School of Computer Engineering, Nanyang Technological University, N4-02b-52, Nanyang Avenue, Singapore 639798, Singapore.
Prog Biophys Mol Biol. 2012 Apr;108(3):119-38. doi: 10.1016/j.pbiomolbio.2012.01.004. Epub 2012 Feb 28.
Low-frequency (LF) ultrasound (20-100 kHz) has a diverse set of industrial and medical applications. In fact, high power industrial applications of ultrasound mainly occupy this frequency range. This range is also used for various therapeutic medical applications including sonophoresis (ultrasonic transdermal drug delivery), dentistry, eye surgery, body contouring, the breaking of kidney stones and eliminating blood clots. While emerging LF applications such as ultrasonic drug delivery continue to be developed and undergo translation for human use, significant gaps exist in the coverage of safety standards for this frequency range. Accordingly, the need to understand the biological effects of LF ultrasound is becoming more important. This paper presents a broad overview of bio-effects and safety of LF ultrasound as an aid to minimize and control the risk of these effects. Its particular focus is at low intensities where bio-effects are initially observed. To generate a clear perspective of hazards in LF exposure, the mechanisms of bio-effects and the main differences in action at low and high frequencies are investigated and a survey of harmful effects of LF ultrasound at low intensities is presented. Mechanical and thermal indices are widely used in high frequency diagnostic applications as a means of indicating safety of ultrasonic exposure. The direct application of these indices at low frequencies needs careful investigation. In this work, using numerical simulations based on the mathematical and physical rationale behind the indices at high frequencies, it is observed that while thermal index (TI) can be used directly in the LF range, mechanical index (MI) seems to become less reliable at lower frequencies. Accordingly, an improved formulation for the MI is proposed for frequencies below 500 kHz.
低频（LF）超声（20-100 kHz）在工业和医学领域有广泛的应用。事实上，高功率工业应用的超声主要占据这个频率范围。这个频率范围也用于各种治疗医学应用，包括声透法（超声经皮药物输送）、牙科、眼科手术、身体轮廓塑造、肾结石破碎和消除血栓。虽然新兴的 LF 应用，如超声药物输送，仍在不断开发和转化为人类使用，但该频率范围内的安全标准的覆盖范围仍存在很大差距。因此，了解 LF 超声的生物效应变得越来越重要。本文综述了 LF 超声的生物效应和安全性，以帮助最小化和控制这些效应的风险。本文特别关注低强度下的生物效应，因为在低强度下最初观察到生物效应。为了清楚地了解 LF 暴露的危害，本文研究了生物效应的机制以及在低频和高频下的主要区别，并介绍了 LF 超声在低强度下的有害效应。机械和热指数广泛应用于高频诊断应用中，作为指示超声暴露安全性的一种手段。这些指数在低频下的直接应用需要仔细研究。在这项工作中，通过基于高频下的数学和物理原理的数值模拟，观察到尽管热指数（TI）可以直接在 LF 范围内使用，但在较低频率下，机械指数（MI）似乎变得不太可靠。因此，提出了一种改进的 MI 公式，用于低于 500 kHz 的频率。
