A diffusion theory model of spatially resolved fluorescence from depth-dependent fluorophore concentrations

Area of Science:

• Biomedical Optics
• Photonic Modeling
• Tissue Optics

Background:

• Accurate modeling of light propagation in tissue is crucial for understanding fluorescence.
• Quantifying fluorophore concentration and optical properties in heterogeneous tissues remains challenging.

Purpose of the Study:

• To develop and validate a photon diffusion model for calculating steady-state, spatially resolved fluorescence in layered tissues.
• To assess the model's capability in simulating excitation reflectance and fluorescence escape.
• To explore the application of spatially resolved fluorescence for monitoring drug diffusion and photobleaching.

Main Methods:

• Developed a photon diffusion model for pencil beam excitation in layered tissue.
• Calculated excitation reflectance and fluorescence escape for continuous depth distributions.
• Validated the model using Monte Carlo simulations and experimental phantom measurements.
• Simulated realistic drug distributions to explore model applications.

Main Results:

• The model accurately calculates steady-state spatially resolved fluorescence.
• Validation confirmed the model's reliability against established methods.
• Simulations demonstrated the potential to quantify topical drug diffusion into skin.
• The technique showed promise for monitoring sensitizer photobleaching in photodynamic therapy.

Conclusions:

• The developed photon diffusion model provides a robust method for analyzing fluorescence in layered tissues.
• Spatially resolved fluorescence offers a viable approach for non-invasive monitoring of pharmacological and therapeutic processes in vivo.
• This modeling approach has significant implications for drug delivery research and photodynamic therapy optimization.