Can temporal analysis of optical coherence tomography statistics report on dextrorotatory-glucose levels in blood?

We report the use of optical coherence tomography (OCT) for measuring dextrorotatory-glucose (D-glucose) in liquid phantoms and in drawn blood based on temporal dynamics of light scattering. The presence of D-glucose alters the medium viscosity, thus affecting the Brownian motion of the scatterers (polystyrene microspheres (PMS) in phantoms, red blood cells (RBCs) in blood) as measured by OCT. To quantify the effect, the signal autocorrelation functions were measured from M-mode OCT data and exponentially fit to obtain the decorrelation times. These were then related to translational (and rotational, in case of asymmetric scatterers) diffusion coefficients which enabled the determination of D-glucose-controlled medium viscosity. Obtained viscosily values agreed well with the literature, and showed expected increase with D-glucose concentrations. Whole blood smears were imaged with microscope and another effect of added glucose, that of red blood cell deformation, was also observed. This phantom and blood OCT study demonstrates the technique’s ability to detect and quantify D-glucose presence in non-flowing liquid suspensions, and suggests several additional research routes necessary to determine its potential for in vivo applications.     

Polarization preservation in diffusive scattering from in vivo turbid biological media: effects of tissue optical absorption in the exact backscattering direction

There is considerable recent interest in using polarized light to investigate turbid biological media. Although tissue multiple scattering randomizes incident polarization states, there are circumstances when appreciable degree of polarization can be observed in diffusive scattering. In this study, we use polarization modulation and synchronous detection to examine in the exact backscattering direction the polarization properties of diffusely reflected visible light from hands of human volunteers of varying pigmentation levels. The surviving polarization fraction increases with increasing pigmentation, likely due to preferential loss of highly scattered, long-pathlength photons; this mechanism lowers the average pathlength traversed by the detected light and hence increases the measured polarization preservation. This behavior is contrasted with the overall diffuse reflectance intensity, whose magnitude decreases with increasing absorption. These experiments demonstrate the important influences of medium optical properties on the polarization characteristics of multiply scattered light, which must be further investigated to enable quantitative polarization evaluation of turbid media such as biological tissues.     

Speckle photography applied to statistical analysis of turbulence

A speckle photographic technique is used for visualizing the planar distribution of the refractive deflection angles of light transmitted through the compressible turbulent flow. Both double and single (prolonged) exposure speckle photography are applied for statistical analysis of such flows. Using single (prolonged) exposure speckle photography (SPESP), instantaneous quantitative measurement of 2-D distribution of turbulence intensity in a flame is performed. Anisotropy of turbulence is visualized by a diffraction halo form and quantitatively evaluated by measuring the diffraction halo diameters. Using double exposure speckle photography (DESP), quantitative visualization of the planar distribution of the refractive deflection angles of the light transmitted through the compressible turbulent flow is done. Turbulent structures are visible in the patterns of the deflection angles isolines. The 2-D correlation functions of these deflection angles are constructed and analyzed. The 3-D density correlation functions are evaluated using the Erbeck–Merzkirch integral transformation.     

Quantitative Flow Visualization

Modern developments in laser and computer technology, electronic cameras, and digital image processing techniques allow to generate planar distributions of quantitative data in turbulent flows. Large amounts of data can be processed easily and analyzed statistically. With these tools, it is possible to quantitatively visualize turbulent coherent structures, even in flows of high Reynolds number, and measure characteristic spatial quantities like vorticity, length scales, spatial correlation functions, etc. These potentials in analyzing spatial characteristics of turbulent flows are demonstrated with two different methods of quantitative flow visualization: speckle photography as a representative of the line-of-sight methods, and particle image velocimetry belonging to the methods that rely on the scattering of laser light from tracer particles.Sommario.I moderni sviluppi nelle tecnologie del laser e dei computers, delle telecamere elettroniche e le tecniche di analisi digitale delle immagini permettono di ottenere distribuzioni quantitative, in un piano, di dati relativi a flussi turbolenti. Una gran quantità di dati può essere con facilità analizzata statisticamente. Con questi mezzi è possibile visualizzare quantitativamente strutture coerenti turbolente anche in flussi da alto numero di Reynolds, e misurare caratteristiche spaziali, come vorticità scale e funzioni di correlazione. Questa potenzialità di studiare caratteristiche spaziali di flussi turbolenti viene qui mostrata per due differenti metodi di visualizzazione quantitativa: fotografia speckle e PIV (particle image velocimetry).     

A Monte Carlo study of penetration depth and sampling volume of polarized light in turbid media

Detection depth and sampling volume of polarized light in highly turbid, cylindrically-shaped samples are estimated using pathlength distributions calculated from a polarization-sensitive Monte Carlo model. Due to defined ranges of the polarized light pathlength distribution, the estimated penetration depth and the interrogated volume of the polarization-maintaining photon subpopulation are smaller than those of the whole collected photon population, the latter exhibiting a wider pathlength distribution resulting from multiple scattering. It is also demonstrated that the spatial interrogation extent of polarized light in turbid media is greatly affected by the experimental detection geometry.