Fig. 4.

(a) Representative bulk absorption (top) and reduced scattering (bottom) coefficient spectra from Fitzpatrick skin types II, III, IV, and VI as measured by spatial frequency domain spectroscopy (SFDS). Spectra are derived from three measurements taken from individual subjects (dorsal forearm) at each of the four skin types. (b) Example of depth-sensitive spectral decomposition of in vivo skin tissue (volar upper arm of a single subject, skin type III). Blue: tissue absorption measured by SFDS; black (dashed line): depth-specific quantification of melanin relative to total volume of tissue interrogated at each wavelength; red: absorption features specific to the dermis and deeper tissue; green (dotted line): least-squares fit for oxy/deoxy hemoglobin. (Residual absorption features between red and green correspond to carotenoids, lipids, and water).