Fiber-optic probe for in vivo monitoring photosensitizer concentration from spatially resolved fluorescence and reflectance measurements

We present a portable fiber-optic system for noninvasive determination of tissue optical properties and photosensitizer concentration from spatially resolved fluorescence and reflectance measurements. The experimental setup consists of four main parts: light sources, modulator, fiber optic probe and signal treatment system. Irradiation produced by two semiconductor lasers (635 nm and 650 nm) is alternately delivered to a tissue via 200-mkm fiber. Modulated fluorescence and reflected light are collected by rectangular coherent fiber. During fluorescence measurements an optical filters are used to attenuate diffusely reflected excitation light. The construction of experimental setup allows to detect fluorescence and reflected light within the range of source-detector distances (from 0.55 mm up to 5.5 mm) with the spatial resolution ∼300 mkm. The experimental setup is tested on a number of tissue-simulating phantoms with different concentration of photosensitizer (chlorine e6). We use a diffusion model of light propagation to determine tissue optical properties and photosensitizer concentration. It is found a good agreement between results obtained by integrating sphere setup and by in vivo measurements. The possibility of using presented fiber-optic system for noninvasive photodynamic therapy dosimetry is discussed.