Governing Equations and Skin Properties
Numerical Code Validation
The research effort being performed in our laboratory consists also of numerical simulations of excitation and fluorescence light transport in human skin. We have developed the modified method of characteristics to solve the transient and steady state light transport equation in absorbing, scattering, and fluorescing medium. The method has been validated against reported numerical results for collimated and diffuse incidence in one and three-dimensional geometries. Good agreement was found confirming the capability of the numerical procedure and the associated computer program. The method was found to be accurate, stable, and fast (Katika and Pilon, 2005). Finally, our method was applied to steady-state and time-resolved fluorescence of human skin.
Zeng et al. (1997) proposed a seven layer optical model for solving steady-state autofluorescence of skin. The model includes the thickness and optical properties (κλ, σλ, c, and Φλ) of each layer of the skin for the excitation wavelength λex=442 nm and the autofluorescence wavelength of λem=520 nm. The above Figure compares our numerical results with those obtained by Zeng et al. (1997) using the Monte Carlo method to solve the above light transport Equations. Good agreement between the two methods (within 5% relative error) is observed. Note that the excitation light is completely attenuated at a depth of 0.6 mm within the skin. In addition, Zeng et al. (1997) compared their numerical results with in vivo measurements of steady-state autofluorescence of skin for Caucasian and Asian patients (Fig.7) thus, confirming the validity of the skin optical model and the simulation tool developed.
Zeng, H. , MacAulay, C. , McLean, D. I. , and Palcic, B. , 1997. Reconstruction of in vivo skin autofluorescence spectrum from microscopic properties by Monte Carlo simulation, Journal of Photochemistry and Photobiology B: Biology, Vol. 38, pp.234-240.
Steady-State Directional Reflectance and Fluorescence of Human Skin