MONTE-CARLO ANALYSIS OF 2-PHOTON FLUORESCENCE IMAGING THROUGH A SCATTERING MEDIUM

The behavior of two-photon fluorescence imaging through a scattering m edium is analyzed by use of the Monte Carlo technique. The axial and t ransverse distributions of the excitation photons in the focused Gauss ian beam are derived for both isotropic and anisotropic scatterers at different numerical apertures and at various ratios of the scattering depth with the mean free path. The two-photon fluorescence profiles of the sample are determined from the square of the normalized excitatio n intensity distributions. For the same lens aperture and scattering m edium, two-photon fluorescence imaging offers a sharper and less aberr ated axial response than that of single-photon confocal fluorescence i maging. The contrast in the corresponding transverse fluorescence prof ile is also significantly higher. Also presented are results comparing the effects of isotropic and anisotropic scattering media in confocal reflection imaging. The convergence properties of the Monte Carlo sim ulation are also discussed. (C) 1998 Optical Society of America.