Speckle Data Research Articles

Tissue perfusion measurements: multiple-exposure laser speckle analysis generates laser Doppler–like spectra

Variations in skin perfusion are easily detected by laser speckle contrast maps, but a robust interpretation of the information has been lacking. We show that multiple-exposure laser speckle methods produce the same spectral information as laser Doppler methods when applied to targets with embedded moving scatterers. This enables laser speckle measurements to be interpreted more quantitatively. We do this by using computer simulation of speckle data, and by experimental measurements on Brownian motion and skin perfusion using a laser Doppler system and a multiple-exposure laser speckle system. The power spectral density measurements of the light fluctuations derived using both techniques are exactly equivalent. Dermal perfusion can therefore be measured by laser Doppler or laser speckle contrast methods. In particular, multiexposure laser speckle can be rapidly processed to generate a full-field map of the perfusion index proportional to the concentration and mean velocity of red blood cells.

Robust sensor for turbidity measurement from light scattering and absorbing liquids

Internationally standardized turbidity measurements for probing solid particles in liquid are problematic in the case of simultaneous light scattering and absorption. A method and a sensor to determine the turbidity in the presence of light absorption are presented. The developed sensor makes use of the total internal reflection of a laser beam at the liquid-prism interface, and the turbidity is assessed using the concept of laser speckle pattern. Using average filtering in speckle data analyzing the observed dynamic speckle pattern, which is due to light scattering from particles and the static speckle due to stray light of the sensor, can be separated from each other. Good correlation between the standard deviation of dynamic speckle and turbidity value for nonabsorbing and for absorbing liquids was observed. The sensor is suggested, for instance, for the measurement of ill-behaved as well as small-volume turbid liquids in both medicine and process industry.

Deconvolution of background-subtracted shift-and-add image by a modeled point-spread-function

Shift-and-add (SAA) is a simple method for celestial speckle imaging. However, the raw SAA-image, a direct output of the SAA operations, is not useful, because a seeing-dependent huge background is superimposed on the high-resolution image of the object. To obtain the latter, a background subtraction (BGS) is applied on the raw SAA-image. The BGS-image so obtained includes negativities due to an over-subtraction that causes brightnesses of the object’s image biased downward. The negativity in the BGS-image can be removed by a deconvolution with a point-spread-function (PSF) that has negative values. In this paper, we model the PSF with a shape that possesses peak and concave portions, and perform a deconvolution by iteratively estimating the object’s image and the model parameters. The simulated experiment has shown that the present algorithm can restore the object’s image with unbiased brightnesses. Processing the observed speckle data of Io (a Jupiter satellite) by the present method has yielded a feasible Io image with reduced negativities.

An iterative method for temperature gradient measurements in two-dimensional thermal boundary layer flows by speckle photography

An iterative method for measuring two-dimensional refractive index fields induced by convective heat transfer phenomena is presented. Starting from the so-called correction parabola, this reconstruction technique takes into account the local second derivative variation of the refractive index field. The efficiency of the method is analytically defined as a function of non-dimensional parameter and numerically investigated using a ray-tracing code for different classic index profiles and a thermal boundary layer case. Finally, as an implementation test, this algorithm is applied to an impinging jet heat transfer experiment using speckle photography measurement data set. The results show a relative dispersion of 20% compared to the parabola reconstruction when the refractive index gradient becomes more severe.

Wave intensity wall analysis: a novel noninvasive method to measure wave intensity

Wave intensity analysis is a concept providing information about the interaction of the heart and the vascular system. Originally, the technique was invasive. Since then new noninvasive methods have been developed. A recently developed ultrasound technique to estimate tissue motion and deformation is speckle-tracking echocardiography. Speckle tracking-based techniques allow for accurate measurement of movement and deformation variables in the arterial wall in both the radial and the longitudinal direction. The aim of this study was to test if speckle tracking-derived deformation data could be used as input for wave intensity calculations. The new concept was to approximate changes of flow and pressure by deformation changes of the arterial wall in longitudinal and radial directions. Flow changes (dU/dt) were approximated by strain rate (sr, 1/s) of the arterial wall in the longitudinal direction, whereas pressure changes (dP/dt) were approximated by sign reversed strain rate (1/s) in the arterial wall in the radial direction. To validate the new concept, a comparison between the newly developed Wave Intensity Wall Analysis (WIWA) algorithm and a commonly used and validated wave intensity system (SSD-5500, Aloka, Tokyo, Japan) was performed. The studied population consisted of ten healthy individuals (three women, seven men) and ten patients (all men) with coronary artery disease. The present validation study indicates that the mechanical properties of the arterial wall, as measured by a speckle tracking-based technique are a possible input for wave intensity calculations. The study demonstrates good visual agreement between the two systems and the time interval between the two positive peaks (W1-W2) measured by the Aloka system and the WIWA system correlated for the total group (r = 0.595, P < 0.001). The correlation for the diseased subgroup was r = 0.797, P < 0.001 and for the healthy subgroup no significant correlation was found (P > 0.05). The results of the study indicate that the mechanical properties of the arterial wall could be used as input for wave intensity calculations. The WIWA concept is a promising new method that potentially provides several advantages over earlier wave intensity methods, but it still has limitations and needs further refinement and larger studies to find the optimal clinical use.

OBSERVATIONS OF BINARY STARS WITH THE DIFFERENTIAL SPECKLE SURVEY INSTRUMENT. I. INSTRUMENT DESCRIPTION AND FIRST RESULTS

First results of a new speckle imaging system, the Differential Speckle Survey Instrument, are reported. The instrument is designed to take speckle data in two filters simultaneously with two independent CCD imagers. This feature results in three advantages over other speckle cameras: (1) twice as many frames can be obtained in the same observation time which can increase the signal-to-noise ratio for astrometric measurements, (2) component colors can be derived from a single observation, and (3) the two colors give substantial leverage over atmospheric dispersion, allowing for subdiffraction-limited separations to be measured reliably. Fifty-four observations are reported from the first use of the instrument at the Wisconsin-Indiana-Yale-NOAO 3.5 m Telescope9The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories. in 2008 September, including seven components resolved for the first time. These observations are used to judge the basic capabilities of the instrument.

Biaxial testing of fibre-reinforced composite laminates

Advanced composite material systems are increasingly used in almost every industrial branch. The structural components manufactured from these composite material systems are usually subjected to complex loading that leads to multi-axial stress and strain fields at critical surface locations. The current practice of using solely uniaxial test data to validate proposed material models is wholly inadequate. In order to test closer to reality, a biaxial test bench using four servo-hydraulic actuators with four load cells was developed. Besides the development of the test facility, a mixed numerical/experimental method was developed to determine the in-plane stiffness parameters from testing a single cruciform test specimen. To obtain the strength data an optimized geometry for the cruciform type specimen was designed. For the optimization procedure a full three-dimensional finite element model was used. The numerical results were validated with strain gauge, digital image correlation, and electronic speckle pattern interferometry data. The material system used for the experimental validation was glass fibre-reinforced epoxy with a lay-up [(+45°−45° 0°)4(+45°−45°)] typically used for wind turbine blades.

Speckle interferometry with adaptive optics corrected solar data

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 resolution.Aims. 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 reconstruction.Methods. 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 telescope.Results. 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.

Three-dimensional mapping of mechanical activation patterns, contractile dyssynchrony and dyscoordination by two-dimensional strain echocardiography: Rationale and design of a novel software toolbox

BackgroundDyssynchrony of myocardial deformation is usually described in terms of variability only (e.g. standard deviations SD's). A description in terms of the spatio-temporal distribution pattern (vector-analysis) of dyssynchrony or by indices estimating its impact by expressing dyscoordination of shortening in relation to the global ventricular shortening may be preferential. Strain echocardiography by speckle tracking is a new non-invasive, albeit 2-D imaging modality to study myocardial deformation.MethodsA post-processing toolbox was designed to incorporate local, speckle tracking-derived deformation data into a 36 segment 3-D model of the left ventricle. Global left ventricular shortening, standard deviations and vectors of timing of shortening were calculated. The impact of dyssynchrony was estimated by comparing the end-systolic values with either early peak values only (early shortening reserve ESR) or with all peak values (virtual shortening reserve VSR), and by the internal strain fraction (ISF) expressing dyscoordination as the fraction of deformation lost internally due to simultaneous shortening and stretching. These dyssynchrony parameters were compared in 8 volunteers (NL), 8 patients with Wolff-Parkinson-White syndrome (WPW), and 7 patients before (LBBB) and after cardiac resynchronization therapy (CRT).ResultsDyssynchrony indices merely based on variability failed to detect differences between WPW and NL and failed to demonstrate the effect of CRT. Only the 3-D vector of onset of shortening could distinguish WPW from NL, while at peak shortening and by VSR, ESR and ISF no differences were found. All tested dyssynchrony parameters yielded higher values in LBBB compared to both NL and WPW. CRT reduced the spatial divergence of shortening (both vector magnitude and direction), and improved global ventricular shortening along with reductions in ESR and dyscoordination of shortening expressed by ISF.ConclusionIncorporation of local 2-D echocardiographic deformation data into a 3-D model by dedicated software allows a comprehensive analysis of spatio-temporal distribution patterns of myocardial dyssynchrony, of the global left ventricular deformation and of newer indices that may better reflect myocardial dyscoordination and/or impaired ventricular contractile efficiency. The potential value of such an analysis is highlighted in two dyssynchronous pathologies that impose particular challenges to deformation imaging.

FIRST RESULTS OF THE OPTICAL SPECKLE INTERFEROMETRY WITH THE 3.5 m TELESCOPE AT CALAR ALTO (SPAIN): MEASUREMENTS AND ORBITS OF VISUAL BINARIES

We present the first results of optical speckle interferometry of visual binaries obtained with the 3.5m telescope at Calar Alto (Almeria, Spain) in July 2005. During this campaign fifty stars were observed with angular separations between 0.​​′058 and 2.​​′1. New orbits for binaries COU 490 and A 2257, and improved orbits for COU 606, A 225, A 2189, COU 1785, COU 2416, and COU 327 AB, along with their systemic masses, were calculated. The first estimations of distance for the COU 490 (145 pc) and the A 2257 (210 pc) were accomplished thanks to the previously obtained dynamical parallaxes and to the known spectral and photometric data. Total masses for systems with both new and improved orbits are given, those being concordant with their known spectral types and photometric data. We conclude that with the 3.5m telescope we can routinely obtain good optical speckle data for binary systems with angular separations close to its diffraction limit.

Image Restoration of Io by Shift-and-Add Method and Deconvolution

ABSTRACTAtmospheric turbulence degrades the image resolution of a ground-based telescope, and a speckle imaging technique can restore the image with high resolution up to the diffraction limit. We have obtained the speckle data of Io (a Jupiter’s satellite) using the 2 m telescope in Nishi-Harima Astronomical Observatory. The speckle data are reduced by the shift-and-add method followed by a background-subtraction procedure. The reduced image is then deconvolved by the similarly reduced image of the unresolved binary star HR6168. The comparison with the close-up image taken by the Voyager 2 spacecraft reveals that the restored image shows well-resolved structural features on the surface of Io.

Quantitative temporal speckle contrast imaging for tissue mechanics

We demonstrate through a series of simulations that by parameterizing the temporal speckle contrast statistic from a sequence of translating speckle images on a number of experimental constants, the local temporal contrast can be used to quantitatively assess local motion, provided that the spatial and temporal Nyquist sampling criteria are both met. We develop a simple exponential model for quantifying speckle motion for speckle patterns that display arbitrary intensity statistics and provide suggestions for optimizing both the experimental acquisition of speckle data and the temporal contrast analysis of the data. The confounding effects of uncorrelated noise are also discussed. The model is demonstrated by applying it to an optical coherence tomography image sequence of an engineered tissue construct undergoing dynamic compression. Applications to tissue mechanics are shown, although the discussion is equally relevant for fluid motion studies.

Feedback controlled ablation of nectrotic and infectious debris on chronic wounds – Application and outcome

Abstract Objective Over 2 million people in Germany suffer from chronic wounds. Only few patients underwent a surgical debridement, because this treatment is painful and has to be performed mostly under general anaesthesia, which is a risk in particular for elderly patients. The aim of this project was to establish a feedback-controlled ablation system dedicated to clean chronic wounds without using anaesthesia. Material and methods We developed an Er:YAG laser system to ablate chronic wounds automatically controlled by a feedback device based on speckle contrast measurement. We use the method of laser speckle imaging (LSI) to provide this feedback control. In contrary to other methods like laser Doppler spectroscopy, LSI is a full-field and real-time method without the need of scanning. Based on the speckle contrast data which are an indicator of perfusion, the ablation pattern on the wound area was calculated for several ablation passes beginning with the thickest layers until the whole area was clean. Four patients were treated with this system under general anaesthesia to evaluate the feedback system and to demonstrate the efficiency of ablation. Results The treatments show the good efficiency of the method. All kinds of debris and necrosis could be recognized with the laser speckle technique and were ablated with the Er:YAG laser. Up to 30 passes and 1000 laser spots per pass were needed. The treatments take between 30 min and 60 min, dependent on the wound area and the thickness of the debris. Discussion Because the first treatments had to be performed under general anaesthesia due to ethical aspects, we cannot yet conclude whether the method is suitable for non-anaesthetized patients. We found that the procedure was very precise and tissue conservative. All patients showed a similar wound healing progress during the follow-up time compared to surgical debridement.

Calculating the Orbit of a Double Star with Visual, Speckle, and Radial Velocity Data

The mathematical technique known as semidefinite programming (SDP) is used with 260 visual and speckle and 129 double-line radial velocities to determine the orbit of the system 24 Aquarii. The fractional mass and the parallax of the system are also determined. SDP calculates a unique ellipse that satisfies the observations and represents a global minimum of the adjustment criterion. SDP also permits great flexibility; the visual and speckle observations are reduced with the robust L1 criterion, whereas least squares are used for the radial velocities. The period of the system is determined as 48.28 yr, the fractional mass as 0.433, and the parallax as 0.019''.

527 Bull's eye presentation of speckle tracking data - A simple and user independent method for detection of regional myocardial ischemia

Bull's eye presentation of speckle tracking data : A simple and user independent method for detection of regional myocardial ischemia

Characterizing Binary Stars Below the Diffraction Limit with CCD?based Speckle Imaging

An analysis of 15 speckle observations taken at the Lowell-Tololo Telescope at Cerro Tololo Inter-American Observatory and 6 speckle observations taken at the WIYN Telescope at Kitt Peak National Observatory indicates that it is possible to characterize the separations, position angles, and magnitude differences of binary stars down to at least one quarter of the diffraction limit with CCD-based speckle imaging. This is made possible by the fact that CCD-based speckle imaging permits the retrieval of reliable photometric information from speckle data, and therefore the elongation of the speckles due to a blended companion may be reliably measured. When observations in two colors are obtained, atmospheric dispersion, which also affects the speckle shape, can be distinguished from binarity in a large number of cases. A regimen for observing sub-diffraction-limited speckle binaries is proposed that could lead to efficient surveys of small-separation binary stars.

Full-field calculation of hole drilling residual stresses from electronic speckle pattern interferometry data

A mathematical method is proposed for calculating residual stresses from hole drilling electronic speckle pattern interferometry (ESPI) data, independent of rigid-body motions. Even though the signal-to-noise ratio of typical ESPI data is modest, the method achieves good computational stability by averaging a large amount of data. It does this without excessive numerical effort by exploiting known trigonometric relationships among the data. The resulting stress calculations are very rapid, and are well suited for future application to non-uniform stress measurements.

Speckle Observations of Binary Stars with a 0.5 m Telescope

ABSTRACTWe present 36 observations of 17 visual binaries of moderate separation (ranging from 0.″15 to 0.″790) made with the 50 cm Cassegrain telescope of the Jagiellonian University in Kraków. The speckle interferometry technique was combined with modest optical hardware and a standard photometric CCD camera. We used broadband VRI filters without a Risley prism to reduce differential color refraction. Thus, we performed a model analysis to investigate the influence of this effect on the results of the measurements. For binary components of spectral type O–F, the difference of three spectral classes between them should bias their relative positions by no more than a couple of tens of milliarcseconds (mas) for moderate zenith distances. The statistical analysis of our results confirmed this conclusion. A cross‐spectrum approach was applied to resolve the quadrant ambiguity. Our separations have rms deviations of 0.″012, and our position angles have rms deviations of 1.°8. Relative photometry in V, R, and I filters appeared to be the less accurately determined parameter. We discuss our errors in detail and compare them to other speckle data. This comparison clearly shows the quite good accuracy of our measurements. We also present an example of the enhancement of image resolution for an extended object with an angular size that is greater than the atmospheric coherence patch, using speckle interferometry techniques.

Coherence experiments using white synchrotron radiation

Experiments at the bending magnet beamline at BESSY II (EDR beamline) profit from the excellent coherence properties of third generation synchrotron sources. Considering the exponentially decaying incident spectrum, and because no optical elements are installed except slits and vacuum windows, coherence experiments can be performed between 5 keV< E<15 keV. First, the energy dependence of spatial coherence properties were determined measuring diffraction at single and double pinholes. Next, the coherent white radiation was used to probe the morphology of thin films in reflection geometry. The recorded intensity maps (reflectivity versus sample position) provide speckle patterns which reveal the locally varying sample morphology. Setting the incident angle, α i , smaller or larger than the critical angle of total external reflection, α c , one should be able to separate the surface height profile from the subsurface density modulation of a sample. The validity of this approach is verified at the example of reciprocal space maps taken from a polymer surface where we could reconstruct the lateral height profile from speckle data.

Bayesian neural-networks-based evaluation of binary speckle data

We present a new method using Bayesian probability theory and neural networks for the evaluation of speckle interference patterns for an automated analysis of deformation and erosion measurements. The method is applied to the fringe pattern reconstruction of speckle measurements with a Twyman-Green interferometer. Given a binary speckle image, the method returns the fringe pattern without noise, thus removing the need for smoothing and allowing a straightforward unwrapping procedure and determination of the surface shape. Because no parameters have to be adjusted, the method is especially suited for continuous and automated monitoring of surface changes.