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Proceedings Paper

Epidermal melanin absorption in human skin
Author(s): Lill Tove Norvang Nilsen; Elisanne Janne Fiskerstrand; J. Stuart Nelson M.D.; Michael W. Berns; Lars Othar Svaasand
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Paper Abstract

The principle of laser induced selective photothermolysis is to induced thermal damage to specific targets in such a manner that the temperature of the surrounding tissue is maintained below the threshold for thermal damage. The selectivity is obtained by selection of a proper wavelength and pulse duration. The technique is presently being used in the clinic for removal of port-wine stains. The presence of melanin in the epidermal layer can represent a limitation to the selectivity. Melanin absorption drops off significantly with increasing wavelength, but is significant in the entire wavelength region where the blood absorption is high. Treatment of port-wine stain in patients with high skin pigmentation may therefore give overheating of the epidermis, resulting in epidermal necrosis. Melanosomal heating is dependent on the energy and duration of the laser pulse. The heating mechanism for time scales less than typically 1 microsecond(s) corresponds to a transient local heating of the individual melanosomes. For larger time scales, heat diffusion out of the melanosomes become of increased importance, and the temperature distribution will reach a local steady state condition after typically 10 microsecond(s) . For even longer pulse duration, heat diffusing from neighboring melanosomes becomes important, and the temperature rise in a time scale from 100 - 500 microsecond(s) is dominated by this mechanism. The epidermal heating during the typical 450 microsecond(s) pulse used for therapy is thus dependent on the average epidermal melanin content rather than on the absorption coefficient of the individual melanosomes. This study will present in vivo measurements of the epidermal melanin absorption of human skin when exposed to short laser pulses (< 0.1 microsecond(s) ) from a Q-switched ruby laser and with long laser pulses (approximately 500 microsecond(s) ) from a free-running ruby laser or a long pulse length flashlamp pumped dye laser. The epidermal melanin absorption coefficient of human skin of various pigmentation and races will be presented.

Paper Details

Date Published: 10 January 1996
PDF: 12 pages
Proc. SPIE 2624, Laser-Tissue Interaction and Tissue Optics, (10 January 1996); doi: 10.1117/12.229548
Show Author Affiliations
Lill Tove Norvang Nilsen, Norwegian Institute of Technology and Univ. of California/Irvine (Norway)
Elisanne Janne Fiskerstrand, Univ. Hospital of Trondheim (Norway)
J. Stuart Nelson M.D., Univ. of California/Irvine (United States)
Michael W. Berns, Univ. of California/Irvine (United States)
Lars Othar Svaasand, Norwegian Institute of Technology and Univ. of Califronia/Irvine (Norway)

Published in SPIE Proceedings Vol. 2624:
Laser-Tissue Interaction and Tissue Optics
Guy P. Delacretaz; Rudolf W. Steiner; Lars Othar Svaasand; Hansjoerg Albrecht; Thomas H. Meier, Editor(s)

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