2.5 μs or 5μs long) linear frequency modulated chirps with bandwidths over the range 1.6-5.4 MHz, rather than of corresponding sine burst pulses, provide SNR improvements very close to theory. Even in the presence of selective tissue attenuation, SNR gains up to 11dB and 13.3dB have been obtained for the short and the longer chirp, respectively. This may be important in clinical Doppler applications where the needed penetration depth is not achieved with sufficient SNR unless very long bursts are transmitted.