Elimination of therapeutic ultrasound noise in phase modulated high intensity focused ultrasound treatment

Abstract

Ultrasound image-guided High Intensity Focused Ultrasound (HIFU) has been become one of the potential surgical techniques for the treatment of the malignant tumor. The ultrasound image during the treatment is severely corrupted by the reflected HIFU wave because HIFU and imaging transducers are simultaneously activated. In our previous study, a new method to selectively eliminate only HIFU noise during the treatment was suggested, but it cannot sufficiently reduce the HIFU noise when the HIFU exposure is phase-modulated with a period less than a few milliseconds. In this study, a new method to selectively eliminate the HIFU noise even when the HIFU exposure is modulated with a certain modulation period. In this study, “multiple HIFU exposure” with a certain modulation period was employed. The focus of HIFU was moved every 25μs sequentially for six positions with spacing proper for thermal conduction. the RF signals of the same modulation period were received with (RF2) and without (RF1) transmitting an imaging pulse, respectively. The HIFU noise was eliminated by subtracting RF1 from RF2. As the result of in vitro study, the fundamental to higher harmonic components of the HIFU noise were reduced by 20 to 30 dB during the HIFU exposure.