Raymond Jason L, Luan Ying, van Rooij Tom, Kooiman Klazina, Huang Shao-Ling, McPherson David D, Versluis Michel, de Jong Nico, Holland Christy K
Biomedical Engineering Program, University of Cincinnati, Cardiovascular Center 3940, 231 Albert Sabin Way, Cincinnati, Ohio 45267-0586.
Department of Biomedical Engineering, Thoraxcenter, Erasmus Medical Center, P.O. Box 2040, 3000 CA, Rotterdam, Netherlands.
J Acoust Soc Am. 2015 Apr;137(4):1693-703. doi: 10.1121/1.4916277.
An optical characterization method is presented based on the use of the impulse response to characterize the damping imparted by the shell of an air-filled ultrasound contrast agent (UCA). The interfacial shell viscosity was estimated based on the unforced decaying response of individual echogenic liposomes (ELIP) exposed to a broadband acoustic impulse excitation. Radius versus time response was measured optically based on recordings acquired using an ultra-high-speed camera. The method provided an efficient approach that enabled statistical measurements on 106 individual ELIP. A decrease in shell viscosity, from 2.1 × 10(-8) to 2.5 × 10(-9) kg/s, was observed with increasing dilatation rate, from 0.5 × 10(6) to 1 × 10(7) s(-1). This nonlinear behavior has been reported in other studies of lipid-shelled UCAs and is consistent with rheological shear-thinning. The measured shell viscosity for the ELIP formulation used in this study [κs = (2.1 ± 1.0) × 10(-8) kg/s] was in quantitative agreement with previously reported values on a population of ELIP and is consistent with other lipid-shelled UCAs. The acoustic response of ELIP therefore is similar to other lipid-shelled UCAs despite loading with air instead of perfluorocarbon gas. The methods described here can provide an accurate estimate of the shell viscosity and damping for individual UCA microbubbles.
本文提出了一种光学表征方法，该方法基于利用脉冲响应来表征充空气的超声造影剂（UCA）外壳所赋予的阻尼。基于暴露于宽带声脉冲激发下的单个回声脂质体（ELIP）的无外力衰减响应，估算了界面壳粘度。基于使用超高速相机获取的记录，通过光学方法测量了半径随时间的响应。该方法提供了一种有效的途径，能够对106个单个ELIP进行统计测量。随着扩张率从0.5×10⁶增加到1×10⁷ s⁻¹，观察到壳粘度从2.1×10⁻⁸降低到2.5×10⁻⁹ kg/s。这种非线性行为在其他脂质壳UCA的研究中已有报道，并且与流变学剪切变稀一致。本研究中使用的ELIP制剂的测量壳粘度[κs = (2.1 ± 1.0) × 10⁻⁸ kg/s]与先前报道的ELIP群体的值在定量上一致，并且与其他脂质壳UCA一致。因此，尽管ELIP中填充的是空气而非全氟化碳气体，但其声学响应与其他脂质壳UCA相似。本文所述方法可为单个UCA微泡的壳粘度和阻尼提供准确估计。
