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

SIGNIFICANCE: Spatial frequency domain imaging (SFDI) is a wide-field diffuse optical imaging technique for separately quantifying tissue reduced scattering ([Formula: see text]) and absorption ([Formula: see text]) coefficients at multiple wavelengths, providing wide potential utility for clinical applications such as burn wound characterization and cancer detection. However, measured [Formula: see text] and [Formula: see text] 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 [Formula: see text] “lightness” parameter) can provide a point of comparison between [Formula: see text] , [Formula: see text] , and skin pigmentation. AIM: We systematically compare SFDI and colorimetry parameters to quantify confounding effects of pigmentation on measured skin [Formula: see text] and [Formula: see text]. We assess the correlation between SFDI and colorimetry parameters as a function of wavelength. APPROACH: [Formula: see text] and [Formula: see text] 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). [Formula: see text] was measured using a Chroma Meter CR-400 (Konica Minolta Sensing, Inc., Tokyo). Linear correlation coefficients were calculated between [Formula: see text] and [Formula: see text] and between [Formula: see text] and [Formula: see text] at all wavelengths. RESULTS: For the ventral forearm, strong linear correlations between measured [Formula: see text] and [Formula: see text] values were observed at shorter wavelengths ([Formula: see text] at [Formula: see text]), where absorption from melanin confounded the measured [Formula: see text]. These correlations were weaker for the palm ([Formula: see text] at [Formula: see text]), which has less melanin than the forearm. Similar relationships were observed between [Formula: see text] and [Formula: see text]. CONCLUSIONS: We quantified the effects of epidermal melanin on skin [Formula: see text] and [Formula: see text] measured with SFDI. This information may help characterize and correct pigmentation-related inaccuracies in SFDI skin measurements.