Kang Shih-Tsung, Huang Yi-Luan, Yeh Chih-Kuang
Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan.
Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan.
Ultrasound Med Biol. 2014 Mar;40(3):551-61. doi: 10.1016/j.ultrasmedbio.2013.10.020. Epub 2014 Jan 13.
This study investigated the manipulation of bubbles generated by acoustic droplet vaporization (ADV) under clinically relevant flow conditions. Optical microscopy and high-frequency ultrasound imaging were used to observe bubbles generated by 2-MHz ultrasound pulses at different time points after the onset of ADV. The dependence of the bubble population on droplet concentration, flow velocity, fluid viscosity and acoustic parameters, including acoustic pressure, pulse duration and pulse repetition frequency, was investigated. The results indicated that post-ADV bubble growth spontaneously driven by air permeation markedly affected the bubble population after insonation. The bubbles can grow to a stable equilibrium diameter as great as twice the original diameter in 0.5-1 s, as predicted by the theoretical calculation. The growth trend is independent of flow velocity, but dependent on fluid viscosity and droplet concentration, which directly influence the rate of gas uptake by bubbles and the rate of gas exchange across the wall of the semipermeable tube containing the bubbles and, hence, the gas content of the host medium. Varying the acoustic pressure does not markedly change the formation of bubbles as long as the ADV thresholds of most droplets are reached. Varying pulse duration and pulse repetition frequency markedly reduces the number of bubbles. Lengthening pulse duration favors the production of large bubbles, but reduces the total number of bubbles. Increasing the PRF interestingly provides superior performance in bubble disruption. These results also suggest that an ADV bubble population cannot be assessed simply on the basis of initial droplet size or enhancement of imaging contrast by the bubbles. Determining the optimal acoustic parameters requires careful consideration of their impact on the bubble population produced for different application scenarios.
本研究调查了在临床相关流动条件下，由声滴汽化（ADV）产生的气泡的操控情况。利用光学显微镜和高频超声成像，观察了在ADV开始后不同时间点由2兆赫超声脉冲产生的气泡。研究了气泡数量对液滴浓度、流速、流体粘度以及包括声压、脉冲持续时间和脉冲重复频率在内的声学参数的依赖性。结果表明，由空气渗透自发驱动的ADV后气泡生长显著影响了超声照射后的气泡数量。如理论计算所预测的，气泡可在0.5 - 1秒内生长至稳定平衡直径，其大小可达原始直径的两倍。生长趋势与流速无关，但取决于流体粘度和液滴浓度，这直接影响气泡的气体吸收速率以及包含气泡的半透管管壁上的气体交换速率，进而影响主体介质的气体含量。只要达到大多数液滴的ADV阈值，改变声压并不会显著改变气泡的形成。改变脉冲持续时间和脉冲重复频率会显著减少气泡数量。延长脉冲持续时间有利于产生大气泡，但会减少气泡总数。有趣的是，增加PRF在气泡破裂方面具有更优的性能。这些结果还表明，不能仅根据初始液滴大小或气泡对成像对比度的增强来评估ADV气泡数量。确定最佳声学参数需要仔细考虑它们对不同应用场景下产生的气泡数量的影响。
