Ultrasound Harmonic Classification of Microemboli

The ultrasound community has experienced dramatic technical advances over the last decades, such as blood °ow measurements with elabo rate Doppler techniques or real time three-dimensional imaging with 2-D phased array transducers. This was partly ascribed to the advantages of ultrasound over other diagnostic modalities, including its low cost, real time character and safety. One of these recent ultrasound technologies is Transcranial Doppler (TCD). TCD is a non-invasive ultrasound method used to assess blood °ow velocity in the major basal intracranial arteries on a real time basis. Since the early 60's, experimental studies have been carried out to evaluate the ability of TCD to detect, quantify and classify intracranial emboli. Many research centers have investigated the appearance of high intensity tran sient signals in the TCD waveform as indicators of circulating microemboli, in a wide variety of clinical areas: cardiac and carotid surgery1;2, following prosthetic heart valve insertion3, cerebral angiography4, atrial ¯brillation5 and decompression sickness6 . Many reports have emphasized the ability of TCD, combined to sophisticated signal processing techniques, to iden tify microemboli in the brain circulation. Unfortunately, this technology presents some limitations to distinguish between emboli and artefacts7¡11 and more importantly to determine the embolus composition12¡14 . There fore, the accuracy and clinical signi¯cance of the TCD technique for emboli classi¯cation has not yet been scienti¯cally established. Further research is currently undergoing to implement an on-line automated embolus de tection and classi¯cation method in clinical routine15¡17.

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