Monte Carlo-based inverse model for calculating tissue optical properties Part I: Theory and validation on synthetic phantoms

A flexible and fast Monte Carlo-based model of diffuse reflectance has been developed for the extraction of the absorption and scattering properties of turbid media, such as human tissues. This method is valid for a wide range of optical properties and is easily adaptable to existing probe geometries, provided a single phantom calibration measurement is made. A condensed Monte Carlo method was used to speed up the forward simulations. This model was validated by use of two sets of liquid-tissue phantoms containing Nigrosin or hemoglobin as absorbers and polystyrene spheres as scatterers. The phantoms had a wide range of absorption $\left(0–20{\text{cm}}^{-1}\right)$ and reduced scattering coefficients $\left(7–33{\text{cm}}^{-1}\right)$. Mie theory and a spectrophotometer were used to determine the absorption and reduced scattering coefficients of the phantoms. The diffuse reflectance spectra of the phantoms were measured over a wavelength range of $350–850\text{\hspace{0.17em} nm}$. It was found that optical properties could be extracted from the experimentally measured diffuse reflectance spectra with an average error of $3\%$ or less for phantoms containing hemoglobin and $12\%$ or less for phantoms containing Nigrosin.