High-intensity focused ultrasound (HIFU) treatment enhanced by cavitation bubbles requires monitoring of the bubbles in the treatment region to ensure the efficacy and safety. In the intraoperative guidance by ultrasound, the bubbles in the treatment region are visualized by detecting nonlinear echoes from them. A triplet pulse sequence (3P) was developed in order to solve the disadvantage of the conventional method by which it is difficult to discriminate between the nonlinear echoes generated by the nonlinear oscillation of bubbles and those by the nonlinear propagation of ultrasound. In this study, we investigated the selectivity of cavitation bubbles in imaging by 3P in various HIFU exposure sequences to improve the efficacy and safety of cavitation-enhanced HIFU therapy. This study proved that the highest contrast could be obtained by 3P in most cases and that the combination of HIFU exposure and imaging sequences was important to obtain a high contrast image.
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