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.
Spectral emissivity of skin and pericardium by J Steketee 1973 Phys. Med. Biol. 18 686-694 doi: 10.1088/0031-9155/18/5/307 Help
J Steketee, Department of Biological and Medical Physics, Erasmus University, Rotterdam, The Netherlands
A monochromator was modified to measure the emissivity, ?(?), of living tissue in the infrared region between 1 and 14 ?m. The infrared radiation from the tissue was compared with blackbody radiation and in this way ?(?) has been determined for white skin, black skin, burnt skin and pericardium.
A compensating skin thermometer was constructed to measure the temperature of the surface of the tissue. The temperature difference before and after contact between a gold ring and the surface was made as small as possible (0.05 K). A reference radiator with the same spectral radiance (experimentally determined) mas used in compensating for the environment.
It appeared that ?(?) for skin is independent of the wavelength and equal to 0.98+-0.01. These results contradict those of Elam, Goodwin and Lloyd Williams, but are in good agreement with those of Hardy and Watmough and Oliver.
In addition there was no difference between ?(?) for normal skin and burnt skin. Epicardium values were found to lie between 0.83 (fresh heart) and 0.90 (after 7 h and after 9 d).
Print publication: Issue 5 (September 1973)
PDF (504 KB)
Reference Title:Non-contact skin emissivity: measurement from reflectance using step change in ambient radiation temperature Citation: T Togawa 1989 Clin. Phys. Physiol. Meas. 10 39-48 doi: 10.1088/0143-0815/10/1/004
Article by T Togawa of Inst. for Med. & Dental Eng., Tokyo Med. & Dental Univ., Japan
A method of estimating skin emissivity based on reflectance measurement upon transient stepwise change in the ambient radiation temperature was proposed. To effect this change, two shades at different temperatures were switched mechanically, and the change in radiation from the skin surface was recorded through an aperture for each shade by a high-resolution, fast-response radiometer having a sensitivity the 8-14 mu m range. Measurements were made on the forehead, forearm, palm and back of the hand in 10 male and 10 female subjects. No significant differences in emissivity were observed among sites and between sexes. The overall average of the skin emissivity obtained was 0.971+or-0.005 (SD). This result is inconsistent with most reported skin emissivity values. However, as the former studies had many inherent inadequacies, both theoretical and experimental, it is considered that most of these reported skin emissivities are unacceptable. The method proposed in the study has the following advantages: (1) relative calibration between instruments in unnecessary, (2) noncontact measurement can be achieved, and (3) each measurement can be made within one minute.
Available for purchase as a PDF (652 KB) downloadable document from the IOP website in the UK.