Evaluation of mechanical properties of the shell materials of ultrasound contrast agent microbubbles by high-speed observation of their radial oscillation.

改进了高速观测系统以提高高速观测的空间和时间分辨率，使用了带高速相机的像增强器，并对短弧闪光灯使用了改进的光学聚光器。这些器件的使用使40倍物镜的最小曝光时间从200 ns减少到20 ns，最大成帧速率从400万fps增加到1600万fps。研制了一种压力相关衰减测量系统在我们之前对生物组织衰减测量研究的基础上，开发了一种测量微泡悬浮液衰减的系统。该系统使用中心频率为10 MHz的宽带脉冲作为探测脉冲，并在3至14 MHz的频率范围内测量与频率相关的衰减。大部分测量过程由计算机控制实现自动化，以实现高精度测量。壳体性能评价…更多的高速观测微气泡被暴露在一个压力幅度不断增大的脉冲序列中，并通过高速摄像机观察到的振荡气泡的径向变化程度来评价气泡的壳层性质。检查了9种类型的微泡、7种超声造影剂、1种亚微米气泡和1种塑料壳气泡。结果表明，含脂类壳的微泡从几十kpa开始径向振荡，振荡幅度随压力的增加而增大，当压力超过阈值压力时，棕榈酸或白蛋白壳微泡开始径向振荡。两种类型气泡随压力变化的不同与临床上使用的两种类型气泡的超声暴露条件一致。通过衰减测量评价气泡的壳层性能使用不同压力幅值的宽带探测脉冲测量了九种类型气泡悬浮液的衰减。由于不同压力下径向振动的变化会引起衰减的变化，因此我们也可以根据气泡悬浮液的压力依赖衰减来估计壳层的性质。测量结果表明，每种类型的气泡都有其随压力变化的衰减特性，这些特性与高速观测的结果一致，表明衰减测量也有助于了解微气泡的壳层特性。较少

Improvement of a high-speed observation systemTo improve spatial and temporal resolutions of high-speed observation, the use of an image intensifier with a high-speed camera and the use of an improved optical condenser for a short-arc flash lamp were examined. The use of these devices resulted in a reduction in minimum exposure time from 200 ns to 20 ns at a 40x objective and an increase in maximum framing rate from 4-million to 16-million fps.Development of a system for measurement of pressure-dependent attenuationA system for measurement of attenuation of microbubble suspensions was developed on the basis of results of our previous study on measurement of attenuation of biological tissues. The system uses a wideband pulse of 10 MHz in center frequency as a probing pulse and measures frequency-dependent attenuation in the frequency range of 3 to 14 MHz. Most of the measurement procedure is automated by computer control to achieve high-precision measurements.Evaluation of shell propert … More ies by high-speed observationA microbubble was exposed to a pulse train of increasing pressure amplitudes, and the shell property of the bubble was evaluated from degree of radial change in the oscillating bubble visualized by the high-speed camera. Nine types of microbubbles, seven ultrasound contrast agents, one type of sub-micron bubbles, and one type of plastic-shelled bubbles were examined. The results showed that microbubbles with lipid shells start radial oscillation from several tens of kPa and oscillation amplitude increases with increase in applied pressure and that Palmitic-acid-or albumin-shelled bubbles start radial oscillation when pressure has exceeded a threshold pressure. The difference in pressure-dependent bubble oscillation is consistent with the ultrasound exposure conditions used for the two shell types of bubbles used in clinical practice.Evaluation of shell properties by attenuation measurementAttenuation of the nine types of bubble suspensions was measured using wideband probing pulses of different pressure amplitudes. Since change in radial oscillation under different pressures causes change in attenuation, we also can estimate shell properties from pressure-dependent attenuation of a bubble suspension. The results of measurements showed that each type of bubble has its own characteristics in pressure-dependent attenuation, and these characteristics are consistent with those found by high-speed observation, suggesting that attenuation measurement is also useful to understand the shell properties of microbubbles. Less