Abstract
We probe volar-side fingertip capillary beds with near-infrared laser light and collect Raman, Rayleigh, and Mie scattered light and fluorescence. The results are interpreted using radiation transfer theory in the single-scattering approximation. The surface topography of the skin is modeled using the Fresnel equations. The skin is treated as a three-layer material, with a mean-field treatment of tissue composition and related optical properties. The model, with a reasonable choice of tissue parameters, gives a remarkably accurate account of the features of actual measurements. It predicts the optimal values for the incident angle of the laser beam and the distance between beam and detector. It explains the correlated temporal changes in the intensities of elastically and inelastically scattered light caused by heart-driven pulses and why they are out of phase. With appropriate boundary conditions, the model can be used to discuss the scattering from ridged skin extruded conformally into an aperture in a metal surface under constant light pressure. The probing results suggest an inherent regularity and similarity in the anatomy and composition of surface and subsurface tissues of a wide range of skin types.
Highlights
In order to measure blood and tissue analytes noninvasively in vivo, we probe volar-side fingertips with near-infrared radiationNIR
Whereas vibrational spectroscopy—Raman scattering with NIR excitation,1,2—provides chemically specific and quantitative information concerning molecules in complex mixtures such as blood[3] in vivo, the elastically scattered light, a probe based on physical optics, provides information relating to the presence and disposition of red blood cellsRBCsin the probed volume
This is in the context of an earlier study[4,5] in which we analyzed the sources of variation in glucose concentrations obtained from in vivo Raman spectroscopy of volar-side fingertip capillaries
Summary
In order to measure blood and tissue analytes noninvasively in vivo, we probe volar-side fingertips with near-infrared radiationNIR. Whereas vibrational spectroscopy—Raman scattering with NIR excitation,1,2—provides chemically specific and quantitative information concerning molecules in complex mixtures such as blood[3] in vivo, the elastically scattered light, a probe based on physical optics, provides information relating to the presence and disposition of red blood cellsRBCsin the probed volume. ͑We assume that the scattering is isotropic—i.e., no preferred scattering angle.͒ It is used to discuss the effects of skin surface topography—i.e., doming and ridges—as well as the layer structure of skin. This is in the context of an earlier study[4,5] in which we analyzed the sources of variation in glucose concentrations obtained from in vivo Raman spectroscopy of volar-side fingertip capillaries
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
