Browsing by Author "Meglinski, I. V."
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Item Open Access Amending of fluorescence sensor signal localization in human skin by matching of the reflective index.(Society of Photo-optical Instrumentation Engineers, 2004-01-01T00:00:00Z) Churmakov, D. Y.; Meglinski, I. V.; Greenhalgh, D. A.Fluorescence diagnostic techniques are notable amongst many other optical methods because they offer high sensitivity and non-invasive measurement of tissue properties. However, a combination of multiple scattering and physical heterogeneity of biological tissue hampers interpretation of the fluorescence measurements. Analyses of the spatial distribution of endogenous and exogenous fluorophores excitation within tissues and their contribution to the detected signal localization are essential for many applications. We have developed a novel Monte Carlo technique that gives a graphical perception of how the excitation and fluorescence detected signal are localized in tissues. Our model takes into account the spatial distribution of fluorophores, the variation of concentrations and quantum yield. We demonstrate that matching the refractive indices of the ambient medium and topical skin layer improves spatial localization of the detected fluorescence signal within the tissues.Item Open Access Analysis of skin tissues spatial fluorescence distribution by the Monte Carlo simulation(Iop Publishing Ltd, 2003-07-21T00:00:00Z) Churmakov, D. Y.; Meglinski, I. V.; Piletsky, Sergey A.; Greenhalgh, D. A.A novel Monte Carlo technique of simulation of spatial fluorescence distribution within the human skin is presented. The computational model of skin takes into account the spatial distribution of fluorophores, which would arise due to the structure of collagen fibres, compared to the epidermis and stratum corneum where the distribution of fluorophores is assumed to be homogeneous. The results of simulation suggest that distribution of auto-fluorescence is significantly suppressed in the near-infrared spectral region, whereas the spatial distribution of fluorescence sources within a sensor layer embedded in the epidermis is localized at an ‘effective’ deItem Open Access Analysis of the Spatial Distribution of Detector Sensitivity in a Multilayer Randomly Inhomogeneous Medium with Strong Light Scattering and Absorption by the Monte Carlo Method.(Springer Science Business Media, 2001-10-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.The spatial distribution of sensitivity in the domain of detection of a fiber- optic sensor used for spectrophotometric studies of skin and other biological tissues is studied. The method and results of modeling the propagation of optical radiation in multilayer randomly inhomogeneous media with strong light scattering and absorption are presented. Owing to the small distances between the source and detector (100–800 µm), the propagation of radiation in the medium under study is modeled by the Monte Carlo method combining the calculation of true paths and the use of statistical weights. For the same reason, we represent the surface and interfaces of layers of skin as rough randomly periodic surfaces corresponding to the actual structure of human skin. The method presented can be recommended as a means for the optimum selection of an arrangement for radiation incoupling and outcoupliItem Open Access Coherent effects in multiple scattering of linearly polarized light.(Springer Science Business Media, 2005-04-01T00:00:00Z) Kuzmin, Vladimir L.; Meglinski, I. V.; Churmakov, D. Y.Comparing the stochastic Monte Carlo technique with the iteration procedure for solving the Bethe–Salpeter equation in the framework of numerical simulation, the time correlation function and the interference component of the coherent backscattering of a linearly polarized light wave in a multiply scattering medium are calculated. The results of the simulation agree well with theoretical results obtained by generalizing the Milne solution, as well as with experimental datItem Open Access Coherent multiple scattering effects and Monte Carlo method(Springer Science Business Media, 2004-02-01T00:00:00Z) Kuzmin, Vladimir L.; Meglinski, I. V.Based on the comparison of the iteration procedure of solving the Bethe-Salpeter equation and the Monte Carlo method, we developed a method for simulating coherent multiple-scattering effects within the framework of a unified stochastic approach. The time correlation function and the interference component were calculated for the coherent backscattering from a multiply scattering medium.Item Open Access Computer simulation of the skin reflectance spectra(Elsevier Science B.V., Amsterdam., 2003-02-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.The reflectance spectra of the human skin in visible and near-infrared (NIR) spectral region have been calculated using the Monte Carlo technique, and the specular and internal reflection on the medium surface is taken into account. Skin is represented as a complex inhomogeneous multi-layered highly scattering and absorbing medium. The model takes into account variations in spatial distribution of blood, index of blood oxygen saturation, volume fraction of water and chromophores content. The simulation of the skin tissues optical properties and skin reflectance spectra are discussed. Comparison of the results of simulation and in vivo experimental results are given.Item Open Access Crossed source-detector geometry for a novel spray diagnostic: Monte Carlo simulation and analytical results(Osa Optical Society of America, 2005-05-01T00:00:00Z) Berrocal, Edouard; Churmakov, D. Y.; Romanov, V. P.; Jermy, Mark C.; Meglinski, I. V.Sprays and other industrially relevant turbid media can be quantitatively characterized by light scattering. However, current optical diagnostic techniques generate errors in the intermediate scattering regime where the average number of light scattering is too great for the single scattering to be assumed, but too few for the diffusion approximation to be applied. Within this transitional single-to-multiple scattering regime, we consider a novel crossed source-detector geometry that allows the intensity of single scattering to be measured separately from the higher scattering orders. We verify Monte Carlo calculations that include the imperfections of the experiment against analytical results. We show quantitatively the influence of the detector numerical aperture and the angle between the source and the detector on the relative intensity of the scattering orders in the intermediate single-to-multiple scattering regime. Monte Carlo and analytical calculations of double light-scattering intensity are made with small particles that exhibit isotropic scattering. The agreement between Monte Carlo and analytical techniques validates use of the Monte Carlo approach in the intermediate scattering regime. Monte Carlo calculations are then performed for typical parameters of sprays and aerosols with anisotropic (Mie) scattering in the intermediate single-to-multiple scattering regime.Item Open Access Diffusing-wave spectroscopy in randomly inhomogeneous media with spatially localized scatterer flows.(Springer Science Business Media, 1998-04-01T00:00:00Z) Skipetrov, S. E.; Meglinski, I. V.Multiple scattering of laser radiation in a randomly inhomogeneous turbid medium with a spatially localized flow of particles is studied. The time autocorrelation function of backscattered light is calculated for the case of a laminar flow of scatterers in a cylindrical capillary embedded in the medium. A new method is proposed and tested experimentally for determining the position of the dynamic region and the dominant form and characteristic velocity of the particle motion there.Item Open Access Effect of photons of different scattering orders on the formation of a signal in optical low-coherence tomography of highly scattering media.(2006-01-01T00:00:00Z) Kirillin, M. Yu; Meglinski, I. V.; Priezzhev, A. V.The influence of photons of different scattering orders on the formation of a detected signal in optical low-coherence tomography (OCT) is considered. The scattering orders are estimated by analysing the spatial distribution of the probability density for the effective optical paths of detected photons calculated by the Monte Carlo method. The influence of photons with different scattering orders on the formation of a signal is estimated quantitatively depending on the optical properties of the medium under study. The results of numerical simulations are interpreted within the framework of possible applications of OCT for non-invasive diagnostics of the human skin and other highly scattering random media. It is shown by the example of calculation of OCT signals from model biological tissues that the OCT method gives reliable information on their internal structure from optical depths up to 0.3 mm.Item Open Access The Enhancement of Confocal Images Of Tissues at Bulk Optical Immersion.(Springer Science Business Media, 2003-01-01T00:00:00Z) Meglinski, I. V.; Bashkatov, A. N.; Genina, E. A.; Churmakov, D. Y.; Tuchin, V. V.The purpose of the present work is a theoretical examination of how localised skin-tissue dehydration affects the depth of the confocal probing and what depth of effective detection can be reached with the chemical administration of skin tissues. A semi-infinite multilayer Monte Carlo model is used to estimate spatial localisation of the output signal offered by a confocal probe. A solution of glycerol is taken in the capacity of innocuous osmotic agent. Diffusion of this bio-compatible chemical agent into the skin temporarily pushes water out of the tissues and results in the matching of the refractive indices of skin structural elements. This temporarily decreases scattering and increases transparency of topical skin layers, which allows for unrestricted light to permeate deeper into the skin. The results of simulation show that signal spatial localization offered by a confocal probe in the skin tissues during their clearing is usable for the monitoring of deep reticular dermis and improving the image contrast and spatial resolution. A discussion of the optical properties of skin tissues and their changes due to diffusion of glycerol into the skin is given. Optical properties of tissues and their changes due to chemical administration are estimated based on the results of experimental in vitro study with rat and human skin.Item Open Access Experimental study of the potential use of diffusing wave spectroscopy to investigate the structural characteristics of blood under multiple scattering(Elsevier Science B.V., Amsterdam., 2000-12-01T00:00:00Z) Korolevich, Alexander N.; Meglinski, I. V.The extension of the photon correlation spectroscopy (PCS) in multiple scattering regime, so-called diffusing wave spectroscopy (DWS) was employed to the study of blood samples. Multiple scattered light from a helium–neon (He–Ne) laser beam incident on the blood samples was detected by a photomultiplier, and both the temporal autocorrelation intensity functions g2(τ) and power spectra S (w) were measured by a spectrum analyzer. The potentials of using DWS for the qualitative and quantitative determination of the structural characteristics of the blood elements were studied experimentally. The experimental studies made, permits the use of DWS for blood cells monitoring in a multiple scattering regime. This paper describes our initial attempts at applying DWS to the study of the discrete blood samples of both healthy donors and patients with the cardiac ischemia. The subsequent experiments provide a verification of DWS of blood cells shape monitoring under multiple scatteItem Open Access Influence of refractive index matching on the photon diffuse reflectance(Iop Publishing Ltd, 2002-12-07T00:00:00Z) Churmakov, D. Y.; Meglinski, I. V.; Greenhalgh, D. A.Photon migration in a randomly inhomogeneous, highly scattering and absorbing semi-infinitemediumwith a plane boundary is considered by aMonte Carlo (MC) technique. The employed MC technique combines the statistical weight scheme and real photon paths simulation, allowing the exclusion of the energy conservation problem. The internal reflection of the scattered radiation on the medium interface is taken into account by allowing the trajectories of photon packets to be split into reflected and transmitted parts. The spatial photon sensitivity profile (SPSP), spatially resolved diffuse reflectance and angular and spatial photon detectorweight distributions are considered in terms of Fresnel’s reflection/refraction on the boundary of the medium. The effect of the refractive index match is predicted correctly by the MC method and by the diffusion approximation. The results demonstrate that matching of the refractive index of the medium significantly improves the contrast and spatial resolution of the spatial photon sensitivity profile (SPSP). The results of simulation of the spatially resolved diffuse reflectance agree well with the results predicted by the diffusion approximation and the experimental results reported earlieItem Open Access Laser ice scaffolds modeling for tissue engineering(John Wiley & Sons, Ltd, 2005-09-01T00:00:00Z) Meglinski, I. V.; Varejka, M.; Woodman, Anthony C.; Turner, Anthony P. F.; Piletsky, Sergey A.Tissue engineering is one of the most exciting and rapidly growing areas in biomedical engineering that offers vast potential for changing traditional approaches to meeting many pharmaceutics and critical health care needs. Currently the bottle-neck area in this multidisciplinary field appears to be materials and fabrication technology for the design of artificial extracellular matrices/scaffolds that support culturing and growth of new tissue. We have shown that stable relief structures can be created and maintained in the bulk of ice by continuous s canning with computer-guided IR CO2 laser. The optimal laser beam intensity and fluence rate distribution within the ice sample, as well as the rate of scanning were estimated based on the Monte Carlo model utilized physical/optical properties of ice. The results of numerical simulation are agreed well with the observed experimental results of thermo-coupling measurements and obtained microscopic images.Item Open Access Low and high orders light scattering in particulate media(2004-07-12T00:00:00Z) Meglinski, I. V.; Romanov, V. P.; Churmakov, D. Y.; Berrocal, Edouard; Jermy, Mark C.; Greenhalgh, D. A.We present the results of a theoretical study providing details of propagation of laser radiation within disperse randomly inhomogeneous intermediately single- to-multiple scattering media. A quantitative analysis of scattering orders in the transition from single to multiple scattering is presented. Crossed source- detector fiber optics geometry used to separate the intensity of single scattering from higher scattering orders. The results demonstrate good agreement between analytical and Monte Carlo techniques. This validates the use of the Monte Carlo approach in the intermediate single-to-multiple scattering regime. The method used can be applied to verify analytical results against experiment via the Monte Carlo calculations that include imperfections of the experiment.Item Open Access Low and high orders light scattering within the dispersible media.(2005-06-01T00:00:00Z) Berrocal, Edouard; Romanov, V. P.; Churmakov, D. Y.; Meglinski, I. V.Sprays, aerosols as well as other industrially relevant turbid media can be characterized by light scattering techniques. However these techniques often fall into the intermediate scattering regime where the average number of times a photon is scattered is too great for single scattering to be assumed, but too few for the diffusion approximation to be applied. We present the results of theoretical study provided details of scattering of laser radiation in the intermediate single-tomultiple scattering regime. Crossed fiber optic source- detector geometry is considered to separate the intensity of single scattering from higher scattering orders. A quantitative analysis of scattering orders in the intermediate single-tomultiple scattering regime is presented. Agreement between the analytical and Monte Carlo techniques both used for the calculation of double light scattering intensity is demonstrated. Influence of detector numerical aperture on the scattering orders is shown for the intermediate single-to-multiple scattering regime. The method used can be applied to verify analytical results indirectly against experiment via Monte Carlo calculations that include the imperfections of the experiment.Item Open Access Modeling the sampling volume for the skin blood oxygenation measurements(Springer Science Business Media, 2001-01-01T00:00:00Z) Meglinski, I. V.; Matcher, S. J.Abstract The absolute quantified measurement of haemoglobin skin blood saturation from collected reflectance spectra of the skin is complicated by the fact that the blood content of tissues can vary both in the spatial distribution and in the amount. These measurements require an understanding of which vascular bed is primarily responsible for the detected signal. Knowing the spatial detector depth sensitivity makes it possible to find the best range of different probe geometries for the measurements of signal from the required zones and group of vessels inside the skin. To facilitate this, a Monte Carlo simulation has been developed to estimate the sampling volume offered by fibre-optic probes with a small source-detector spacing (in the current report 250 μm, 400 μm and 800 μm). The optical properties of the modelled medium are taken to be the optical properties of the Caucasian type of skin tissue in the visible range of the spectrum. It is shown that, for a small source-detector separation (800 μm and smaller), rough boundaries between layers of different refractive index can play a significant role in skin optics. Wavy layer interfaces produce a deeper and more homogeneous distribution of photons within the skin and tend to suppress the direct channelling of photons from source to detector. The model predicts that a probe spacing of 250 μm samples primarily epidermal layers and papillary dermis, whereas spacings of 400–800 μm sample upper blood net dermis andItem Open Access Monte Carlo modeling of polarized light propagation in biological tissues.(Springer Science Business Media, 2004-01-01T00:00:00Z) Gangnus, S. V.; Matcher, S. J.; Meglinski, I. V.The application of polarization-sensitive optical coherence tomography (PS-OCT) creates new possibilities for biomedical imaging. In this work, we present a numerical simulation of the signal from a PS-OCT interferometer. We explore the possibility to retrieve information concerning the optical birefringence properties of multiple layered tissues from the depth-resolved PS-OCT interferometric signal in the presence of strong elastic light scattering. Our simulation is based on a Monte Carlo algorithm for the propagation of polarized light in a birefringent multiple scattering medium. Confocal and time-gated detection are also included. To describe the polarization state of light, we use the Jones formalism, which reduces the calculation time compared with the full Stokes-Müller formalism. To analyse the polarization state of the partially polarized back-scattered light, we applied a standard method using the Stokes vector, which is derived from the Jones vector. In this work, we examined the Stokes vector variations with depth for different tissue types. The oscillations of the Stokes vector are clearly demonstrated in the case of a uniform birefringent medium. We also investigated a two-layered tissue with a different birefringence of each layer. The Stokes vector variation with depth is compared to the uniform case and used to assess the depth-sensitivity of PS-OCT. Our simulation results are also compared with published experimental results of other groupsItem Open Access Monte Carlo simulation of coherent effects in multiple scattering(Royal Society, 2005-01-08T00:00:00Z) Meglinski, I. V.; Kuzmin, Vladimir L.; Churmakov, D. Y.; Greenhalgh, D. A.Using a combination of the stochastic Monte Carlo technique and the iteration procedure of the solution to the Bethe-Salpeter equation, it has been shown that the simulation of the optical path of a photon packet undergoing an nth scattering event directly corresponds to the nth-order ladder diagram contribution. In this paper, the Monte Carlo technique is generalized for the simulation of the coherent back-scattering and temporal correlation function of optical radiation scattered within the randomly inhomogeneous turbid medium. The results of simulation demonstrate a good agreement with the diffusing wave theory and experimental results.Item Open Access Multiple scattering of light in optical diagnostics of dense sprays and other complex turbid media(Cranfield University, 2006) Berrocal, Edouard; Meglinski, I. V.Sprays and other industrially relevant turbid media can be quantitatively and qualitatively characterized using modern optical diagnostics. However, current laser based techniques generate errors in the dense region of sprays due to the multiple scattering of laser radiation e ected by the surrounding cloud of droplets. In most industrial sprays, the scattering of light occurs within the so-called intermediate scattering regime where the average number of scattering events is too great for single scattering to be assumed, but too few for the di usion approximation to be applied. An understanding and adequate prediction of the radiative transfer in this scattering regime is a challenging and non-trivial task that can significantly improve the accuracy and e ciency of optical measurements. A novel technique has been developed for the modelling of optical radiation propagation in inhomogeneous polydisperse scattering media such as sprays. The computational model is aimed to provide both predictive and reliable information, and to improve the interpretation of experimental results in spray diagnostics. Results from simulations are verified against the analytical approach and validated against the experiment by the means of homogeneous solutions of suspended polystyrene spheres. The ability of the technique to simulate various detection conditions, to di erentiate scattering orders and to generate real images of light intensity distributions with high spatial resolution is demonstrated. The model is used for the real case of planar Mie imaging through a typical hollow cone water spray. Versatile usage of this model is exemplified with its applications to image transfer through turbid media, correction of experimental Beer-Lambert measurements, the study of light scattering by single particles in the farfield region, and to simulate the propagation of ultra-short laser pulses within complex scattering media. The last application is fundamental for the development and testing of future optical spray diagnostics; particularly for those based on time-gating detection such as ballistic imaging.Item Open Access New model for light propagation in highly inhomogeneous polydisperse turbid media with applications in spray diagnostics(Optical Society of America (OSA), 2005-11-14T00:00:00Z) Berrocal, Edouard; Meglinski, I. V.; Jermy, Mark C.Modern optical diagnostics for quantitative characterization of polydisperse sprays and other aerosols which contain a wide range of droplet size encounter difficulties in the dense regions due to the multiple scattering of laser radiation with the surrounding droplets. The accuracy and efficiency of optical measurements can only be improved if the radiative transfer within such polydisperse turbid media is understood. A novel Monte Carlo code has been developed for modeling of optical radiation propagation in inhomogeneous polydisperse scattering media with typical drop size ranging from 2 µm to 200 µm in diameter. We show how strong variations of both particle size distribution and particle concentration within a 3D scattering medium can be taken into account via the Monte Carlo approach. A new approximation which reduces ~20 times the computational memory space required to determine the phase function is described. The approximation is verified by considering four log-normal drop size distributions. It is found valid for particle sizes in the range of 10-200 µm with increasing errors, due to additional photons scattered at large angles, as the number of particles below than 10 µm increases. The technique is applied to the simulation of typical planar Mie imaging of a hollow cone spray. Simulated and experimental images are compared and shown to agree well. The code has application in developing and testing new optical diagnostics for complex scattering media such as dense spr