Showing papers on "Speckle imaging published in 2008"
TL;DR: This technique can visualize vessel-size-dependent vascular shutdown and transient vascular occlusion during Visudyne photodynamic therapy and may provide opportunities for studying therapeutic effects of antivascular treatments without on exogenous contrast agent.
Abstract: We report on imaging of microcirculation by calculating the speckle variance of optical coherence tomography (OCT) structural images acquired using a Fourier domain mode-locked swept-wavelength laser. The algorithm calculates interframe speckle variance in two-dimensional and three-dimensional OCT data sets and shows little dependence to the Doppler angle ranging from 75 degrees to 90 degrees . We demonstrate in vivo detection of blood flow in vessels as small as 25 microm in diameter in a dorsal skinfold window chamber model with direct comparison with intravital fluorescence confocal microscopy. This technique can visualize vessel-size-dependent vascular shutdown and transient vascular occlusion during Visudyne photodynamic therapy and may provide opportunities for studying therapeutic effects of antivascular treatments without on exogenous contrast agent.
677 citations
TL;DR: A new Multi-Exposure Speckle Imaging (MESI) instrument that has potential to obtain quantitative baseline flow measures and a new speckle model which can discriminate flows in the presence of static scatters is presented.
Abstract: Laser Speckle Contrast Imaging (LSCI) is a minimally invasive full field optical technique used to generate blood flow maps with high spatial and temporal resolution. The lack of quantitative accuracy and the inability to predict flows in the presence of static scatterers such as an intact or thinned skull have been the primary limitation of LSCI. We present a new Multi-Exposure Speckle Imaging (MESI) instrument that has potential to obtain quantitative baseline flow measures. We show that the MESI instrument extends the range over which relative flow measurements are linear. We also present a new speckle model which can discriminate flows in the presence of static scatters. We show that in the presence of static scatterers the new model used along with the new MESI instrument can predict correlation times of flow consistently to within 10% of the value without static scatterers compared to an average deviation of more than 100% from the value without static scatterers using traditional LSCI. We also show that the new speckle model used with the MESI instrument can maintain the linearity of relative flow measurements in the presence of static scatterers.
311 citations
TL;DR: Through a series of simulations and experiments, it is demonstrated that the frequently cited criterion of matching speckle size to detector element (pixel) size in laser Speckle contrast imaging (LSCI) has the detrimental effect of reducing the contrast and thereby decreasing the variation in the laser speckel contrast image.
Abstract: Through a series of simulations and experiments, we demonstrate that the frequently cited criterion of matching speckle size to detector element (pixel) size in laser speckle contrast imaging (LSCI) has the detrimental effect of reducing the contrast and thereby decreasing the variation in the laser speckle contrast image. Unlike quasi-elastic light scattering, where this matching condition has been shown to maximize the signal-to-noise ratio, in LSCI, the minimum speckle size must exceed the Nyquist criterion in order to maximize the contrast of the speckle patterns.
232 citations
TL;DR: The underlying theory is reviewed, the impact of various analytic models for relating measured intensity fluctuations to scatterer motion is explored, and some of the practical issues associated with the measurement and subsequent data processing are addressed.
Abstract: The ultimate objective of laser speckle flowmetry (and a host of specific implementations such as laser speckle contrast analysis, LASCA or LSCA; laser speckle spatial contrast analysis, LSSCA; laser speckle temporal contrast analysis, LSTCA; etc.) is to infer flow velocity from the observed speckle contrast. Despite numerous demonstrations over the past 25 years of such a qualitative relationship, no convincing quantitative relationship has been proven. One reason is a persistent mathematical error that has been propagated by a host of workers; another is a misconception about the proper autocorrelation function for ordered flow. Still another hindrance has been uncertainty in the specific relationship between decorrelation time and local flow velocity. Herein we attempt to dispel some of these errors and misconceptions with the intent of turning laser speckle flowmetry into a quantitative tool. Specifically we review the underlying theory, explore the impact of various analytic models for relating measured intensity fluctuations to scatterer motion, and address some of the practical issues associated with the measurement and subsequent data processing.
226 citations
TL;DR: In this article, the authors investigated the reconstruction properties of the Kiepenheuer-Institut Speckle Interferometry Package (KISIP) code, with focus on its phase reconstruction capabilities and photometric accuracy.
Abstract: Context Adaptive optics systems are used on several advanced solar telescopes to enhance the spatial resolution of the recorded data In all cases, the correction remains only partial, requiring post-facto image reconstruction techniques such as speckle interferometry to achieve consistent, near-diffraction limited resolutionAims This study investigates the reconstruction properties of the Kiepenheuer-Institut Speckle Interferometry Package (KISIP) code, with focus on its phase reconstruction capabilities and photometric accuracy In addition, we analyze its suitability for real-time reconstructionMethods We evaluate the KISIP program with respect to its scalability and the convergence of the implemented algorithms with dependence on several parameters, such as atmospheric conditions To test the photometric accuracy of the final reconstruction, comparisons are made between simultaneous observations of the Sun using the ground-based Dunn Solar Telescope and the space-based Hinode/SOT telescopeResults The analysis shows that near real-time image reconstruction with high photometric accuracy of ground-based solar observations is possible, even for observations in which an adaptive optics system was utilized to obtain the speckle data
194 citations
TL;DR: This work demonstrates that this local contrast can be characterized in terms of a log-normal distribution and shows that the two defining parameters of this model can in turn be expressed in Terms of the minimum speckle size and the extent of the local neighborhood.
Abstract: In describing the first-order properties of laser speckle under polarized illumination conditions, it is almost an article of faith that the contrast is unity. In many processing schemes, however, the contrast defined as the quotient of the standard deviation and the mean is calculated over a localized spatial region. In such cases, this local contrast displays a distribution of values that can depart substantially from unity. Properties of this distribution depend on details of the data acquisition and on the size of the local neighborhood over which the contrast is calculated. We demonstrate that this local contrast can be characterized in terms of a log-normal distribution. Further, we show that the two defining parameters of this model can in turn be expressed in terms of the minimum speckle size and the extent of the local neighborhood. Performance of the model is illustrated with some typical optical coherence tomography data.
136 citations
TL;DR: This study evaluated the use of two velocity distribution assumptions (Lorentzian- and Gaussian-based) to calculate speckle flow index (SFI) values and derived equations form the basis for simplified calculations of SFI values.
Abstract: Since blood flow is tightly coupled to the health status of biological tissue, several instruments have been developed to monitor blood flow and perfusion dynamics. One such instrument is laser speckle imaging. The goal of this study was to evaluate the use of two velocity distribution assumptions (Lorentzian- and Gaussian-based) to calculate speckle flow index (SFI) values. When the normalized autocorrelation function for the Lorentzian and Gaussian velocity distributions satisfy the same definition of correlation time, then the same velocity range is predicted for low speckle contrast (0 < C < 0.6) and predict different flow velocity range for high contrast. Our derived equations form the basis for simplified calculations of SFI values.
126 citations
TL;DR: This work derives the second-order oriented partial-differential equations for denoising in electronic-speckle-pattern interferometry fringe patterns from two points of view based on variational methods and a filtering method based on controlling diffusion direction.
Abstract: We derive the second-order oriented partial-differential equations (PDEs) for denoising in electronic-speckle-pattern interferometry fringe patterns from two points of view. The first is based on variational methods, and the second is based on controlling diffusion direction. Our oriented PDE models make the diffusion along only the fringe orientation. The main advantage of our filtering method, based on oriented PDE models, is that it is very easy to implement compared with the published filtering methods along the fringe orientation. We demonstrate the performance of our oriented PDE models via application to two computer-simulated and experimentally obtained speckle fringes and compare with related PDE models.
88 citations
TL;DR: It was shown that application of a diffractive optical element (DOE) with a Barker code phase shape could use only natural display scanning motion for speckle suppression and did not need an additional image plane and complicated relay optics.
Abstract: The theory of speckle noise in a scanning beam is presented. The general formulas for the calculation of speckle contrast, which apply to any scanning display, are obtained. It is shown that the main requirement for successful speckle suppression in a scanning display is a narrow autocorrelation peak and low sidelobe level in the autocorrelation function of the complex amplitude distribution across a scanning light beam. The simple formulas for speckle contrast for a beam with a narrow autocorrelation function peak were obtained. It was shown that application of a diffractive optical element (DOE) with a Barker code phase shape could use only natural display scanning motion for speckle suppression. DOE with a Barker code phase shape has a small size and may be deposited on the light modulator inside the depth of the focus of the reflected beam area, and therefore, it does not need an additional image plane and complicated relay optics.
81 citations
TL;DR: A novel approach for three-dimensional measurements that includes the projection of coherent light through ground glass that generates random speckle patterns on the object or on the camera, depending if the configuration is transmissive or reflective.
Abstract: We present a novel approach for three-dimensional (3D) measurements that includes the projection of coherent light through ground glass. Such a projection generates random speckle patterns on the object or on the camera, depending if the configuration is transmissive or reflective. In both cases the spatially random patterns are seen by the sensor. Different spatially random patterns are generated at different planes. The patterns are highly random and not correlated. This low correlation between different patterns is used for both 3D mapping of objects and range finding.
78 citations
TL;DR: Digital holography generally offers more flexibility than conventional holographic interferometry and speckle interferometrics because of its simple setup and easy accessibility for 3D surfaces as discussed by the authors.
Abstract: Digital holography generally offers more flexibility than conventional holographic interferometry and speckle interferometry because of its simple setup and easy accessibility for 3D surfaces.
TL;DR: Experimental results demonstrate that speckle noise is effectively avoided in severely distorted signals, thus improving the signal-to-noise ratio (SNR) significantly.
TL;DR: The performance of the BEMD method to denoise DSPI fringes is analyzed using computer-simulated data, and the results are compared with those obtained by means of a previously developed one-dimensional empirical mode decomposition approach.
Abstract: We propose a bidimensional empirical mode decomposition (BEMD) method to reduce speckle noise in digital speckle pattern interferometry (DSPI) fringes The BEMD method is based on a sifting process that decomposes the DSPI fringes in a finite set of subimages represented by high and low frequency oscillations, which are named modes The sifting process assigns the high frequency information to the first modes, so that it is possible to discriminate speckle noise from fringe information, which is contained in the remaining modes The proposed method is a fully data-driven technique, therefore neither fixed basis functions nor operator intervention are required The performance of the BEMD method to denoise DSPI fringes is analyzed using computer-simulated data, and the results are also compared with those obtained by means of a previously developed one-dimensional empirical mode decomposition approach An application of the proposed BEMD method to denoise experimental fringes is also presented
TL;DR: GPU (Graphics Processing Unit) is introduced into the data processing framework of laser speckle contrast imaging to achieve fast and high-resolution blood flow visualization on PCs by exploiting the high floating-point processing power of commodity graphics hardware.
Abstract: Laser speckle contrast analysis (LASCA) is a non-invasive, full-field optical technique that produces two-dimensional map of blood flow in biological tissue by analyzing speckle images captured by CCD camera. Due to the heavy computation required for speckle contrast analysis, video frame rate visualization of blood flow which is essentially important for medical usage is hardly achieved for the high-resolution image data by using the CPU (Central Processing Unit) of an ordinary PC (Personal Computer). In this paper, we introduced GPU (Graphics Processing Unit) into our data processing framework of laser speckle contrast imaging to achieve fast and high-resolution blood flow visualization on PCs by exploiting the high floating-point processing power of commodity graphics hardware. By using GPU, a 12-60 fold performance enhancement is obtained in comparison to the optimized CPU implementations.
TL;DR: This approach to generating sequences of random realizations with prescribed correlations should prove useful in modeling such phenomena as dynamic light scatter, flow-dependent laser speckle contrast, and propagation of spatial coherence.
Abstract: Use of a copula for generating a sequence of correlated speckle patterns is introduced. The chief characteristic of this algorithm is that it generates a continuous speckle sequence with a specified evolution of the correlation and does so with just two arrays of random numbers. Thus, physically realistic temporally varying speckle patterns with proper first- and second-order statistics are easily realized. We illustrate use of the algorithm for generating sequences with prescribed Gaussian, exponential, and equal-interval correlations and demonstrate how correlation times can be specified independently. This approach to generating sequences of random realizations with prescribed correlations should prove useful in modeling such phenomena as dynamic light scatter, flow-dependent laser speckle contrast, and propagation of spatial coherence.
TL;DR: In this paper, a simple camera with electron-multiplication CCD, fast frame rate, and a pixel scale of 15 mas was tested at the SOAR 4m telescope in the speckle-interferometry regime.
Abstract: A simple camera with electron-multiplication CCD, fast frame rate, and a pixel scale of 15 mas is described. This instrument was tested at the SOAR 4-m telescope in the speckle-interferometry regime. The data were processed by the standard speckle algorithm permitting derivation of binary-star parameters. We observed 29 objects with separations from 21 mas to 1.32'', mostly southern binaries with known orbits. Some pairs require orbit revision. Two spectroscopic binaries HIP 9631 and HIP 11072 and the astrometric binary κ For are resolved for the first time, while three objects were unresolved.
TL;DR: The presented speckle interferometry code is capable to run in future real-time reconstruction applications at solar telescopes if care is taken that the multi-processor environments have low latencies between the processing nodes.
Abstract: We present a speckle interferometry code for solar data taken with the help of an adaptive optics (AO) system.
As any AO correction is only partial there is a need to use post-facto reconstruction algorithms to achieve the
diffraction limit of the telescope over a large field of view most of the observational time. However, data rates of
current and future solar telescopes are ever increasing with camera chip sizes. In order to overcome the tedious
and expensive data handling, we investigate the possibility to use the presented speckle reconstruction program
in a real-time application at telescope sites themselves. The program features Fourier phase reconstruction
algorithms using either an extended Knox-Thompson or a triple correlation scheme. The Fourier amplitude
reconstruction has been adjusted for use with models that take the correction of an AO system into account.
The code has been written in the C programming language and optimized for parallel processing in a multi-processor
environment. We analyze the scalability of the code to find possible bottlenecks. Finally, the phase
reconstruction accuracy is validated by comparison of reconstructed data with satellite data. We conclude that
the presented code is capable to run in future real-time reconstruction applications at solar telescopes if care is
taken that the multi-processor environments have low latencies between the processing nodes.
TL;DR: In this article, an effective method for reducing the speckle noise in digital holography is proposed, which utilizes the multiple holograms which are generated by rotating the illuminating light continuously.
Abstract: An effective method for reducing the speckle noise in digital holography is proposed in this paper. Different from the methods based on classical filtering technique, it utilizes the multiple holograms which are generated by rotating the illuminating light continuously. The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns. Hence by properly averaging the reconstructed intensity fields, the speckle noises can be reduced greatly. Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.
TL;DR: In this paper, a phase unwrapping software has been developed using discrete cosine transform (DCT) to generate the three-dimensional (3-D) profiles of the machined surface.
TL;DR: Results show that leached fiber bundles may reliably transmit laser speckle images in the presence of cardiac motion, providing a viable option to conduct intracoronary LSI.
Abstract: Laser speckle imaging (LSI), a new technique that measures an index of plaque viscoelasticity, has been investigated recently to characterize atherosclerotic plaques. These prior studies demonstrated the diagnostic potential of LSI for detecting high-risk plaques and were conducted ex vivo. To conduct intracoronary LSI in vivo, the laser speckle pattern must be transmitted from the coronary wall to the image detector in the presence of cardiac motion. Small-diameter, flexible optical fiber bundles, similar to those used in coronary angioscopy, may be incorporated into an intravascular catheter for this purpose. A key challenge is that laser speckle is influenced by inter-fiber leakage of light, which may be exacerbated during bundle motion. In this study, we tested the capability of optical fiber bundles to transmit laser speckle patterns obtained from atherosclerotic plaques and evaluated the influence of motion on the diagnostic accuracy of fiber bundle-based LSI. Time-varying helium-neon laser speckle images of aortic plaques were obtained while cyclically moving the flexible length of the bundle to mimic coronary motion. Our results show that leached fiber bundles may reliably transmit laser speckle images in the presence of cardiac motion, providing a viable option to conduct intracoronary LSI.
TL;DR: This paper combines the spatial and temporal approaches to quantifying the laser speckle to achieve a flexible, quantitative scheme that allows incorporation of prior knowledge of the subject motion.
Abstract: The objective in many laser speckle imaging schemes is to relate the calculated laser speckle contrast to the object
motion. In quantifying the laser speckle there are camps that advocate either the spatial or the temporal approach. Each
has its merits. In this paper, we attempt to combine these two approaches to achieve a flexible, quantitative scheme.
Additionally, we present some approaches that allow incorporation of prior knowledge of the subject motion. These
algorithms are flexible and fast because they rely on vectorized processing. We demonstrate performance of these
processing schemes on simulated and experimental speckle data.
TL;DR: In this article, a microscopic TV holographic system using a long working distance microscope with an extended zoom range has been developed for microelements and MEMS deformation and 3-D surface profile analysis.
TL;DR: An optical phase measurement method based on the Hilbert transform for the analysis of a time series of speckle interferograms modulated by a temporal carrier is presented and the equivalence between the phase recovery approaches that are based onThe Hilbert and the Fourier transforms is shown.
Abstract: We present an optical phase measurement method based on the Hilbert transform for the analysis of a time series of speckle interferograms modulated by a temporal carrier. We discuss the influence of nonmodulating pixels, modulation loss, and noise that affect the bias and modulation intensities of the interferometric signal and propose the application of the empirical mode decomposition method for its minimization. We also show the equivalence between the phase recovery approaches that are based on the Hilbert and the Fourier transforms. Finally, we present a numerical comparison between these methods using computer-simulated speckle interferograms modulated with a temporal carrier.
TL;DR: In this paper, the authors studied the formation cause of speckle noise in the reconstructed image of digital holography and acquired the conclusion that the small size of hologram aperture diffraction aggravates the noise of reconstructed image and has been one of the primary noise sources in the reconstruction process.
TL;DR: In this paper, the calibration of a full-field speckle interferometry strain measurement system using the calibration specimen and protocol defined in the Standardisation Project for Optical Techniques of Strain measurement (SPOTS) standard was described.
Abstract: This study describes the calibration of a full-field speckle interferometry strain measurement system using the calibration specimen and protocol defined in the Standardisation Project for Optical Techniques of Strain measurement (SPOTS) standard. The specimen was based on the monolithic embodiment of a four-point bending test and was manufactured from aluminium following the SPOTS design. Strain-gauge rosettes attached to the upper and lower faces of the beam were used to derive two correction factors of an analytical expression that predicted the strains generated in the gauge section of the beam. Following the SPOTS protocol, the comparison of measured and predicted strains yielded two fit parameters and their associated uncertainties for each of three displacement-load steps which indicated the closeness of the data sets. An acceptable calibration was achieved for the single normal component of in-plane strain considered in this study, for each load step employed. For the highest load range, which generated a maximum strain of approximately 810 μstrain in the gauge section, the overall calibration uncertainty was found to be 35.3 μstrain, which in relative terms can be expressed as 2.2% of the strain measurement range for which the instrument was calibrated.
TL;DR: In this article, a variety of algorithms for simulating objective and subjective speckle for static and dynamic object fields are presented, including Electronic Speckle Pattern Interferometry (ESPI), LSI, OCT, Optical Coherence Tomography (OCT), etc.
Abstract: The speckle phenomenon is observed in any coherent imaging modality such as synthetic aperture radar, optical coherence tomography, ultrasound, or any number of measurement schemes involving laser illumination. Quantitative interpretation of the data from such measurement schemes (whether imaging or non-imaging) often hinges on accurate knowledge of the statistical behavior of the speckle phenomenon. To complement experimental measurements, researchers often turn to computer simulation of the phenomenon of interest. Over the years we have developed a variety of algorithms for simulating objective and subjective speckle for static and dynamic object fields. In this paper we detail the implementation of these algorithms and illustrate their use in a range of applications that include Electronic Speckle Pattern Interferometry (ESPI), Laser Speckle Imaging (LSI), Optical Coherence Tomography (OCT), etc.
TL;DR: In this article, the authors presented results for 353 speckle interferometric observations of double stars, obtained in 2003 and 2004 at the USNO Flagstaff Station using the 1.55 m Kaj Strand Astrometric Reflector.
Abstract: Results are presented for 353 speckle interferometric observations of double stars, obtained in 2003 and 2004 at the USNO Flagstaff Station using the 1.55 m Kaj Strand Astrometric Reflector. Separations range from 012 to 742, with a median of 042. These two observing runs concentrated on systems in need of improved orbital elements, and new solutions have been determined for 17 systems as a result.
TL;DR: An algorithm able to retrieve the phase in speckle interferometry by a single intensity pattern acquired in a deformed state is presented, provided that the integrated Speckle field is resolved in the reference condition in terms of mean intensity, modulation amplitude and phase.
Abstract: The paper presents an algorithm able to retrieve the phase in speckle interferometry by a single intensity pattern acquired in a deformed state, provided that the integrated speckle field is resolved in the reference condition in terms of mean intensity, modulation amplitude and phase. The proposed approach, called throughout the paper "one-step", can be applied for studying phenomena whose rapid evolution does not allow the application of a standard phase-shifting procedure, which, on the other hand, must be applied at the beginning of the experiment. The approach was proved by an experimental test reported at the end of the paper.
TL;DR: In this article, a strategy to overcome the distortions in the calculated phase profiles is discussed, where the double aperture mask in front of the imaging system is one of the methods for introducing the spatial carrier frequency for phase evaluation, and the contrast of the correlation fringe obtained using this approach is much improved.
Abstract: Spatial phase shifting technique in digital speckle pattern interferometry (DSPI) and digital shearography (DS) provides the phase information due to the object displacement from two images, one stored before and other after loading. The technique needs a carrier fringe system. The double aperture mask in front of the imaging system is one of the methods for introducing the spatial carrier frequency for phase evaluation. The size of the apertures and their separation are important criteria to obtain appropriate phase shift/column within the desired size of the speckle for phase retrieval. The assumptions of constant intensity and phase on adjacent pixels of the camera while calculating phase in spatial phase shifting (SPS) are not met as the speckled object wave contains intensity and phase gradients, resulting in distortions in the calculated phase profiles. In this paper we discuss a strategy to overcome these problems. The contrast of the correlation fringe obtained using this approach is much improved...
TL;DR: In this article, surface strain measurements made using a pulsed laser shearography system from a thermally loaded test object, rotating at 610 rpm, are presented, where Fibre-optic imaging bundles are used to transfer images from the observation positions to the shearing interferometer and CCD camera.
Abstract: In this paper, surface strain measurements made using a pulsed laser shearography system from a thermally loaded test object, rotating at 610 rpm, are presented. The shearography instrument described here has four measurement channels consisting of four observation directions and a single illumination direction. The use of multiple channels, combined with orthogonal shear directions, enables the measurement of the six orthogonal components of displacement gradient required to determine the surface strain. Fibre-optic imaging bundles are used to transfer images from the observation positions to the shearing interferometer and CCD camera. Spatial multiplexing of the images onto the CCD camera allows for simultaneous acquisition of data from the four views. The repetition rate of a pulsed Nd:YAG laser and the framing rate of the CCD camera were synchronized with the rotation rate of the test object, which enabled the capture of images recorded on subsequent revolutions of the object. Analysis of the deformation-induced phase change between recordings was performed using the spatial carrier technique. The orthogonal displacement gradient components were obtained from the unwrapped phase measurements using a matrix transformation based on the sensitivity vector of each of the four measurement channels.