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 × 106 to 1 × 107 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.
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机译:基于脉冲响应的使用,提出了一种光学表征方法,以表征由充气超声造影剂(UCA)的外壳赋予的阻尼。基于暴露于宽带声脉冲激励下的单个回声脂质体(ELIP)的非强迫衰减响应,估算界面壳的粘度。半径对时间的响应是根据使用超高速相机获得的记录进行光学测量的。该方法提供了一种有效的方法,可以对106个单独的ELIP进行统计测量。壳粘度从2.1×viscosity10 −8 sup>降至2.5×10 −9 sup> kg / s,随膨胀率的增加从0.5×10 降低。 6 sup>到1×10 7 sup> s -1 sup>。这种非线性行为在脂质壳UCA的其他研究中已有报道,并且与流变剪切稀化相一致。本研究中使用的ELIP制剂的测得的壳粘度[κs=(2.1±1.0)×10 −8 sup> kg / s]与先前报道的ELIP种群的数值定量一致,为与其他带脂壳的UCA一致。因此,尽管充满了空气而不是全氟化碳气体,但ELIP的声学响应与其他带脂质壳的UCA相似。此处描述的方法可以为单个UCA微气泡提供壳粘度和阻尼的准确估算。
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