Laser Speckle Technique Research Articles

Assessment of the efficiency of dental excavation methods using laser speckle imaging.

This paper introduces a novel application of the laser speckle technique in dentistry, focusing on assessing the efficiency of dental excavation methods used to remove decayed tooth structure. The aim is to evaluate the efficiency of two chemo-mechanical agents and the high-speed drill using the laser speckle technique, which offers objective, non-invasive, and real-time evaluation capabilities. Extracted human primary molars with active occlusal carious lesions were sectioned into three parts, with each part allocated to one of three groups: Group 1 (Brix3000®), Group 2 (Papacarie DUO®), and Group 3 (High-speed drill mechanical caries removal). Caries removal was performed using the designated agent or method for each group. After caries excavation, speckle imaging using a 632.8 nm laser was conducted. Additionally, SEM was used to acquire micro-photographs of the surface morphology of the treated samples. The findings reveal insights into the comparative efficiency of the three dental excavation agents and methods using the laser speckle technique. The speckle parameters extracted from speckle patterns generated by treated teeth provide valuable information for evaluating the performance of the excavation methods. The scanning electron microscopy images also offer detailed visual evidence to support the analysis. This paper demonstrates the potential of the laser speckle technique for assessing the efficiency of dental excavation methods. The objective, non-invasive, and real-time evaluation provided offers advantages over subjective visual assessment and manual measurements.

Quality evaluation of eggs during shelf-life ambient storage by laser speckle technique

Laser speckle technique is non-destructive, cost-effective with a simple experimental setup, and has been used in the field of agriculture, food processing, medicines etc. A coherent laser source, CCD Camera, and a recording system are needed to record the speckle image. Our objective of this work is to both quantify and visualize the quality of chicken eggs using the non-destructive Laser speckle technique and also to verify the outcomes with other established destructive techniques such as calculation of Haugh Unit (HU), Yolk Index (YI), PH value etc. In this work, we have done the single exposure speckle image as well as the biospeckle activity analysis of eggs stored under ambient conditions at room temperature (29±3°C) for seven days of shelf-life storage. We have approached a new probabilistic method to quantify a single exposure speckle image and the Frequent Motion Image (FMI) method to construct the speckle activity map of the egg's internal constituents. As a result, we have found that the biospeckle activity of eggs decreased by 24–38% after seven days, its internal activity map changed significantly. An egg on the first day of storage shows high biospeckle activity compared to other days. For the single exposure speckle image, the calculated Average energy decreased by 40–60%, and Entropy increased by 10–15%, with significant differences for each day during seven days of shelf storage. The average HU decreases by around 15%, and the YI decreases by 10% during seven days of ambient storage.

Investigation of renal calculi fragmented tracer particles in lithotripsy model by laser speckle technique

We have developed a laser sheet method to evaluate micro-sized fragmented calcium oxalate granular particles created kidney stones suspended in a Newtonian fluid in an in vitro model. These tracer particles are examined by laser optical techniques. An optical setup is configured with a laser sheet to conduct image velocimetry on these calcium oxalate seed particles in the urine environment. The experimental setup involves the application of ultrasonic waves to fragment the calcium oxalate tiny stones of varying sizes and disperse them in random directions in the fluid. The data acquisition process employs double frame-single exposure imaging, which captures images at specified time intervals using a high-resolution CCD camera. This provides information regarding particle displacement and track the flow path within the Newtonian fluid. In addition, the bigger fragmented particles are identified, and their sizes are also measured.

Laser speckle-based estimation of surface condition for designing quieter material

Laser speckle is a non-contact, non-interfering, non-destructive, rapid and controllable technique with a large area of coverage that has attracted much attention for surface analysis of materials. The emergence of different natural cellulosic materials as potential candidates for the replacement of synthetic ones is promising, but their sustainability from the point of view of material design is still in question. Machining of the surface of cellulosic components for making sound-dampening materials has a critical effect on determining their surface condition. Laser speckle is an emerging tool for surface analysis of a variety of materials, and it has important applications in material design and analysis. As a cutting-edge research tool, ultrasonic wave technology has maintained a significant contribution to the design and structural monitoring of composite materials. The present work uses date palm leaf fibers for composite reinforcement. The sound-dampening properties, such as sound absorption and transmission, were analyzed on the basis of surface roughness observed with the laser speckle technique and modified by ultrasonically blended surfactants. The surface roughness of the synthesized material was found to increase with sonication time with an R 2 value of 0.944 and observed fluctuation in roughness data on the surface of the material. The sound absorption coefficient is 0.98 with a transmission loss of 60 dB, for which the material is classified as an ASTM E1050 Class A acoustic material. Further, the method of laser speckle-based roughness estimation is found to be potential tool for the design of any type of quieter material.

Assessment of adulteration in honey by artificial sweeteners using dynamic laser speckle technique

Our research work uses the dynamic laser speckle technique for the first time to analyze the adulteration of “Dabur Honey” with two golden syrups Dhampur Green Golden Syrup (DGGS) and Solar Golden Syrup (SGS) as adulterate. Identifying 25% adulteration in honey by sweeteners is challenging due to several reasons, such as the complexity of honey composition and the similarity of some sweeteners to honey. A spatially filtered He-Ne laser beam is made to pass through adulterated samples. Forwarding scattered light is captured using a charge-coupled device (CCD) camera and Digital Image Processing is used to analyze the images. Seven textures and six features of images are evaluated. For 20% adulteration in honey by both the adulterates, a significant percentage change of 17%, 16%, 16%, 13%, and 11% is observed in Angular Second Moment, Covariance, Autocorrelation, Inertia, and Kurtosis respectively. Additionally, for a 20% adulteration in honey by DGGS and SGS separately, a notable percentage change of 3.8% and 6.6% respectively in the value of Inertia Moment (IM) is obtained. Thus, it is concluded that the above image processing algorithms can be used to detect 20% adulteration in pure honey.

Estimation of reflection loss in a microwave absorbing material based on the laser speckle method

Microwave absorption has received much attention due to its prospective implementation in the extenuation of electromagnetic interference (EMI). The effectiveness of any microwave absorbing material (MAM) is demonstrated by its dielectric dependent properties, such as electric permittivity, magnetic permeability and computed parameters like tangent loss, attenuation and reflection loss (RL) etc. RL is one of the special features of MAMs, allowing the quality of a MAM to be identified by its surface condition and the composition of the fabricated material. As a surface phenomenon, RL depends on factors such as the surface roughness, thickness of the layering of the material and the nature of the surface. The present work emphasizes the effect of surface roughness on RL, studied using the laser speckle technique (LST). Three different compositions of 10 wt%, 30 wt% and 50 wt% of two carbon-based natural fiber composites are studied for microwave absorption. The surface roughness of the material is analyzed, based on the scattering signal of laser speckles recorded in a digital storage oscilloscope. Further, the roughness of the same composition was recorded through a stylus-based profilometer and compared with the measurements from the LST. The results indicate the effectiveness of the laser contrast technique for determining the surface roughness in the design of stealth materials for EMI shielding applications. The RLs of the designed material are found to be greatly enhanced, having a larger surface roughness value with increasing wt%. The RL of the material with 50 wt% composition has been found to be −23.62 dB at 10.498 GHz. This result clearly indicates the applicability of the LST for the estimation of surface conditions to assess the suitability of MAMs in the design of stealth materials.

Assessment of the Use of Infrared Laser for Dynamic Laser Speckle (DLS) Technique

Dynamic laser speckle (DLS) analysis is a very sensitive technique to measure biological activity within samples. In agriculture, the technique is applied to monitor seed germination, but external light, water content, and pigments affect the measurements. DLS systems use visible light sources, typically red lasers, which may exacerbate their influences. The main objective of this work is to assess whether infrared (IR) lasers improve the robustness of DLS measurements in seed germination applications. We develop a system where DLS analysis can be performed simultaneously on visible and IR light. Using the system, we quantify how the DLS signal is affected by pigments and scattering. The results show that the use of IR light reduces the variability of the measurements acquired. DLS systems based on IR light appear to be less sensitive to pigments, and the greater penetration of IR light into samples, which is due to reduced scattering, may contribute to the signal collected being correlated to relevant biological processes within the inner tissue. Additionally, water activity provides less influence on the DLS signal when an IR laser is used. These findings support the wider use of IR lasers in DLS-based instruments for applications in biological samples.

Analysis of peripheral arterial disease (PAD) patients by laser speckle measurement techniques.

Diabetic foot is a well-known problem among patients suffering from peripheral arterial diseases (PAD). This article presents an optical sensor for contactless measurement of the anatomical site based on laser speckle techniques. The sensor illuminates the inspected tissue and analyzes the captured back-reflected light from the time-changing speckle patterns. An occlusion test was implemented to provide a statistical parameter to differentiate between a low perfused and a healthy foot. A clinical study of 15 subjects was conducted. The video was analyzed by two methods: dynamic laser speckle (DLS) and laser speckle contrast analysis (LASCA). Data analysis included several classification models, where the KNN model exhibited maximum performance. These findings suggest that a simple and inexpensive system for PAD monitoring can be designed for home use and/or in community clinics.

Assessment of milk fermentation process at three temperatures using laser speckle technique

This research work contains information on speckle activity at different stages of the milk fermentation process at temperatures of 24 °C, 32 °C and 40 °C, using the dynamic laser speckle technique for the first time, to the best of our knowledge. Image processing algorithms such as inertia moment (IM), the absolute value of differences, the probability mass function of regular difference, spatial-temporal speckle correlation and 3D graphs of spectral images have been applied to show the speckle activity of the samples. All the methods show that the speckle activity of the sample is higher at the semisolid stage than at the liquid stage of the sample. Also, higher speckle activity of the curd has been observed at 40 °C (11 576.18 using IM) than at 32 °C (8550.92 using IM), followed by that at 24 °C (4855.88 using IM). At 40 °C, the thermal motion of curd particles is higher than that of the curd particles at the other two temperatures, and are responsible for the higher speckle activity. The preparation time for curd at 40 °C (5 h) is lower in comparison to the curds at 24 °C (10 h) and 32 °C (6 h). The lowest value for the titratable acidity of the curd prepared at 24 °C shows a lower % lactic acid than the curd at 32 °C and that at 40 °C. The lowest value of susceptibility to syneresis of the curd at 40 °C (30.00) represents a more compact curd than the curds at 32 °C (37.50) and 24 °C (45.00). The horizontal speckle grain size of the curd has been calculated using an autocovariance function; the highest is for curd fermented at 40 °C (12.34 μm), followed by that at 32 °C (11.59 μm), then that at 24 °C (10.96 μm).

Downregulation of miR-491-5p promotes neovascularization after traumatic brain injury.

MicroRNA-491-5p (miR-491-5p) plays an important role in regulating cell proliferation and migration; however, the effect of miR-491-5p on neovascularization after traumatic brain injury remains poorly understood. In this study, a controlled cortical injury model in C57BL/6 mice and an oxygen-glucose deprivation model in microvascular endothelial cells derived from mouse brain were established to simulate traumatic brain injury in vivo and in vitro, respectively. In the in vivo model, quantitative real-time-polymerase chain reaction results showed that the expression of miR-491-5p increased or decreased following the intracerebroventricular injection of an miR-491-5p agomir or antagomir, respectively, and the expression of miR-491-5p decreased slightly after traumatic brain injury. To detect the neuroprotective effects of miR-491-p, neurological severity scores, Morris water maze test, laser speckle techniques, and immunofluorescence staining were assessed, and the results revealed that miR-491-5p downregulation alleviated neurological dysfunction, promoted the recovery of regional cerebral blood flow, increased the number of lectin-stained microvessels, and increased the survival of neurons after traumatic brain injury. During the in vitro experiments, the potential mechanism of miR-491-5p on neovascularization was explored through quantitative real-time-polymerase chain reaction, which showed that miR-491-5p expression increased or decreased in brain microvascular endothelial cells after transfection with an miR-491-5p mimic or inhibitor, respectively. Dual-luciferase reporter and western blot assays verified that metallothionein-2 was a target gene for miR-491-5p. Cell counting kit 8 (CCK-8) assay, flow cytometry, and 2?,7?-dichlorofluorescein diacetate (DCFH-DA) assay results confirmed that the downregulation of miR-491-5p increased brain microvascular endothelial cell viability, reduced cell apoptosis, and alleviated oxidative stress under oxygen-glucose deprivation conditions. Cell scratch assay, Transwell assay, tube formation assay, and western blot assay results demonstrated that miR-491-5p downregulation promoted the migration, proliferation, and tube formation of brain microvascular endothelial cells through a metallothionein-2-dependent hypoxia-inducible factor-1α/vascular endothelial growth factor pathway. These findings confirmed that miR-491-5p downregulation promotes neovascularization, restores cerebral blood flow, and improves the recovery of neurological function after traumatic brain injury. The mechanism may be mediated through a metallothionein-2-dependent hypoxia-inducible factor-1α/vascular endothelial growth factor signaling pathway and the alleviation of oxidative stress. All procedures were approved by Ethics Committee of the First Affiliated Hospital of Chongqing Medical University, China (approval No. 2020-304) on June 22, 2020.

Evaluation of stability of laser ablated colloidal silver nanoparticles using dynamic laser speckle technique

Dynamic laser speckle technique is a non-destructive optical method used for evaluating the activities of biological and non-biological specimens. Since stability of nanoparticles is one of the main concerns for its various applications, this work presents a novel approach of dynamic laser speckle technique to study the stability of colloidal silver nanoparticles in ethanol solution. Pulsed laser ablation process using nanosecond laser was used for synthesizing the nanoparticles. The size of silver nanoparticles was measured using Dynamic Light Scattering (DLS) technique. Statistical methods such as intensity structure function, inertia moment of time history of speckle patterns and two dimensional cross-correlation were used to extract the information regarding the stability of nanoparticles. The stability analysis of the nanoparticles was further confirmed using UV-Visible absorption spectroscopy.

Surface Roughness Analysis of Cotton Fabric by Laser Speckle Technique

In the textile industry, disposing the waste products after dyeing causes a major environmental issue. The mordants used leads to adverse effect for the human and other living organisms. Plasma processing is ecofriendly and it does not produce any waste, pollution free on the environment. Therefore, low temperature plasma treatments are set to make a revolution in textile industry. The present work is to modify the surface of cotton fabric by oxygen plasma treatment with operating parameters such as exposure time, discharge potential and base pressure are kept constant as 5 min, 400V and 9 Pascal respectively. The surface roughness of the fabric is analyzed by laser speckle technique for plasma treated and mordanted fabric and then corresponding results were reported. Further, we observed the increase in surface roughness of the fabric after plasma treatment.

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.

Digital laser speckle technique for generating deflection, slope, and curvature contours of bent plates

A digital method is proposed whereby spatial speckles created when an optically rough surface is illuminated by a diffuse coherent laser beam are used to generate slope contour fringes. This is done by photographing the speckles contained in a parallel plane in front of the plate before and after deformation. The resulting photographs are then fast Fourier transformed twice and numerically compared with the digital speckle correlation software called computer-aided speckle interferometry to produce slope contours of the plate. The slope contour data are then stored in a computational array. The curvature contours are generated by numerical differentiation of the slope data; similarly, the deflection contours are generated by numerical integration of the slope data. The curvature data can then be further used in conjunction with plate theory to obtain the bending and twisting moments the plates experience as well as the stress distribution in the surface of the plate. The method is simple and straight forward. A comparison with several other techniques is presented.

Non-contact surface roughness measurement using laser speckle technique

This paper deals with selected contact type stylus method and non-contact type machine vision method using laser speckle for components prepared by grinding of AISI 1040 steel with a variety of wheels and varied depth of cut. In this interactive study, Optical method based on statistical properties of binary images is proposed for machined surfaces. Grounded metal surfaces are used to develop a binary digitized speckle pattern by a beam of He-Ne laser light source. High end camera is used to capture the image of a speckle pattern. White to black pixels ratios is computed from the binary images using image processing toolbox in Matlab. The correlation is developed between white to black pixels ratio and measured two-dimensional surface roughness parameter. Two-dimensional surface roughness parameters are recorded using a contact-type surface profilometer. The results which opted, clearly supports that these parameters have a relationship with a degree of surface roughness. A linear relationship is observed between parameter obtained from proposed technique and measured value of surface roughness using surface profilometer. The statistical analysis represents the performance of maximum relative error in prediction of surface roughness is 9%.

Study on the cerebral microcirculation of rats with subarachnoid hemorrhage by using laser speckle technique

Objective To study the value of laser speckle technique in measuring blood flow changes in the cerebral microcirculation of rats with subarachnoid hemorrhage (SAH). Methods Rat double blood injection method was used to establish the model of SAH. Rats were divided into control group, SAH 5-day group, SAH 7-day group, saline 5-day group and saline 7-day group. After sensory nerve function examination, cerebral cortical blood flow was measured by laser speckle technique, and apoptotic index and electron microscopy were detected. SPSS 17.0 statistical software was used to make statistical analysis by variance analysis or non-parametric test. Results SAH 5-day group showed significant sensory dysfunction. There were significant differences between SAH 5-day group (12.100±1.287) and control group (15), SAH 7-day group (14.700±0.675), saline 5-day group (14.900±0.316) and saline 7-day group (15) (Z values were -4.059, -3.655, -3.908, -4.059, respectively; respectively P<0.01); Electron microscopy showed that the morphology of neurons in the control group and saline injection groups was basically normal; neurons in the SAH 5-day group showed obvious edema and extensive neuronal degeneration or necrosis; neurons in the SAH 7-day group showed slight swelling and some neurons had degeneration or necrosis. There were obvious apoptotic cells in cerebral cortex of SAH groups. The apoptotic index of SAH 5-day group [(19.870±1.909)%] and control group [(1.840±0.474)%], SAH 7-day group [(13.770±1.924)%], saline 5-day group [(1.740±0.299)%], saline 7-day group [(1.790±0.407)%] had statistical differences (t values were 28.985, 7.117, 29.670, 29.291, respectively; respectively P<0.01). SAH 7-day group and control group, SAH 5-day group, saline 5-day group, saline 7-day group had statistical differences (t values were 19.037, -7.117, 19.537, 19.263, respectively; respectively P<0.01). Cerebral cortical blood flow in SAH groups decreased, and the most obvious decrease was found in SAH 5-day group (64.000±6.218), compared with control group (106.000±13.081), SAH 7-day group (75.700±8.274), saline 5-day group (105.100±13.169), saline 7-day group (104.100±10.609). There were significant differences (t values were -9.170, -3.575, -8.924, -10.312, respectively; successively P<0.01, 0.05, 0.01, 0.01). There were significant differences between SAH 7-day group and control group, SAH 5-day group, saline 5-day group and saline 7-day group (t values were -6.191, 3.575, -5.978 and -6.675, respectively; successively P<0.01, 0.05, 0.01, 0.01, 0.01). Conclusion Laser speckle technique is suitable for studying the blood flow changes of cerebral microcirculation in SAH rats. Key words: Subarachnoid hemorrhage; Cerebral microcirculation; Cerebral blood flow; Laser speckle

A Review On Absorption Spectroscopy and Laser Speckle Techniques for Wound Healing Assessment

A Review On Absorption Spectroscopy and Laser Speckle Techniques for Wound Healing Assessment

Decreased cerebral blood flow and hemodynamic parameters during acute hyperglycemia in mice model observed by dual-wavelength speckle imaging.

In this study, we use dual-wavelength optical imaging-based laser speckle technique to assess cerebral blood flow and metabolic parameters in a mouse model of acute hyperglycemia (high blood glucose). The effect of acute glucose levels on physiological processes has been extensively described in multiple organ systems such as retina, kidney, and others. We postulated that hyperglycemia also alters brain function, which in turn can be monitored optically using dual-wavelength laser speckle imaging (DW-LSI) platform. DW-LSI is a wide-field, noncontact optical imaging modality that integrates the principles of laser flowmetry and oximetry to obtain macroscopic information such as hemoglobin concentration and blood flow. A total of eight mice (C57/BL6) were used, randomized into two groups of normoglycemia (control, n = 3) and hyperglycemia (n = 5). Hyperglycemia was induced by intraperitoneal injection of a commonly used anesthetic drug combining ketamine and xylazine (KX combo). We found that this KX combo increases blood glucose (BG) levels from 150 to 350 mg/dL, approximately, when measured 18 minutes post-administration. BG continues to increase throughout the test period, with BG reaching an average of 463 ± 20.34 mg/dL within 60 minutes. BG levels were measured every 10 minutes from tail blood using commercially available glucometer. Experimental results demonstrated reductions in cerebral blood flow (CBF) by 55%, tissue oxygen saturation (SO2 ) by 15%, and cerebral metabolic rate of oxygen (CMRO2 ) by 75% following acute hyperglycemia. The observed decrease in these parameters was consistent with results reported in the literature, measured by a variety of experimental techniques. Measurements with laser Doppler flowmetry (LDF) were also performed which confirmed a reduction in CBF following acute hyperglycemia. In summary, our findings indicate that acute hyperglycemia modified brain hemodynamic response and induced significant changes in blood flow and metabolism. As far as we are aware, the implementation of the DW-LSI to monitor brain hemodynamic and metabolic response to acute hyperglycemia in intact mouse brain has not been previously reported.

Application of transparent soil model tests to study the soil-rock interfacial sliding mechanism

When transparent soil technology is used to study the displacement of a slope, the internal deformation of the slope can be visualized. We studied the sliding mechanism of the soil-rock slope by using transparent soil technology and considering the influence of the rock mass Barton joint roughness coefficient, angle of the soil mass, angle of the rock mass and soil thickness factors on slope stability. We obtained the deformation characteristics of the soil and rock slope with particle image velocimetry and the laser speckle technique. The test analysis shows that the slope sliding can be divided into three parts: displacements at the top, the middle, and the bottom of the slope; the decrease in the rock mass Barton joint roughness coefficient, and the increase in soil thickness, angles of the rock mass and soil mass lead to larger sliding displacements. Furthermore, we analyzed the different angles between the rock mass and soil thickness. The test result shows that the displacement of slope increases with larger angle of the rock mass. Conclusively, all these results can help to explain the soil-rock interfacial sliding mechanism.

Different methods for characterizing surface roughness using laser speckle technique

In this work, results from an optical technique (laser speckle technique) for measuring surface roughness was done by using statistical properties of speckle pattern from the point of view of computer image texture analysis. Four calibration relationships were used to cover wide range of measurement with the same laser speckle technique. The first one is based on intensity contrast of the speckle, the second is based on analysis of speckle binary image, the third is on size of speckle pattern spot, and the latest one is based on characterization of the energy feature of the gray level co-occurrence matrices for the speckle pattern. By these calibration relationships surface roughness of an object surface can be evaluated within these relations ranges from single speckle pattern image which was taken from the surface.