Clinical CARS imaging shows potential for early diagnosis of skin diseases

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The first clinical CARS (Coherent Anti-Stokes Raman Scattering) imaging in patients with dermatological disorders has been conducted at the Charité hospital in Berlin.

Further clinical studies are currently being performed within the German BMBF project ChemoPraevent to evaluate the potential of the hybrid tomograph MPT-CARS for early diagnosis of skin diseases, optimisation of treatment procedures, the evaluation of the efficacy of cosmetics, and the investigation of side effects of pharmaceutical drugs such as chemotherapy agents.

The label-free 3D optical in vivo biopsies from the skin provided information on morphology at a subcellular level and also lipid and water content. Optical biosies were obtained completely non-invasively, that is without any mechanical or chemical treatments.

The novel certified clinical hybrid tomograph MPT-CARS is a combination of the clinical multiphoton tomograph DermaInspect from Jenlab and the add-on CARS module based on APE's optical parametric oscillator (OPO). The OPO provides the required second laser beam for CARS imaging. The CARS signal relies on the wavelength difference between DermaInspect's tuneable femtosecond 'pump' laser beam (710-920nm) and the OPO's 'Stokes' laser beam (1,000-1,300nm) that has to be tuned to match vibrational modes of the molecule of interest.

In order to image the intratissue lipid distribution in patients suffering from psoriasis, cancer, and other skin diseases, the tomograph MPT-CARS wavelengths were tuned to 811nm and 1,053nm, respectively. The combined mean power of both beams did not exceed 50mW as required by the European Notified Body for the approval of medical products (Zulassungsstelle). The standard acquisition time for an optical section (0.4 x 0.4mm) was seven seconds. Up to 20 sections at different tissue depths were obtained per region of interest.

The distribution of topically applied lipid-water-emulsions was investigated in time-lapse studies that are of high interest for cosmetics and pharmaceutical companies.