Probing depth in diffuse reflectance spectroscopy of biotissues: a Monte Carlo study

Diffuse reflectance spectroscopy (DRS) is an optical imaging modality based on extraction of tissue structural and functional information from back-reflectance spectra. In this paper we analyze the spectral dependence of DRS probing depth for different source-detector separations (SDSs) in the range of 1.5-7.0 mm by means of Monte Carlo simulations. The simulated spectra are employed to analyze the effect of the selected spectral range on the accuracy of oxygen saturation (StO(2)) reconstruction for different parameters of skin. It is shown that the probing depth varies in the range of 1-4 mm depending on SDS and tissue parameters, and in the hemoglobin absorption band for particular medium configuration it demonstrates a 2-fold decrease as compared to the neighboring spectral ranges. Comparison of different spectral ranges for StO(2) reconstruction from the measured spectra at different SDSs demonstrated that the range of 480-600 nm and the full range of 480-900 nm benefit over near infrared (NIR) range (700-900 nm) in the reconstruction accuracy. The 480-600 nm range provides the best reconstruction accuracy for low blood volume content, while the full range of 480-900 nm provides better accuracy for larger blood volume content. The comprehensive study of the spectral dependency of probing depth in DSR for SDSs in the range of 1.5-7.0 mm based on MC simulations for multi-layered skin model depending on skin layers properties and numerical aperture combined with analysis of StO(2) reconstruction accuracy was conducted for the first time to our knowledge.