Laser based devices with ability to heat sub-surface zones at certain depths within skin have several potential applications. Methods to achieve such heating at different depths have been explored in this work. Monte Carlo modeling and heat transfer calculations were performed to calculate fluence distribution, temperature distribution, and thermal damage for various laser wavelengths in the range of 1,200-1,800 nm with various pulse durations. The treatment consisted of laser irradiation combined with contact cooling. Cooling leads to preservation of the top layer leading to a zone of thermally damaged tissue under the top layer. The results indicated that the thickness and mean depth of the thermally damaged sub-surface zone can be controlled by choice of laser wavelength and cooling and irradiation times. Thermally damaged zone was deeper with lower absorbing wavelengths and/or with longer pulse durations. Histological evaluation of ex vivo pig skin immediately after treatment was done to determine thermal damage band depth and thickness for various wavelengths and pulse durations. Histological evaluation supported the modeling results. Thus, variable depth heating can be achieved through selection of the wavelength and/or laser pulse duration. With a chosen wavelength device, a variable depth heating device can be constructed by varying the cooling and laser irradiation durations.

Date Published: 23 March 2007
PDF: 6 pages
Proc. SPIE 6424, Photonic Therapeutics and Diagnostics III, 64240P (23 March 2007); doi: 10.1117/12.701307

Published in SPIE Proceedings Vol. 6424:
Photonic Therapeutics and Diagnostics III
Henry Hirschberg M.D.; Brian Jet-Fei Wong M.D.; Reza S. Malek M.D.; Kenton W. Gregory M.D.; Nikiforos Kollias M.D.; Bernard Choi; Steen J. Madsen; Guillermo J. Tearney M.D.; Justus F. R. Ilgner M.D.; Haishan Zeng, Editor(s)