The melanosome: threshold temperature for explosive vaporization and internal absorption coefficient during pulsed laser irradiation.
The explosive vaporization of melanosomes in situ in skin during pulsed laser irradiation (pulse duration less than 1 microsecond) is observed as a visible whitening of the superficial epidermal layer due to stratum corneum disruption. In this study, the ruby laser (694 nm) was used to determine the threshold radiant exposure, H0 (J/cm2), required to elicit whitening for in vitro black (Negroid) human skin samples which were pre-equilibrated at an initial temperature, Ti, of 0, 20, or 50 degrees C. A plot of H0 vs Ti yields a straight line whose x-intercept indicates the threshold temperature of explosive vaporization to be 112 +/- 7 degrees C (SD, N = 3). The slope, delta H0/delta Ti, specifies the internal absorption coefficient, mua, within the melanosome: mua = -rho C/(slope(1 + 7.1 Rd)), where rho C is the product of density and specific heat, and Rd is the total diffuse reflectance from the skin. A summary of the absorption spectrum (mua) for the melanosome interior (351-1064 nm) is presented based on H0 data from this study and the literature. The in vivo absorption spectrum (380-820 nm) for human epidermal melanin was measured by an optical fiber spectrophotometer and is compared with the melanosome spectrum.
Jacques
S L
SL
Laser Biology Research Laboratory, University of Texas M.D. Anderson Cancer Center, Houston 77030.
McAuliffe
D J
DJ
D000818:Animals; D044383:Black People; D002460:Cell Line; D002478:Cells, Cultured; D006168:Guinea Pigs; D006801:Humans; D007834:Lasers; D008544:Melanocytes / Q000502:physiology / Q000528:radiation effects*; D008546:Melanoma, Experimental; D051379:Mice; D012867:Skin / Q000528:radiation effects; D013552:Swine; D013556:Swine, Miniature