Polarisation-sensitive optical coherence tomography (PSOCT) is a non destructive technique with great potential for
tendinopathy diagnosis. Functional optical assessment can be used in operating theatres to delineate in depth the margin
of the non-healthy area, and limit the amount of tissue to be removed. A clinical study of 21 patients has been undertaken
to correlate the optical properties of tendons to their clinical conditions. Tendons were scanned ex vivo with a fibre based
time domain PSOCT. The beam from a superluminescent diode with a bandwidth of 52nm is sent through a polarizer and
a polarizer modulator, and split into a sample and reference arm. After passing through polarization beam splitter, the
interferences fringes are detected with two balanced detectors, for horizontal and vertical polarization. Scattering,
birefringence and in depth stokes vectors are extracted from the measurements. Direct microstructural variation and
changes in scattering properties are correlated with different tendinopathy and presence of scar tissue, which is cross-validated
by histology. Lack of tissue organization, detected as the disappearance of the bands of birefringence, is
representative of tendon degeneration. Special attention is paid to the difference between crimp patterns of different
patient's tendons. As in polarization microscopy, the crimp pattern appears as extinction bands, and is particularly
important as its alteration is generally symptomatic and could be used as an early diagnosis. Its optical origin is
investigated by varying polarization and scanning conditions.
Doppler Optical Coherence Tomography (DOCT) technique was applied to non-invasive monitoring of cross-sectional
velocity profiles distributions within complex geometry vessels. A set of micro vessels of different diameters with T-shaped
and Y-shaped bifurcation and vessels with aneurysm were built. The shape of the vessel was chosen to mimic
human vessel shapes of similar characteristics. Intralipid, set in motion at constant input volume flow rate by a syringe
pump, was used in the experiments. The influence of vessels geometry, including bifurcation (T- and Y- junctions) and
the aneurysms, on the flow dynamics under different inlet flow rates was studied. We show that under constant input
volume flow rate, the flow velocities distribution measured along a cross-sectional plane orthogonal to the inlet arm,
located at 20 mm off the junction, exhibited stationary and laminar behaviour. A non-homogeneous distribution of flow
velocity along a cross-sectional plane located at the junction was observed. The relation between the acquired velocity
distribution and the vessel geometry is analyzed. The feasibility of DOCT for mapping the velocity profiles along the
vessels junction with a spatial resolution of about 10×10×10 μm3 and a minimum detectable velocity of about 2 mm·s-1 is
presented.
In this study, the refractive index of glucose-hemoglobin solutions at different glucose concentrations was measured.
Measurements were performed using Abbe refractometer at 589 nm and OCT system at 1300 nm. The different amount
of glucose was added to hemoglobin solution. Theoretical values of refractive index of the glucose-hemoglobin solutions
were calculated in assumption that hemoglobin and glucose molecules do not interact. The difference between the
measured and calculated values of refractive index can be connected with glucose binding to hemoglobin. It is shown
that the refractive index measurements can be applied to the evaluation of glycated hemoglobin amount.
We develop a Monte Carlo model for optical coherence signal
simulation and providing accurate and high resolution information on
the birefringence properties of the connective tissues. To
understand the polarized sensitive optical coherence tomography
imaging mechanism the Monte Carlo technique is generalized for
simulation of polarized low-coherent back-scattering of optical
radiation scattered within the randomly inhomogeneous turbid medium
like the connective tissues. The results of simulation demonstrate a
good agreement both with the theoretical and experimental
predictions.
Using a combination of the stochastic technique and the iteration procedure of the solution to BSE, numerical computational method is developed for stochastic modelling of coherent effects in a multiple scattering medium. It is shown that additional phase-related factors in framework of ladder diagrams are equivalent to multiplication of the statistical weights by corresponding factors after each scattering event during the random walk of a photon packet. The Monte Carlo technique is generalized for the simulation of the coherent backscattering and temporal field correlation function of optical radiation. The developed model yields qualitative results that are ready for direct comparison against theoretical predications.
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.
Based on the collation of the stochastic Monte Carlo technique and the iteration procedure of the solution of Bethe-Salpeter equation, it is shown that simulation of optical path of photons undergoing n-th scattering event is directly agreed with the n-th order ladder diagram calculation approach. In frame of this correspondence the Monte Carlo technique is generalised for simulation of coherent back-scattering and temporal intensity/field auto-correlation functions 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.
Fluorescence diagnostic techniques are notable amongst many other optical methods, as they offer high sensitivity and non-invasive measurements of tissue properties. However, a combination of multiple scattering and physical heterogeneity of biological tissues hampers the interpretation of the fluorescence measurements. The analyses of the spatial distribution of endogenous and exogenous fluorophores excitations 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 spatial distribution of fluorophores and their quantum yields. We demonstrate that matching of the refractive indices of ambient medium and topical skin layer improves spatial localization of the detected fluorescence signal within the tissue. This result is consistent with the recent conclusion that administering biocompatible agents results in higher image contrast.
The novel Monte Carlo technique of simulation of spatial fluorescence distribution within the human skin is presented. The computational model of skin takes into account spatial distribution of fluorophores following the collagen fibers packing, whereas in epidermis and stratum corneum the distribution of fluorophores assumed to be homogeneous. The results of simulation suggest that distribution of auto-fluorescence is significantly suppressed in the NIR spectral region, while fluorescence of sensor layer embedded in epidermis is localized at the adjusted depth. The model is also able to simulate the skin fluorescence spectra.
A novel Monte Carlo (MC) technique for photon migration through 3D media with the spatially varying optical properties is presented. The employed MC technique combines the statistical weighting variance reduction and real photon paths tracing schemes. The overview of the results of applications of the developed MC technique in
optical/near-infrared reflectance spectroscopy, confocal microscopy, fluorescence spectroscopy, OCT, Diffusing Wave Spectroscopy (DWS) and Doppler flowmetry are presented.
Fluorescence diagnostic techniques are notable amongst many other optical methods, as they offer high sensitivity and non-invasive measurements of tissue properties. However, a combination of multiple scattering and physical heterogeneity of biological tissues hampers the interpretation of the fluorescence measurements. The analyses of the spatial distribution of endogenous and exogenous fluorophores excitations 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 spatial distribution of fluorophores and their quantum yields. We demonstrate that matching of the refractive indices of ambient medium and topical skin layer improves spatial localization of the detected fluorescence signal within the tissue. This result is consistent with the recent conclusion that administering biocompatible agents results in higher image contrast.
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