Monte Carlo Modeling Of Polarized Light Scattering Spectroscopy

Polarized light scattering spectroscopy, a non-invasive diagnostic technique, can be used to extract morphological information of epithelial cell nuclei. It has a great potential application in precancerous diagnosis. However, so far there lacks perfect theoretical method to study the mechanism of this technique. Monte Carlo simulation can be used to study light transportation in turbid media and has been used to study kinds of biomedical optical techniques. Limited by computing resource, Monte Carlo simulation can be hardly used to study spectroscopy. With the techniques of parallel computing, a Monte Carlo program, which can be used to simulate polarized light scattering spectra of turbid media, was developed in this paper. Based on this program, the mechanism of polarized light scattering spectroscopy was studied.At first, Monte Carlo algorithm was described in detail.Biological tissue is modeled as suspension of micro-spheres and its optical properties, such as anisotropic factor, scattering coefficient, Mueller matrix and so on, are calculated by Mie theory. Stokes vector is applied to describe light polarization. Stokes vector and reference coordinate are tracked while simulating. At last, physical quantities are calculated statistically to provide experimental results.Furthermore, the relation between wavelengths is neglectable, so all photons obey independent identical distribution. A Monte Carlo program for spectroscopy simulation is implemented with parallel computing. Results showed that this program was provided with good parallel efficiency. Comparison of simulated and experimental results validated our program.At last, based on our parallel Monte Carlo program, some basic issues of polarized light scattering spectroscopy, such as polarization gating, characters of single and multiple scattering spectra and so on, were studied. It's found that, 1) oscillation frequency and amplitude of spectra are much affected by particle diameter and standard deviation. 2) The change of anisotropy factor and incident angle affects the detection depth much. 3) For one-layer model, the characters of single and multiple scattering spectra are much similar. 4) For two-layer model, bottom layer has much effect on detection of top layer's polarized light scattering spectra, as top layer is thin or has large anisotropic factor. This effect can be decreased or even removed by increasing incident angle.