Quantifying the confounding effect of pigmentation on measured skin tissue optical properties: a comparison of colorimetry with spatial frequency domain imaging.

Abstract

.SignificanceSpatial frequency domain imaging (SFDI) is a wide-field diffuse optical imaging technique for separately quantifying tissue reduced scattering () and absorption () coefficients at multiple wavelengths, providing wide potential utility for clinical applications such as burn wound characterization and cancer detection. However, measured and can be confounded by absorption from melanin in patients with highly pigmented skin. This issue arises because epidermal melanin is highly absorbing for visible wavelengths and standard homogeneous light–tissue interaction models do not properly account for this complexity. Tristimulus colorimetry (which quantifies pigmentation using the “lightness” parameter) can provide a point of comparison between , , and skin pigmentation.AimWe systematically compare SFDI and colorimetry parameters to quantify confounding effects of pigmentation on measured skin and . We assess the correlation between SFDI and colorimetry parameters as a function of wavelength.Approach and from the palm and ventral forearm were measured for 15 healthy subjects with a wide range of skin pigmentation levels (Fitzpatrick types I to VI) using a Reflect RS® (Modulim, Inc., Irvine, California) SFDI instrument (eight wavelengths, 471 to 851 nm). was measured using a Chroma Meter CR-400 (Konica Minolta Sensing, Inc., Tokyo). Linear correlation coefficients were calculated between and and between and at all wavelengths.ResultsFor the ventral forearm, strong linear correlations between measured and values were observed at shorter wavelengths ( at ), where absorption from melanin confounded the measured . These correlations were weaker for the palm ( at ), which has less melanin than the forearm. Similar relationships were observed between and .ConclusionsWe quantified the effects of epidermal melanin on skin and measured with SFDI. This information may help characterize and correct pigmentation-related inaccuracies in SFDI skin measurements.