| 研究実績の概要 |
This research proposes a novel ultrasonic transducer named DPLUS that outputs powerful ultrasound from a thin waveguide using double parabolic reflections, and its basic characteristics are studied.
In this year, optimal design of the DPLUS thin waveguide for therapeutic ultrasound was firstly studied. Quantitative modeling for the vibration in the thin waveguide, the acoustic and thermal fields in the tissue was conducted. It was found that for inducing tumor ablation, the optimal ratio of the thin waveguide radius to the wavelength is 0.2392, e.g., the optimal frequency is 2.2 MHz if the radius is 0.6 mm. Under the optimal design, ex-vivo chicken tissue ablation experiments were successfully conducted using DPLUS with a 0.6-mm radius and 1-m long low-loss fused quartz thin waveguide. The ablated area was very precise, and the size increases from 1 mm to 2 mm under the ultrasound exposure time of 10 s to 30 s. The experimental results are significant that it is the first time in the literature showing tissue thermal ablation is possible by an acoustic waveguide. Compared with common tumor ablation methods like HIFU, DPLUS has the advantages of realizing precise and minimally invasive treatment. In addition, using one DPLUS device for realizing wide-band (from 20 kHz to 1 MHz) acoustic cavitation has also been demonstrated, and such feature is impossible for traditional HIFU transducers. Therefore, using wide-band acoustic cavitation, DPLUS is possible to open up new research directions such as studying the frequency dependence of tumor ablation, chemical reaction, etc.
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