Design and validation of a combined system for in situ measurement of photosensitizer fluorescence and tissue diffuse reflectance

Abstract

Background: Quantitative measurement of photosensitizer during photodynamic therapy (PDT) is critical. One of the practical approaches is to measure photosensitizer's fluorescence, however, the influence of tissue optic properties needs to be considered in in situ measurement. Objective: To design and validate a combined system for dual detection of fluorescence and tissue diffuse reflectance. Materials and Method：For fluorescence detection, a 405 nm laser was used for excitation, a power meter for monitoring laser power and a fiber optic spectrometer for recording fluorescence. For diffuse reflectance measurement, a halogen lamp was used as light source and a fiber optic spectrometer for recording diffuse reflectance. Hemoporfin (HMME) was used as a model photosensitizer. Mice were used to evaluate the dual detection function of fluorescence and tissue diffuse reflectance after i.v. injection of HMME. Results: Solutions of different concentrations of HMME were used to test the intensity responses of the fluorescence detection system. A linear correlation was observed at HMME concentration lower than 10 μg/ml. Dual-band correction using corresponding diffuse reflectance data was used for the correction of original fluorescence spectrum. Diffuse reflectance corrected fluorescence data might truly reflect HMME concentration in the skin tissue. Conclusion: The preliminary evaluation suggests that the combined system can be used for quantitative measurement of photosensitizer fluorescence.