Firbank M, Arridge S R, Schweiger M, Delpy D T
Department of Medical Physics and Bioengineering, University College London, UK.
Phys Med Biol. 1996 Apr;41(4):767-83. doi: 10.1088/0031-9155/41/4/012.
Near-infra-red (NIR) spectroscopy is increasingly being used for monitoring cerebral oxygenation and haemodynamics. One current concern is the effect of the clear cerebrospinal fluid upon the distribution of light in the head. There are difficulties in modelling clear layers in scattering systems. The Monte Carlo model should handle clear regions accurately, but is too slow to be used for realistic geometries. The diffusion equation can be solved quickly for realistic geometries, but is only valid in scattering regions. In this paper we describe experiments carried out on a solid slab phantom to investigate the effect of clear regions. The experimental results were compared with the different models of light propagation. We found that the presence of a clear layer had a significant effect upon the light distribution, which was modelled correctly by Monte Carlo techniques, but not by diffusion theory. A novel approach to calculating the light transport was developed, using diffusion theory to analyze the scattering regions combined with a radiosity approach to analyze the propagation through the clear region. Results from this approach were found to agree with both the Monte Carlo and experimental data.
近红外（NIR）光谱法越来越多地用于监测脑氧合和血流动力学。当前一个令人担忧的问题是清澈的脑脊液对头部光分布的影响。在散射系统中对透明层进行建模存在困难。蒙特卡罗模型应该能够准确处理透明区域，但速度太慢，无法用于实际几何形状。扩散方程可以快速求解实际几何形状，但仅在散射区域有效。在本文中，我们描述了在固体平板模型上进行的实验，以研究透明区域的影响。将实验结果与不同的光传播模型进行了比较。我们发现透明层的存在对光分布有显著影响，蒙特卡罗技术能正确模拟这种影响，但扩散理论却不能。我们开发了一种计算光传输的新方法，即使用扩散理论分析散射区域，并结合辐射度方法分析通过透明区域的传播。发现该方法的结果与蒙特卡罗数据和实验数据均一致。
