Light transport in biological tissue using three-dimensional frequency-domain simplified spherical harmonics...

Area of Science:

• Biomedical Optics
• Computational Physics
• Medical Imaging

Background:

• The diffusion approximation is widely used in diffuse optical tomography (DOT).
• Its accuracy is limited in highly absorbing media and near light sources.
• Accurate light transport modeling is essential for reliable DOT reconstructions.

Purpose of the Study:

• To develop and evaluate a higher-order light transport model for DOT.
• To compare the accuracy of the simplified spherical harmonics (SP(N)) approximation against the diffusion approximation.
• To assess the impact of strong absorption on DOT model accuracy.

Main Methods:

• Developed a 3D frequency-domain simplified spherical harmonics (SP(N)) model for N up to 7.
• Validated SP(N) results against a multi-layered Monte Carlo model.
• Analyzed fluence calculations in scenarios with strong optical absorption.

Main Results:

• The SP(N) approximation (N > 1) shows improved accuracy over the diffusion equation.
• Accuracy gains are most significant near light sources and absorption boundaries.
• Errors between diffusion and SP(N) (N=7) models can reach 60% near sources.

Conclusions:

• Higher-order SP(N) approximations are necessary for accurate DOT in highly absorbing media.
• The diffusion approximation's limitations restrict its use in small animal imaging and critical source regions.
• SP(N) models offer a more robust alternative for challenging DOT applications.