Evaluation of low viscosity variations in fluids using temporal and spatial analysis of the speckle pattern

Single speckle image analysis for monitoring the hardening kinetics of glass ionomer cements

In this paper, we monitor the setting reaction of commercial glass ionomer cements using a laser speckle technique and adopting a spatial approach in the analysis of recorded speckle images. Experimental results showed that spatial contrast and speckle grain size increased as two studied cements underwent their setting reactions. After combining two geometrical configurations to measure the intensities of backscattered and transmitted light, we concluded that the increase in speckle grain size was caused by an increase in size of the scattering centers, since cement components aggregate and hence transition from a Rayleigh to a Mie scattering regime. Finally, two main phases were distinguished in the hardening process, as reported in the literature; however, the technique we propose has the advantage of easily identifying these two phases. The analysis of a single speckle image offers multiple advantages over the temporal analysis of a series of speckle images, in particular due to the low number of images recorded and a far shorter image processing time.

Real-time monitoring of bacterial growth kinetics in suspensions using laser speckle imaging

In microbiology, monitoring the growth of any microorganism in culture is important for studying and optimizing the growth kinetics, the biomass and the metabolite production. In this work, we show that laser speckle imaging is a reliable technique that can be used to perform real-time monitoring of bacteria growth kinetic in liquid culture media. Speckle parameters, specifically speckle grain size and the spatial contrast of the speckle images, and standard analytical parameters (optical density, pH and colony forming units) were measured during the culture of different strains of Bacillus thuringiensis. Our results show that both speckle grain size and spatial contrast decrease with bacterial growth. Furthermore, speckle parameters are sensitive to the fermentation conditions. Statistical analysis revealed a relatively high correlation between speckle and analytical parameters.

Monitoring the curing kinetics of glass ionomer cements by modeling the temporal correlation of speckle images

Glass ionomer cements (GIC) originated in the mid-twentieth century with the rising demand for dental materials to be biocompatible and cost-effective. Due to their unique ability to bond to tooth structure, coupled with their fluoride-releasing potential, GIC are widely used in pediatric dentistry. However, the curing kinetics of these materials are not extensively documented. In this study, we show that dynamic laser speckle is an efficient method for monitoring the acid-base reaction that occurs during the self-setting of conventional GIC. Plotted temporal correlation curves, showing the degree of similarity between several recorded speckle patterns, indicate that the GIC kinetics reaction slows down during the curing phenomenon. Furthermore, the numerical fit of the temporal correlation curves with a Lorentzian profile gives the characteristic times of the reaction and reveals two phases during GIC hardening.

Fourier transforms for fast and quantitative Laser Speckle Imaging

Laser speckle imaging is a powerful imaging technique that visualizes microscopic motion within turbid materials. At current two methods are widely used to analyze speckle data: one is fast but qualitative, the other quantitative but computationally expensive. We have developed a new processing algorithm based on the fast Fourier transform, which converts raw speckle patterns into maps of microscopic motion and is both fast and quantitative, providing a dynamnic spectrum of the material over a frequency range spanning several decades. In this article we show how to apply this algorithm and how to measure a diffusion coefficient with it. We show that this method is quantitative and several orders of magnitude faster than the existing quantitative method. Finally we harness the potential of this new approach by constructing a portable laser speckle imaging setup that performs quantitative data processing in real-time on a tablet.

A New Insight into Biospeckle Activity in Apple Tissues

The monitoring and characterization of agricultural products before harvest or during ripening, storage, and shelf life has recently been increasingly explored in the literature. The analysis of biospeckle activity has potential for the determination of the optimal harvest window, the monitoring of the fruit ripening process, and the detection of diseases and bruising. In this technique, the specimen is illuminated with coherent light and speckle intensity fluctuations are analyzed using diverse methodologies. Prior work shows that biospeckle activity is strongly correlated to physiological indexes conventionally used to evaluate fruit texture and composition. Here, we scrupulously investigate the biospeckle activity of Gala apple fruits during postharvest stages. We simulate realistic conditions for shelf-life monitoring, namely an unknown history of the fruit and storage in an uncontrolled atmosphere. Scattering spot images are acquired with multiple exposure times using a simple optical setup. The contrast, reflecting biospeckle activity, is computed after eliminating inhomogeneous zones. The results show, for the first time, speckle activity at short time scales. The retrieved correlations between speckle parameters and the ratio of apples’ firmness to their soluble solids content reveal significant links despite the unknown fruit’s origin, harvest date, and storage history.

Intensity fluctuation-invariant maximum likelihood estimation of speckle order

We present a speckle order estimation method invariant to mean intensity variations inside the sample. It is based on the acquisition of two statistically independent speckle images. The Cramer-Rao lower bound and the maximum likelihood estimator in the presence of pure speckle noise are derived and shown to have performance very close to classical estimation methods that are not invariant to mean intensity fluctuations. This method is also shown to be robust to Poisson shot noise and additive noise, and is validated on an optical experiment with a standard camera. Thus, it is useful for estimating speckle order in real-world coherent images.

Strong cytoskeleton activity on millisecond timescales upon particle binding revealed by ROCS microscopy

Cells change their shape within seconds, cellular protrusions even on subsecond timescales enabling various responses to stimuli of approaching bacteria, viruses or pharmaceutical drugs. Typical response patterns are governed by a complex reorganization of the actin cortex, where single filaments and molecules act on even faster timescales. These dynamics have remained mostly invisible due to a superposition of slow and fast motions, but also due to a lack of adequate imaging technology. Whereas fluorescence techniques require too long integration times, novel coherent techniques such as ROCS microscopy can achieve sufficiently high spatiotemporal resolution. ROCS uses rotating back-scattered laser light from cellular structures and generates a consistently high image contrast at 150 nm resolution and frame rates of 100 Hz-without fluorescence or bleaching. Here, we present an extension of ROCS microscopy that exploits the principles of dynamic light scattering for precise localization, visualization and quantification of the cytoskeleton activity of mouse macrophages. The locally observed structural reorganization processes, encoded by dynamic speckle patterns, occur upon distinct mechanical stimuli, such as soft contacts with optically trapped beads. We find that a substantial amount of the near-membrane cytoskeleton activity takes place on millisecond timescales, which is much faster than reported ever before.

Elastography with low-frame-rate laser speckle contrast imaging using the aliasing effect

Elastography is an attractive technique for quantifying the mechanical properties of biological tissue. Here, we report an elastography method with low-frame-rate laser speckle contrast imaging (LSCI) using the aliasing effect. This method needs only one excitation source, a low-frame-rate camera, and no synchronization between excitation and acquisition. The accuracy of the elasticity measurement was validated on tissue-mimicking phantoms by comparing the value with the elasticity measured by a high-frame-rate LSCI and by the rheometer. Elastography was also performed on chicken breast in vitro.

Assessing White Wine Viscosity Variation Using Polarized Laser Speckle: A Promising Alternative to Wine Sensory Analysis

In this paper, we report measurements of wine viscosity, correlated to polarized laser speckle results. Experiments were performed on white wine samples produced with a single grape variety. Effects of the wine making cellar, the grape variety, and the vintage on wine Brix degree, alcohol content, viscosity, and speckle parameters are considered. We show that speckle parameters, namely, spatial contrast and speckle decorrelation time, as well as the inertia moment extracted from the temporal history speckle pattern, are mainly affected by the alcohol and sugar content and hence the wine viscosity. Principal component analysis revealed a high correlation between laser speckle results on the one hand and viscosity and Brix degree values on the other. As speckle analysis proved to be an efficient method of measuring the variation of the viscosity of white mono-variety wine, one can therefore consider it as an alternative method to wine sensory analysis.