Emerging contrast imaging studies have highlighted the potential of nanobubbles for both intravascular and extravascular applications. Reports to date on nanobubbles have generally utilized low frequencies (<12 MHz), high concentrations (>109 mL-1), and B-mode or contrast-mode on preclinical and clinical systems. However, none of these studies directly examined nanobubble acoustic signatures systematically to implement nonlinear imaging schemes in a methodical manner based on nanobubble behaviour. Here, nanobubble nonlinear behaviour is investigated at high frequencies (12.5, 25, 30 MHz) and low concentration (106 mL-1) in a channel phantom, with different pulse types in single- and multi-pulse sequences to examine behaviour under conditions relevant to high frequency imaging. Porphyrin nanobubbles are demonstrated to initiate nonlinear scattering at high frequencies in a pressure-threshold dependent manner, as previously observed at low frequencies. This threshold behaviour was then utilized to demonstrate enhanced nanobubble imaging with pulse inversion, amplitude modulation, and a combination of the two, progressing towards the improved sensitivity and expanded utility of these ultrasound contrast agents.

中文翻译：

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卟啉纳米气泡的高频超声非线性散射

新兴的对比成像研究强调了纳米气泡在血管内和血管外应用中的潜力。迄今为止，关于纳米气泡的报告通常在临床前和临床系统中使用低频 (<12 MHz)、高浓度 (>109 mL-1) 和 B 模式或对比模式。然而，这些研究都没有系统地检查纳米气泡声学特征，以基于纳米气泡行为有条不紊地实施非线性成像方案。在这里，纳米气泡非线性行为在通道幻象中以高频（12.5、25、30 MHz）和低浓度（106 mL-1）进行研究，在单脉冲和多脉冲序列中使用不同的脉冲类型来检查相关条件下的行为到高频成像。正如先前在低频观察到的那样，卟啉纳米气泡被证明以压力阈值相关的方式在高频下引发非线性散射。然后利用这种阈值行为来证明具有脉冲反转、幅度调制和两者组合的增强纳米气泡成像，朝着提高这些超声造影剂的灵敏度和扩大效用的方向发展。