Browsing by Author "Greenhalgh, D. A."

Now showing 1 - 6 of 6
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    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.
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    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’ de
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    Flow imaging using femtosecond-laser-induced two-photon fluorescence
    (Optical Society of America, 2004-08) Kelman, J. B.; Greenhalgh, D. A.; Ramsay, Euan; Xiao, Dong; Reid, Derryck T.
    A novel technique is demonstrated for the imaging of turbulent flows in which a single window to the flow is the only optical access required. A femtosecond laser is used to excite two-photon fluorescence in a disodium fluorescein-seeded water jet. The fluorescence signal is generated only at the focal point of the laser due to the highly nonlinear nature of the two-photon absorption and is collected in a direction counterpropagating to the excitation beam. Tight focusing of the laser is used to limit the probe volume and the two dimensional mean and RMS concentration images are collected by raster scanning the laser.
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    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 earlie
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    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.
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    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.