Wang Ruikang K
Institute of BioScience and Technology, Cranfield University at Silsoe, Bedfordshire, UK.
Phys Med Biol. 2002 Jul 7;47(13):2281-99. doi: 10.1088/0031-9155/47/13/307.
Multiple scattering is a major source that limits light penetration into biotissues, thereby preventing visualization of the deep microstructures for high-resolution optical imaging techniques. The optical clearing approach is a new adventure in biomedical optics for manipulating the optical properties of tissue; for example, the scattering coefficient and the degree of forward scattering of photons, by the use of the chemical administration method in order to improve the optical imaging depth, particularly for the recently developed optical coherence tomography (OCT). This paper investigates systematically how the multiple scattering affects signal attenuation and localization in general, and how the alterations of optical properties of tissue enhance the optical imaging depth and signal localization in particular, by the use of Monte Carlo simulations through the separate considerations of the least scattered photons (LSP) and multiple scattered photons (MSP). The LSP are those photons that contribute to the precise OCT signal, i.e. localization, and the MSP are those that degrade the OCT signal. It is shown that with either the reduction of the scattering coefficient or the increase of the degree of forward scattering, signal localization and imaging depth for OCT is enhanced. Whilst the increase of the anisotropic factor of the medium is more efficient in improving signal localization, it introduces more scattering events for the photons travelling within the tissue for both the LSP and MSP. It is also found that the OCT imaging resolution is almost reduced exponentially with the increase of the probing depth as opposed to the claimed system resolution. We demonstrate that optical clearing could be a useful tool to improve the imaging resolution when the light progressively penetrates the high scattering medium. Experimental results are also presented to show intuitively how multiple scattering affects OCT signal profiles by the use of intralipid solution and healthy human whole blood, representing moderately and highly scattering media respectively.
多次散射是限制光穿透生物组织的主要因素，从而阻碍了高分辨率光学成像技术对深部微观结构的可视化。光学透明化方法是生物医学光学领域中一种用于操控组织光学特性的新尝试；例如，通过化学给药方法来改变散射系数和光子前向散射程度，以提高光学成像深度，特别是对于最近发展起来的光学相干断层扫描（OCT）技术。本文通过蒙特卡罗模拟分别考虑最少散射光子（LSP）和多次散射光子（MSP），系统地研究了多次散射如何总体上影响信号衰减和定位，以及组织光学特性的改变如何特别地增强光学成像深度和信号定位。LSP是那些对精确的OCT信号即定位有贡献的光子，而MSP是那些会降低OCT信号的光子。结果表明，无论是降低散射系数还是增加前向散射程度，OCT的信号定位和成像深度都会增强。虽然介质各向异性因子的增加在改善信号定位方面更有效，但它会为在组织内传播的LSP和MSP光子引入更多散射事件。还发现，与所宣称的系统分辨率相反，OCT成像分辨率几乎随着探测深度的增加呈指数下降。我们证明，当光逐渐穿透高散射介质时，光学透明化可以成为提高成像分辨率的有用工具。还给出了实验结果，直观地展示了多次散射如何分别通过使用代表中等散射介质的脂质乳剂溶液和代表高散射介质的健康人全血来影响OCT信号剖面。
