Vladislav V. Lychagov

Finger tissue model and blood perfused skin tissue phantom

Measurements of optical properties of fingernail and underlying tissues using OCT are presented. Review and measurements of Raman spectra of tissue and phantom compounds were done. Updating of modeling algorithm for scattering coefficient calculation on the basis of integrating sphere measurements accounting for particle size-distribution was also done. The adequate fingernail and underlying tissue optical model at 830 nm was evaluation. Tissue phantoms potentially suitable for calibration of Raman instrumentation for glucose sensing were designed and tested on the basis of epoxy resin, TiO2-nanoparticles and micron-sized silica particles with the capillary net-work.

THE EXPERIMENTAL STUDY OF STRESS-RELATED PATHOLOGICAL CHANGES IN CEREBRAL VENOUS BLOOD FLOW IN NEWBORN RATS ASSESSED BY DOCT

In experiments on newborn rats with stress-related intracranial hemorrhage (ICH) using Doppler optical coherence tomography (DOCT) we have shown that latent stage of ICH (4 h after stress) is characterized by decrease of venous blood outflow and the loss of sensitivity of sagittal vein to vasoconstrictor effect of adrenaline. The incidence of ICH (24 h after stress) was accompanied by progression of early pathological changes in cerebral venous blood flow (CVBF) and development of venous insufficiency. Taking into consideration of this fact, we suggest that the suppression of CVBF related to the severity to the deleterious effect of stress on the brain hemodynamics in newborn rats. These facts allow us to conclude that the venous insufficiency with the loss of vasoconstrictor response to adrenaline is an informative and sensitive component of pattern of CVBF that can be important diagnostic criteria of risk of ICH development in newborns.

Longitudinal coherence length of an optical field

Longitudinal coherence of an optical field depending on the parameters of its frequency and angular spectra is considered. Expressions for the function and length of longitudinal coherence depending on the width of the frequency and angular spectra are obtained. The competitive influence of the angular and frequency spectra of the field on its longitudinal coherence is discussed. Experimental studies using a longitudinal shearing Michelson interferometer that proves theoretical results are performed.

Experimental study of NIR transmittance of the human skull

The results of measurements of transmittance of high power laser irradiation through skull bones and scalp are presented. Dependences of transmittance on sample thickness were received. Character of transmittance was investigated and characteristics of heterogeneity of the scattering structure of the skull bones are proposed. Besides that, variation of temperature of skull and scalp surfaces under exposure of high power laser irradiation during experiments was controlled. Experimental results were verified by Monte-Carlo simulations.

WAVELET-BASED ANALYSIS OF CEREBROVASCULAR DYNAMICS IN NEWBORN RATS WITH INTRACRANIAL HEMORRHAGES

Intracranial hemorrhage (IH) is a major problem of neonatal intensive care. The incidence of IH is typically asymptomatic and cannot be effectively detected by standard diagnostic methods. The mechanisms underlying IH are unknown but there is evidence that stress-induced disorders in adrenergic regulation of cerebral venous blood flow (CVBF) are among the main reasons. Quantitative and qualitative assessment of CVBF could significantly advance understanding of the nature of IH in newborns. In this work, we analyze variations of CVBF in newborn rats with an experimental model of stress-induced IH and adrenaline injection. Our analysis is based on the Doppler optical coherence tomography (DOCT) and a proposed adaptive wavelet-based approach that provides sensitive markers of abnormal reactions of the sagittal vein to external factors. The obtained results demonstrate that the incidence of IH in newborn rats is accompanied by a suppression of CVBF with the development of venous insufficiency and areactivity to adrenaline. We introduce a numerical measure θ, quantifying reactions of CVBF and show that the values θ < 1.23 estimated in the low-frequency (LF) spectral range corresponding to the sympathicus indicate abnormal reactions associated with the development of IH. We conclude that the revealed areactivity of the cerebral veins to adrenaline represents a possible mechanism responsible for pathological changes in CVBF.

Polychromatic low-coherence interferometry of stratified structures with digital interferogram recording and processing

The processes of formation and digital recording of interference patterns arising in partially coherent polychromatic light in the course of interference monitoring of surface microrelief in objects having stratified volume structure are considered. The expressions for the intensity distribution in the interference pattern depending on the surface relief and the object structure are derived taking the spectral properties of the photodetector array into account. The results of numerical simulation of interference fringes in polychromatic light and experimentally measured digital white light microinterferograms are presented. These results demonstrate the agreement between the theoretical model and the experimental interferograms and the possibility of solving the direct problem of low-coherence interferometry using numerical simulation of the interference pattern.

What type of coherence of the optical field is observed in the Michelson interferometer

The types and corresponding coherence functions of the optical field are considered depending on the frequency and angular spectra of the field. The main concepts of the theory of coherence effects in the interference experiment with the amplitude splitting of the initial field are discussed. It is shown that, in strict correspondence with the theory of coherence of the random wave fields, the Michelson interferometer reveals manifestations of the transverse and longitudinal spatial (rather than temporal, as it is commonly adopted) coherence of the optical field; the purely temporal coherence of the optical field is revealed only under special conditions of the interference experiment. Beyond these conditions, either spatial or spatiotemporal coherence is revealed.

Longitudinal purely spatial coherence of a light field

The effects of longitudinal purely spatial coherence of light and the results of observation of these effects in an interference experiment are considered under the condition that the length of temporal coherence lc is considerably smaller than the length of longitudinal spatial coherence ρ‖ of the field. It is shown that, for lc ≪ ρ‖, the longitudinal purely spatial coherence of the light field in fact governs the coherence of the wave train in the process of its propagation. The length and the time of coherent (“free”) path of the wave train are considered as new spatial and temporal scales of a partially coherent light field.

OCT monitoring of diffusion of water and glycerol through tooth dentine in different geometry of wetting

In our previous work optical coherence tomography (OCT) has been proved to be a useful tool for monitoring of diffusion of chemical agents (water, glycerol) within human tooth dentine. Such diffusion studies are interesting for tooth therapy (diffusion of medicinal preparations) and cosmetics (chemical whitening agents). Here we compare different wetting schemes in which the sample is either merged in the liquid agent so that the probe beam is to pass through a layer of liquid, or subjected to wetting through a special window from the back side. In spite of certain difference revealed, the order of magnitude of the diffusion time constant and the permeability coefficient are shown to be the same in both cases.

Low-Coherence interference microscopy of the internal structure of crystallized blood plasma

The possibility of using full-field low-coherence (white light) interferometry to investigate the surface profile and the internal spatial structure of crystallized drops of blood plasma and to study plasma structuring in real time is discussed. The experimental microtomograms of the central and peripheral regions of a plasma drop are presented. A method is proposed to estimate the contact angle using two-dimensional cross sections of the drop optical structure in the peripheral region.