Transcranial ultrasound in acute stroke: from diagnosis to therapy

In the last few years, several studies have improved our knowledge and understanding of the dynamic nature of the recanalization process during stroke thrombolysis. Transcranial Doppler ultrasound provides a unique opportunity to assess several aspects of clot dissolution by means of continuous monitoring of recanalization during and after administration of tissue plasminogen activator. This approach allows us to evaluate at the patient's bedside and in real time the beginning, timing, speed and degree of artery reopening, as well as to document reocclusion after successful recanalization. Moreover, the simultaneous clinical assessment during transcranial Doppler monitoring allows correlation of the hemodynamic changes with the clinical course and outcome. Experimental studies have shown that ultrasound (US)-accelerated thrombolysis may be further enhanced by administration of microbubbles (MBs). Low-frequency US with high power has been demonstrated to produce cavitation and fluid motion in the thrombus. The MBs, by acting as cavitation nuclei, lower the amount of energy needed for cavitation. Application of high-acoustic-pressure US has been shown to induce nonlinear oscillations of MBs, leading to a continuous absorption of energy until the bubbles explode, releasing the absorbed energy. A multicenter randomized phase II trial of MB-enhanced thrombolysis in acute stroke is under way.