Enhancement of Localized Heating by Ultrasonically Induced Cavitation in High Intensity Focused Ultrasound Treatment

Abstract

There are reports that ultrasonically induced cavitation bubbles locally enhance tissue heating in high intensity focused ultrasound (HIFU) treatment. In this study, a high-intensity burst (named ''a triggering pulse'') above the cavitation threshold was used to trigger cavitation. Immediately after that, CW ultrasound (named ''heating waves''), at an intensity level and duration typical for conventional HIFU ablation was irradiated. Before the ablating sonication, it is necessary to determine the optimum intensity and duration of the triggering pulse. Immediately after a test triggering pulse, low-intensity CW ultrasound (named ''a sustaining pulse'') was irradiated for a short duration of time, and we detected the cavitation noises (subharmonics and higher harmonics) generated in the focus spot. The relationship between the 1/2 subharmonic signal amplitude and the coagulation volume after the ablating sonication was investigated. The result of this experiment suggests that we can optimize the triggering pulse by detecting the 1/2 subharmonic signal amplitude. #

Selective detection of cavitation bubbles by triplet pulse sequence in high-intensity focused ultrasound treatment

“…The above-described problem is expected to be overcome by utilizing such cavitation microbubbles. We have proposed cavitationenhanced HIFU treatment using an exposure sequence, [5][6][7][8] which we named the "trigger HIFU" sequence, consisting of a highly intense short "trigger pulse" to generate cavitation and an immediately following moderate-intensity long "sustaining burst" to oscillate the generated microbubbles. The effectiveness of the proposed exposure sequence has been confirmed in regard to the thermal effect of ultrasound.…”

Cavitation Control and Applications

“…Takagi et al (2010) and Nakamura et al (2013) used a © 2010 IEEE high-intensity burst above the cavitation threshold to generate cavitation bubbles in chicken fillets, immediately followed by application of a low-intensity continuous-wave ultrasound at a certain intensity level and duration to sustain the triggered cavitation and to heat the tissue (Fig. 6.65).…”

“…First, phase-shift nanoemulsions (PSNEs) which are sensitive to both temperature and acoustic pressure, and their response to environmental changes should be comprehensively studied. Second, systems that use a combination of multiple waves with different amplitudes have also been investigated to enhance cavitation effect (Takagi et al 2010). We discuss these two cases in Sects.…”

Enhancement of High-Intensity Focused Ultrasound Heating by Short-Pulse Generated Cavitation

“…Although increased heat depositions were obtained using microbubbles in the previous research, distorted coagulation regions or temperature distribution were observed, such as tad-pole shaped [12,22,24] or pre-focal [13,19,[24][25][26] heating regions. A "trigger 2 of 20 HIFU" sequence that consists of high-intensity short pulses and following moderate-intensity long bursts has been investigated to avoid such distorted coagulation regions while enhancing the ultrasonic heating [27][28][29][30][31][32][33][34][35][36].…”