Optical properties of albino rat skin heated in vitro: comparison of photoacoustic and integrating sphere measurement techniques

Abstract

The optical properties represented by the absorption coefficient ((mu) a ) and reduced scattering coefficient [(mu) s (1-g) or (mu) ' s ] at (lambda) equals 355 nm of thermally altered albino rat skin were measured in vitro by two methods: (1) a time-resolved stress detection (TRSD) technique which directly measured the effective attenuation coefficient ((mu) eff ) and the absorption coefficient ((mu) a ), and (2) the well-known integrating sphere technique which measured total transmittance (T t ) nd total diffuse reflectance (R d ). The skin pieces were wrapped in water-tight packets and heated for 20 minutes in a calibrated water bath (temperature range: 20 degree(s) - 90 degree(s)C) and the same skin samples were used for both measurement methods. The experimental data were analyzed to specify the absorption and the scattering properties. The results, which were in general agreement for both methods, indicated that denaturation of the rat skin caused a decrease in scattering due to melting of the collagen fibers. The decrease began at 55 degree(s)C and plateaued at 65 degree(s) - 70 degree(s)C and was essentially unchanged at higher temperatures. Absorption was not significantly affected by denaturation except for a transient rise at 50 degree(s) - 60 degree(s)C.