Poster presentation, P7

Official XXIst International Pigment Cell Conference website - 21-24 Sept 2011, Bordeaux - France | updated: September 04 2011

Imaging the Distributions of Eumelanin and Pheomelanin in Human Tissue

Melanoma diagnosis poses tremendous challenges in dermatopathology; recent studies show discordance rates in pathology as high as one in seven¹, and the severe consequences of missing a melanoma diagnosis has increased the number of biopsies taken and lowered the threshold for diagnosis of early melanoma.² This leads to unknown but likely significant societal costs and morbidity from associated unnecessary treatments. Clinicians need better technology to increase the specificity of current diagnostic techniques. We have previously reported a technique that resolves eumelanin and pheomelanin using nonlinear optics, specifically two-color pump-probe microscopy.³ This technique, which is compatible with standard pathology procedure, has been used to image the microscopic morphology of the distribution of eumelanin and pheomelanin in human tissue slides. It has revealed that melanomas tend to have an inhomogeneous distribution of melanins and higher fractional eumelanin content compared to other lesions. Here we report on a variety of extensions of that work. Studies on the dependence of laser parameters (pump and probe wavelengths, polarization) reveal the effects of the increased ground state depletion signal in pheomelanin relative to eumelanin. We have quantified eumelanin and pheomelanin morphology using wavelet analysis and other image processing methods to further improve specificity. High resolution imaging has identified microstructure with variable eumelanin/pheomelanin ratios in individual melanosomes. We have demonstrated epi-mode detection and imaging in vivo (of lesions induced in human skin grafted to nude mice). Finally, we have demonstrated three-dimensional sectioning capabilities. As a result, it can be used for imaging thick slices of tissue (to a depth of around 120µm), allowing a clinician to examine a large section of a lesion all at once. This has been demonstrated with a fresh, excised human mole, on which the rete ridges can be seen using melanin as a source of contrast. Taken together, these results provide new insights on the chemical morphology and biochemical heterogeneity of normal and diseased tissue, and provide valuable diagnostic information. 1. B. A. Shoo et al. J. Am. Acad. Dermatol. 62, 751 (2010). 2. E. J. Glusac. J. Cutan. Pathol. 38, 264 (2011). 3. T. E. Matthews et al. Sci. Transl. Med. 3, 71ra15 (2011).

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