Analytic expression of fluorescence ratio detection correlates with depth in multi-spectral sub-surface imaging

Area of Science:

• Biomedical Optics
• Medical Imaging
• Biophysics

Background:

• Accurate depth assessment of fluorescent molecules in biological tissues is crucial for applications like fluorescence-guided surgery.
• Current methods may lack precision in determining the distribution depth of endogenous or exogenous fluorophores.

Purpose of the Study:

• To derive analytical solutions for diffuse light transport in biological tissue based on spectral deformation of near-infrared measurements.
• To establish a method for predicting the depth of fluorescent molecule distribution using fluorescence ratios at different wavelengths.

Main Methods:

• Derived analytical solutions for diffuse light transport in biological tissue.
• Utilized spectral deformation of diffused near-infrared measurements.
• Employed a multi-spectral fluorescence imaging system with a hemoglobin-containing diffusive phantom for experimental validation.

Main Results:

• Developed a closed-form mathematical expression relating fluorescence ratios at two wavelengths to the depth of fluorescent molecules.
• Demonstrated a linear relationship between the logarithm of fluorescence ratio and depth under specific conditions (depth > few mm, homogeneous tissue).
• Experimental results confirmed a significant correlation between predicted and measured depths of protoporphyrin IX molecules.

Conclusions:

• The derived analytical solutions provide a novel approach for depth assessment of fluorescence contrast in biological tissues.
• This method holds potential for improving intra-operative delineation of tumor margins in fluorescence-guided surgery.
• The findings suggest that optical properties of tissue influence the accuracy of depth prediction.