Improving Performance of Pulse Compression in a Doppler Ultrasound System Using Amplitude Modulated Chirps and Wiener Filtering

The use of coded excitation and pulse compression in transcranial Doppler (TCD) ultrasound systems is in the very early stages; the optimal processing scheme has yet to be determined. This study uses linear frequency-modulated (FM) chirps with 0.8-MHz bandwidth and compares the use of pulses with and without amplitude modulation and also matched filtering vs. Wiener filtering. The results demonstrate that using amplitude-modulated pulses vastly improves the axial resolution and provides a more predictable mainlobe-to-sidelobe distance in the radiofrequency (RF) signal. It is also shown that a Wiener filter can provide better performance than a matched filter, in terms of axial resolution and sidelobe level in the RF signal and signal-to-noise ratio in conventional sonograms. Although this study uses a TCD system, the techniques described are equally as applicable in other Doppler ultrasound devices. (E-mail: j.cowe@le.ac.uk)