Discrimination of skin diseases using the multimodal imaging approach

Optical microspectroscopic tools reveal great potential for dermatologic diagnostics in the clinical day-to-day routine. To enhance the diagnostic value of individual nonlinear optical imaging modalities such as coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG) or two-photon excited fluorescence (TPF), the approach of multimodal imaging has recently been developed. Here, we present an application of nonlinear optical multimodal imaging with Raman-scattering microscopy to study sizable human-tissue cross-sections. The samples investigated contain both healthy tissue and various skin tumors. This contribution details the rich information content, which can be obtained from the multimodal approach: While CARS microscopy, which – in contrast to spontaneous Raman-scattering microscopy – is not hampered by single-photon excited fluorescence, is used to monitor the lipid and protein distribution in the samples, SHG imaging selectively highlights the distribution of collagen structures within the tissue. This is due to the fact, that SHG is only generated in structures which lack inversion geometry. Finally, TPF reveals the distribution of autofluorophores in tissue. The combination of these techniques, i.e. multimodal imaging, allows for recording chemical images of large area samples and is – as this contribution will highlight – of high clinically diagnostic value.