Vaporization dynamics of volatile perfluorocarbon droplets: A theoretical model and in vitro validation
Vaporization dynamics of volatile perfluorocarbon droplets: A theoretical model and in vitro validation
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DOI：
10.1118/1.4894804
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发表时间：
2014-10-01
期刊：
影响因子：
3.8
通讯作者：
Dayton, Paul A.
中科院分区：
文献类型：
--
作者：
Doinikov, Alexander A.;Sheeran, Paul S.;Dayton, Paul A.
目的：全氟化碳（PFC）微滴，称为相变造影剂（PCCA），是一种有前途的工具，在超声成像和治疗。对PCCA的兴趣是由于它们可以通过外部施加的声脉冲触发从液态转变到气态的事实。这一特性为超声医学的应用开辟了新的途径。深入了解PFC液滴的蒸发物理特性对于有效使用PCCA和预测生物效应至关重要。由挥发性PFC（具有低沸点）组成的PCCA表现出复杂的动力学行为：在通过短声脉冲蒸发之后，PFC液滴变成蒸汽泡，蒸汽泡经历过度膨胀和阻尼径向振荡直到沉降到最终直径。迄今为止，这种行为在理论上还没有得到很好的描述。我们研究的目的是开发一种改进的理论模型，描述挥发性PFC液滴的汽化动力学，并验证此模型与体外实验data.Methods：该模型的推导是基于应用流体动力学和热力学的数学方法的PFC液滴的声汽化的过程。所使用的方法纠正了现有模型的缺点。通过将模拟结果与高速视频显微镜获得的不同尺寸的八氟丙烷（OFP）和十氟丁烷（DFB）微滴的体外实验数据进行比较，对模型进行了验证。所开发的理论允许人们模拟PFC液滴内的蒸汽气泡的生长，直到液体PFC完全转化为蒸汽，以及随后的蒸汽泡的过度膨胀和阻尼振荡，包括外部施加的声脉冲的影响。为了定量评估模拟和实验结果之间的差异，L2范数误差计算的所有情况下，模拟和实验结果进行了比较。发现这些误差对于OFP和DFB液滴分别在0.043-0.067和0.037-0.088的范围内。这些值允许人们认为模拟结果和实验结果之间的一致性良好。这种协议是通过改变只有2的16个模型参数，描述了气体和液体PFC和周围的PFC液滴的液体的材料特性。拟合参数是周围液体的粘度和表面张力。所有其他模型参数保持不变。结论：良好的协议之间的理论和实验结果表明，开发的模型是能够正确地描述挥发性PFC液滴的蒸发动力学的关键物理过程。改变周围液体的参数来拟合实验曲线的必要性可以通过以下事实来解释：PFC液滴的初始磷脂壳的部分在振荡阶段保留在蒸汽气泡的表面上，并且它们的存在影响气泡动力学。(C)2014年美国医学物理学家协会。
Purpose: Perfluorocarbon (PFC) microdroplets, called phase-change contrast agents (PCCAs), are a promising tool in ultrasound imaging and therapy. Interest in PCCAs is motivated by the fact that they can be triggered to transition from the liquid state to the gas state by an externally applied acoustic pulse. This property opens up new approaches to applications in ultrasound medicine. Insight into the physics of vaporization of PFC droplets is vital for effective use of PCCAs and for anticipating bioeffects. PCCAs composed of volatile PFCs (with low boiling point) exhibit complex dynamic behavior: after vaporization by a short acoustic pulse, a PFC droplet turns into a vapor bubble which undergoes overexpansion and damped radial oscillation until settling to a final diameter. This behavior has not been well described theoretically so far. The purpose of our study is to develop an improved theoretical model that describes the vaporization dynamics of volatile PFC droplets and to validate this model by comparison with in vitro experimental data.Methods: The derivation of the model is based on applying the mathematical methods of fluid dynamics and thermodynamics to the process of the acoustic vaporization of PFC droplets. The used approach corrects shortcomings of the existing models. The validation of the model is carried out by comparing simulated results with in vitro experimental data acquired by ultrahigh speed video microscopy for octafluoropropane (OFP) and decafluorobutane (DFB) microdroplets of different sizes.Results: The developed theory allows one to simulate the growth of a vapor bubble inside a PFC droplet until the liquid PFC is completely converted into vapor, and the subsequent overexpansion and damped oscillations of the vapor bubble, including the influence of an externally applied acoustic pulse. To evaluate quantitatively the difference between simulated and experimental results, the L2-norm errors were calculated for all cases where the simulated and experimental results are compared. These errors were found to be in the ranges of 0.043-0.067 and 0.037-0.088 for OFP and DFB droplets, respectively. These values allow one to consider agreement between the simulated and experimental results as good. This agreement is attained by varying only 2 of 16 model parameters which describe the material properties of gaseous and liquid PFCs and the liquid surrounding the PFC droplet. The fitting parameters are the viscosity and the surface tension of the surrounding liquid. All other model parameters are kept invariable.Conclusions: The good agreement between the theoretical and experimental results suggests that the developed model is able to correctly describe the key physical processes underlying the vaporization dynamics of volatile PFC droplets. The necessity of varying the parameters of the surrounding liquid for fitting the experimental curves can be explained by the fact that the parts of the initial phospholipid shell of PFC droplets remain on the surface of vapor bubbles at the oscillatory stage and their presence affects the bubble dynamics. (C) 2014 American Association of Physicists in Medicine.