Analysis of embolic signals by transcranial Doppler for the characterization of emboli

Recent reports have indicated that the transcranial Doppler (TCD) method makes it possible to detect microemboli originated from various sources. However, the embolic signal obtained by TCD varies in sound, pitch and duration according to its size and materials of which it is composed. Moreover, some artificial sounds mimic embolic ones. Considering this, the authors tried to analyze acoustic power, frequency and duration of embolic TCD signals and also tried to clarify the deference between embolic and artificial TCD signals. As a result, the authors have confirmed that the frequency of embolic signal was considerably higher than that of artificial noise and that the duration was shorter in case of emboli originating from carotid lesions than those of cardiac origin. These results suggest that analysis of each component of the embolic TCD signal sound might make it possible to differentiate the embolic signal from artificial ones and to confirm its source.