Browsing by Author "Tuchin, V. V."

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    Coherent fibre bundles in full-field swept-source OCT
    (2009-02-20T00:00:00Z) Ford, Helen D.; Tatam, Ralph P.; Fujimoto, J. G.; Izatt, J. A.; Tuchin, V. V.
    Endoscopic OCT probes deliver light to the measurement region via a single optical fibre mounted in a probe head. The output beam is focused onto the sample, providing a single point measurement. The beam is translated, using mechanical scanning at the probe tip, to address a line or area of sampling points and produce an image. We are investigating a swept-source OCT system incorporating coherent fibre bundles, to allow many measurement points to be addressed, within an area of the sample, without the need for mechanical motion within the endoscope probe. Scanning components are still present at the input of our system, but are no longer required within the flexible ndoscope section. This allows a small-diameter, electrically passive probe to be engineered using off-the-shelf scanning components. A common-path probe design is proposed, in which the bundle is external to the OCT interferometer. This eliminates contrast variations caused by non-controllable differences in the state of polarisation between fibres. Imaging bundle fibres are typically few-moded, which can lead to ghost features and reduced SNR in OCT images, but the common-path configuration also removes cross-mode interference problems, and reduces dispersion artefacts. OCT images of a microscope cover-slip and a sample of spring onion, acquired using the swept-source, bundle-based OCT system are presented. Features peculiar to the inclusion of the fibre bundle are discussed, and directions for future development of the system are outlined.
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    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.
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    Full-field optical coherence tomography using a fibre imaging bundle
    (2006-12-31T00:00:00Z) Ford, Helen D.; Tatam, Ralph P.; Tuchin, V. V.; Izatt, J. A.; Fujimoto, J. G.
    An imaging fibre bundle is demonstrated for spatially-multiplexed probe beam delivery in OCT, with the aim of eliminating the mechanical scanning currently required at the probe tip in endoscopic systems. Each fibre in the bundle addresses a Fizeau interferometer formed between the bundle end and the sample, allowing acquisition of information across a plane with a single measurement. Depth scanning components are now contained within a processing interferometer external to the completely passive endoscope probe. The technique has been evaluated in our laboratory for non-biological samples. Images acquired using the bundle-based system are presented. The potential of the system is assessed, with reference to SNR performance and acquisition speed.
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    Study of the possibility of increasing the probing depth by the method of reflection confocal microscopy upon immersion clearing of near-surface human skin layers.
    (Turpion Ltd., 2002-01-01T00:00:00Z) Meglinski, I. V.; Bashkatov, A. N.; Genina, E. A.; Churmakov, D. Y.; Tuchin, V. V.
    The possibility of increasing the human-skin probing depth by the method of reflection confocal microscopy (RCM) upon decreasing the amplitude of spatial fluctuations of the refractive index of the upper skin layers is considered. A change in the probing depth is estimated by analysing the spatial distribution of the probability density of the effective optical paths of detected photons calculated by the Monte Carlo method. The results of the numerical simulation are interpreted within the framework of the possible application of RCM to the study of the human skin exposed to an immersion liquid compatible to it. A diffusion of the immersion agent into the skin depth involves the equalising of the refractive indices of the structural elements of near-surface skin layers, which in turn causes a decrease in the scattering intensity and a certain increase in the transparency of the upper tissue layers. It is shown that a decrease in the light scattering in the near-surface skin layers leads to a significant increase in the probing depth obtained with the RCM technique.