Depth and structure information in fluorescence molecular tomography obtained from time resolved spectroscopy

Abstract

In concentrated fluorescent solutions, the reabsorption and reemission of fluorescence light affects the temporal shape of the registered emission on the ps to ns time scale. Time-of-flight spectroscopy and intensity based tomography employ light transport models to characterize scattering of biological tissue providing information on the effective path length of the photons and the origin of emission. We propose the evaluation of fluorescence decay curves after reabsorption events to i) determine correction factors for time resolved fluorescence spectroscopy and tomography and ii) to exploit the information in the specific time resolved fluorescence traces to obtain information on the depth of signal generation in tissue and/or determination of reabsorbing structures as for example dye loaded micelles and cell compartments. The expected fluorescence decay curves after reabsorption events were modelled with rate equations for reabsorption and reemission. The fluorescence traces were fitted with the developed model in dependency of fluorophore concentration and path length. The results indicate that reabsorption can be quantitatively determined and depth information can be reconstructed from the time-course of the fluorescence signal. The applicability of the proposed technique to time-resolved fluorescence tomography is discussed.