Hu Dong, Lu Renfu, Ying Yibin, Fu Xiaping
Opt Express. 2019 Jan 21;27(2):1124-1141. doi: 10.1364/OE.27.001124.
This research was conducted to estimate the optical absorption and reduced scattering coefficients of two-layer turbid media using a stepwise method from the spatial-frequency domain reflectance generated by Monte Carlo (MC) simulation. The stepwise method's feasibility for optical property estimations was first investigated by comparing the reflectance generated by the diffusion model and MC simulation for one-layer and two-layer turbid media. The results showed that, with proper frequency selection, the one-layer model could be used for estimating the optical properties of the first layer of the two-layer turbid media. A sample-based calibration method was proposed for calibrating discrepancies of the reflectance between the diffusion model and MC simulation. This significantly improved the parameter estimation accuracy. Results showed that the stepwise method's parameter estimation efficacy and accuracy were much better than that for the one-step method. This was especially true when estimating the absorption coefficient. Absolute error contour maps were generated in order to determine the constraining conditions for the first-layer thickness. It was found that, when each layer's optical properties are within the range of 0.005 mm ≤ μa ≤ 0.04 mm and 0.69 mm ≤ μs'≤ 2.2 mm, the first-layer's minimum thickness-for which the first layer's optical properties could be accurately estimated-could be as small as 0.2 mm. Further, the first layer's maximum thickness could not exceed 2.0 mm, in order to have acceptable estimations of the optical properties of the second layer.
本研究旨在利用蒙特卡罗（MC）模拟生成的空间频域反射率，通过逐步方法估算双层混浊介质的光吸收系数和约化散射系数。首先，通过比较扩散模型和MC模拟生成的单层和双层混浊介质的反射率，研究了逐步方法在光学特性估算方面的可行性。结果表明，通过适当选择频率，单层模型可用于估算双层混浊介质第一层的光学特性。提出了一种基于样本的校准方法，用于校准扩散模型和MC模拟之间反射率的差异。这显著提高了参数估计的准确性。结果表明，逐步方法的参数估计效率和准确性比一步法要好得多。在估计吸收系数时尤其如此。生成了绝对误差等高线图，以确定第一层厚度的约束条件。结果发现，当每层的光学特性在0.005 mm≤μa≤0.04 mm和0.69 mm≤μs'≤2.2 mm范围内时，能够准确估算第一层光学特性的第一层最小厚度可小至0.2 mm。此外，为了能够对第二层的光学特性进行可接受的估计，第一层的最大厚度不能超过2.0 mm。
