涂层微泡次谐波响应的环境压力敏感性：声激励参数的影响。
Ambient Pressure Sensitivity of the Subharmonic Response of Coated Microbubbles: Effects of Acoustic Excitation Parameters.
机构信息
Department of Mechanical and Aerospace Engineering, George Washington University, Washington, DC, USA.
Department of Radiology, Thomas Jefferson University, Philadelphia, PA, USA.
出版信息
Ultrasound Med Biol. 2023 Jul;49(7):1550-1560. doi: 10.1016/j.ultrasmedbio.2023.02.019. Epub 2023 Apr 25.
OBJECTIVE
The sensitivity of the acoustic response of microbubbles, specifically a strong correlation between their subharmonic response and the ambient pressure, has motivated development of a non-invasive subharmonic-aided pressure estimation (SHAPE) method. However, this correlation has previously been found to vary depending on the microbubble type, the acoustic excitation and the hydrostatic pressure range. In this study, the ambient pressure sensitivity of microbubble response was investigated.
METHODS
The fundamental, subharmonic, second harmonic and ultraharmonic responses from an in-house lipid-coated microbubble were measured for excitations with peak negative pressures (PNPs) of 50-700 kPa and frequencies of 2, 3 and 4 MHz in the ambient overpressure range 0-25 kPa (0-187 mmHg) in an in vitro setup.
RESULTS
The subharmonic response typically has three stages-occurrence, growth and saturation-with increasing excitation PNP. We find distinct decreasing and increasing variations of the subharmonic signal with overpressure that are closely related to the threshold of subharmonic generation in a lipid-shelled microbubble. Above the excitation threshold, that is, in the growth-saturation phase, subharmonic signals decreased linearly with slopes as high as -0.56 dB/kPa with ambient pressure increase; below the threshold excitation (at atmospheric pressure), increasing overpressure triggers subharmonic generation, indicating a lowering of subharmonic threshold, and therefore leads to an increase in subharmonic with overpressure, the maximum enhancement being ∼11 dB for 15 kPa overpressure at 2 MHz and 100 kPa PNP.
CONCLUSION
This study indicates the possible development of novel and improved SHAPE methodologies.
目的
微泡的声响应的灵敏度，特别是其次谐波响应与环境压力之间的强相关性，促使开发了一种非侵入式次谐波辅助压力估计（SHAPE）方法。然而，此前已经发现这种相关性取决于微泡类型、声激励和静压范围。在这项研究中，研究了微泡响应的环境压力灵敏度。
方法
在体外装置中，用峰值负压（PNP）为 50-700 kPa 和频率为 2、3 和 4 MHz 的声激励，测量了自制脂质包裹微泡的基波、次谐波、二次谐波和超高谐波响应，环境过压范围为 0-25 kPa（0-187 mmHg）。
结果
次谐波响应通常随着激励 PNP 的增加经历三个阶段——出现、增长和饱和。我们发现次谐波信号随过压的变化存在明显的下降和上升趋势，这与脂质壳微泡中次谐波产生的阈值密切相关。在激励阈值以上，即在增长-饱和阶段，次谐波信号随过压线性下降，斜率高达-0.56 dB/kPa；在低于激励阈值（在大气压下）时，增加过压会触发次谐波产生，表明次谐波阈值降低，因此导致次谐波随过压增加，在 2 MHz 和 100 kPa PNP 时，15 kPa 过压下的最大增强约为 11 dB。
结论
本研究表明可能开发出新型和改进的 SHAPE 方法。
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