Light Diffusion Model Research Articles

The Development of Spectroscopy System for Non-Invasive Measurement of Skin Blood Oxygen Saturation

This paper presents the use of the developed spectroscopic system for noncontact measurement of one’s skin blood oxygen saturation (StO2). This study employed light diffusion model in the prediction of the required value using light source of wavelength 488 nm, 522 nm and 684 nm. The performance of this system was tested on ten volunteers of different skin tone to investigate the robustness of the system. The mean and standard deviation of StO2 value calculated for the recruited subjects is given by 71 ± 4.7 %. The results revealed differences in the predicted value with the recruits’ skin tone. This work concluded that the developed system may potentially be used in clinical settings to determine skin oxygen saturation and to monitor wound healing progress.

Crank-Nicholson method for rate equations in powder random lasers

In this work, we show the resolution of the rate equations in powder random lasers by using the Crank-Nicholson finite difference method. Light propagation in our powders is described by the model of light diffusion. The generalized time-dependent random laser equations describing our system are formed by three differential coupled equations: two diffusion equations for the pump and emitted light and a rate equation for the density of the dopant molecules in the excited state. The system has been solved for two pumping schemes (one-photon and two-photon excitation) and for a wide range of temporal incident pulses (from femtoseconds to nanoseconds).

A reflectance model for non-contact mapping of venous oxygen saturation using a CCD camera

A method of non-contact mapping of venous oxygen saturation (SvO2) is presented. A CCD camera is used to image skin tissue illuminated alternately by a red (660nm) and an infrared (800nm) LED light source. Low cuff pressures of 30–40mmHg are applied to induce a venous blood volume change with negligible change in the arterial blood volume. A hybrid model combining the Beer–Lambert law and the light diffusion model is developed and used to convert the change in the light intensity to the change in skin tissue absorption coefficient. A simulation study incorporating the full light diffusion model is used to verify the hybrid model and to correct a calculation bias. SvO2 in the fingers, palm, and forearm for five volunteers are presented and compared with results in the published literature. Two-dimensional maps of venous oxygen saturation are given for the three anatomical regions.

Probing acoustics of liquid foams by optical diffusive wave spectroscopy

Sound propagation through liquid foams, which are dispersions of gas bubbles in a continuous liquid phase, is not well known yet. To characterize foam acoustics at the local scale, we have studied the effect of an external acoustic wave on bubble displacements inside an aqueous foam. We quantify these displacements by using a technique based on optical diffusive wave spectroscopy, that we specially developed to resolve tiny deformations in materials. Bubble displacements induce a modulation on the photon correlation curve. Measurements for various sound frequencies and amplitudes are interpreted using a light diffusion model. It allows us to unravel a nontrivial acoustic displacement profile inside the foam; in particular, we find that the acoustic wave creates a localized shear in the vicinity of the solid walls holding the foam, as a consequence of inertial contributions. This study of how bubbles “dance” inside a foam as a response to sound turns out to provide new insights on foam acoustics and sound transmission into a foam, foam deformation at high frequencies, and analysis of light scattering data in samples undergoing nonhomogeneous deformations.

Light diffusion model for determination of optical properties of rectangular parallelepiped highly scattering media

A method to determine the absorption and reduced scattering coefficients of rectangular parallelepiped highly scattering media from frequency-domain photon migration measurements is presented. An analytical model for photon diffusion propagation in the rectangular parallelepiped media is established using the method of images and extrapolated boundary conditions. This present technique has simplicity, accuracy, and rapid computability as compared with the Monte Carlo or finite element methods. The theoretical predictions are verified with experimental measurements using a white polyacetal resin, and the errors introduced by using the slab geometry for the optical property determination are identified.

Skin Melanin, Hemoglobin, and Light Scattering Properties can be Quantitatively Assessed In Vivo Using Diffuse Reflectance Spectroscopy

Noninvasive and real-time analysis of skin properties is useful in a wide variety of applications. In particular, the quantitative assessment of skin in terms of hemoglobin and melanin content, as well as in terms of its light scattering properties, is a challenging problem in dermatology. We present here a technique for examining human skin, based on the in vivo measurement of diffuse reflectance spectra in the visible and near-infrared ranges of the electromagnetic spectrum. Spectra were measured by means of a fiber optic probe, and they were analyzed using an analytical model of light diffusion in the skin. The results of the analysis indicate that it is possible to obtain quantitative information about hemoglobin and melanin content, as well as basic information regarding the scattering properties of the skin.

Diffuse reflectance spectroscopy of human adenomatous colon polyps in vivo

Diffuse reflectance spectra were collected from adenomatous colon polyps (cancer precursors) and normal colonic mucosa of patients undergoing colonoscopy. We analyzed the data by using an analytical light diffusion model, which was tested and validated on a physical tissue model composed of polystyrene beads and hemoglobin. Four parameters were obtained: hemoglobin concentration, hemoglobin oxygen saturation, effective scatterer density, and effective scatterer size. Normal and adenomatous tissue sites exhibited differences in hemoglobin concentration and, on average, in effective scatterer size, which were in general agreement with other studies that employ standard methods. These results suggest that diffuse reflectance can be used to obtain tissue information about tissue structure and composition in vivo.

Cloud cover and daylight illuminance

Continous measurements of daylight illuminance were made at Nottingham, England, during 1985 and 1986. Cloud quantities were measured from simultaneous field photographs of the sky, and the association between global horizontal illuminance and cloudiness was calculated. It was found that cloud quantity, as a single variable, could account for between one-third and one-half of the variation in illuminance at a given solar altitude. The measured data are compared with values predicted using standard formulae and with calculations based on a model of light diffusion through a cloudy sky.