Source of error in calculation of optical diffuse reflectance from turbid media using diffusion theory

Area of Science:

• Optics
• Biomedical Optics
• Photonics

Background:

• Diffusion theory and similarity relations are widely used in photomedicine for light transport analysis.
• Accurate modeling of light interaction with turbid media is crucial for applications like optical imaging and therapy.

Purpose of the Study:

• To evaluate the accuracy of diffusion theory and similarity relations for calculating optical diffuse reflectance.
• To identify the limitations and conditions under which these models are most effective.

Main Methods:

• Calculated optical diffuse reflectance using diffusion theory and similarity relations for a narrow laser beam on a semi-infinite turbid medium.
• Validated results against high-accuracy Monte Carlo simulations with a large number of traced photon packets.

Main Results:

• Diffusion theory and similarity relations yield accurate results for isotropic photon sources deeper than one transport mean free path.
• Monte Carlo simulations revealed detailed discrepancies in diffusion theory and similarity relations under certain conditions.
• The conversion of a narrow laser beam to an isotropic point source significantly impacts diffusion theory accuracy.

Conclusions:

• Diffusion theory and similarity relations are reliable for deep, isotropic light sources in turbid media.
• The approximation of a narrow beam as a point source is a critical factor limiting diffusion theory's accuracy.
• Further refinement of source modeling is needed for precise optical modeling in photomedicine.