Multiphoton tomography offers a painless method to examine patients under natural physiological conditions in vivo.
Multiphoton excitation induces a weak autofluorescence of naturally endogenous fluorescent bio-molecules, such as
flavines, NAD(P)H, metal-free porphyrines, components of lipofuscin, elastin and keratin. Additionally, collagen can be
detected by second harmonic generation (SHG). Due to the nonlinearity, the effects occur only in a very tight focus,
where the photon density is high enough. This leads to high axial and lateral resolution of <1μm without any need of a
confocal detection and avoids out-of-focus damage. The limited depth range, given by the working distance of the
focusing optics, is overcome with a gradient index-lens (GRIN-lens) based endoscope.
In this work we present the first results of clinical applications in vivo of gradient-index lens endoscopes. Images of e.g.
elastin and collagen (SHG) in the dermal layer of human skin are presented.