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Research projects

Estimation of melanin and hemoglobin contents in skin tissue using diffuse reflectance spectroscopy

Various optical methods have been reported for effective and noninvasive medical diagnostics of living human skin tissue. Quantitative estimation of the melanin and blood concentrations and blood oxygenation is important for detecting various skin diseases, including cancers; monitoring health status and tissue metabolism; and evaluating convalescence. The major chromophores in the superficial skin layer are melanin, oxygenated hemoglobin, and deoxygenated hemoglobin, which show distinctive optical absorption properties in the visible wavelength range. If the concentration of each chromophore varies, then the corresponding change may be visible in light diffusely reflected from the skin tissue in this wavelength range. Therefore, analysis of the diffuse reflectance spectra may provide us with useful information on tissue activities that are related to melanin and hemoglobin. On the other hand, the diffuse reflectance spectra also depend on the light scattering that is due to the structures of tissues and cells, such as collagen fibers and other cellular structures. Thus, estimation of the melanin and hemoglobin concentrations requires knowledge of the scattering properties of light in skin tissue as well as its absorption properties.

To estimate the concentrations of melanin and blood and the oxygen saturation in human skin tissue, we propose a method using a multiple regression analysis aided by a Monte Carlo simulation for diffuse reflectance spectra in visible wavelength range (500-600 nm) from the skin tissue. By using the absorbance spectrum as a response variable and the extinction coefficients of melanin, oxygenated hemoglobin, and deoxygenated hemoglobin as predictor variables, the multiple regression analysis gives regression coefficients. The concentrations of melanin and blood are determined from the regression coefficients using conversion vectors that are estimated numerically in advance, while the oxygen saturation is obtained directly from the regression coefficients. Numerical and experimental investigations were performed for layered skin tissue models and phantoms. Measurements of human skin were also carried out to monitor variations in the melanin and blood contents and oxygenation during cuff occlusion. The results confirmed the usefulness of the proposed method.