Assessment of tissue optical parameters in a spherical geometry using three different optical spectroscopy methods: comparison based on a theoretical approach

Abstract

The non-invasive research of information inside the biological tissues can be made by means of continuous, time dependent or frequency modulated light source, emitting in the visible or infrared range. Moreover, the biological structures such as brain, breast or fruits, can be seen as closer to a spherical shape than a slab. This paper focus on the retrieval of tissue optical parameters in a spherical geometry using fittings with an analytical solution adapted for semi infinite geometry. The data were generated using three different optical spetroscopy methods: frequency-resolved, spatially-resolved, and time-resolved. Simulations based on a Monte Carlo code were performed on a homogeneous sphere, with 18 spaced detectors located at the periphery. First, data are examinated in the frequency domain, then, they are treated with optimization algorithms to assess the optical coefficients. The computations show that the spatially resolved measurements are often more robust than those obtained by the frequency-resolved mode. In the temporal domain, errors on the estimates are also exhibited with the fitting by the Fourier transform of a solution based on the semi-infinite geometry. Furthermore, when the analytical solution is modified to take into account the sphere geometry, the retrieval of the coefficients is improved.