Fluorescence sensing system by Soret-band LED light excitation for estimating relative talaporfin sodium concentration in skin

The purpose of this study is to establish a sensing system to estimate relative talaporfin sodium concentration in skin to evaluate the risk of skin photosensitivity after photodynamic therapy (PDT) using percutaneous fluorescence spectroscopy. A prototype fluorescence sensing probe was made using a pair of 5-cm-long diffuse tips of plastic optical fibers for excitation light irradiation and fluorescence collection. Talaporfin sodium (2.5mg/kg) was intravenously administrated to three pigs, and the talaporfin sodium concentration in plasma was measured. The fluorescence sensing probe was attached to the skin and excited by a LED light with a peak wavelength of 409±16nm to obtain the mean area of the talaporfin sodium fluorescence spectral peak (S_fluo). The time history of the talaporfin sodium concentration in tissue was estimated using a two-compartment pharmacokinetic model. The time history of S_fluo was described as a composite function of the time history of the measured talaporfin sodium concentration in plasma and that of the estimated concentration in tissue as a double exponential decay function. The relative talaporfin sodium concentration in tissue and the relative contributions of fluorescence from tissue and plasma to S_fluo were estimated by the fluorescence system with the numerical pharmacokinetic model. Results also show that tissue compression equivalent to venous pressure might be effective to suppress the contribution of talaporfin sodium fluorescence in plasma.