In Vivo 3d Quantification of Melanin in Human Skin Based on Multiphoton Microscopy and Image Processing

Multiphoton microscopy is a recent non-invasive skin imaging technique that allows the human skin three-dimensional structure to be characterized in vivo with sub-μm resolution. This technique, in combination with specific 3D image processing tools, allows an automatic segmentation of the different skin layers and an extraction of several quantitative parameters characterizing skin in terms of morphology, density and organization. In this paper, we propose a new specific 3D melanin detection and quantification method based on multiphoton microscopy and fluorescence lifetime imaging, compatible with in vivo human skin investigations. We applied this specific melanin analysis method in two clinical trials: i) 15 young (18-25y) and 15 aged (70-75y) human female volunteers focusing on the ventral and dorsal sides (unexposed vs. exposed) of their forearm, and ii) 45 female volunteers (1855y) with different skin phototypes (ITA values of their ventral forearm ranging from grade I to V). Our specific 3D melanin quantification method allowed us to bring out age related melanin changes between the ventral and dorsal sides of the forearm and discriminate the different skin phototypes. This innovative approach could have large applications in both the dermatological and cosmetic fields, since easily applied to the characterization of pigmentation disorders or to the assessment of compounds able to modulate skin melanin content.