An approach for correcting optical paths of different wavelength lasers in diffusive medium based on Monte Carlo simulation

Abstract

Near-infrared spectroscopy (NIRS) generally uses multiple wavelengths of light to obtain functional information. When different wavelengths are employed together, their optical paths are different in the medium and it can potentially cause errors. In this study, we introduced an approach of correcting optical paths when laser sources are used. Laser can be approximated by a point source in a diffusive medium and its depth depends on the wavelength. By multiplying the ratio of detected weights emitted from different point sources, they are conceptually moved to the same position. Monte Carlo simulation was implemented to accumulate required data. As an example for verifying this method, optical properties of the white matter of the brain was used. All combinations of four wavelengths (400, 550, 700, and 850 nm) and six source-detector distances (0.5 mm to 3.0 mm at intervals of 0.5 mm) were simulated. Under the same example conditions, the difference between the simulation results and this method was about '1.28%'. The results showed that this approach is applicable to short source-detector distance conditions.