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Journal of Biomedical Optics

Mitigating thermal mechanical damage potential during two-photon dermal imaging
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Paper Abstract

Two-photon excitation fluorescence microscopy allows in vivo high-resolution imaging of human skin structure and biochemistry with a penetration depth over 100 μm. The major damage mechanism during two-photon skin imaging is associated with the formation of cavitation at the epidermal-dermal junction, which results in thermal mechanical damage of the tissue. In this report, we verify that this damage mechanism is of thermal origin and is associated with one-photon absorption of infrared excitation light by melanin granules present in the epidermal-dermal junction. The thermal mechanical damage threshold for selected Caucasian skin specimens from a skin bank as a function of laser pulse energy and repetition rate has been determined. The experimentally established thermal mechanical damage threshold is consistent with a simple heat diffusion model for skin under femtosecond pulse laser illumination. Minimizing thermal mechanical damage is vital for the potential use of two-photon imaging in noninvasive optical biopsy of human skin in vivo. We describe a technique to mitigate specimen thermal mechanical damage based on the use of a laser pulse picker that reduces the laser repetition rate by selecting a fraction of pulses from a laser pulse train. Since the laser pulse picker decreases laser average power while maintaining laser pulse peak power, thermal mechanical damage can be minimized while two-photon fluorescence excitation efficiency is maximized.

Paper Details

Date Published: 1 November 2004
PDF: 6 pages
J. Biomed. Opt. 9(6) doi: 10.1117/1.1806135
Published in: Journal of Biomedical Optics Volume 9, Issue 6
Show Author Affiliations
Barry R. Masters, Univ. of Illinois/Urbana-Champaign (United States)
Peter T. C. So, Massachusetts Institute of Technology (United States)
Christof Buehler, Univ. of Illinois/Urbana-Champaign (United States)
Nicholas P. Barry, Univ. of Colorado Health Science Ctr. (United States)
Jason D. B. Sutin, Univ. of Illinois/Urbana-Champaign (United States)
William W. Mantulin, Univ. of Illinois/Urbana-Champaign (United States)
Enrico Gratton, Univ. of Illinois/Urbana-Champaign (United States)


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