Shock-induced heating and millisecond boiling in gels and tissue due to high intensity focused ultrasound.
Shock-induced heating and millisecond boiling in gels and tissue due to high intensity focused ultrasound.
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DOI：
10.1016/j.ultrasmedbio.2009.09.010
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发表时间：
2010-02
影响因子：
2.9
通讯作者：
Crum, Lawrence A.
中科院分区：
文献类型：
--
作者：
Canney, Michael S.;Khokhlova, Vera A.;Bessonova, Olga V.;Bailey, Michael R.;Crum, Lawrence A.
关键词：
非线性传播导致高强度超声波失真并产生高次谐波，这些谐波比基频更容易被吸收并转化为热量。虽然这种非线性效应之前已经被研究过，并发现不会显着改变高强度聚焦超声 (HIFU) 治疗，但这里报告的两个结果改变了这种范式。一是在临床相关强度水平下，HIFU 波不仅会扭曲，还会在组织中形成冲击波。另一个原因是，所产生的冲击波将组织加热至沸腾的时间比未扭曲或弱扭曲波的预测时间短得多。在这项研究中，使用峰值强度高达 25,000 W/cm2 的 2 MHz HIFU 源来加热透明的模拟组织模型和离体牛肝脏样本。使用高速摄影、20 MHz 无源空化检测器和 HIFU 源驱动电压的波动来检测沸腾的开始。实验获得的沸腾时间用于量化加热速率，并与使用弱冲击理论的计算以及从非线性建模和光纤水听器测量获得的冲击幅度进行比较。正如实验观察和计算预测的那样，冲击焦点波形在短短 3 毫秒内产生沸腾，并且启动沸腾的时间对 HIFU 输出的微小变化很敏感。因此，冲击波引起的非线性加热对于 HIFU 很重要，临床医生应该意识到非常快速沸腾的可能性，因为它会改变治疗。
Nonlinear propagation causes high intensity ultrasound waves to distort and generate higher harmonics, which are more readily absorbed and converted to heat than the fundamental frequency. Although such nonlinear effects have previously been investigated and found not to significantly alter high intensity focused ultrasound (HIFU) treatments, two results reported here change this paradigm. One is that at clinically relevant intensity levels, HIFU waves not only become distorted but form shock waves in tissue. The other is that the generated shock waves heat the tissue to boiling in much less time than predicted for undistorted or weakly distorted waves. In this study, a 2-MHz HIFU source operating at peak intensities up to 25,000 W/cm2 was used to heat transparent tissue-mimicking phantoms and ex vivo bovine liver samples. Initiation of boiling was detected using high-speed photography, a 20-MHz passive cavitation detector, and fluctuation of the drive voltage at the HIFU source. The time to boil obtained experimentally was used to quantify heating rates and was compared to calculations using weak shock theory and the shock amplitudes obtained from nonlinear modeling and from measurements with a fiber optic hydrophone. As observed experimentally and predicted by calculations, shocked focal waveforms produced boiling in as little as 3 ms and the time to initiate boiling was sensitive to small changes in HIFU output. Nonlinear heating due to shock waves is therefore important to HIFU and clinicians should be aware of the potential for very rapid boiling since it alters treatments.
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