We present an alternative approach for using dynamic laser speckle data to quantify biophysical dynamics including ordered flows and random motions. The approach yields images that superficially resemble traditional laser speckle contrast images, but instead of relying on the statistics of the local time integrated intensity values calculated over temporal and sliding spatial windows as is done in LSCI to create images, ellipticity imaging (EI) directly yields images that quantify the relative dominance of long-range correlations in the temporal dimension of a series of speckle patterns to the short-range correlations in the same dimension. The approach relies on a Poincaré analysis of the speckle data which yields metrics that statistically describe both the short-terms variations in the temporal speckle intensity (i.e., the standard deviation in successive differences) and also the corresponding long term variations. These metrics are plotted against each other (Poincaré plots) and an ellipse fit to the data. The ratio of the semi-major axis to the semi-minor axis of this ellipse for each temporal speckle sequence is then used as the data to form the images (thus the term EI). The results of flow phantom and mouse EI studies will be presented. Various flow rates of dilute intralipid were illuminated with a coherent laser source and EI images were generated. The same speckle data were analyzed using spatial and temporal LSCI approaches. Flows in anesthetized mouse brain vessels were analyzed using EI and LSCI approaches. The results of the studies using the different speckle analyses will be discussed.
A characteristic sign of aging skin is loss of firmness. Current bioinstruments to measure the influence of formulations on skin mechanics are limited in sensitivity and have high operator variability. To address these issues an optical elastography system was developed. Regions of the upper inner bicep were treated with various commercial formulations including wrinkle reducers, firming films, and moisturizers. These regions along with adjacent untreated areas that served as internal controls were imaged with a custom designed optical elastography system. The elastography system employed a polarized 50 mW 532 nm cw laser as an illumination source, a CCD camera imaging the skin at 160 Hz frame rate and a polarization analyzer aligned parallel to the incident beam. The skin was mechanically loaded using compressed air reduced in pressure and modulated using a proportional valve to provide a 1 Hz sinusoidally varying pressure to the skin with a peak force of 0.15 N. Subjects ranging in ages from 19 to 60 years old were recruited with IRB approval. Displacement and strain encoded elastograms were generated simultaneously for the treated and untreated areas. The ratio of the strain response in the two regions was calculated to quantify the relative effect of the skin agents. Significant differences were found in the strain response to the imposed loads between treated and control areas in all age groups and genders. Optical elastography systems such as the one prototyped in this study may prove to be useful for the cosmetics industry for assessing product efficacy.
Light scattered from dynamic random media has numerous applications in medicine, biology, engineering, physics and numerous other fields. Short term and long term variations and correlations in the scattered intensity (“speckle”) provide information about the crossing of scattering paths as a result of the local structure and dynamics within the medium. Poincaré descriptors are statistical tools used to study variations or self-similarity in neighboring values of a quantity. Herein, we modify this definition to examine correlations not only between neighboring (temporally and spatially) values of dynamic speckle patterns, but also between values with larger spatial and temporal distances between them. The effects of incoherently summed, that is, time-averaged speckle patterns will be examined, as will be the separate cases of incoherently summed correlated and un-correlated speckle patterns. The unique case of elongated speckle will also be presented. The ratio of short-term to long-term differences in the pattern, a term referred to as the ‘ellipticity’ of the data, yields information on the dominance of long-term variations in the scattered intensity compared to the short-term variations. We will show that Poincaré descriptors are useful in quantifying the width of the coherence areas in all 3 dimensions in the scattered intensity patterns and also for quantifying motions in speckle patterns from which information about the dynamics of the medium can be inferred.
Laser speckle patterns are granular patterns produced as a result of random interference of light waves. Optical vortices (OVs) are phase singularities in such speckle fields, characterized by zero intensity and an undefined phase. Decorrelation of the speckle fields causes these OVs to move in both time and space. In this work, a variety of parameters of these OVs have been studied. The speckle fields were simulated to undergo three distinct decorrelation behaviors- Gaussian, Lorentzian and constant decorrelations. Different decorrelation behaviors represent different dynamics. For example, Lorentzian and Gaussian decorrelations represent Brownian and ordered motions, respectively. Typical dynamical systems in biophysics are generally argued to be a combination of these. For each of the decorrelation behaviors under study, the vortex trails were tracked while varying the rate of decorrelation. Parameters such as the decorrelation length, average trail length and the deviation of the vortices as they traversed in the speckle field, were studied. Empirical studies were also performed to define the distinction between trails arising from different speckle decorrelation behaviors. The initial studies under stationary speckle fields were followed up by similar studies on shifting fields. A new idea to employ Poincaŕe plots in speckle analysis has also been introduced. Our studies indicate that tracking OVs can be a potential method to study cell and tissue dynamics.
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