Novel approach to assess the emissivity of the human skin
J. Biomed. Opt., Vol. 14, 024006 (2009); DOI:10.1117/1.3086612 Published 6 March 2009
by: Francisco J. Sanchez-Marin, Sergio Calixto-Carrera, and Carlos Villaseñor-Mora
Centro de investigaciones en optica, Loma del Bosque 115, Lomas del Campestre, Leon, Guanajuato 37150, Mexico
To study the radiation emitted by the human skin, the emissivity of its surface must be known. We present a new approach to measure the emissivity of the human skin in vivo. Our method is based on the calculation of the difference of two infrared images: one acquired before projecting a CO2 laser beam on the surface of the skin and the other after such projection. The difference image contains the radiation reflected by the skin, which is used to calculate the emissivity, making use of Kirchhoff’s law and the Helmholtz reciprocity relation. With our method, noncontact measurements are achieved, and the determination of the skin temperature is not needed, which has been an inconvenience for other methods. We show that it is possible to make determinations of the emissivity at specific wavelengths. Last, our results confirm that the human skin obeys Lambert’s law of diffuse reflection and that it behaves almost like a blackbody at a wavelength of 10.6 µm.
Editor’s Note: Back in the 1960s there were several serious projects mounted by the US Army Medical Research Laboratory’s BioPhysics Division on determining injury thresholds of laser radiation on human skin analogs. The article “THRESHOLD LESIONS INDUCED IN PORCINE SKIN BY CO2 LASER RADIATION” by Brownell, Arnold S. ; Parr, Wordie H. ; Hysell, David K. ; Dedrick, Robert, USAMRL Report No. 7327, June 1967, is available as a pdf download at: http://handle.dtic.mil/100.2/AD659347.
Although not fully described in the article, the measured results compared favorably with a semi-infinite solid model of heat conduction for a surface that was essentially black (10.6 micron spectral absorptivity or emissivity very close to 1.0) or fully absorbing at 10.6 microns. This editor was a member of the USAMRL BioPhysics Division staff at that time and helped with the dosimetry of the experiments described.