We present an improved Laser speckle imaging approach to investigate the cerebral blood flow response following function stimulation of a single vibrissa. By synchronising speckle analysis with the cardiac cycle we are able to obtain robust averaging of the correlation signals while at the same time removing the contributions due to the pulsation of blood flow and associated tissue adaptation. With our inter-pulse correlation analysis we can follow second-scale dynamics of the cortical vascular system in response to functional brain activation. We find evidence for two temporally separated processes in the blood flow pattern following stimulation we tentatively attribute to vasodilation and vasoconstriction phases, respectively.
A general simulation framework has been developed for characterising eye motion artefacts in the ophthalmic imaging of ocular media. The optimisation of the scanning strategy for an optical coherence tomography of the anterior eye chamber has been presented as the first example of an application for the simulator.
The application of the full-field optical coherence tomography (OCT) microscope to the characterisation of skin
morphology is described. An automated procedure for analysis and interpretation of the OCT data has been developed
which provides measures of the laterally averaged depth profiles of the skin reflectance. The skin at the dorsal side of the
upper arm of 22 patients with Type 1 Diabetes Mellitus has been characterised in a non-contact way. The OCT signal
profile was compared with the optical histological data obtained with a commercial confocal microscope (CM). The
highest correlation to the epidermal thickness (ET) obtained using CM was found for the distance from the entrance OCT
peak to the first minimum of the reflection profile (R2=0.657, p<0.0001). The distance to the second OCT reflection
peak was found to be less correlated to ET (R2=0.403, p=0.0009).
A further analysis was undertaken to explore the relation between the subjects' demographical data and the OCT
reflection profile. The distance to the second OCT peak demonstrated a correlation with a marginal statistical
significance for the body-mass index (positive correlation with p=0.01) and age (negative correlation with p=0.062). At
the same time the amplitude of the OCT signal, when compensated for signal attenuation with depth, is negatively
correlated with age (p<0.0002). We suggest that this may be an effect of photo degradation of the dermal collagen.
In the patient population studied, no relation could be determined between the measured skin morphology and the
duration of diabetes or concentration of glycated haemoglobin in the blood.
A dual-wavelength reflectance optical sensor for monitoring cutaneous blood perfusion is presented as a part of
multisensor glucose monitoring system. A Monte-Carlo simulation of partial differential pathlengths has been used for
the optimization of the distance from light source to detector. The simulation indicated that the light pathlength within
the upper vascularised skin layers increases before reaching saturation at separation distances larger than 3 mm. Thus the
sensor sensitivity does not benefit from larger source-detector distances. At the same time with a higher separation of the
detector from the source, the intensity exponentially decreases while undesirable sensitivity to the muscle perfusion
increases. The hardware prototype has been developed based on the simulation findings and tested in a laboratory setting
and in a home use study by patients with diabetes. For both testing procedures the optical sensor demonstrated high
sensitivity to perfusion changes. The effect of initial cutaneous blood increase under the sensor has been observed which
can be associated with pressure-induced vasodilation as a response to the sensor application.
We discuss a new approach to laser speckle biomedical imaging with the goal to establish a quantitative link between the
measured signal and the local dynamic properties of Brownian motion or blood flow. We demonstrate that the presence of a
static component in laser speckle imaging signal can significantly complicate the quantitative interpretation of the imaging
data. With Monte-Carlo simulations and model experiments we show that the error in the mean particles velocity extracted
using traditional approaches can reach several orders of magnitude. With a proper data treatment on the other side the error
can be substantially reduced. We suggest a simple data processing scheme that properly accounts for a static component in
the scattered light intensity.
The structural properties of LiveJournal social network have been studied. The power-law region in in- and out- degrees
distributions has been revealed and analyzed. A large highly isolated social cluster corresponding to the Russian-speaking
users was discovered and treated separately and peculiarities of its structure were discussed. The opinion dynamics simulation
on LiveJournal network was conducted and stable states with multiple consensuses were found reflecting the impact
of the social network geometry on the opinion formation.
Dynamic Light Scattering together with Diffusing Wave Spectroscopy are common and well acknowledged techniques to study micro and macro dynamics of a complex media. In the past these methods were successfully applied for the characterization of colloidal particles of different kind, foam, sand, interfacial boundaries, blood cells etc. The shape and decay of auto-correlation function (ACF) of scattered light intensity fluctuations are used to study the type and time scale of scatters dynamics. This is usually done by collecting the light by a point-like detector for a time period much larger than the correlation time. But in case of slow or arrested scatter motion the obtained time-averaged ACF may depend on the detector position (non-ergodicity problem). Special averaging techniques required for this case are presented in the current paper.
We introduce a CCD camera detection scheme in dynamic light scattering that provides information on the single-scattered
auto-correlation function even for fairly turbid samples. Our approach allows access to the extensive range of systems
that show low-order scattering by selective detection of the singly scattered light. Model experiments on slowly relaxing
suspensions of latex spheres in glycerol were carried out to verify validity range of our approach.
The behavior of interfaces between liquid and gaseous phases in the course of non-stationary mass transfer in the porous media is studied by use of correlation and spectral analysis of spatial-temporal fluctuations of speckles induced due to laser light scattering by the probed medium. The following types of interface growth in the porous media are considered: the development of global boundaries between gaseous and liquid phases in the course of liquid evaporation from the porous layers and the development of interfaces driven by capillary forces in the porous layers. Some peculiarities of light scattering in the porous media with growing interfaces such as the anomalous behavior of the power spectra of speckle intensity fluctuations and manifestation of avalanches in the course of interface pinning are discussed. Various approaches to processing of the light scattering data are considered. Possible applications of these phenomena for porous media characterization are outlined.
The methods of wavelet analysis and Hilbert transform are used to study the intensity fluctuations of a laser light scattered by interphase boundaries in the layer of a porous medium (paper) during evaporation of a volatile liquid with which the layer was impregnated. The analysis was performed using the Morlet wavelet as the base transformation function. The obtained spectra reflect characteristic features of the development of the evaporation front, which correspond to various stages of the process of nonstationary mass transfer in the porous layer-volatile liquid system studied.
Laser speckle correlometry was used to study interphase boundary development in paper sheet. The active imbibition area was clearly defined and observed for all samples by higher rate of speckle intensity fluctuations. In some cases wetting of paper lead to formation of rough front which static shape and dynamics of the motion shows considerable complexity. This effect comes out from randomness in porous system and existence of macroscopic obstacles that require additional pressure to be overpassed.
Wavelet analysis of scattered light intensity fluctuations was used to improve performance of speckle correlometry of porous systems. The further development of technique was proposed to study structural characteristics of such systems. The intensity fluctuations of multiple-scattered light is a non-stationary noise-like signal. Previously reported spectral analysis of such signals based on windowed Fourier transformation faces the well-known difficulties in a case of short time series. The effect of aliasing in frequency domain prevent us from determining spectral characteristics accurately. But by use of continuous wavelet analysis it can be defined with maximal time-frequency resolution.
Speckle correlation diagnostics was used to study non- stationary multiple scattering multi-phase systems with spatially separated components on the instance of porous media in the course of liquid-phase evaporation. We propose a phenomenological model in which the local interfaces between air-filled and liquid-filled spaces in the probed medium act as an ensemble of the elementary dynamic scatters. The motions of local interface boundaries in such a scattering coherently illuminated system cause the dynamics of speckle patterns, and their decorrelation rate is related to mass transfer rate in the porous medium. Thus, correlation or spectral analysis of the speckle dynamics allows us to evaluate structural characteristics of such an object under given evaporation conditions. In this paper the results of experimental study of sequences of speckle images for model porous media (paper) are compared with computer simulation of irreversible growth. Possible applications of speckle correlation technique for porous media structure diagnostics in industry, biology and medicine are discussed.
Existence of non-zero residual polarization in case of backscattering of linearly polarized coherent light from semi-infinite disordered half-space is considered. This effect is caused by the significant contribution of the low- step scattered components for the backscattering mode and can be described phenomenologically by using the concept of distribution of effective optical paths of scattered light partial components. Influence of effective optical path statistics on the residual polarization degree was studied in the experiments with various phantom multiply scattering media. Corresponding results are presented.
Temperature dynamics of the hands of human subjects was investigated by means of dynamical thermography and shown to depend on the personality and psychological conditions of the subjects. For neurotic personalities, especially under stress, the temperature is shown not to change at all in most cases. Stress resistant `independent' persons show very stable dynamics with relatively small temperature changes (about 2 degrees). The dependence of temperature patterns of `intermediate,' or `active,' personalities on the conditions of stress, mental concentration, and so on, is discussed.
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