In conventional ultrasonic monitoring of high-intensity focused ultrasound (HIFU) treatment, a significant interval between consecutive HIFU shots is set for monitoring target tissue to avoid the interference of HIFU noise with RF echo signals. Thus, it is difficult to detect changes in tissue on the order of milliseconds, which are required to dynamically control the HIFU exposure. In this study, a new filtering method to eliminate the HIFU noise in the RF signals before beamforming is proposed. The CW response was estimated from RF signals with no pulse response to the imaging exposure, and the estimated CW response was subtracted from the entire RF signal to selectively eliminate the HIFU noise for each channel of the array probe before dynamic focusing was applied. The HIFU noise was selectively eliminated by this method when it existed. The results imply that the proposed filtering method is useful for true real-time detection of changes in tissue due to thermal coagulation during HIFU exposure.
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