The use of the wavelet transform to describe embolic signals

A number of methods to detect cerebral emboli and differentiate them from a rtefacts using Doppler ultrasound have been described in the literature. In most, Fourier transform-based (FT) spectral analysis has been used, The FT is not ideally suited to analysis of short-duration embolic signals due to an inherent trade-off between temporal and frequency resolution. An altern ative approach that might be expected to describe embolic signals well is t he wavelet transform. Wavelets are ideally suited for the analysis of sudde n short-duration signal changes, Therefore, we have implemented a wavelet-b ased analysis acid compared the results of this with a conventional FFT-bas ed analysis. The temporal resolution, as measured by the half-width maximum , was significantly better for the continuous wavelet transform (CWT), mean (SD) 8.40 (8.82) ms, compared with the 128-point FFT, 12.92 (9.70) ms, and 64-point FFT, 10.80 (5.69) ms. Time localization of the CWT for the emboli c signal was also significantly better than the FFT, The wavelet transform appears well suited to the analysis of embolic signals offering superior ti me resolution and time localization to the FFT, (C) 1999 World Federation f or Ultrasound in Medicine & Biology.