A fresh look at the validity of the diffusion approximation for modeling fluorescence spectroscopy in biological tissue

Abstract

Fluorescence has become a widely used technique for applications in noninvasive diagnostic tissue spectroscopy. The standard model used for characterizing fluorescence photon transport in biological tissue is based on the diffusion approximation. On the premise that the total energy of excitation and fluorescent photon flows must be conserved, we derive the widely used diffusion equations in fluorescence spectroscopy and show that there must be an additional term to account for the transport of fluorescent photons. The significance of this additional term in modeling fluorescence spectroscopy in biological tissue is assessed.

Generalized coupled photon transport equations for handling correlated photon streams with distinct frequencies

“…In our previous work we have specifically developed this theory for fluorescence [7] and phosphorescence [8]. In our previous work we have specifically developed this theory for fluorescence [7] and phosphorescence [8].…”

“…For example, in fluorescence spectroscopy, H G;couple 1 ∕ τϕ eff σ 1 a;fl ∕ 4π R 4π R t 0 exp−t − t 0 ∕ τI 1 r; Ω; t 0 dt 0 dΩ and H L;couple σ 1 a;fl I 1 r; Ω; t, where τ is the fluorescence lifetime, ϕ eff is the quantum efficiency, and σ 1 a;fl is the absorption coefficient of fluorophores at ν 1 [7]. In phosphorescence imaging, H G;couple exp−t ∕ τ ∕ τϕ eff σ 1 a;ph ∕ 4π R 4π R t 0 I 1 r; Ω; t 0 dt 0 dΩ and H L;couple σ 1 a;ph I 1 r; Ω; t, where σ 1 a;ph is the absorption coefficient of phosphors at ν 1 [8].…”