Optical Properties Of Skin Research Articles

PARAMETER ESTIMATION FOR A BIOLOGICAL SYSTEM : MODEL AND EXPERIMENTATIONS

Temperature evolution and skin burn process in biological samples exposed to laser radiation are investigated in this communication. A one-dimensional multi-layered model is presented and transient temperature is numerically estimated using a finite difference method. A damage function corresponding to the extent of burn injury and using the Arrhenius assumptions is proposed. Two experimental benches are presented in order to estimate human skin optical and thermal properties.

Determination of human skin optical properties from spectrophotometric measurements based on optimization by genetic algorithms

We present an initial study on applying genetic algorithms (GA) to retrieve human skin optical properties using visual reflectance spectroscopy (VRS). A three-layered skin model consisting of 13 parameters is first used to simulate skin and, through an analytical model based on optical diffusion theory, we study their independent effects on the reflectance spectra. Based on a preliminary analysis, nine skin parameters are chosen to be fitted by GA. The fitting procedure is applied first on simulated reflectance spectra with added white noise, and then on measured spectra from normal and port wine stain (PWS) human skin. A normalized residue of less than 0.005 is achieved for simulated spectra. In the case of measured spectra from human skin, the normalized residue is less than 0.01. Comparisons between applying GA and manual iteration (MI) fitting show that GA performed much better than the MI fitting method and can easily distinguish melanin concentrations for different skin types. Furthermore, the GA approach can lead to a reasonable understanding of the blood volume fraction and other skin properties, provided that the applicability of the diffusion approximation is satisfied.

Measurement of Optical Parameters: Absorption Scattering And Autofulorescence of Skin in Vitro

From an applied point of view the outer most skin layers contain numerous structures by which penetrating radiation may be scattered as well as absorbed. The nature and strength of scattering and absorbtion may strongly influence the length of penetration. We illuminated the chicken breast skin tissues with collimated radiation of 400-700 nm ND- YAG pumped dye laser, and measured skin optical properties for dry and hydrated sample in vitro. Total reflectance and transmitted intensities were recorded by which scattering, absorption and anisotropic factors of the sample obtained using double integrating sphere setups. The in vitro optical parameters are higher than in vivo measurements. Our in vitro results are in agreements with other data available in literature. Hydration of skin is found to influence its scattering. Dry sample scatter less then hydrated sample. Skin autoflourescence spectra were acquired under different excition wavelength; it shows difference between normal and malignant tissues. Key Words: transmittance, reflectance, absorption, scattering, autoflourescence, in vitro, and double integrating sphere.

In vivo noninvasive measurement of blood glucose by near-infrared diffuse-reflectance spectroscopy.

This paper reports in situ noninvasive blood glucose monitoring by use of near-infrared (NIR) diffuse-reflectance spectroscopy. The NIR spectra of the human forearm were measured in vivo by using a pair of source and detector optical fibers separated by a distance of 0.65 mm on the skin surface. This optical geometry enables the selective measurement of dermis tissue spectra due to the skin's optical properties and reduces the interference noise arising from the stratum corneum. Oral glucose intake experiments were performed with six subjects (including a single subject with type I diabetes) whose NIR skin spectra were measured at the forearm. Partial least-squares regression (PLSR) analysis was carried out and calibration equations were obtained with each subject individually. Without exception among the six subjects, the regression coefficient vectors of their calibration models were similar to each other and had a positive peak at around 1600 nm, corresponding to the characteristic absorption peak of glucose. This result indicates that there is every possibility of glucose detection in skin tissue using our measurement system. We also found that there was a good correlation between the optically predicted values and the directly measured values of blood samples with individual subjects. The potential of noninvasive blood glucose monitoring using our methodology was demonstrated by the present study.

Anisotropy of light propagation in human skin

Using spatially resolved, steady state diffuse reflectometry, a directionaldependence was found in the propagation of visible and near infrared lightthrough human skin in vivo. The skin's reduced scattering coefficientµ's varies by up to a factor of two between different directions ofpropagation at the same position. This anisotropy is believed to be caused bythe preferential orientation of collagen fibres in the dermis, as described byLanger's skin tension lines. Monte Carlo simulations that examine the effectof partial collagen fibre orientation support this hypothesis. The observationhas consequences for non-invasive diagnostic methods relying on skin opticalproperties, and it could be used non-invasively to determine the direction oflines of cleavage in order to minimize scars due to surgical incisions.

Chapter 2: Optical properties of skin.

Chapter 2: Optical properties of skin.

The development of a finger joint phantom for the optical simulation of early inflammatory rheumatic changes

In the field of rheumatology, conventional diagnostic methods permit the detection only of advanced stages of the disease, which is at odds with the current clinical demand for the early diagnosis of inflammatory rheumatic diseases. Prompted by current needs, we developed a finger joint phantom that enables the optical and geometrical simulation of an early stage of rheumatoid arthritis (RA). The results presented here form the experimental basis for an evaluation of new RA diagnostic systems based on near infrared light. The early stage of RA is characterised mainly by a vigorous proliferation of the synovial membrane and clouding of the synovial fluid. Using a double-integrating-sphere technique, the absorption and scattering coefficients (mua, mus') are experimentally determined for healthy and pathologically altered synovial fluid and capsule tissue. Using a variable mixture of Intralipid Indian ink and water as a scattering/absorption medium, the optical properties of skin, synovial fluid or capsule can be selected individually. Since the optical and geometrical properties of bone tissue remain constant in early-stage RA, a solid material is used for its simulation. Using the finger joint phantom described herein, the optical properties of joint regions can be adjusted specifically, enabling an evaluation of their effects on an optical signal--for example, during fluorography--and the investigation of these effects for diagnostically useful information. The experimental foundation for the development of a new optical system for the early diagnosis of RA has now been laid.

A compartment model for fluorometric indication of tissue perfusion

Sodium fluorescein is an in vivo blood perfusion indicator for soft tissue. When fluorescein dye is introduced into the blood, it distributes throughout the vasculature and the extravascular space. Incident light from an external source causes the dye to fluoresce, the level of which is monitored by a photodetector placed over the tissue. In this study, theoretical analysis incorporating a multicompartmental model for dye distribution is applied to describe the relationship among perfusion, dye kinetics, and fluorescence readings. Errors in calculating perfusion from fluorescence are related to dye concentrations and to measurement errors. These error sources are minimized by selecting the measurement time. The alternatives of measurement during wash-in or during wash-out of dye are compared, as well as the alternatives of introducing dye by bolus injection or by constant infusion. Compensation of wash-in measurements for differences in skin pigmentation is accomplished by the matching of skin optical properties between incident and fluorescing wavelengths. A laboratory study at 80 measurement sites (from ten graded perfusion canine flaps) demonstrated a correlation of wash-in and wash-out perfusion data ranging from 0.88 to 0.96 at typical levels of fluorescein in blood. Since wash-in can be completed in a matter of a few minutes, this is likely to be preferable in the clinical setting to wash-out which can take much longer to complete.

Mathematical model of skin exposed to thermal radiation

Abstract : Prediction of dermal injury resulting from exposure to thermal energy of any given intensity and duration depends entirely upon the resultant skin temperature-time history. Means are now available for assessing heat transfer by low temperature radiation, convection and conduction to the bare skin and through thin protective coverings of known physical properties. However, thermal effects of nuclear detonations constitute a special problem because much of the radiation lies in the visible range where the optical properties of the skin and its coverings, if any, greatly influence the heating pattern. Blackening of the skin eliminates effects due to its optical properties but enhances the ever-present variations in the thermal 'constants' of the skin. The present report describes the utilization of a mathematical equation and computer techniques for extracting these variations from empirical data obtained at relatively low levels of radiation (<0.5 Cal/sq cm sec.), and applying extrapolations of these values in calculations of temperature-time histories at higher levels of irradiance where empirical data are lacking. This procedure is subject to validation by experimentation within a limited range of exposures. If validation is achieved in the blackened skin then the entire system may be utilized in the determination of optical properties of unblackened skin.

Thermal conductivity and diathermancy of human skin for sources of intense thermal radiation employed in flash burn studies.

Some of the thermal and optical properties of skin have been determined for sources and exposure conditions involved in the study of the effects of intense radiation on uncovered and subfabric skin. The surface temperatures of irradiated painted and unpainted skin were measured with fine-wire thermocouples for exposure times ranging from 0.1 to 20 seconds, at radiation levels lower than those which would cause pain in the subject. The value of the important thermal parameter, the kρc product (k, thermal conductivity; , density; c, specific heat), as determined from the measured surface temperatures of blackened skin was found to be 8.6 x 10−4 centimeter-gram-second units. The surface temperatures of skin when exposed to carbon-arc, to 3000°K tungsten, and to infrared radiation are approximately one-half those of blackened skin, and 30% less than those computed from opaque-solid theory. Good agreement between heat-flow theory and experiment on human skin is obtained if it is assumed that the skin is a homogeneous diathermous solid with a diathermancy which varies with wavelength. Submitted on January 18, 1957

Tables of the integrals $$CI_n \left( x \right) = \int\limits_1^\infty {u^{ - n} \left( {1 - u^{ - 2} } \right) \cos ux du} $$ and $$SI_n \left( x \right) = \int\limits_1^\infty {u^{ - n} \left( {1 - u^{ - 2} } \right) \sin ux du} $$

The integrals CIn(x) and SIn(x), required in the theory of the anomalous skin effect and optical properties of metals, are tabulated to six decimals for integer values of n up to four and for values ofx = 0 (.1) 1 (.2) 5 (.5) 20.

Tables of the integrals $$CI_n (x) = \int\limits_1^\infty {u^{ - n} } (1 - u^{ - 2} )$$ cosux du and $$SI_n (x) = \int\limits_1^\infty {u^{ - n} } (1 - u^{ - 2} )$$ sinux du

The integrals CI n (x) and SI n (x), required in the theory of the anomalous skin effect and optical properties of metals, are tabulated to six decimals for integer values ofn up to four and for values ofx=0 (.1) 1 (.2) 5 (.5) 20.