Sergei R. Utz

Tissue optics, light distribution, and spectroscopy

A model of multilayered tissue is considered. The Monte Carlo simulation technique is used to study laser beam transport through tissues with varying optical properties for each layer (absorption, scattering, scattering anisotropy factor, and refractive index). Calculations are performed for some models of the human skin and adjacent tissues for visible and UV wavelength ranges. New technology for human epidermis optical parameters determination is presented. This technology includes epidermis upper layers glue stripping; in vitro measurements of total transmission, diffuse reflection, and angular scattering of stripping samples; and using an inverse calculation technique based on four-flux approximation of radiation transport theory. The technology was successfully used for depth dependence monitoring of epidermis optical parameters. An inverse Monte Carlo technique for determining the optical properties of tissues based on spectrophotometric measurements is developed. This technique takes into account the 2-D geometry of the experiment, finite sizes of incident beam and integrating sphere ports, boundary conditions, and sideways losses of light.

In Vivo Fluorescence Spectroscopy of the Human Skin: Experiments and Models

The results of the experimental investigation of autofluorescence spectra of human skin in vivo caused by the UV radiation of the skin and by the external mechanical pressure applied to the skin are presented. These results are compared with results of Monte Carlo modeling of the autofluorescence of the skin with variable blood content. The proposed simple model of the skin gives the possibility of evaluation of changes of the blood and melanin content within the skin.

Fluorescence spectroscopy of human skin

The advantages of optical spectroscopy in skin are discussed. The basis for fluorescence spectroscopy is briefly presented. The potential for in vitro and in vivo fluorescence spectroscopy of biotissues is significant, but not yet well developed. With the help of fluorescence spectroscopy and layer-by-layer skin surface strippings technique the important knowledge for autofluorescence spectra from different skin layers have been obtained. Resolution of autofluorescence spectra into discrete excitation-emission bands is presented, related to various skin fluorophores.

Fluorescence spectroscopy in combination with reflectance measurements in human skin examination: what for and how

Reflectance and fluorescence spectroscopy are successfully used for skin disease diagnostics. Human skin optical parameters are defined by its turbid, scattering properties with nonuniform absorption and fluorescence chromophores distribution, its multilayered structure, and variability under different physiological and pathological conditions. Theoretical modeling of light propagation in skin could improve the understanding of these conditions and may be useful in the interpretation of in vivo reflectance and autofluorescence spectra. In the present work the temporal behavior of in vivo reflectance and autofluorescence (excitation wavelength 337 nm) spectra of human skin under ultraviolet irradiation and external mechanical pressure were investigated. Experimental results and Monte Carlo modeling of light distribution in skin were compared and demonstrated good agreements. Combination of diffuse reflectance and autofluorescence measurements is a very promising technique for precise erythema and pigmentation of the human skin evaluation.

Effects of low-energy laser biostimulation on rheological properties of blood

The study was performed to establish the influence of low energy red ((lambda) equals 633 nm) laser radiation on some rheological parameters of blood irradiated in vivo as well as in vitro.

Coherent, low-coherent, and polarized light interaction with tissues undergoing refractive-index matching control

It is shown experimentally and theoretically that due to interaction of totally or partially coherent light beams with such tissues as the human eye sclera and skin which undergo the refractive indices matching the collimated and total transmission, diffuse reflection and speckle structure of transmitted beams are changing in accordance with transition from multiple to low-step scattering. The scleral samples in a final stage of tissue optical clearing have the same properties as an optical retarder.

Optical and imaging techniques for in-vivo sunscreens investigation

The methods available for testing the efficacy of topical sunscreens have improved considerably in recent years. Nevertheless, so far no simple and rapid test has been proposed to measure in vivo transmission spectra of sunscreens in the UVA region. Spectral changes that occur after sunscreen application were measured with a fluorescence spectrometer (LS 50B, Perkin Elmer, UK) equipped with a Y-shape quartz guide for in vivo measurements. Three sunscreens with different protection factors in the UVA range were tested. The excitation-emission maps of human collagen, skin, and sunscreens were analyzed. Visual demonstrations of the protective effects of sunscreens were also performed with photo- and video imaging techniques. As a consequence of the human skin and sunscreens fluorescence map analysis, the optimal spectral regions (both for direct and indirect fluorescence measurements) were detected. In vivo fluorescence and remittance spectroscopy were used to investigate the time dependence in transmission spectra of epidermis with applied sunscreens. We also evaluate the feasibility of in vivo fluorescence measurements for the investigation of the sunscreens water-resistance. The procedure is simple, and values obtained can be used to predict UVA protection on the basis of the mathematical algorithms.

Skin optical parameters determination for laser photochemotherapy

The results of measurements of the optical parameters of the upper layers of human epidermis in UV wavelength range are presented. For making samples, the technique of skin surface strippings was used. For calculations of linear scattering and absorption coefficients, the Kubelka - Munk approximation was applied, taking into account the sample method. Use of skin surface strippings allows the transmission and diffuse reflection spectra of psoriatic epidermis.

Simulation of fluorescent measurements in the human skin

Reflectance and fluorescence spectroscopy are successfully used for skin disease diagnostics. Human skin optical parameters are defined by its turbid, scattering properties with nonuniform absorption and fluorescence chromophores distribution, its multilayered structure, and variability under different physiological and pathological conditions. Theoretical modeling of light propagation in skin could improve the understanding of these condition and may be useful in the interpretation of in vivo reflectance and autofluorescence (AF) spectra. Laser application in medical optical tomography, tissue spectroscopy, and phototherapy stimulates the development of optical and mathematical light-tissue interaction models allowing to account the specific features of laser beam and tissue inhomogeneities. This paper presents the version of a Monte Carlo method for simulating of optical radiation propagation in biotissue and highly scattering media, allowing for 3D geometry of a medium. The simulation is based on use of Greens function of medium response to single external pulse. The process of radiation propagation is studied in the area with given boundary conditions, taking into account the processes of reflection and refraction at the boundaries of layers inside the medium under study. Results of Monte Carlo simulation were compared with experimental investigations and demonstrated good agreement.

Investigation of formation and dynamics of human skin erythema and pigmentation by in vivo fluorescence spectroscopy

Erythema and pigmentation are the most important visible phenomenons in the ultraviolet irradiated skin. The diffuse reflection has long been used to in vivo monitor skin chromophores (hemoglobin and melanin). In this paper, the temporal behavior of the autofluorescence spectra (excitation wavelength 337 nm) of the human skin under ultraviolet irradiation (4 MED) are presented. A simple model of the skin was used for analysis of blood content in different skin layers. In vivo autofluorescence measurements are suggested for improving the precise detection of blood and melanin content in the human skin.