Liu Hao-Li, Chen Wen-Shiang, Chen Jhao-Syong, Shih Tzu-Ching, Chen Yung-Yaw, Lin Win-Li
Department of Electrical Engineering, Chang-Gung University, Taoyuan, Taiwan.
Ultrasound Med Biol. 2006 May;32(5):759-67. doi: 10.1016/j.ultrasmedbio.2006.01.010.
This paper demonstrates a novel approach for enhancing ultrasound-induced heating by the introduction of acoustic cavitation using simultaneous sonication with low- and high-frequency ultrasound. A spherical focused transducer (566 or 1155 kHz) was used to generate the thermal lesions, and a low-frequency planar transducer (40 or 28 kHz) was used to enhance the bubble activity. Ex vivo fresh porcine muscles were used as the target of ultrasound ablation. The emitted signals and the signals backscattered from the bubble activity were also recorded during the heating process by a PVDF-type needle hydrophone, and thermocouples were inserted to measure temperatures. Compared with the lesions formed by a single focused transducer, the size of the lesions generated by this approach were as much as 140% larger along the axial direction and 200% larger along the radial direction for combined 566- and 40-kHz sonication. They were 47% and 66% larger along the axial and radial directions, respectively, for combined 1155- and 28-kHz sonication. Cavitation activities enhanced by low-frequency ultrasound were confirmed by the presence of subharmonics in the spectrum and temperature increase as a result of increased tissue absorption. These observations imply that cavitation-enhanced lesions can be generated without reducing the penetration ability; they also show the advantage of producing larger and more uniform thermal lesions by multiple sonications. This technique provides an easy and effective way to achieve cavitation-enhanced heating, and may be useful for generating large and deep-seated thermal lesions.
本文展示了一种通过同时使用低频和高频超声进行超声处理来引入声空化以增强超声诱导加热的新方法。使用球形聚焦换能器（566或1155千赫兹）产生热损伤，使用低频平面换能器（40或28千赫兹）增强气泡活性。将离体新鲜猪肌肉用作超声消融的靶标。在加热过程中，还通过聚偏二氟乙烯型针状水听器记录发射信号和由气泡活性反向散射的信号，并插入热电偶测量温度。与单个聚焦换能器形成的损伤相比，对于566千赫兹和40千赫兹联合超声处理，通过这种方法产生的损伤在轴向方向上大140%，在径向方向上大200%。对于1155千赫兹和28千赫兹联合超声处理，它们在轴向和径向方向上分别大47%和66%。频谱中次谐波的存在以及由于组织吸收增加导致的温度升高证实了低频超声增强的空化活性。这些观察结果表明，可以在不降低穿透能力的情况下产生空化增强的损伤；它们还显示了通过多次超声处理产生更大且更均匀热损伤的优势。该技术提供了一种实现空化增强加热的简便有效方法，可能有助于产生大的深部热损伤。
