Frequency and scale domain analysis of complex quadrature embolic Doppler ultrasound signals

Early and accurate detection of emboli is important for monitoring of preventive therapy in stroke-prone patients. One of the problems in detection of emboli is the identification of an embolic signal caused by very small emboli. The amplitude of the embolic signal may be so small that advanced processing methods are required to distinguish these signals from Doppler signals arising from red blood cells. The windowed Fourier transform has been widely used by commercial Doppler ultrasonic systems. An alternative approach is the wavelet transform. Here, we present comparison of time-frequency (based on complex fast Fourier transform) and time-scale (based on complex wavelet transform) analysis. The results reveal that the wavelet transform provides an optimized temporal resolution and time localization for analysis and detection of embolic signals.