Multimodal mapping of human skin

Background The combination of CARS (coherent anti-Stokes Raman scattering), SHG (second harmonic generation) and TPEF (two photon excited fluorescence) imaging – referred to as multimodal imaging – provides complementary contrast based on molecular vibrations, the structure of various tissue components and endogenous fluorophores, respectively. Objectives A comprehensive overview of the appearance of human skin in multimodal imaging is presented. Methods Multimodal imaging of unstained skin cross sections of 32 individuals is performed using a Laser scanning microscope (LSM) and picosecond laser pulse for excitation. Results The epidermis, dermis and subcutis are distinguishable in all three applied modalities, but is unveiled best in multimodal images. While the subcutis is dominated by CARS signal, predominately SHG and secondary TPEF signal are observed for the dermis. In contrast, no SHG signal is detected in the epidermis, whereas CARS and TPEF show equal contributions. Additionally, the appearance of the major skin appendages, i.e. the hair follicle, sebaceous and sweat gland as well as blood vessels belonging to the vascular system is described. All four investigated functional units show a characteristic morphochemistry in TPEF and CARS allowing to distinguish further subunits, e.g. the major components of the hair follicle, while the SHG signal delineates the localization of the functional units. Conclusion Multimodal imaging is a powerful tool to investigate human skin by providing high contrast based on the molecular constitution. It is therefore suggested that multimodal imaging has a high potential in the application for dermatological research and clinical diagnostics of various skin alterations.