Key Laboratory of Modern Acoustics, MOE, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People's Republic of China.
J Acoust Soc Am. 2012 Jun;131(6):4358-64. doi: 10.1121/1.4707512.
Sub-harmonic response from ultrasound contrast agent microbubbles has been demonstrated to be an effective modality for noninvasive pressure measurement. In the present study, the dependence of ultra-harmonic response on the ambient overpressure was investigated by both experimental measurements and simulations. In the measurements, the microbubbles were exposed to Gaussian pulses with varied driving frequencies and pulse lengths, at an acoustic pressure of 0.3 MPa. The amplitudes of sub- and ultra-harmonic components were measured when the ambient overpressures varied from 0-25 kPa. At the driving frequency of 1.33 MHz, the ultra-harmonic energy decreased but the sub-harmonic energy increased with the increasing overpressure; while at the driving frequency of 4 MHz, both the sub- and ultra-harmonic components showed the same tendency that the corresponding energy decreased as the overpressure was increased. A 4-MHz Gaussian pulse with 64 cycles could provide an ultra-harmonic response with both good ambient pressure sensitivity and high linearity. Furthermore, the effects of shell parameters of a microbubble on the generation of ultra- and sub-harmonic responses were discussed based on simulations using Marmottant's model. This study suggests that the ultra-harmonic response from contrast microbubbles might be applicable for noninvasive pressure measurement.
超声对比剂微泡的次谐波响应已被证明是一种非侵入性压力测量的有效方法。本研究通过实验测量和模拟研究了超谐波响应对环境过压的依赖性。在测量中，微泡在声压为 0.3 MPa 的情况下，用不同驱动频率和脉冲长度的高斯脉冲进行照射。当环境过压从 0 增加到 25 kPa 时，测量了次谐波和超谐波分量的幅度。在 1.33 MHz 的驱动频率下，超谐波能量随着过压的增加而减小，但次谐波能量随着过压的增加而增加；而在 4 MHz 的驱动频率下，次谐波和超谐波分量都表现出相同的趋势，即随着过压的增加，相应的能量减小。一个具有 64 个周期的 4 MHz 高斯脉冲可以提供具有良好环境压力灵敏度和高线性度的超谐波响应。此外，根据 Marmottant 模型的模拟，讨论了微泡的壳参数对超谐波和次谐波响应产生的影响。本研究表明，对比微泡的超谐波响应可能适用于非侵入性压力测量。
