Detection of embolic signals using wavelet transform

Early and accurate detection of microemboli is important for monitoring of preventive therapy in stroke-prone patients. Embolic signals have large amplitude and show transient characteristics because of their reflectivity and size compared to the blood cells. One of the problems in detection of microemboli is the identification of an embolic signal caused by very small microemboli. The amplitude of the embolic signal may be so small as to require some sort of advanced processing techniques to distinguish these signals from Doppler signals arising from red blood cells. The windowed Fourier transform (WFT) has been widely used by commercial Doppler ultrasonic systems. However it is not ideally suited to analysis of short duration embolic signals due to an inherent trade-off between time and frequency resolution. An alternative approach is the wavelet transform, which might be expected to describe embolic signals well. In this paper we show that the temporal resolution and time localisation of the wavelet transform are better than that of the WFF.