The dependence of total fluorescence escape from a homogeneous, semi-infinite tissue on tissue optics has been examined. A measurement of total fluorescence escape F is related to the intrinsic fluorescence coefficient \beta by a factor that depends on the optical properties of the tissue: F(\lambda)=\beta(\lambdax,\lambda) \intO\infty \Phi(z, \lambdax) E(z, \lambda) dz. \beta is the product of fluorophore absorption coefficient and fluorophore quantum yield. \Phi is the fluence rate of excitation light \lambdax in the tissue. E is a dimensionless function that describes the probability for escape to the surface of emission light \lambda originating at a depth z . The source strength of fluorescence emission at depth z is the product \beta \Phi . Accurate expressions have been developed for the depth dependence of \Phi and E , valid for both absorption-dominant and scattering- dominant light wavelengths in a tissue. These expressions have been based on Monte Carlo simulations of photon transport. They have been used to evaluate the integral in the above equation to yield an analytic expression for fluorescence escape which is a function of the total diffuse reflectance Rd and optical penetration depth \delta at both the excitation and emission wavelengths. Tissue phantoms have been used to experimentally verify the theory of total fluorescence escape. Non-invasive measurements of total fluorescence escape, diffuse reflectance, and penetration depth allow determination of the intrinsic fluorescence spectrum.
C. M. Gardner, S. L. Jacques, A. J. Welch, "Fluorescence and reflectance spectra specify intrinsic fluorescence spectrum corrected for tissue optics distortion," SPIE Proceedings of Advances in Fluorescence Sensing Technology, edited by J. R. Lakowicz, R. B. Thompson, 1885, 122-128 (1993).