Chromophore concentrations, absorption and scattering properties of human skin in-vivo

Abstract

Absorption and reduced scattering coefficients of in-vivo human skin provide critical information on non-invasive skin diagnoses for aesthetic and clinical purposes. To date, very few in-vivo skin optical properties have been reported. Previously, we reported absorption and scattering properties of in-vivo skin in the wavelength range from 650 to 1000 nm using the diffusing probe in the "modified two-layer geometry". In this study, we determine the spectra of skin optical properties continuously in the range from 500 to 1000 nm. It was found that the concentration of chromophores, such as oxy-hemoglobin, deoxy-hemoglobin, and melanin, calculated based on the absorption spectra of eighteen subjects at wavelengths above and below 600 nm were distinct because of the inherent difference in the interrogation region. The scattering power, which is related to the average scatterer's size, demonstrates a clear contrast between skin phototypes, skin sites, and wavelengths. We also applied venous occlusion on forearms and found that the concentrations of oxy- and deoxy-hemoglobin as assessed at wavelengths above and below 600 nm were different. Our results suggest that diffuse reflectance techniques with the visible and near infrared light sources can be employed to investigate the hemodynamics and optical properties of upper dermis and lower dermis.

Fig. 1

Configuration of the diffusing probe.

Fig. 2

Average and standard deviation of age of 6 subjects in each skin photo-type category.

Fig. 3

Normalized photon fluence distribution maps of the diffusing probe with (a) a light source of 500nm wavelength and (b) a light source of 900nm wavelength. Whiter region represent higher fluence rate area. Note that the contour line “−4” in (b) encloses larger region than that in (a). Please refer to text for the parameters used.

Fig. 4

50% threshold maps for the diffusing probe of 1.5mm source-detector separation with (a) 500nm light source and (b) 900nm light source, and for the diffusing probe of 3mm source-detector separation with (c) 500nm light source and (d) 900nm light source. White region in the tissue sample represents the area that has top 50% fluence rate. Please refer to text for the parameters used.

Fig. 5

(a) absorption coefficient and (b) reduced scattering coefficient of in-vivo dorsal forearm of 18 subjects. Each skin phototype group has 6 subjects. Solid squares, open circles, and open stars represent optical properties of skin type I–II, III–VI, and V–VI, respectively.

Fig. 6

(a) absorption coefficient and (b) reduced scattering coefficient of in-vivo upper inner arm of 18 subjects. Each skin phototype group has 6 subjects. Solid squares, open circles, and open stars represent optical properties of skin type I–II, III–VI, and V–VI, respectively.

Fig. 7

The difference between the (a) mean absorption coefficient, and (b) mean reduced scattering coefficient of dorsal forearm and upper inner arm of twelve subjects of skin type I–IV. (The mean coefficient of upper inner arm is subtracted from that of dorsal forearm)

Fig. 8

Two typical chromophore fitting examples with full range fitting method and two-region fitting method. (a) and (b) demonstrate the fitting results of two fitting methods with the same raw data. (c) and (d) demonstrate another example. Solid squares represent raw data and open circles represent fit spectra.

Fig. 9

Two-region power law fitting of the reduced scattering spectra of the (a) dorsal forearm and (b) upper inner arm of a subject. Open squares represent raw data. Solid lines are the power law fitting to the raw data in 500nm to 600nm range while the dash lines are the power law fitting results in the 600nm to 1000nm range.

Fig. 10

Scattering power calculated from two-region fitting to the reduced scattering spectra of dorsal forearm and upper inner arm of 18 subjects. Each skin phototype group has 6 subjects.

Fig. 11

Oxy- and deoxy-hemoglobin concentration of volar forearm before (white bars) and after (gray bars) applying 50mmHg venous occlusion recovered at (a) 500–600nm region and (b) 600–1000nm region. “P” stands for the P-value.