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8 February 2008 Two-photon absorption and transient photothermal imaging of pigments in tissues
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As a main pigment in skin tissues, melanin plays an important role in photo-protecting skin from UV radiation. However, melanogenesis may be altered due to disease or environmental factors; for example, sun exposure may cause damage and mutation of melanocytes and induce melanoma. Imaging pigmentation changes may provide invaluable information to catch the malignant transformation in its early stage and in turn improve the prognosis of patients. We have demonstrated previously that transmission mode, two-photon, one- or two-color absorption microscopy could provide remarkable contrast in imaging melanin in skin. In this report we demonstrate significantly improved sensitivity, so that we are now able to image in epi-mode (or back reflection) in two-photon absorption. This improvement makes possible for us to characterize the different types of pigmentation on the skin in vivo at virtually any location. Another finding is that we can also image transient photothermal dynamics due to the light absorption of melanin. By carefully choosing excitation and probe wavelengths, we might be able to image melanin in different structures under different micro-environments in skin, which could provide useful photochemical and photophysical insights in understanding how pigments are involved in photoprotection and photodamage of cells.
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Tong Ye, Dan Fu, Thomas E. Matthews, Lian Hong, John D. Simon, and Warren S. Warren "Two-photon absorption and transient photothermal imaging of pigments in tissues", Proc. SPIE 6842, Photonic Therapeutics and Diagnostics IV, 684206 (8 February 2008);

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