Changes In Speckle Pattern Research Articles

Microsaccades Tracking by Secondary Speckle Pattern Analysis.

Here we propose a not pupil-dependent microsaccades tracking technique and a novel detection method. We present a proof of concept for detecting microsaccades using a non-contact laser-based photonic system recording and processing the temporal changes of speckle patterns scattered from an eye sclera. The data, simultaneously recorded by the speckle-based tracker (SBT) and the video-based eye tracker (Eyelink), was analyzed by the frequently used detection method of Engbert and Kliegl (E&K) and by advanced machine learning detection (MLD) techniques. We detected 93% of microsaccades in the SBT data out of microsaccades detected in the Eyelink data with the E&K method. By utilizing MLD, a precision of 86% was achieved. The findings of our study demonstrate a potential improvement in measuring tiny eye movements, such as microsaccades, using speckle-based eye tracking and, thus, an alternative to video-based eye tracking for detecting microsaccades.

Correction of thermal airflow distortion in warpage measurements of microelectronic packaging structures via deep learning-based digital image correlation

The projected speckle-based three-dimensional digital image correlation method (3D-DIC) is being increasingly used in the reliability measurement of microelectronic packaging structures because of its noninvasive nature, high precision, and low cost. However, during the measurement of the thermal reliability of packaging structures, the thermal airflow generated by heating introduces distortions in the images captured by the DIC measurement system, impacting the accuracy and reliability of noncontact measurements. To address this challenge, a thermal airflow distortion correction model based on the transformer attention mechanism is proposed specifically for the measurement of thermal warpage in microelectronic packaging structures. This model avoids the oversmoothing issue associated with convolutional neural networks and the lack of physical constraints in generative adversarial networks, ensuring the precision of grayscale gradient changes in speckle patterns and minimizing adverse effects on DIC calculation accuracy. By inputting the distorted images captured by the DIC measurement system into the network, corrected images are obtained for 3D-DIC calculations, thus allowing the thermal warpage measurement results of the sample to be acquired. Through experiments measuring topography with customized step block specimens, the effectiveness of the proposed method in improving warpage measurement accuracy is confirmed; this is particularly true when captured images are affected by thermal airflow at 140 °C and 160 °C, temperatures commonly encountered in thermal reliability testing of packaging structures. The method successfully reduces the standard deviation from 9.829 to 5.943 µm and from 12.318 to 6.418 µm, respectively. The results demonstrate the substantial practical value of this method for measuring thermal warpage in microelectronic packaging structures.

Three-dimensional, label-free cell viability measurements in tissue engineering scaffolds using optical coherence tomography.

In the field of tissue engineering, 3D scaffolds and cells are often combined to yield constructs that are used as therapeutics to repair or restore tissue function in patients. Viable cells are often required to achieve the intended mechanism of action for the therapy, where the live cells may build new tissue or may release factors that induce tissue regeneration. Thus, there is a need to reliably measure cell viability in 3D scaffolds as a quality attribute of a tissue-engineered medical product. Here, we developed a noninvasive, label-free, 3D optical coherence tomography (OCT) method to rapidly (2.5min) image large sample volumes (1 mm3 ) to assess cell viability and distribution within scaffolds. OCT imaging was assessed using a model scaffold-cell system consisting of a polysaccharide-based hydrogel seeded with human Jurkat cells. Four test systems were used: hydrogel seeded with live cells, hydrogel seeded with heat-shocked or fixed dead cells and hydrogel without any cells. Time series OCT images demonstrated changes in the time-dependent speckle patterns due to refractive index (RI) variations within live cells that were not observed for pure hydrogel samples or hydrogels with dead cells. The changes in speckle patterns were used to generate live-cell contrast by image subtraction. In this way, objects with large changes in RI were binned as live cells. Using this approach, on average, OCT imaging measurements counted 326 ± 52 live cells per 0.288 mm3 for hydrogels that were seeded with 288 live cells (as determined by the acridine orange-propidium iodide cell counting method prior to seeding cells in gels). Considering the substantial uncertainties in fabricating the scaffold-cell constructs, such as the error from pipetting and counting cells, a 13% difference in the live-cell count is reasonable. Additionally, the 3D distribution of live cells was mapped within a hydrogel scaffold to assess the uniformity of their distribution across the volume. Our results demonstrate a real-time, noninvasive method to rapidly assess the spatial distribution of live cells within a 3D scaffold that could be useful for assessing tissue-engineered medical products.

Comparison of Ballistocardiogram Processing Methods Based on Fiber Specklegram Sensors

The ballistocardiogram (BCG) is a graphic representation of the movements of the body associated with cardiac activity. In this article, a 10-min BCG has been captured for ten different volunteers with a polymer optical fiber (POF) specklegram sensor. This transducer, which is composed of a charge-coupled device (CCD) camera, a laser emitting diode, and two meters of POF, allows capturing the BCG by analyzing how the induced speckle pattern changes over time. These changes are related to cardiac activity. Several processing methods have been compared to determine which method achieves the best performance: complex cepstrum, power of spectral density (PSD), Pam–Tompkins algorithm, wavelet, autocorrelation, Savitzky–Golay filter, mean absolute deviation, and Hilbert transform. Accuracy and resource consumption have been characterized and compared for these methods. Hilbert, PSD, and Savitzky–Golay exhibit both small errors and computational costs. This article describes a baseline for the main frequency determination of POF-based BCG signals in real-time.

COMPARATIVE STUDY OF RESONANCE FREQUENCY OF CIRCULAR PIEZO MICROPHONE BASED ON PHOTOACOUSTIC, LASER SPECKLE, AND PIEZOELECTRIC EFFECTS

Resonance frequency of a circular piezoelectric microphone was measured by two types of methods which were named as photoacoustic and speckle method. In the photoacoustic method; acoustic waves were obtained due to the optical excitation and resulting thermally induced mechanical distortion was measured by the piezoelectric layer of microphone. Photoacoustic effect is a type of optical excitation, which creates an acoustic wave due to the absorbed light energy which causes thermal expansion of material. In contrast to the photoacoustic method, speckle method was conducted by electrical excitation of the piezoelectric layer which results in mechanical distortion and this distortion was detected by using changes in laser speckle pattern. Measurements were taken from 6 different piezo microphones in 3 different diameters of 15 mm, 35 mm, and 50 mm and the same thickness of brass plate in the frequency range of 0-11 kHz. As a conclusion, it is found that the resonance frequencies of same diameter microphones determined by the photoacoustic method are close but different with the results of the speckle method. It is believed that the differences in the results are caused by differences of excitation/detection mechanism for same microphones and shape, material parameter differences between microphones for different microphones.

Spatial statistics of superposition of two uncorrelated speckle patterns with polarization diversity

A detailed theoretical and experimental study on the effect of the superposition of uncorrelated speckle patterns with polarization diversity on the spatial statistics of the superposed speckle pattern is presented. It is shown that depending on the mutual orientation of the polarization vectors of the constituent speckle patterns, the maximum degree of coherence (DoC) and degree of polarization (DoP) of the superposed speckle pattern changes between a maximum and minimum value in a sinusoidal fashion. Moreover, the average intensity ratio of the constituent speckle patterns is also found to be affecting these variations. A study of the change in the visibility of the two-point intensity correlation function also reveals a sinusoidal nature of the variation and its dependence on the ratio of the average intensity, which are found to be similar to the variations of the maximum DoC and DoP. A detailed study on the changes in the normalized probability density function is also performed for better understanding of the effect on the spatial statistics.

On accounting for speckle extinction via DIC and PCA

Digital Image Correlation (DIC) is a full-field measurement technique that generally relies on brightness conservation principles. This work aims to analyze cases in which the speckle pattern vanished after heating, thereby severely altering the brightness. Sets of images acquired during 6 experiments were registered and then used to obtain optimal sets of reference images for each time step via Principal Component Analysis (PCA). The proposed methodology significantly reduced the gray level residuals and provided insight into brightness variations that occurred in the analyzed cases. It was possible to study cases with severe speckle pattern changes by updating the reference image when standard DIC did not converge and using the PCA methodology to obtain optimal reference states.

Evaluation of Laser Bio speckle as a new tool to detect exposure to ionizing radiation: A new dosimetric approach

Everyone in the world is exposed continuously to radiation. Exposure to ionizing radiation is known to have lethal effects in blood cells and other body organs and tissues. This work aimed to describe a new and simple method to evaluate the effect of chronic versus acute doses of ionizing radiation (IR) on animal blood model by the laser bio speckle measurements.The study concerned the biological effect for three groups of rats including control, chronically and acutely exposed to 1 Gy of gamma irradiation using Cesium-137 source. The blood samples of the three groups were then smeared over glass slides homogenously and fixed for further analysis. The bio-speckle images were produced using a coherent laser beam of green wavelengths 532.0 nm with output power < 50 mW illuminating the blood slides of the irradiated animals. Laser bio-speckle contrast measurements was used to detect the change in speckle pattern to visualize the change in blood components due to the deformation in shape and number of cells. Digital images are taken for each group samples. The chronic and acute dose reduction of the hemoglobin, hematocrit, red cell count, creatinine in serum were (8.4 vs. 16.5), (7.2 vs. 18.4), (12.1 vs. 20.7), (12.5 vs. 23.2) respectively. The components of blood that showed no specific trend observed between chronic versus acute exposure were white cell count (83.2 vs. 49.9), total protein (7.0 vs. 3.8), MCV (−5.2 vs. −3.1), MCH (−4.4 vs. −5.6), MCHC (0.69 vs. −2.1), RDW (−13.9 vs. −4.9).The study pointed that ionized radiation causes a change in blood structure components in a dose-delivery dependent manner. While this finding is expected, the capability shown by bio-speckle patterns to be consistent with mode of radiation delivery is an interesting finding that might drive the scientific community for potential future applications. From the graph representing the relation between the dose delivery and laser bio speckle contrast, it appeared that there is a direct relationship between the response of some blood components and magnitude of laser bio speckle contrast. Thus, it highly suggestive of transferring the concept of bio-speckle to other organs and tissues. Further studies are recommended to establish the relationship not only between blood components but other molecular signatures and the measurement of laser bio speckle.

3D printed hand-held refractometer based on laser speckle correlation

Measurement of very small refractive index changes is very important from a material's characterization point of view. This paper demosntrates a compact, simple and accurate technique for measuring refractive indices of transparent liquids, based on Snell's law and laser speckle correlation. Furthermore, considering the cutting-edge technology of 3D printing and its ability to enhance a technique's functionality by providing a sturdy framework, a 3D printed hand-held device for measurement of refractive indices is also demonstrated. The device measures very small change in refractive index by measuring the change in the objective speckle pattern arising due to the change in laser light passing the liquid solution, which is caused by the apparent shift of a point source. Change in the speckle pattern is presented in terms of correlation coefficient which is computed by comparing a speckle pattern corresponding to distilled de-ionized water with that of the speckle pattern corresponding to a liquid whose refractive index is to be measured. This change in speckle pattern is related to the change in concentration which in turn is related to refractive index of the liquid. The device can measure changes in refractive index as small as 0.00038 with an average error less than 4.5%.

Universal sensitivity of speckle intensity correlations to wavefront change in light diffusers

Here, we present a concept based on the realization that a complex medium can be used as a simple interferometer. Changes in the wavefront of an incident coherent beam can be retrieved by analyzing changes in speckle patterns when the beam passes through a light diffuser. We demonstrate that the spatial intensity correlations of the speckle patterns are independent of the light diffusers, and are solely determined by the phase changes of an incident beam. With numerical simulations using the random matrix theory, and an experimental pressure-driven wavefront-deforming setup using a microfluidic channel, we theoretically and experimentally confirm the universal sensitivity of speckle intensity correlations, which is attributed to the conservation of optical field correlation despite multiple light scattering. This work demonstrates that a light diffuser works as a simple interferometer, and presents opportunities to retrieve phase information of optical fields with a compact scattering layer in various applications in metrology, analytical chemistry, and biomedicine.

Preliminary investigations on changes in speckle patterns projected from a multimode optical fiber due to external disturbances to be applied onto the fiber

Changes in speckle patterns due to certain external disturbances to be applied onto a multimode optical fiber were observed. In the first attempt, a multimode optical glass fiber was placed onto a support plate and a speckle pattern in an output light spot projected from the fiber was observed while rotating or tilting the support plate. The resultant speckle pattern appeared to be rotating in accordance with the rotation or tilt motion of the support plate, and the pattern rotation angle was almost proportional to the rotation angle of the support plate. In the second attempt, a jacket-covered communication-grade multimode optical glass fiber was placed in a load application section so that corrugated bending of the fiber was intentionally induced by means of alternately disposed plurality of ridges. When a certain level of load (up to 15 kg) was applied onto the fiber in the load application section and then removed, the number of speckles observed in an output light spot projected from the fiber showed decreases upon load application onto the fiber and then recovery with the load removal.

Learning of speckle statistics for in vivo and noninvasive characterization of cutaneous wound regions using laser speckle contrast imaging

Laser speckle contrast imaging (LSCI) provides a noninvasive and cost effective solution for in vivo monitoring of blood flow. So far, most of the researches consider changes in speckle pattern (i.e. correlation time of speckle intensity fluctuation), account for relative change in blood flow during abnormal conditions. This paper introduces an application of LSCI for monitoring wound progression and characterization of cutaneous wound regions on mice model. Speckle images are captured on a tumor wound region at mice leg in periodic interval. Initially, raw speckle images are converted to their corresponding contrast images. Functional characterization begins with first segmenting the affected area using k-means clustering, taking wavelet energies in a local region as feature set. In the next stage, different regions in wound bed are clustered based on progressive and non-progressive nature of tissue properties. Changes in contrast due to heterogeneity in tissue structure and functionality are modeled using LSCI speckle statistics. Final characterization is achieved through supervised learning of these speckle statistics using support vector machine. On cross evaluation with mice model experiment, the proposed approach classifies the progressive and non-progressive wound regions with an average sensitivity of 96.18%, 97.62% and average specificity of 97.24%, 96.42% respectively. The clinical information yield with this approach is validated with the conventional immunohistochemistry result of wound to justify the ability of LSCI for in vivo, noninvasive and periodic assessment of wounds.

Following the drying process of Fevicol (adhesive) by dynamic speckle measurement

This work presents the study of drying of Fevicol (adhesive) using dynamic laser speckle technique. Dynamic laser speckle analysis is a non-invasive method that does not disturb the drying process. A low power laser light illuminates the sample and corresponding speckle images of the sample resulting from the phenomenon of interference are registered. If the sample shows activity, the speckle pattern changes in time. Following this evolution, we can analyze the drying process by means of image processing algorithms. In this work, the application of dynamic speckle technique to follow the drying process of Fevicol with different drying times is presented. Results obtained using numerical methods of Inertia Moment and cross-correlation show that quantitative evaluation of spatial temporal speckle activities can be used to monitor Fevicol drying process. The approaches such as auto-correlation and speckle contrast using temporal correlation allowed differentiating different stages of drying. In addition, the techniques allowed their applicability to follow the slow streaming of Fevicol from the coin surface.

Influence of graphene coating on speckle-pattern rotation of light in gyrotropic optical fiber.

In the present work, change in speckle-pattern of linearly polarized light passed through graphene-covered optical fiber placed in external magnetic field is investigated. The possibility of magnetic speckle-pattern rotation suppression and inverse speckle-pattern rotation effect is shown. This effect can be controlled by a chemical potential of graphene layer, which can be changed easily by a gate voltage, for example. For quartz optical fiber at wavelength 0.633μm, core diameter 9μm, and fiber length 5cm, an inverse rotation value of 17° is reached at chemical potential of graphene layer about 1eV and magnetic field strength 30kOe. Results of the work may be useful for different magneto-optics, opto-electronics, and photonics applications.

Two-dimensional blood flow velocity estimation using ultrasound speckle pattern dependence on scan direction and A-line acquisition velocity

We have previously investigated the change of apparent lateral speckle size caused by the direction and spatial rate of scanner A-line acquisition (scan velocity). An algorithm which measures the lateral component of blood flow velocity was developed based on the increase in speckle size resulting from relative motion between moving scatterers and the scan velocity. In this paper, the change of the apparent dominant angle of the speckle pattern in a straight vessel was investigated and a new method of two-dimensional blood flow velocity estimation is introduced. Different scan velocities were used for data acquisition from blood flow traveling at an angle relative to the ultrasound beam. The apparent angle of the speckle pattern changes with different scan velocities because of misregistration between the ultrasound beam and scatterers. The apparent angle of the speckle pattern was resolved by line-to-line cross-correlation in the fast-time (axial) direction on a region-of-interest (ROI) in each blood flow image and used to spatially align the ROI. The resulting lateral speckle size within the aligned ROI was calculated. The lateral component of the blood flow is shown to be closest to the scan velocity which gives the maximum speckle size and the apparent angle of speckle pattern collected by this scan velocity is the best estimate for the actual angle of blood flow. These two components produce two-dimensional blood flow velocity estimations. This method was studied through both computer simulation and experiments with a blood flow phantom. Nine scan velocities were used to collect blood flow data with velocities ranging from 33 to 98 cm/s and four beam-to-flow angles. In simulated plug blood flow, the mean bias of angle estimation is below 2% with an average standard deviation of 3.6%. In simulated parabolic blood flow, the angle of blood flow is overestimated because of speckle decorrelation caused by flow gradients and the estimation bias increases with decreasing beam-to-flow angle, which has an average value of 8.8% and standard deviation of 10%. Because of the complexity of flow profiles in the blood flow phantom, the angle of blood flow is also overestimated and the mean bias is increased by a factor of two compared with simulated parabolic flow. For the velocity estimation results, the mean bias is below 5% with an average standard deviation of 4.6% in the simulated plug blood flow. In the simulated parabolic flow and blood flow phantom, the velocity is underestimated because of speckle decorrelation. The mean bias of velocity estimation in the simulated parabolic flow is -6% with an average standard deviation of 11.2%. In the blood flow phantom, the mean bias of the velocity estimation is -5% with a higher average standard deviation of 21.5%. This method can resolve the angle and amplitude of two-dimensional blood flow simultaneously. The accuracy of the estimation can be further improved by using more scanning velocities.

Reflectance Speckle of Retinal Nerve Fiber Layer Reveals Axonal Activity

This study investigated the retinal nerve fiber layer (RNFL) reflectance speckle and tested the hypothesis that temporal change of RNFL speckle reveals axonal dynamic activity. RNFL reflectance speckle of isolated rat retinas was studied with monochromatic illumination. A series of reflectance images was collected every 5 seconds for approximately 15 minutes. Correlation coefficients (CC) of selected areas between a reference and subsequent images were calculated and plotted as a function of the time intervals between images. An exponential function fit to the time course was used to evaluate temporal change of speckle pattern. To relate temporal change of speckle to axonal activity, in vitro living retina perfused at a normal (34°C) and a lower (24°C) temperature, paraformaldehyde-fixed retina, and retina treated with microtubule depolymerization were used. RNFL reflectance was not uniform; rather nerve fiber bundles had a speckled texture that changed with time. In normally perfused retina, the time constant of the CC change was 0.56 ± 0.26 minutes. In retinas treated with lower temperature and microtubule depolymerization, the time constants increased by two to four times, indicating that the speckle pattern changed more slowly. The speckled texture in fixed retina was stationary. Fixation stops axonal activity; treatments with either lower temperature or microtubule depolymerization are known to decrease axonal transport. The results obtained in this study suggest that temporal change of RNFL speckle reveals structural change due to axonal activity. Assessment of RNFL reflectance speckle may offer a new means of evaluating axonal function.

Pyramidal Refinement of Lucas Kanade Optical Flow based Tracking of Peripheral Air Embolism in OCT Contrast Imaging

Air embolism often causes severe consequences in patients, in which several cases need fast treatment at the earlier stage. This paper proposes a computerized approach for detection as well as estimation of motion trajectory of air emboli using OCT contrast imaging technique. Due to change in optical properties, speckle pattern changes from fluid to air bubble and so does the speckle pattern on the image plane. This phenomenon helps to track the air bubble due to change in brightness pattern over a sequence of images. A top-down approach has been demonstrated from the image acquisition to the application of different image processing algorithms. Segmentation of the embolus has been carried out primarily by selecting seed contour through anisotropic diffusion (AD) technique and then implementation of a snake based active contour (AC) method. Both the techniques reduce the manual labour and computational time, thereby substantially increasing the segmentation accuracy (92% 94%). Besides, pyramidal construction of the Lucas – Kanade optical flow precisely optimizes the flow velocities of air bubble and also increases larger motion tracking ability. Hence, the proposed technique can becoming an assisting tool to the clinician for early detection of air embolism and tracking the air bubble through microcirculation. General Terms Image Processing, Optical Coherence Tomography, Medical Imaging, Computer Vision.

MO‐F‐220‐04: Quantitative Ultrasound Imaging

The objective measurement of tissue pathological state by medical imaging plays an increasing role in clinical practice. The ultrasound imaging modality offers dedicated solutions based on image‐derived quantitative measurements for evaluating a variety of diseases in cardiology, radiology and oncology. Our presentation will show three solutions developed by Toshiba for quantifying myocardial contractility, liver fibrosis and tumor perfusion, respectively.The first part of the presentation will demonstrate a solution for quantification of left ventricular contractility, which is an important clinical indicator of the cardiac function. To quantity regional motion abnormalities, a 3D wall motion tracking technique was implemented in an analysis software application. The technique tracks the speckle pattern, frame‐by‐ frame, over a cardiac cycle to calculate a field of motion vectors in 3D. This field is then processed to measure clinical parameters, such as strain values in different directions (longitudinal, circumferential and radial) and volumetric values (left ventricle ejection fraction).The second part of the presentation will demonstrate a solution for evaluating liver fibrosis. Tissue characterization consists in differentiating subtle changes in ultrasound speckle patterns, indicative of the tissue microstructures, which remain non perceptible to human visual inspection. The solution, named Acoustic Structure Quantification (ASQ), was developed to quantify the homogeneity of the speckle pattern using the probability function (PDF) of the echo amplitude in a region of interest. The PDF is estimated using a modified chi‐square distribution. The peak value of that distribution was found to be a promising quantitative parameter to distinguish fibrotic tissue from normal tissue in liver.The last part of the presentation will describe a solution for quantifying perfusion using dynamic contrast enhanced ultrasound (D‐CEUS). The technique utilizes an intravenous injection of microbubble contrast agent, which supports ultrasound imaging of macro‐vascularization. The D‐CEUS technique is a promising application for monitoring tumor response to cancer therapies. Our approach uses a mathematical function to model the contrast uptake (or time‐intensity‐curve) in a region of interest outlining a tumor. From that function, quantitative parameters are derived that are indicative of blood flow dynamics, which vary during the course of the therapy.

G030122 スペックル干渉法における画像相関法を利用した位置補正の剛体回転に関する検討([G03012]材料力学部門一般セッション(12):実験・検出手法)

An effect of rigid body rotation for the speckle image correction for electronic speckle pattern interferometry using DIC is investigated. The relationship between rigid body rotation and the change of static speckle pattern by single beam illumination is compared with the relation of rigid body translation and the change of static pattern. Additionally, the elimination of the interference fringe caused by rotation is examined by the position and the phase correction of the speckle image. Results show that the intensity error of the static speckle pattern by rotation is larger than the intensity error by translation, and the fringe pattern by rotation can be eliminated by the correction in the rotation range less than 10-3 rad.

Optical mouse acting as biospeckle sensor

In this work we propose some experiments with the use of optical computer mouse, associated to low cost lasers that can be used to perform several measurements with applications in industry and in human health monitoring. The mouse was used to grab the movements produced by speckle pattern changes and to get information through the adaptation of its structure. We measured displacements in wood samples under strain, variations of the diameter of an artery due to heart beat and, through a hardware simulation, the movement of an eye, an experiment that could be of low cost help for communication to severely handicapped motor patients. Those measurements were done in spite of the fact that the CCD sensor of the mice is monolithically included into an integrated circuit so that the raw image cannot be accessed. If, as was the case with primitive optical mouse, that signal could be accessed, the quality and usefulness of the measurements could be significantly increased. As it was not possible, a webcam sensor was used for measuring the drying of paint, a standard phenomenon for testing biospeckle techniques, in order to prove the usefulness of the mouse design. The results showed that the use of the mouse associated to a laser pointer could be the way to get metrological information from many phenomena involving the whole field spatial displacement, as well as the use of the mouse as in its prime version allowed to get images of the speckle patterns and to analyze them.