Determination of the optical property changes by photodynamic therapy using inverse Monte Carlo method between 350 nm and 1000 nm

Abstract

The clinical outcome of photodynamic therapy (PDT) may be improved by the accurate knowledge about the light distribution within the tissue. Optical properties [absorption coefficient (μ_a), scattering coefficient (μ_s), anisotropy factor (g), refractive index, etc.] of tissues help us realizing a light propagation through the tissue. The aim of this study is acquisition of the knowledge of light propagation within tissue with the optical property of mouse tumor tissue performed PDT. We evaluated the optical property of mouse tumor tissue before and after PDT using the double integrating sphere setup and algorithms based on the inverse Monte Carlo method in the wavelength range from 350 to 1000 nm. During PDT, the reduced scattering coefficient spectra were decreased entirely after 5 and 10 min irradiation. 1, 2, 7 days after PDT, the absorption coefficient was increased in the wavelength range from 400 to 660 nm. And, the reduced scattering coefficient at the wavelength of 664 nm was increased with the passage of time. These results are used for medical diagnostic applications for the quantitative assessment of the PDT effect. 7 days after PDT, the reduced scattering coefficient at the wavelength of 664 nm was increased significantly from 0.64 mm^-1 to 1.24 mm^-1, which results in the optical penetration depth decreased from 1.49 mm to 0.84 mm, respectively. To ensure the effective procedure, an adjustment of the laser parameter for the decreasing penetration depth is recommended for a second PDT.