Quantitative fluorescence molecular imaging in highly light-absorbing melanomas using a dual-tracer kinetic modeling normalization method

Tissues with high light absorption, such as melanomas, present a significant challenge to fluorescence imaging approaches that seek to estimate molecular expression in vivo, since any fluorescence originating in the tissue will suffer substantial attenuation prior to detection. This can lead to sizable underestimations in estimated fluorescent tracer concentration in these tissues using conventional fluorescence imaging. In this study, a dual-tracer fluorescence imaging approach was employed to correct for severe tissue absorption by 1) using simultaneous injection and imaging of an untargeted tracer to normalize tissue absorption effects on the targeted tracer, and 2) using kinetic modeling that capitalizes on subtle differences in the dynamics of targeted and untargeted tracer uptake to quantify targeted molecule concentrations in the high absorbing tissue. Monte Carlo simulation and kinetic models demonstrated that the effect of optical properties on the approach could be eliminated by a pixel-by-pixel normalization of the targeted and untargeted tracer uptakes prior to 5 min post-tracer injection for fluorescence planar dynamic imaging.