University of Houston, Department of Biomedical Engineering, Houston, Texas, United States.
University of Houston, Department of Mechanical Engineering, Houston, Texas, United States.
J Biomed Opt. 2020 Mar;25(3):1-13. doi: 10.1117/1.JBO.25.3.035004.
Shear wave optical coherence elastography is an emerging technique for characterizing tissue biomechanics that relies on the generation of elastic waves to obtain the mechanical contrast. Various techniques, such as contact, acoustic, and pneumatic methods, have been used to induce elastic waves. However, the lack of higher-frequency components within the elastic wave restricts their use in thin samples. The methods also require moving parts and/or tubing, which therefore limits the extent to which they can be miniaturized.
To overcome these limitations, we propose an all-optical approach using photothermal excitation. Depending on the absorption coefficient of the sample and the laser pulse energy, elastic waves are generated either through a thermoelastic or an ablative process. Our study aimed to experimentally determine the boundary between the thermoelastic and the ablative regimes for safe all-optical elastography applications.
Tissue-mimicking graphite-doped phantoms and chicken liver samples were used to investigate the boundary between thermoelastic and ablative regimes. A pulsed laser at 532 nm was used to induce elastic waves in the samples. Laser-induced elastic waves were detected using a line field low coherence holography instrument. The shape of the elastic wave amplitude was analyzed and used to determine the transition point between thermoelastic and ablative regimes.
The transition from the thermoelastic to the ablative regime is accompanied by the nonlinear increase in surface wave amplitude as well as the transformation of the wave shape. Correlation between the absorption coefficient and the transition point energy was experimentally determined using graphite-doped phantoms and applied to biological samples ex vivo.
Our study described a methodology for determining the boundary region between thermoelastic and ablative regimes of elastic wave generation. These can be used for the development of a safe method for completely noncontact, all-optical microscale assessment of tissue biomechanics using laser-induced elastic waves.
剪切波光相干弹性成像是一种新兴的组织生物力学特征技术，它依赖于弹性波的产生来获得力学对比。已经使用了各种技术，如接触、声学和气动方法来产生弹性波。然而，弹性波内缺乏较高频率的成分限制了它们在薄样品中的应用。这些方法还需要移动部件和/或管道，因此限制了它们的小型化程度。
为了克服这些限制，我们提出了一种使用光热激发的全光学方法。根据样品的吸收系数和激光脉冲能量，弹性波可以通过热弹或烧蚀过程产生。我们的研究旨在实验确定安全的全光学弹性成像应用的热弹和烧蚀区域之间的边界。
使用组织模拟的含石墨的仿体和鸡肝样本来研究热弹和烧蚀区域之间的边界。使用 532nm 的脉冲激光在样品中产生弹性波。使用线场低相干全息仪检测激光诱导的弹性波。分析弹性波幅度的形状，并用于确定热弹和烧蚀区域之间的过渡点。
从热弹到烧蚀区域的转变伴随着表面波幅度的非线性增加以及波形状的转变。使用含石墨的仿体和离体生物样本实验确定了吸收系数与过渡点能量之间的相关性。
我们的研究描述了一种确定弹性波产生的热弹和烧蚀区域之间边界区域的方法。这些方法可用于开发一种安全的方法，用于使用激光诱导的弹性波对组织生物力学进行完全非接触的、全光学的微尺度评估。
