Speckle Distribution Research Articles

Surface patterning for multi-scale strain analysis of in-situ SEM mechanical experiments

Scanning electron microscopy (SEM) enables microstructure characterization at multi-scale, having potential to quantify strain distribution across multiple fields of view (FOVs) and exploring coordinated relationships among the deformations of multi-scale microstructures. Optimizing distribution of multi-scale speckles is crucial for achieving high precision and efficiency in digital image correlation (DIC) computations. In this work, a multi-scale strain measurement method is proposed for in-situ SEM mechanical experiments, which relies on an uncomplicated multi-scale speckle preparation method. Multi-scale speckle preparation can be achieved by the combination of spin-coating and magnetron sputtering. By using micro- and macro-speckle, multi-scale strain calculations can be achieved during the in-situ SEM mechanical loading. The InSn macro-speckle is composed of controllable-sized InSn nanoscale speckles, ensuring that the accuracy of DIC measurements in the microscopic regions are not compromised by the coverage of macro-speckles in the testing region. In regions covered exclusively by SiO2 nano-speckles, in-situ SEM mechanical loading allows for the acquisition of high-resolution DIC (HR-DIC) and electron backscatter diffraction (EBSD) data from the same region and under the same deformation state. Experiments are conducted to illustrate the functionality and utility of the multi-scale speckles. Such experimental analyses offer an opportunity to further explore multi-scale strain heterogeneity in some advanced structural materials and provide reliable experimental verification for material mechanics simulations.

Long noncoding RNAs heat shock RNA omega nucleates TBPH and promotes intestinal stem cell differentiation upon heat shock

In Drosophila, long noncoding RNA Hsrω rapidly assembles membraneless organelle omega speckles under heat shock with unknown biological function. Here, we identified the distribution of omega speckles in multiple tissues of adult Drosophila melanogaster and found that they were selectively distributed in differentiated enterocytes but not in the intestinal stem cells of the midgut. We mimicked the high expression level of Hsrω via overexpression or intense heat shock and demonstrated that the assembly of omega speckles nucleates TBPH for the induction of ISC differentiation. Additionally, we found that heat shock stress promoted cell differentiation, which is conserved in mammalian cells through paraspeckles, resulting in large puncta of TDP-43 (a homolog of TBPH) with less mobility and the differentiation of human induced pluripotent stem cells. Overall, our findings confirm the role of Hsrω and omega speckles in the development of intestinal cells and provide new prospects for the establishment of stem cell differentiation strategies.

Illumination homogenization of highly coherent light source based on phase modulation

When using a fly’s eye lens system to homogenize highly coherent light sources, the interference effect between the sub-beams can cause a periodic speckle distribution of illumination intensity, thereby disrupting illumination uniformity. It has been shown that using a rotating optical phase-shift plate behind the fly’s eye lens can eliminate interference patterns, but it only demonstrates engineering realizations. And the theoretical analysis and technical guidance on the phase modulation method and statistical averaging method for fly’s eye lens homogenization systems are still lacking. In this work, a simulation model of fly’s eye random phase modulation homogenization system is developed and studied in detail. Each sub-beam of the fly’s eye lens is randomly phase-modulated to break the coherence condition, and the illumination intensity of multiple independent modulations is accumulated to eliminate the interference pattern. The more times the intensity is accumulated, the better the homogenization is. Meanwhile, studied in this paper are the influence of the diffraction effect on homogenization, and the influence of the sub-lens size and focal length on the homogenization, which result in the diffracting-type system and the imaging-type system respectively. For an imaging type system, it is necessary to ensure that the first fly’s eye lens is in the front focal plane of the second fly’s eye lens. By optimizing the parameters of the fly’s eye lens and using an imaging-type system with <i>p</i> = 1.8 mm and <i>f</i><sub>A</sub> = 9 mm, a Gaussian beam with the non-uniformity of 117% is homogenized into a flat-topped beam with the non-uniformity of 1.2% in a square illumination area of 100 mm<sup>2</sup>. This fly’s eye lens random phase modulation homogenization system has a simple structure, low energy loss, and good illumination uniformity, and can be used in systems that require high coherent laser input and high resolution. This technology can be used in the field of deep-ultraviolet mask defect detection.

Statistical Analysis of RGB Speckle Grains for Simulating Color Speckle Distributions

Statistical Analysis of RGB Speckle Grains for Simulating Color Speckle Distributions

SPECKLE IMAGES OF THE VESSELS AND HYDRODYNAMIC PHANTOMS IN OPTICAL COHERENCE TOMOGRAPHY

The results of a study of a series of sequential images of a vessel and a hydrodynamic phantom of biological tissues obtained using a Spectral Domain Optical Coherence Tomography (SP OCT) are presented. Acquired data were processed and histograms of speckle distributions were created. They demonstrated differences in the intensity distribution for three different areas of the OCT image: (1) free space, (2) wall of the vessel, and (3) the flow of scatterers. Using an optimization algorithm the histograms were approximated by various distribution functions, best result was demonstrated by the beta distribution with the determination coefficient R2 ~ 0.95. The resulting distributions quantitatively demonstrate effect of tissue heterogeneity. They show significant differences in the values of the shape and scale parameters, corresponding to the obtained beta distribution parameters, which were α ~ 1.7, β ~ 20.5 for free space, α ~ 3.1, β ~ 5.5 for the wall region of the phantom, α ~ 2.6, β ~ 1.7 for the flow of the scattering liquid. Variance matrices of the OCT images, which show correlation of speckles between adjacent pixels and those of the successive images were also obtained. Brighter areas of the variance matrix indicate a dynamic speckle structure in OCT images, while low brightness of the areas indicates static speckle structure, on the contrary.

Single-shot absolute 3D measurement based on speckle-embedded fringe projection

In this paper, we propose a single-shot absolute three-dimensional (3D) imaging method that only needs one speckle-embedded fringe pattern. In terms of algorithm, we develop a computational framework to achieve 3D measurement through: 1). extracting the fringe phase from speckle-embedded fringe images by performing a two-dimensional (2D) band-pass filtering on the Fourier spectrum; 2). utilizing the local speckle distribution to eliminate the periodic ambiguity of fringes and achieve integer-pixel matching; 3). utilizing the wrapped phase to refine the disparity map at the sub-pixel level. In terms of system setup, we design an optical system which can project a speckle-embedded fringe pattern in a large depth-of-field. The experiments are conducted to demonstrate the feasibility and effectiveness of the proposed method. The 3D measurement rate of our method is equal to the frame rate of cameras, not limited by projection devices.

The Kidneys Are Not All Normal: Transplanted Kidneys and Their Speckle Distributions.

Modelling ultrasound speckle to characterise tissue properties has generated considerable interest. As speckle is dependent on the underlying tissue architecture, modelling it may aid in tasks such as segmentation or disease detection. For the transplanted kidney, where ultrasound is used to investigate dysfunction, it is unknown which statistical distribution best characterises such speckle. This applies to the regions of the transplanted kidney: the cortex, the medulla and the central echogenic complex. Furthermore, it is unclear how these distributions vary by patient variables such as age, sex, body mass index, primary disease or donor type. These traits may influence speckle modelling given their influence on kidney anatomy. We investigate these two aims. B-mode images from n=821 kidney transplant recipients (one image per recipient) were automatically segmented into the cortex, medulla and central echogenic complex using a neural network. Seven distinct probability distributions were fitted to each region's histogram, and statistical analysis was performed. The Rayleigh and Nakagami distributions had model parameters that differed significantly between the three regions (p ≤ 0.05). Although both had excellent goodness of fit, the Nakagami had higher Kullbeck-Leibler divergence. Recipient age correlated weakly with scale in the cortex (Ω: ρ=0.11, p=0.004), while body mass index correlated weakly with shape in the medulla (m: ρ=0.08, p=0.04). Neither sex, primary disease nor donor type exhibited any correlation. We propose the Nakagami distribution be used to characterize transplanted kidneys regionally independent of disease etiology and most patient characteristics.

P‐15.3: Color Speckle Evaluation Using Eigenvalues Method

In the current international standard (IEC 62906‐5‐4), the variance and covariance of color coordinates u’ and v’, as well as photometric speckle contrast are used to evaluate color speckle. There are some shortcomings in the covariance method that it is difficult for users to match the speckle distribution with covariance intuitively. In this paper, the eigenvalues of the sample covariance matrix generated by u’ and v’ are proposed to evaluate color speckle, which can be more intuitive and more suitable as an evaluation metric in measurement.

Path sampling and integration method to calculate speckle patterns.

A stable speckle pattern is generated when a coherent beam illuminates a stationary scattering medium that contains numerous scatterers with fixed positions. To date, there has been no valid method to the best of our knowledge for calculating the speckle pattern of a macro medium with a large number of scatterers. Here, a new method based on possible path sampling with corresponding weights and coherent superposition is presented for the simulation of optical field propagation in a scattering medium and output speckle patterns. In this method, a photon is launched onto a medium with fixed scatterers. It propagates in one direction; upon collision with a scatterer, its direction is updated. The procedure is repeated until it exits the medium. A sampled path is obtained in this manner. By repeatedly launching photons, numerous independent optical paths can be sampled. A speckle pattern, corresponding to the probability density of the photon, is formed by the coherent superposition of sufficiently sampled path lengths ending on a receiving screen. This method can be used in sophisticated studies of the influences of medium parameters, motion of scatterers, sample distortions on speckle distributions, and morphological appearances. It can be used for micro-examination of optical fields in scattering media and may inspire new methods and techniques for non-invasive precision detection and diagnosis of scattering media.

Comparison Reproducibility of Measured and Calculated Color Speckle Distributions in CIE xyY Color Space

Comparison Reproducibility of Measured and Calculated Color Speckle Distributions in CIE xyY Color Space

Scale factor effect of RGB monochromatic speckle grains on color speckle distribution

Scale factor effect of RGB monochromatic speckle grains on color speckle distribution

2D shape reconstruction of irregular particles with deep learning based on interferometric particle imaging.

Interferometric particle imaging (IPI) technology is widely used in the measurement of various particles. Obtaining particle shape information directly by IPI is challenging because of the complex relationship between the speckle distribution of interference-defocused speckle patterns and the shape of the corresponding irregular particles. Considering this challenge, we implement a deep learning method based on the convolutional neural network (CNN) to reconstruct defocused images of sand particles with sparse features. We also introduce the negative Pearson correlation coefficient as the loss function. To verify the feasibility of our method, we implemented it to reconstruct defocused images obtained from IPI experiments. Finally, compared with another common CNN-based structure, we confirmed that our network structure has good performance in the shape reconstruction of irregular particles.

Optical Flow Based Background Oriented Schlieren for Compressible Flows

Optical flow provides an opportunity to e levate the resolution and s ensitivity of deflection se nsing in background oriented schlieren (BOS). Despite extensive relevant literature within the field of computer v ision, with regards to BOS, there is a lack of proper quantification of its abilities and l imitations. Thus, this study performs a comparative assessment characterizing accuracy and resolution limits in different flow field scenarios utilizing background patterns generated with speckle and wavelet noise distributions. Accordingly, a synthetic assessment over direct numerical simulations of a buoyancy driven turbulence is performed with variations introduced in the background patterns and operational parameters of optical flow where a c lear s uperiority o f a ccuracy a nd r esolvable r ange o f density gradient amplitudes over cross-correlation is demonstrated. Moreover, an experimental assessment of supersonic flow features over multiple models is conducted to characterize the influence of experimental considerations related to the application of optical flow in BOS and its comparative performance against the block-matching counterpart.

Определение деформаций цилиндрических образцов оптическим способом с использованием метода цифровой корреляции изображений

A provision of location tolerances and their retention in the postoperative period is one of the main hard-hitting process tasks when producing long-length low-rigidity shaft-type parts. Mixed treatment – tensile straightening or thermal-power treatment is one of the technological methods intended to provide this group of geometrical indicators, including axle linearity. The efficiency improvement of this technology is impossible without knowing the features of the formation of plastic deformations distribution along the length of long-length blank parts. The paper considers the application of an optical method for controlling deformation on the surface using the method of digital image correlation at axial deformation of cylindrical parts. The work describes an experimental device for optic control of deformations when loading a specimen using digital cameras. The authors studied the influence of various modes of paint deposition to a sample (deposition rate, distance, deposition mode – continuous or pulsed) on the features of a produced speckle in the form of random distribution of mixed-size paint spots over the specimen surface; obtained histograms of the intensity distribution of various speckles. The authors carried out the experiments to identify deformations based on the technology of the local gradient digital image correlation method for the specimens of polymer tubes with different speckle types. The study identified the distribution of the deformation over the length of samples within the deformable area selected for analysis with the specified degree of smoothing provided by choice of correlation kernel size and the choice of its displacement step for fixing deformation processes with a precise error. The authors obtained distributions of axial deformations along the length of specimens and errors of deformations determination depending on a speckle nature. The study specifies necessary speckle parameters ensuring minimal error for long-length samples up to 200 mm in length and appropriate technology for paint depositing. It is a speckle with a wide range of spot sizes rarefied with their locations and the Gaussian filter image smoothing before the analysis.

Speckle-reduced reconstruction of a single-shot hologram by multiple tip-tilt modulations.

Speckle can be attenuated by averaging the reconstructed images of each sub-hologram or being filtered with different filters, at the expense of resolution. We propose a de-speckling method for a single-shot digital hologram while maintaining the resolution. Different tip-tilt phases are demonstrated to cause changes only for the speckle distributions of the reconstructed image. The speckle is attenuated by averaging these intensity images with different speckle distributions. The normalized contrast can be reduced to 0.56 by averaging only 20 different reconstructed images. When the averaged image is processed with block matching and 3D filtering, a further de-speckled image at a normalized contrast of 0.46 can be obtained with highly preserved resolution.

The effect of intraocular pressure elevation and related ocular biometry changes on corneal OCT speckle distribution in porcine eyes.

The aim of this study was to evaluate the influence of increase in intraocular pressure (IOP) and cooccurring changes in ocular biometry parameters on the corneal optical coherence tomography (OCT) speckle distribution in ex-vivo experiments on porcine intact eyes. Twenty-three eyeballs were used in the inflation test where IOP in the anterior chamber was precisely set from 10 mmHg to 40 mmHg in steps of 5 mmHg and where eye biometry was utilized (IOL Master 700). To assess the influence of the duration of the experiment on the OCT speckle statistics, the second experiment was performed with 10 eyeballs at the constant IOP of 15 mmHg. Based on the OCT scans of central cornea (Copernicus REVO), spatial maps of the scale parameter (a) and the shape parameter (v) of the gamma distribution speckle model were estimated. The means of both parameters for each spatial map were computed within the 2 mm of the central stroma. Both distributional parameters statistically significantly varied with IOP and time (one way repeated measures ANOVA, all p-values < 0.001). The a parameter revealed a faster statistically significant increase in IOP up to 25 mmHg, regardless of time. Central corneal thickness (CCT), the anterior chamber depth, and the mean equivalent spherical power varied significantly with IOP, whereas CCT and axial length changed statistically significantly with time. Statistically significant correlation was found between CCT and the a parameter, after removing IOP as a confounding factor (r = −0.576, p < 0.001). The parameters of the gamma distribution can be used not only for identifying IOP induced changes in the optical scattering within the corneal stroma, but also in corneal geometry. The approach of corneal speckle analysis could be potentially utilized for an indirect and noninvasive assessment of some properties of corneal stroma.

Bayesian analysis of depth resolved OCT attenuation coefficients

Optical coherence tomography (OCT) is an optical technique which allows for volumetric visualization of the internal structures of translucent materials. Additional information can be gained by measuring the rate of signal attenuation in depth. Techniques have been developed to estimate the rate of attenuation on a voxel by voxel basis. This depth resolved attenuation analysis gives insight into tissue structure and organization in a spatially resolved way. However, the presence of speckle in the OCT measurement causes the attenuation coefficient image to contain unrealistic fluctuations and makes the reliability of these images at the voxel level poor. While the distribution of speckle in OCT images has appeared in literature, the resulting voxelwise corruption of the attenuation analysis has not. In this work, the estimated depth resolved attenuation coefficient from OCT data with speckle is shown to be approximately exponentially distributed. After this, a prior distribution for the depth resolved attenuation coefficient is derived for a simple system using statistical mechanics. Finally, given a set of depth resolved estimates which were made from OCT data in the presence of speckle, a posterior probability distribution for the true voxelwise attenuation coefficient is derived and a Bayesian voxelwise estimator for the coefficient is given. These results are demonstrated in simulation and validated experimentally.

Vascular morphology and blood flow signatures for differential artery-vein analysis in optical coherence tomography of the retina.

Differential artery-vein (AV) analysis is essential for retinal study, disease detection, and treatment assessment. This study is to characterize vascular reflectance profiles and blood flow patterns of retinal artery and vein systems in optical coherence tomography (OCT) and OCT angiography (OCTA), and establish them as robust signatures for objective AV classification. A custom designed OCT was employed for three-dimensional (3D) imaging of mouse retina, and corresponding OCTA was reconstructed. Radially resliced OCT B-scans revealed two, i.e. top and bottom, hyperreflective wall boundaries in retinal arteries, while these wall boundaries were absent in OCT of retinal veins. Additional OCTA analysis consistently displayed a layered speckle distribution in the vein, which may indicate the venous laminar flow. These OCT and OCTA differences offer unique signatures for objective AV classification in OCT and OCTA.

RATIO-BASED SIMILARITY CRITERIA FOR POLARIMETRIC SAR IMAGE

Abstract. Dealing with multi-look polarimetric synthetic aperture radar (PolSAR) images requires averaging several independent looks to generate a sample covariance matrix of similar target scattering vectors. Along this, estimation of optimal similarity between target scattering vectors is still an open issue. In the literature, this intrinsic task has been mainly addressed in the information-based, geometric-based and detection-based frameworks. However, the derived measures mainly rely on the model assumption such as fully developed speckle and circular complex Gaussian distribution of the scattering vectors, which may not be held in high-resolution images of urban environments. To cope with this possible issue a discriminative model-free measure is proposed, where the similarity of target scattering is computed in the framework of non-local or patch based algorithm. In particular, the discriminative measure is constructed using the ratio between two pre-estimated covariance matrices of the scattering vectors. Experimental validation of the proposed measure is provided using ALOS-PALSAR image and compared with existing criterions in the literature.

Expression and Distribution Pattern of Pnn in Ischemic Cerebral Cortex and Cultured Neural Cells Exposed to Oxygen-Glucose Deprivation.

Pinin (Pnn), a multifunctional protein, participates in embryonic development as well as in cellular apoptosis, proliferation, and migration through regulating mRNA alternative splicing and gene transcription. Previous studies have shown that Pnn plays important roles in neural system development and the expression level of Pnn in astrocytes is altered by ischemic stress and associated with cellular apoptosis. In the present study, we further utilized primary cultured rat neurons and astrocytes with oxygen-glucose deprivation (OGD) and a mouse model with middle cerebral artery occlusion (MCAO)-induced ischemic stroke to examine the effect of ischemic stress on Pnn expression and distribution in different types of neural cells. Under normoxia, Pnn is mainly localized in the nuclear speckle of primary cultured neurons. The expression level of Pnn was increased after the OGD treatment and then decreased in the reoxygenation period. Moreover, the cytoplasmic expression of Pnn was observed in neurons with OGD and reoxygenation (OGD/R). Unlike that in neurons, the Pnn expression in astrocytes was decreased after OGD treatment and then gradually increased during the reoxygenation period. Of interest, the nuclear–cytoplasmic translocation of Pnn was not observed in astrocytes with OGD/R. In the MCAO mouse model, the neuronal expression of Pnn in the peri-ischemic region was reduced by three days post induction of ischemic stroke. However, the Pnn expression in astrocytes was not altered. Moreover, the nuclear speckle distribution of Pnn in neurons was also diminished following ischemic stroke. In conclusion, the Pnn expression and distribution after OGD and during reoxygenation showed distinct manners in neurons and astrocytes, implying that Pnn may play different roles in different types of neural cells in the stress response to ischemic injury.