Northeastern University, Computer and Electrical Engineering, Boston, Massachusetts, United States.
Boston University, Mechanical Engineering, Boston, Massachusetts, United States.
J Biomed Opt. 2017 Oct;22(10):1-10. doi: 10.1117/1.JBO.22.10.106004.
In optical imaging, the depth and resolution are limited due to scattering. Unlike light, scattering of ultrasound (US) waves in tissue is negligible. Hybrid imaging methods such as US-modulated optical tomography (UOT) use the advantages of both modalities. UOT tags light by inducing phase change caused by modulating the local index of refraction of the medium. The challenge in UOT is detecting the small signal. The displacement induced by the acoustic radiation force (ARF) is another US effect that can be utilized to tag the light. It induces greater phase change, resulting in a stronger signal. Moreover, the absorbed acoustic energy generates heat, resulting in change in the index of refraction and a strong phase change. The speckle pattern is governed by the phase of the interfering scattered waves; hence, speckle pattern analysis can obtain information about displacement and temperature changes. We have presented a model to simulate the insonation processes. Simulation results based on fixed-particle Monte Carlo and experimental results show that the signal acquired by utilizing ARF is stronger compared to UOT. The introduced mean irradiance change (MIC) signal reveals both thermal and mechanical effects of the focused US beam in different timescales. Simulation results suggest that variation in the MIC signal can be used to generate a displacement image of the medium.
在光学成象中，由于散射的存在，深度和分辨率受到限制。与光不同，组织中超声波（US）波的散射可以忽略不计。US 调制光学层析成像（UOT）等混合成像方法利用了两种模式的优势。UOT 通过调制介质局部折射率引起的相位变化来标记光。UOT 的挑战在于检测小信号。声辐射力（ARF）引起的位移是另一种可用于标记光的 US 效应。它会引起更大的相位变化，从而产生更强的信号。此外，吸收的声能会产生热量，导致折射率发生变化和强相位变化。散斑图案受干涉散射波相位的控制；因此，散斑图案分析可以获得有关位移和温度变化的信息。我们提出了一个模型来模拟超声照射过程。基于固定粒子蒙特卡罗的模拟结果和实验结果表明，与 UOT 相比，利用 ARF 获得的信号更强。引入的平均辐照度变化（MIC）信号揭示了聚焦 US 束在不同时间尺度上的热和机械效应。模拟结果表明，MIC 信号的变化可用于生成介质的位移图像。
