Time-scale analysis of quadrature Doppler ultrasound signals

Most Doppler ultrasound systems employ quadrature demodulation techniques a t the detection stage. The information concerning flow direction, encoded i n the phase relationship between in-phase and quadrature-phase channels, is not obvious at this stage. The complex fast Fourier transform can be used to obtain directional information in the frequency domain, as well as time- frequency analysis of Doppler signals. However, it has an inherent time-fre quency resolution limitation. The wavelet transform allows the time-frequen cy resolution compromise to be optimised. Mapping directional information i n the scale domain is also desirable. A method is described, based on the u tilisation of complex wavelets and negative scales. It eliminates the inter mediate processing stages for obtaining directional Doppler signals for tim e-scale analysis.