二重放物面集束構造を有する導波路型振動子(DPLUS)による医用応用デバイス

提出了一种利用双抛物线反射从薄波导输出高功率超声的新型超声换能器DPLUS，并对其基本特性进行了研究。在这一年里，首次研究了用于治疗性超声的DPLUS薄波导的优化设计。对薄波导中的振动、组织中的声场和热场进行了定量建模。结果表明，诱导肿瘤消融的最佳波导半径与波长之比为0.2392，即半径为0.6 mm时的最佳频率为2.2兆赫兹。在优化设计下，利用半径0.6 mm、长1 m的低损耗熔融石英薄波导，成功地进行了鸡组织的体外消融实验。在10 S~30 S的超声辐照时间下，消融面积从1 mm增大到2 mm。实验结果表明，这是文献中第一次利用声波导管进行组织热消融。与HIFU等常见的肿瘤消融方法相比，DPLUS具有实现精确、微创治疗的优点。此外，还展示了用一台DPLUS装置实现宽带(从20 kHz到1 MHz)声空化，这是传统HIFU换能器所不能实现的。因此，利用宽带声空化技术，DPLUS有可能开辟新的研究方向，如研究肿瘤消融、化学反应等的频率依赖性。

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.