Theoretical model of two-photon fluorescence microscopy in a layered turbid medium

摘要

A theoretical model of a two-photon fluorescence microscopy imaging in a scattering medium has been developed. Unlike the existing approaches, this model, based on the small-angle approximation of the radiative transfer equation, takes into account the effects of multiple small-angle scattering of probing and fluorescent light in the medium. The expression for a detected signal from an object observed by its fluorescence at the two-photon absorption of pulsed IR focused light beam, and also at the one-photon absorption, has been obtained. The model has been applied for constructing the images of a) a continuous uniformly fluorescent turbid medium and b) a thin fluorescent layer buried under a thick layer of non-fluorescent scattering medium. On the basis of the proposed model, general properties of the calculated images, such as the registered fluorescence signal dependence on the focusing depth and the influence of the scattering in the medium, have been studied.