We have been developing a tumor treatment method by high-intensity focused ultrasound (HIFU). To ensure the safety of HIFU treatment, it is essential to monitor the HIFU focal region prior to treatment. For this purpose, we have proposed an estimation method for the HIFU focal region based on acoustic radiation force (ARF) imaging just before the therapeutic sonication, since the ARF region induced by HIFU coincides with the HIFU focal region, under the condition that the shear-wave propagation is negligible. In this method, a short-duration HIFU burst is delivered to induce ARF, and the resulting tissue displacement is measured with an ultrasonic imaging probe. To reduce the influence of shear-wave propagation, tissue displacement must be measured immediately after HIFU sonication, particularly in tissues with high shear-wave speeds such as pancreatic cancer tissue. However, immediately after the HIFU sonication, HIFU reverberation noise interferes with imaging signals, degrading the accuracy of tissue-displacement measurement. In this study, we demonstrate that frequency filtering with high-pass and notch filters can effectively reduce HIFU reverberation noise at both the fundamental and harmonic frequencies of HIFU, enabling accurate tissue-displacement measurements as early as 0.1 ms after HIFU sonication in chicken gizzard tissue (shear-wave speed is approximately 3 m/s).
Mori et al. (2025) studied this question.