Separating melanin from hemodynamics in nevi using multimode hyperspectral dermoscopy and spatial frequency domain spectroscopy

Abstract

Changes in the pattern and distribution of both melanocytes (pigment producing) and vasculature (hemoglobin containing) are important in distinguishing melanocytic proliferations. The ability to accurately measure melanin distribution at different depths and to distinguish it from hemoglobin is clearly important when assessing pigmented lesions (benign versus malignant). We have developed a multimode hyperspectral dermoscope (SkinSpect™) able to more accurately image both melanin and hemoglobin distribution in skin. SkinSpect uses both hyperspectral and polarization-sensitive measurements. SkinSpect’s higher accuracy has been obtained by correcting for the effect of melanin absorption on hemoglobin absorption in measurements of melanocytic nevi. In vivo human skin pigmented nevi (N=20) were evaluated with the SkinSpect, and measured melanin and hemoglobin concentrations were compared with spatial frequency domain spectroscopy (SFDS) measurements. We confirm that both systems show low correlation of hemoglobin concentrations with regions containing different melanin concentrations (R=0.13 for SFDS, R=0.07 for SkinSpect).

Fig. 1

The absorption spectra of melanin and hemoglobin.^,,

Fig. 2

Skin absorption spectra at various epidermal thicknesses and melanin and hemoglobin concentrations: (a) variations at the percentage of epidermis occupied by melanosome (1% to 5%), (b) variations on concentration of hemoglobin in the blood (100 to $200\mathrm{g}/\mathrm{L}$), (c) epidermal thickness variations (50 to $150\mu \mathrm{m}$), and (d) overlapping skin absorption spectral regions at all three skin properties variations described at (a)–(c).

Fig. 3

SkinSpect system diagram with dual camera hand-piece configuration.

Fig. 4

A schematic diagram of the SFDS system.

Fig. 5

Skin lesion analysis by (a) RGB color image at parallel polarization, (b) RGB color image at perpendicular polarization, (c) total melanin concentration map, and (d) deep melanin concentration map.

Fig. 6

Skin lesion analysis by total Hb before melanin attenuation correction (top) and total Hb after melanin attenuation correction (bottom). The images in total Hb maps are contrast enhanced for each individual subject to improve the visibility.

Fig. 7

Normalized total melanin and total Hb scatterplot in subject #1 (a) before correcting melanin-Hb crosstalk and (b) crosstalk corrected. Normalized total melanin and total Hb scatterplot in subject #19 (c) before correcting melanin-Hb crosstalk and (d) crosstalk corrected.

Fig. 8

(a) Melanin and total Hb correlation analysis estimated by SFDS system using layered model approach. (b) Melanin estimation correlation analysis between SFDS and SkinSpect.