Comparison of photosensitizer (AlPcS2) quantification techniques: In situ fluorescence microsampling versus tissue chemical extraction

A noninvasive in situ fluorescence-based method for the quantification of t he photosensitizer chloroaluminum disulfonated phthalocyanine was compared to the highly accurate but nonreal time ex vivo spectrofluorometry method. Our in vivo fluorescence technique is designed to allow real-time assessmen t of photosensitizer in tumor and normal tissues and therefore temporally o ptimal light delivery. Laser-induced fluorescence was used to measure photo sensitizer concentration from multiple microscopic regions of tissue. Ex vi vo chemical extraction was used to quantify photosensitizer concentration i n the same volume of tissue. The amount of photosensitizer in the vascular and/or parenchymal compartments of skeletal muscle and liver was determined by quantifying fluorescent signal in vivo, ex vivo and after blood removal . Confocal microscopy was used to spatially document photosensitizer locali zation 30 min and 24 h after delivery. While a linear correlation can exist between the fluorescence intensity measured by our fiber-optic bundle syst em and actual tissue concentration, temporal changes to this calibration li ne exist as the photosensitizer changes its partitioning fraction between t he blood (vasculature) and the tissue parenchyma. In situ photosensitizer f luorescence microsampling (dosimetry) systems can be performed in real time and linearly correlated to actual tissue concentration with minimal intert issue variance. Tissue-specific differences may require temporal alteration s in the calibration.