Regan Caitlin, Hayakawa Carole, Choi Bernard
Beckman Laser Institute, University of California-Irvine, 1002 Health Sciences Road East, Irvine, CA 92612, USA.
Department of Biomedical Engineering, University of California-Irvine, 3120 Natural Sciences II, Irvine, CA 92697, USA.
Biomed Opt Express. 2017 Nov 17;8(12):5708-5723. doi: 10.1364/BOE.8.005708. eCollection 2017 Dec 1.
Due to its simplicity and low cost, laser speckle imaging (LSI) has achieved widespread use in biomedical applications. However, interpretation of the blood-flow maps remains ambiguous, as LSI enables only limited visualization of vasculature below scattering layers such as the epidermis and skull. Here, we describe a computational model that enables flexible study of the impact of these factors on LSI measurements. The model uses Monte Carlo methods to simulate light and momentum transport in a heterogeneous tissue geometry. The virtual detectors of the model track several important characteristics of light. This model enables study of LSI aspects that may be difficult or unwieldy to address in an experimental setting, and enables detailed study of the fundamental origins of speckle contrast modulation in tissue-specific geometries. We applied the model to an in-depth exploration of the spectral dependence of speckle contrast signal in the skin, the effects of epidermal melanin content on LSI, and the depth-dependent origins of our signal. We found that LSI of transmitted light allows for a more homogeneous integration of the signal from the entire bulk of the tissue, whereas epi-illumination measurements of contrast are limited to a fraction of the light penetration depth. We quantified the spectral depth dependence of our contrast signal in the skin, and did not observe a statistically significant effect of epidermal melanin on speckle contrast. Finally, we corroborated these simulated results with experimental LSI measurements of flow beneath a thin absorbing layer. The results of this study suggest the use of LSI in the clinic to monitor perfusion in patients with different skin types, or inhomogeneous epidermal melanin distributions.
由于其简单性和低成本，激光散斑成像（LSI）已在生物医学应用中得到广泛使用。然而，血流图的解读仍然不明确，因为LSI仅能有限地可视化表皮和颅骨等散射层下方的脉管系统。在此，我们描述了一种计算模型，该模型能够灵活地研究这些因素对LSI测量的影响。该模型使用蒙特卡罗方法来模拟光和动量在异质组织几何结构中的传输。模型的虚拟探测器追踪光的几个重要特性。此模型能够研究在实验环境中可能难以或不便解决的LSI方面问题，并能够详细研究特定组织几何结构中散斑对比度调制的基本起源。我们将该模型应用于深入探索皮肤中散斑对比度信号的光谱依赖性、表皮黑色素含量对LSI的影响以及信号的深度依赖性起源。我们发现，透射光的LSI能够更均匀地整合来自整个组织块的信号，而对比度的落射照明测量仅限于光穿透深度的一部分。我们量化了皮肤中对比度信号的光谱深度依赖性，并且未观察到表皮黑色素对散斑对比度有统计学上的显著影响。最后，我们用薄吸收层下方血流的实验LSI测量结果证实了这些模拟结果。这项研究的结果表明，在临床上可使用LSI来监测不同皮肤类型或表皮黑色素分布不均匀的患者的灌注情况。
