Ariel University, Department of Electrical and Electronics Engineering, Ariel, Israel.
J Biomed Opt. 2018 Mar;23(3):1-9. doi: 10.1117/1.JBO.23.3.035007.
A practical algorithm for estimating the wavelength-dependent refractive index (RI) of a turbid sample in the spatial frequency domain with the aid of Kramers-Kronig (KK) relations is presented. In it, phase-shifted sinusoidal patterns (structured illumination) are serially projected at a high spatial frequency onto the sample surface (mouse scalp) at different near-infrared wavelengths while a camera mounted normally to the sample surface captures the reflected diffuse light. In the offline analysis pipeline, recorded images at each wavelength are converted to spatial absorption maps by logarithmic function, and once the absorption coefficient information is obtained, the imaginary part (k) of the complex RI (CRI), based on Maxell's equations, can be calculated. Using the data represented by k, the real part of the CRI (n) is then resolved by KK analysis. The wavelength dependence of n ( λ ) is then fitted separately using four standard dispersion models: Cornu, Cauchy, Conrady, and Sellmeier. In addition, three-dimensional surface-profile distribution of n is provided based on phase profilometry principles and a phase-unwrapping-based phase-derivative-variance algorithm. Experimental results demonstrate the capability of the proposed idea for sample's determination of a biological sample's RI value.
提出了一种实用的算法，用于借助克喇末-克龙尼克（Kramers-Kronig，KK）关系在空间频域中估计混浊样品的波长相关折射率（RI）。在该算法中，相位偏移正弦图案（结构照明）以高空间频率顺序投射到样品表面（鼠头皮）上的不同近红外波长，而安装在样品表面上的相机则正常捕获漫反射光。在离线分析管道中，在每个波长记录的图像通过对数函数转换为空间吸收图，并且一旦获得吸收系数信息，就可以根据麦克斯韦方程计算出复 RI（CRI）的虚部（k）。然后，使用 k 表示的数据通过 KK 分析来解析 CRI 的实部（n）。然后，分别使用四个标准色散模型（Cornu、Cauchy、Conrady 和 Sellmeier）拟合 n 的波长依赖性。此外，基于相位轮廓测量原理和基于相位解缠的相位导数方差算法提供了 n 的三维表面轮廓分布。实验结果证明了该方法对生物样品 RI 值的确定能力。
