Showing papers on "Speckle pattern published in 1996"

Laser speckle contrast analysis (LASCA): a nonscanning, full-field technique for monitoring capillary blood flow

Abstract: A new noninvasive technique for monitoring capillary blood flow has been developed. Based on the phenomenon of time-varying laser speckle, it is a digital version of single-exposure speckle photography. It provides a velocity map of the area of interest in real time without the need for scanning. The results of some initial experiments on volunteers are presented.

Holographic Interferometry: Principles and Methods

Abstract: Holography and holographic interferometry quantitative evaluation of the interference phase processing of the interference phase speckle metrology. Appendices: the Fourier transform diffraction theory computer-aided tomography Bessel functions.

Adaptive speckle reduction filter for log-compressed B-scan images

Abstract: A good statistical model of speckle formation is useful for designing a good adaptive filter for speckle reduction In ultrasound B-scan images. Previously, statistical models have been used, but they failed to account for the log compression of the echo envelope employed by clinical ultrasound systems. Log-compression helps in reducing the dynamic range of the B-scan Images for display on a monitor as well as enhancing weak backscatters. In this article, statistics of log-compressed echo images, using the K-distribution statistical model for the echo envelope, are used to derive a parameter that can be used to quantify the extent of speckle formation. This speckle quantification can be used with an unsharp masking filter to adaptively reduce speckle. The effectiveness of the filter is demonstrated on images of contrast detail phantoms and on in-vivo abdominal images obtained by a clinical ultrasound system with log-compression.

High resolution device and method for imaging concealed objects within an obscuring medium

Abstract: A method and apparatus are provided for imaging and identifying concealed objects within an obscuring medium using radiation (optical, photo-acoustic, ionizing, and/or acoustic) optimized for imaging (e.g. temporal properties, spectral bandwidth, directionality, polarization, etc.). Radiation propagates through, interacts with, exits the medium and the object, and is detected/imaged. Image quality can be improved if radiation is collimated and/or if transmission and/or backscattered measurements from a number of perspectives are used to improved image reconstruction. Coupling materials can be employed during image acquisition to enhance radiation coupling as well as providing desirable absorption and scattering properties. Contrast materials and agents can also aid in the detection of concealed objects. Adaptive methods, e.g. using reference objects, including implementations based on the concept of guide stars, can improve the imaging process. The surface can be monitored and groomed to enhance the imaging process. Tomosynthesis techniques can be used to reconstruct images. Acousto-optic effects may be observed when both optical radiation and acoustic radiation are introduce into the medium. A laser vibrometry, speckle, or holographic interferometry imaging technique can be used to readout the acoustic waveform exiting the medium surface directly or after interacting with a deformable mirrored or reflective layer coupled to the medium. The medium may be prepared prior to imaging in order to reduce surface irregularities and roughness. Multilayer mirrors and capillary optics can be used to enhance imaging systems which use ionizing radiation. Resistance images can be obtained using probes to penetrate the medium.

Vibration measurement by the time-averaged electronic speckle pattern interferometry methods

Abstract: Three different image-processing methods based on the time-averaged technique were compared by the electronic speckle pattern interferometry (ESPI) technique for vibration measurement The three methods are the video-signal-addition method, the video-signal-subtraction method, and the amplitude-fluctuation method Also, errors introduced by using the zero-order Bessel function directly into the analysis of the fringe pattern were investigated The video-signal-addition method has been the most generally used ESPI technique for vibration measurement However, without additional image and/or signal-processing procedures, the fringe pattern obtained directly by the video-signal-addition method is rather difficult to observe The reason for poor visibility of the experimentally obtained fringe pattern with this method is explained To increase the fringe pattern's visibility without additional image and/or signal processes, we tried two video-signal-subtraction methods One of the two methods is the video-signal-subtraction method that has normally been used in the static applications The other method, called the amplitude-fluctuation method, and its associated theory are reported here

Statistics of the Stokes parameters and of the complex coherence parameters in one-look and multilook speckle fields

Abstract: Barakat [1987] derived the Stokes parameter statistics, applicable to one-look synthetic aperture radar (SAR) images, of a partially polarized wave backscattered from a Gaussian area. In this paper, the statistics of the Stokes parameters and of the phase difference are derived as a function of the mean effective phase difference and the degree of coherence for one-look and multilook SAR data. The statistics of the degree of coherence are also derived for multilook SAR data. It is shown that the estimator currently used for calculation of the degree of coherence is biased under low coherence conditions.

Lateral displacement estimation using tissue incompressibility

Abstract: Using the incompressibility property of soft tissue, lateral displacements can be reconstructed from axial strain measurements. Results of simulations and experiments on gelatin-based tissue equivalent phantoms are compared with theoretical displacements, as well as estimates derived from traditional speckle tracking. Incompressibility processing greatly improves the accuracy and signal-to-noise ratio (SNR) of lateral displacement measurements compared with more traditional speckle tracking.

Laser Doppler and time-varying speckle: a reconciliation

Abstract: The techniques of laser Doppler and time-varying speckle can both be used to measure velocities. The two techniques have developed separately, and there has been little interchange of ideas between them. The essential equivalence of the two techniques for measuring line-of-sight velocities is demonstrated, and ways in which the two techniques might learn from each other are suggested.

Evaluation of phase-diversity techniques for solar-image restoration

Abstract: Phase-diversity techniques provide a novel observational method for overcomming the effects of turbulence and instrument-induced aberrations in ground-based astronomy. Two implementations of phase-diversity techniques that differ with regard to noise model, estimator, optimization algorithm, method of regularization, and treatment of edge effects are described. Reconstructions of solar granulation derived by applying these two implementations to common data sets are shown to yield nearly identical images. For both implementations, reconstructions from phase-diverse speckle data (involving multiple realizations of turbulence) are shown to be superior to those derived from conventional phase-diversity data (involving a single realization). Phase-diverse speckle reconstructions are shown to achieve near diffraction-limited resolution and are validated by internal and external consistency tests, including a comparison with a reconstruction using a well-accepted speckle-imaging method.

Determination of Teflon thickness with laser speckle. I. Potential for burn depth diagnosis

Abstract: A quantitative method for determining the depth of burn eschar would aid surgeons in determining whether to excise and subsequently graft a burn wound. We hypothesize that tissue viability could be assessed by an analysis of the spatial modulation of near-field laser speckle by flowing blood. A feasibility study of the technique was performed with two-layer tissue phantoms used to simulate a burn wound. A sheet of polytetrafluoroethylene (PTFE) was used to simulate nonperfused burn eschar, and tissue perfusion within deeper layers was represented by Brownian motion from a scattering solution. A low-power He–Ne laser was focused onto the target, and the resulting speckle image was captured with a CCD camera and stored on a computer for further processing. The diameter of the speckle pattern was found to be directly proportional to the thickness of the overlying layer. These data suggest that the thickness of PTFE can be determined to ±100-μm accuracy with 95% confidence and may be suitable for burn depth detection in vivo.

Speckle reduction in coherent information processing

Abstract: Speckle reduction techniques have been developed as one of the most active research fields in coherent optical information processing, together with the investigations of speckle statistics and coherence theory. The principles of speckle reduction are classified to five categories: 1) control of spatial coherence, 2) control of temporal coherence, 3) spatial sampling, 4) spatial averaging, and 5) digital image processing. This paper surveys the research works in the field of speckle reduction techniques involving four categories 1)-4) which have been conducted in the past 30 years.

A comprehensive evaluation of filters for radar speckle suppression

Abstract: This paper presents the result of a comprehensive evaluation of filters for radar speckle suppression. Seven filters in the Radar Module of Erdas/IMAGINE(R) were evaluated, including the mean filter, the median filter, the Lee-sigma filter, the local region filter, the Lee filter, the Frost filter, and the MAP (maximum a posteriori) filter. The performance of these filters was measured in terms of five criteria: speckle suppression index, edge enhancing index, feature preserving index (for both linear features and point features), image detail preserving coefficient, and speckle image analysis. Visual effect of filtered image and its filter theoretical basis were discussed. The relationship between filter performance and speckle patterns was also examined.

Theory of speckles in diffractive optics and its application to beam shaping

Abstract: The design of diffractive phase elements (DPEs) for solving the general beam shaping problem where the signal wave is specified by an intensity distribution on a continuous support in a finite signal window is considered. In this case serious design problems due to speckles may arise. After introducing a mathematical definition and description of speckles, the influence of the phase of the signal wave on the design process is examined. It turns out that depending on the application a pseudo-random or a spherical phase should be used as an initial phase of the signal wave for an iterative design procedure. Due to its smoothness the spherical phase prevents the occurrence of speckles during the iteration process whereas the pseudo-random phase is accompanied by speckle effects. For applications where the imaging properties of the spherical phase are undesirable, a soft coding method is presented which significantly reduces the number of speckles of the pseudo-random phase. For cases where speckles ...

An illumination system and method employing a deformable mirror and defractive optical elements

Abstract: An illumination system for use in photolithography using a laser or radiation beam source. A deformable mirror is used to shape the beam of laser radiation to obtain global uniformity. A profile sensing means is used to detect any global non-uniformities. The output of this sensing means is fed to a controller for calculating a mirror contour and controlling actuators that shape the deformable mirror to obtain a globally uniform intensity. A diffractive or diffusive optical element, such as a microlens array, eliminates local non-uniformities. Movement of this element eliminates speckle caused by interference due to the coherent beam source. A uniform intensity profile and appropriate angular spread is achieved with very little transmission loss and is automatically compensated for degraded or changing source performance. The illumination system is particularly applicable to a scanning photolithography process as used in the manufacture of semiconductor substrates.

New method of short-coherence interferometry in human skin (in vivo) and in solid volume scatterers

Abstract: We adapted a method, the 'coherence radar', that was originally developed for the precise measurement of surface topology, to measure bulk properties within strongly scattering media. The sensor is based on short-coherence- interferometry. It enables the 2D observation of light propagation in scattering media with a high temporal resolution. The measurements are carried out by observing photons that traveled form an entrance focus through the bulk of the sample, and back to the surface. The source of information is the speckle contrast. One important result is that during the propagation a sharp photon horizon evolves. This photon horizon can be used for the detection on inhomogeneities in the scattering properties. In solid samples we measured absorbing obstacles with a depth of 320 micrometers and a depth uncertainty of < 5 percent. The measuring time is about 30 seconds. The observation of the photon horizon can also be realized in 'life' volume scatterers with moving scattering particles. First in vivo measurements of human skin have been successful.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Speckle noise reduction in television holography fringes using wavelet thresholding

Abstract: Recently, a novel wavelet method to reduce speckle noise in synthetic aperture radar images was presented. The method, based on the thresholding of the wavelet coefficients of the transformed image, is computationally efficient and maintains sharp image features. The application of a similar method is explored to reduce speckle noise in TV holography fringes, which is a very important problem in the quantitative analysis of transient phenomena. Several thresholding approaches are used to test the noise reduction algorithm on computer-simulated fringes and results are assessed through the evaluation of two comparative parameters: the image fidelity and the speckle index. It is shown that the method achieves the highest speckle reduction when speckle grains have the same average size of the image pixels.

Ultrasound image texture control using adaptive speckle control algorithm

Abstract: A method for controlling the contrast resolution and the tissue texture of ultrasonic images employs a signal processing algorithm to adjust an image by changing the tissue texture (speckle grain size). The algorithm increases the image contrast by allocating a different speckle pattern to different grey scale levels. This signal processing algorithm is based on the Hilbert transform (122). It uses the property of the Hilbert transform to generate a quadrature component of the given image which is modulated by the speckle pattern as well as all other image information. The quadrature component is then squared (126) before being selectively added to (128) or subtracted from the square of the in-phase component of the given image to control the information in the image. The added or subtracted signals have different textures (or spatial frequency components). The arithmetic operation (140) between the in-phase and quadrature phase components determines the image texture. If this operation is done selec-tively, then the contrast and the texture of the image can be selectively controlled.

The First Diffraction-Limited Images from the W. M. Keck Telescope

Abstract: The first diffraction limited, 0.05s resolution, images on the W. M. Keck Telescope have been obtained at a wavelength of 2.2 micrometers. These images were part of an experiment to test the suitability of the Keck Telescope for speckle imaging. In order to conduct this test, it was necessary to modify the pixel scale of the Keck facility Near Infrared Camera (NIRC) to optimally sample the spatial frequencies made available by the Keck telescope. The design and implementation of the external reimaging optics, which convert the standard fl25 beam from the secondary mirror to fl182, are described here. Techniques for reducing speckle data with field rotation on an alt-az telescope are also described. Three binary stars were observed in this experiment with separations as small as 0.05s. With only 100 frames of data on each, a dynamic range of at least 3.5 mag was achieved in all cases. These observations imply that a companion as faint as 14.5 mag at 2.2 micrometers could be detected around an 11th magnitude point source.

Optical implementation of image encryption using random phase encoding

Abstract: In the optical implementation of image encryption using ran- dom phase encoding proposed by Refregier and Javidi the random phase mask is not band limited. Speckle noise can thus destroy optical reconstruction of the encrypted images. We demonstrate encryption of speckle-free kinoforms by smoothed random phase masks. Optical veri- fication of the encrypted images is shown. © 1996 Society of Photo-Optical

Interferometric methods and biomedical research

Abstract: Optical metrology based on the principle of interference can be applied as a testing tool in biomedical research. Interferograms in form of fringe patterns can be produced in two-beams interferometers, holographic or speckle interferometers, in setups realizing moire techniques or in deflectometers. By analyzing of the fringe pattern images, information about the shape or mechanical behavior of the object under study can be retrieved. Here, some of the techniques for creating fringe pattern images were presented along with methods of analysis. Possible applications of interferometric methods, especially in the field of experimental orthopedics, endoscopy and ophthalmology will be pointed out.

Biased motion-adaptive temporal filtering for speckle reduction in echocardiography

Abstract: Describes a new fully motion-adaptive spatio-temporal filtering technique to reduce the speckle in ultrasound images. The advantages of this approach are demonstrated in echocardiographic boundary detection and in comparison with other techniques. The first stage of many automated echocardiographic image interpretation schemes is filtering to reduce the amount of speckle noise. The authors show how the two-dimensional least mean squares (TDLMS) filter can be configured as a motion-compensated filter for a time sequence of ultrasound images that eliminates the blurring associated with direct averaging. For an image corrupted by multiplicative speckle noise, the mode of the intensity distribution approximates the maximum likelihood estimator. In consequence, the temporal filter's output is biased towards the mode from the mean, using information contained within the speckle itself. A new adaptive algorithm for controlling the filter's convergence is also included. To evaluate performance, application to simulated, phantom, and an in vivo test sequence of the carotid artery are considered in comparison with other techniques. The effect of filtering on edges is of great importance, as these are used by subsequent image interpretation schemes. Quantitative measurements demonstrate the effectiveness of the Biased TDLMS filter, for both noise reduction and edge preservation. Echocardiographic images have a high noise content and suffer from poor contrast. Despite this challenging environment, the Biased TDLMS filter is shown to produce images that are better inputs for subsequent feature extraction. The benefits for echocardiographic images are highlighted by considering the problems of mitral valve analysis and extraction of the left atrium boundary.

Speckle noise reduction of airborne SAR images with symmetric Daubechies wavelets

Abstract: We report the study of a multiresolution speckle reduction method for airborne synthetic aperture radar (SAR) images. The SAR image is first subband-coded using complex symmetric Daubechies wavelets, followed by a noise estimate on the three high-pass bands. An elliptic wavelet coefficient thresholding rule is then applied, that preserves the global orientation of the complex wavelet coefficient distribution. FInally, a multiresolution synthesis (inverse wavelet transform) is done in a last small dim objects. A speckle index is computed to quantify the speckle reduction performance. We compare our results with those obtained using median and geometrical (Crimmins) filters.

Speckle reduction and enhancement of SAR images in the wavelet domain

Abstract: Three methods are investigated for speckle reduction and enhancement of synthetic aperture radar (SAR) images in the orthogonal wavelet domain. The first method is a nonlinear method based on soft thresholding the wavelet coefficients for logarithmically transformed SAR image data (Guo et al. 1994). The second method uses an enhanced adaptive Lee filter (Lopes et al., 1990) of the wavelet coefficients of SAR images. Finally, the third method introduces nonlinear speckle reduction based on adaptive sigmoid thresholding of the wavelet coefficients for logarithmically transformed SAR images. The wavelet methods show great promise for speckle removal and hence provide better detection performance for SAR based recognition.

ICCD Speckle Observations of Binary Stars. XIII. Measurements During 1989- 1994 From the Cerro Tololo 4 M Telescope

Abstract: One-thousand eighty-eight observations of 947 binary star systems, observed by means of speckle interferometry with the 4 m telescope on Cerro Tololo, are presented. These measurements, made during the period 1989-1991, comprise the second installment of results stemming from the expansion of our speckle program to the southern hemisphere

Rear projection screen with reduced speckle

Abstract: A rear projection screen which includes a front lenticular surface, a diffusion region behind the lenticular surface, a non-diffusion region behind the diffusion region, and a rear phase grating surface, when used with high magnification projection systems, exhibits reduced speckle when compared to other rear projection screen without such a grating

Transient phenomena analysis using dynamic speckle patterns

Abstract: The full width at half maximum (FWHM) is sometimes used to characterize the autocorrelation function of the time history of a speckle pattern. We propose to include more autocorrelation points to diminish the variability of the measurement. The width of the equivalent rectangle (WER) and the X*LOG X measurements are defined and some simulations and experimental results obtained are shown.

Coherent imaging of the cone mosaic in the living human eye

Abstract: A new system for the recording of high-resolution images of the cone mosaic in the living human fovea has been developed. The experimental method is inspired by stellar speckle interferometry, used in astronomy to resolve binary stars. Series of short-exposure images of small areas of the fovea are registered under coherent illumination. These images show speckle patterns that have some correlation with the topography of the cone mosaic and retain high-resolution information. Such correlation is better revealed in the power spectrum (square modulus of the Fourier transform). The signal-to-noise ratio is increased, without loss of high frequencies, by averaging the power spectra of a number of such speckle patterns. The average power spectra show, in most of the cases, an elliptical ring (or hexagon), whose mean radius corresponds to the characteristic spatial frequency of the cone mosaic (or the inverse of the mean row-to-row cone spacing) at a given retinal location. Good results are obtained in the five normal observers tested, at various retinal eccentricities, up to 1 visual degree, including the center of the fovea for two eyes. We find a decrease in the spatial frequency of the mosaic with the eccentricity and an important intersubject variability, in agreement with anatomical studies.