Multiphoton tomography of epidermis and dermis

Multiphoton imaging has developed into an important technique for in-vivo research in life sciences in the last few years. A near-infrared laser beam is focused into a sample such that multiphoton-absorption can be generated which stimulates a fluorescence signal as well as second harmonic generation (SHG). Recently it has been shown that it is possible to image the epidermis in vivo with a resolution of about 1 μm. It was possible to produce 3-dimensional autofluorescence maps of the investigated tissue. However, the depth range of this technique is limited through the working distance of the focusing optics mostly to the epidermal part of the skin. Gradient index lenses offer possibilities to expand the imaging depth into the dermal layer. With typical diameters of up to 2mm and lengths between 2 and 6 cm they are capable of transmitting the laser, fluorescence and SHG radiation and to be integrated into an imaging system. First results of the applicability of gradient index lenses for imaging of skin are presented.