Diffuse Reflectance Spectroscopy as a Tool to Measure the Absorption Coefficient in Skin: South African Skin Phototypes

Abstract

In any laser skin treatment, the optical properties (absorption and scattering coefficients) are important parameters. The melanin content of skin influences the absorption of light in the skin. The spread in the values of the absorption coefficients for the South African skin phototypes are not known. A diffuse reflectance probe consisting of a ring of six light delivery fibers and a central collecting fiber was used to measure the diffused reflected light from the arms of 30 volunteers with skin phototypes I-V (on the Fitzpatrick scale). The absorption coefficient was calculated from these measurements. This real-time in vivo technique was used to determine the absorption coefficient of sun-exposed and -protected areas on the arm. The range of typical absorption coefficients for the South African skin phototypes is reported. The values for the darker South African skin types were much higher than was previously reported for darker skin phototypes. In the analysis, the contributions of the eumelanin and pheomelanin were separated, which resulted in improved curve fitting for volunteers of southern Asian ethnicity without compromising the other groups.

Objective determination of skin phototypes in healthy children by diffuse reflectance spectroscopy

“…Axilla (armpit) from the inner side of the upper arm was selected as the default part of the body for the spectrophotometric evaluation of constitutive skin pigmentation, presented as standard also by other authors (4,7,10,14,15,17,29). This part of the body seems to be most appropriate due to the minimum load rating sunlight since this part of the body is usually not exposed to the sun.…”

Variations in laser energy outputs over a series of simulated treatments

“…9 Practitioners would be unlikely to expect the same response for these different skin types when applying the same laser parameters. However, whereas the difference in skin absorption is known, the difference in laser outputs leading to overtreatment, or undertreatment, is not routinely measured.…”

Reflectance spectroscopy for noninvasive evaluation of hair follicle stage

“…It is well know that the reflectance spectrum of skin carries information about the skin composition, such as melanin and hemoglobin. [11][12][13][14][15] In this work, the melanin contents in skin were extracted by reflectance spectroscopy. The melanin content increases with the progress of anagen, and decreases with the transition of catagen and telogen.…”

“…[11][12][13][14][15][16] The reflectance spectrum carries information of the tissue structure and components, for instance, the chromospheres' concentration such as melanin and hemoglobin. [11][12][13][14] Besides, reflectance spectroscopy documents information of topical skin area, which should afford a promising tool for distinguishing interindividual variation. 15 In this study, a commercial optical fiber spectrometer was used to measure the diffuse reflectance of mouse skin during a hair follicle cycle, then the melanin value of skin was calculated based on the spectroscopy.…”