Diffuse reflectance relations based on diffusion dipole theory for large absorption and reduced scattering

Area of Science:

• Optical Physics
• Biomedical Optics
• Spectroscopy

Background:

• Diffuse reflectance spectroscopy (DRS) is crucial for determining biological sample optical properties.
• Current DRS analysis often relies on diffusion approximation, limiting its use in highly absorbing or scattering tissues.
• Accurate optical property measurement is vital for medical diagnostics and forensic analysis.

Purpose of the Study:

• To evaluate the accuracy of diffuse reflectance equations for biological samples with high absorption and scattering properties.
• To determine if existing models can be extended beyond the typical limitations of diffusion approximation.
• To enable more robust optical property measurements in challenging biological and forensic contexts.

Main Methods:

• Phantom experiments with varying absorption and scattering coefficients were conducted.
• Reflectance measurements were compared against the diffuse reflectance equation by Zonios et al.
• Analysis included comparisons with the diffusion dipole approximation for validation.

Main Results:

• Excellent agreement (r2=0.994) was observed between measurements and the Zonios et al. equation, even at high absorption coefficients (up to 20 mm-1).
• The model showed accuracy despite deviations from standard diffusion theory assumptions, attributed to its mathematical structure.
• The diffusion dipole approximation also agreed with measurements under high absorption and scattering conditions.

Conclusions:

• Diffuse reflectance equations derived from diffusion dipole theory can accurately analyze samples with high absorption relative to scattering.
• This facilitates the calibration of fiber-probe setups for reliable absorption measurements in complex samples.
• Findings significantly broaden DRS applicability in medicine (e.g., whole blood analysis) and forensics (e.g., bloodstains, fabrics).