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Journal articles on the topic 'Multi Exposure Speckle Imaging'

Author: Grafiati

Published: 4 June 2021

Last updated: 2 February 2022

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1

Parthasarathy, Ashwin B., W. J. Tom, Ashwini Gopal, Xiaojing Zhang, and Andrew K. Dunn. "Robust flow measurement with multi-exposure speckle imaging." Optics Express 16, no. 3 (2008): 1975. http://dx.doi.org/10.1364/oe.16.001975.

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2

Kazmi, Syed Mohammad Shams, Ashwin B. Parthasarthy, Nelly E. Song, Theresa A. Jones, and Andrew K. Dunn. "Chronic Imaging of Cortical Blood Flow using Multi-Exposure Speckle Imaging." Journal of Cerebral Blood Flow & Metabolism 33, no. 6 (April 10, 2013): 798–808. http://dx.doi.org/10.1038/jcbfm.2013.57.

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Chronic imaging of cerebral blood flow (CBF) is an important tool for investigating vascular remodeling after injury such as stroke. Although techniques such as Laser Speckle Contrast Imaging (LSCI) have emerged as valuable tools for imaging CBF in acute experiments, their utility for chronic measurements or cross-animal comparisons has been limited. Recently, an extension to LSCI called Multi-Exposure Speckle Imaging (MESI) was introduced that increases the quantitative accuracy of CBF images. In this paper, we show that estimates of chronic blood flow are better with MESI than with traditional LSCI. We evaluate the accuracy of the MESI flow estimates using red blood cell (RBC) photographic tracking as an absolute flow calibration in mice over several days. The flow measures computed using the MESI and LSCI techniques were found to be on average 10% and 24% deviant ( n = 9 mice), respectively, compared with RBC velocity changes. We also map CBF dynamics after photo-thrombosis of selected cortical microvasculature. Correlations of flow dynamics with RBC tracking were closer with MESI ( r = 0.88) than with LSCI ( r = 0.65) up to 2 weeks from baseline. With the increased quantitative accuracy, MESI can provide a platform for studying the efficacy of stroke therapies aimed at flow restoration.

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3

Richards, Lisa M., SM Shams Kazmi, Katherine E. Olin, James S. Waldron, Douglas J. Fox, and Andrew K. Dunn. "Intraoperative multi-exposure speckle imaging of cerebral blood flow." Journal of Cerebral Blood Flow & Metabolism 37, no. 9 (January 23, 2017): 3097–109. http://dx.doi.org/10.1177/0271678x16686987.

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Multiple studies have demonstrated that laser speckle contrast imaging (LSCI) has high potential to be a valuable cerebral blood flow monitoring technique during neurosurgery. However, the quantitative accuracy and sensitivity of LSCI is limited, and highly dependent on the exposure time. An extension to LSCI called multi-exposure speckle imaging (MESI) overcomes these limitations, and was evaluated intraoperatively in patients undergoing brain tumor resection. This clinical study ( n = 8) recorded multiple exposure times from the same cortical tissue area spanning 0.5–20 ms, and evaluated images individually as single-exposure LSCI and jointly using the MESI model. This study demonstrated that the MESI estimates provided the broadest flow sensitivity for sampling the flow magnitude in the human brain, closely followed by the shorter exposure times. Conservation of flow analysis on vascular bifurcations was used to validate physiological accuracy, with highly conserved flow estimates (<10%) from both MESI and 1 ms LSCI ( n = 14 branches). The MESI model had high goodness-of-fit with proper image calibration and acquisition, and was used to monitor blood flow changes after tissue cautery. Results from this study demonstrate that intraoperative MESI can be performed with high quantitative accuracy and sensitivity for cerebral blood flow monitoring.

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4

Wu, Qiong, Jialin Liu, Baoteng Xu, Wei Zhou, Chi Wang, Xibin Yang, and Daxi Xiong. "Laparoscopic multi-exposure speckle imaging for quantitative flow measurement." AIP Advances 11, no. 1 (January 1, 2021): 015031. http://dx.doi.org/10.1063/5.0033464.

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5

Shams Kazmi, S. M., Rebecca K. Wu, and Andrew K. Dunn. "Evaluating multi-exposure speckle imaging estimates of absolute autocorrelation times." Optics Letters 40, no. 15 (July 30, 2015): 3643. http://dx.doi.org/10.1364/ol.40.003643.

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6

Kazmi, S. M. Shams, Satyajit Balial, and Andrew K. Dunn. "Optimization of camera exposure durations for multi-exposure speckle imaging of the microcirculation." Biomedical Optics Express 5, no. 7 (June 10, 2014): 2157. http://dx.doi.org/10.1364/boe.5.002157.

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7

Parthasarathy, Ashwin B., S. M. Shams Kazmi, and Andrew K. Dunn. "Quantitative imaging of ischemic stroke through thinned skull in mice with Multi Exposure Speckle Imaging." Biomedical Optics Express 1, no. 1 (July 16, 2010): 246. http://dx.doi.org/10.1364/boe.1.000246.

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8

Sivakumar, Panneer Selvam, Keiichiro Kagawa, Christian Crouzet, Bernard Choi, Keita Yasutomi, and Shoji Kawahito. "Multi-exposure laser speckle contrast imaging using a video-rate multi-tap charge modulation image sensor." Optics Express 27, no. 18 (August 30, 2019): 26175. http://dx.doi.org/10.1364/oe.27.026175.

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9

Dragojević, Tanja, Danilo Bronzi, Hari M. Varma, Claudia P. Valdes, Clara Castellvi, Federica Villa, Alberto Tosi, Carles Justicia, Franco Zappa, and Turgut Durduran. "High-speed multi-exposure laser speckle contrast imaging with a single-photon counting camera." Biomedical Optics Express 6, no. 8 (July 14, 2015): 2865. http://dx.doi.org/10.1364/boe.6.002865.

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10

Rice, Tyler B., Elliott Kwan, Carole K. Hayakawa, Anthony J. Durkin, Bernard Choi, and Bruce J. Tromberg. "Quantitative, depth-resolved determination of particle motion using multi-exposure, spatial frequency domain laser speckle imaging." Biomedical Optics Express 4, no. 12 (November 19, 2013): 2880. http://dx.doi.org/10.1364/boe.4.002880.

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11

Sun, Shen, Barrie R. Hayes-Gill, Diwei He, Yiqun Zhu, and Stephen P. Morgan. "Multi-exposure laser speckle contrast imaging using a high frame rate CMOS sensor with a field programmable gate array." Optics Letters 40, no. 20 (October 5, 2015): 4587. http://dx.doi.org/10.1364/ol.40.004587.

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12

Möller, Johannes, Yuriy Chushkin, Sylvain Prevost, and Theyencheri Narayanan. "Multi-speckle X-ray photon correlation spectroscopy in the ultra-small-angle X-ray scattering range." Journal of Synchrotron Radiation 23, no. 4 (June 15, 2016): 929–36. http://dx.doi.org/10.1107/s1600577516008092.

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Multi-speckle X-ray photon correlation spectroscopy (XPCS) measurements in the ultra-small-angle range are performed using a long pinhole collimation instrument in combination with two-dimensional photon-counting and high-sensitivity imaging detectors. The feasibility of the presented setup to measure dynamics on different time and length scales pertinent to colloidal systems is shown. This setup offers new research opportunities, such as for example in the investigation of non-equilibrium dynamics in optically opaque, complex systems over length scales from tens of nanometres to several micrometres. In addition, due to the short duration of the X-ray exposure involved in the ultra-small-angle range, possible radiation-induced effects are alleviated. Furthermore, the performance of two different detectors, a photon-counting Pilatus 300K and an integrating FReLoN CCD, are compared, and their applicability for accurate XPCS measurements is demonstrated.

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13

Le Coroller, H., M. Nowak, P. Delorme, G. Chauvin, R. Gratton, M. Devinat, J. Bec-Canet, et al. "K-Stacker: an algorithm to hack the orbital parameters of planets hidden in high-contrast imaging." Astronomy & Astrophysics 639 (July 2020): A113. http://dx.doi.org/10.1051/0004-6361/202037605.

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Context. Recent high-contrast imaging surveys, using the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE) or the Gemini Planet Imager in search of planets in young, nearby systems, have shown evidence of a small number of giant planets at relatively large separation beyond 10–30 au, where those surveys are the most sensitive. Access to smaller physical separations between 5 and 30 au is the next step for future planet imagers on 10 m telescopes and the next generation of extremely large telescopes in order to bridge the gap with indirect techniques such as radial velocity, transit, and soon astrometry with Gaia. In addition to new technologies and instruments, the development of innovative observing strategies combined with optimized data processing tools is participating in the improvement of detection capabilities at very close angular separation. In that context, we recently proposed a new algorithm, Keplerian-Stacker, which combines multiple observations acquired at different epochs and takes into account the orbital motion of a potential planet present in the images to boost the ultimate detection limit. We showed that this algorithm is able to find planets in time series of simulated images of the SPHERE InfraRed Dual-band Imager and Spectrograph (IRDIS) even when a planet remains undetected at one epoch. Aims. Our goal is to test and validate the K-Stacker algorithm performances on real SPHERE datasets to demonstrate the resilience of this algorithm to instrumental speckles and the gain offered in terms of true detection. This will motivate future dedicated multi-epoch observation campaigns of well-chosen, young, nearby systems and very nearby stars carefully selected to search for planets in emitted and reflected light, respectively, to open a new path concerning the observing strategy used with current and future planet imagers. Methods. To test K-Stacker, we injected fake planets and scanned the low signal-to-noise ratio (S/N) regime in a series of raw observations obtained by the SPHERE/IRDIS instrument in the course of the SPHERE High-contrast ImagiNg survey for Exoplanets. We also considered the cases of two specific targets intensively monitored during this campaign: β Pictoris and HD 95086. For each target and epoch, the data were reduced using standard angular differential imaging processing techniques and then recombined with K-Stacker to recover the fake planetary signals. In addition, the known exoplanets β Pictoris b and HD 95086 b previously identified at lower S/N in single epochs have also been recovered by K-Stacker. Results. We show that K-Stacker achieves a high success rate of ≈100% when the S/N of the planet in the stacked image reaches ≈9. The improvement of the S/N is given as the square root of the total exposure time contained in the data being combined. At S∕N < 6−7, the number of false positives is high near the coronagraphic mask, but a chromatic study or astrophysical criteria can help to disentangle between a bright speckle and a true detection. During the blind test and the redetection of HD 95086 b, and β Pic b, we highlightthe ability of K-Stacker to find orbital solutions consistent with those derived by the current Markov chain Monte Carlo orbital fitting techniques. This confirms that in addition to the detection gain, K-Stacker offers the opportunity to characterize the most probable orbital solutions of the exoplanets recovered at low S/N.

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14

Christou, J. C. "Speckle Interferometry." Highlights of Astronomy 8 (1989): 561–62. http://dx.doi.org/10.1017/s1539299600008340.

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Speckle interferometry is a technique which utilizes the full diffraction-limited imaging potential of ground-based telescopes. Short exposure images, or specklegrams, with an exposure time less than that of the atmospheric correlation time (~5- 50 ms) preserve the high-spatial frequency information lost in long exposure imaging. In 1970, Labeyrie computed the power spectrum of a set of specklegrams and showed that they contained diffraction-limited information. Since then the field has grown with improvements in both instrumentation and the phase recovery algorithms necessary for imaging. It has been applied at both visible and near-infrared wavelengths although, until recently, the latter has used slit-scanning techniques with single pixel detectors because of the lack of array detectors. The current state of speckle interferometry has been well covered in the proceedings of two recent joint National Optical Astronomy Observatories – European Southern Observatory workshops on Interferometric Imaging in Astronomy (Oracle, 1987 & Garching, 1988).

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15

Jespersen, Søren K., Jens E. Wilhjelm, and Henrik Sillesen. "Multi-Angle Compound Imaging." Ultrasonic Imaging 20, no. 2 (April 1998): 81–102. http://dx.doi.org/10.1177/016173469802000201.

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This paper reports on a scanning technique, denoted multi-angle compound imaging (MACI), using spatial compounding. The MACI method also contains elements of frequency compounding, as the transmit frequency is lowered for the highest beam angles in order to reduce grating lobes. Compared to conventional B-mode imaging MACI offers better defined tissue boundaries and lower variance of the speckle pattern, resulting in an image with reduced random variations. Design and implementation of a compound imaging system is described, images of rubber tubes and porcine aorta are shown and effects on visualization are discussed. The speckle reduction is analyzed numerically and the results are found to be in excellent agreement with existing theory. An investigation of detectability of low-contrast lesions shows significant improvements compared to conventional imaging. Finally, possibilities for improving diagnosis of atherosclerotic diseases using MACI are discussed.

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16

Horch, Elliott Pierce. "Speckle Imaging with the Multi-Anode Microchannel Array Detector." Publications of the Astronomical Society of the Pacific 106 (June 1994): 688. http://dx.doi.org/10.1086/133430.

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17

Liu, Jialin, Hongchao Zhang, Jian Lu, Xiaowu Ni, and Zhonghua Shen. "Simultaneously extracting multiple parameters via multi-distance and multi-exposure diffuse speckle contrast analysis." Biomedical Optics Express 8, no. 10 (September 19, 2017): 4537. http://dx.doi.org/10.1364/boe.8.004537.

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18

Reinheimer, T., K. H. Hofmann, and G. Weigelt. "Optical Interferometry in the Multi-Speckle Mode." Symposium - International Astronomical Union 158 (1994): 373–75. http://dx.doi.org/10.1017/s007418090010796x.

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We have studied interferometric imaging in the multi-speckle mode by computer simulations. From various simulated data sets diffraction-limited images were reconstructed by the speckle masking method and the iterative building block method. The reconstructed images show the dependence of the signal-to-noise ratio on photon noise.

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19

Сдобнов, А. Ю., В. В. Кальченко, А. В. Быков, А. П. Попов, Г. Молодый, and И. В. Меглинский. "Визуализация кровотока методом лазерных спекл-контрастных измерений в условиях неэргодичности." Журнал технической физики 128, no. 6 (2020): 773. http://dx.doi.org/10.21883/os.2020.06.49410.35-20.

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In current work, the influence of static structural inclusions in heterogeneous highly scattering media such as biotissue on the results of laser speckle contrast imaging using both temporal and spatial processing algorithms has been investigated. The applicability of laser speckle contrast imaging technique has been studied in case of non-ergodic conditions. It was shown using the phantom model that increment of amount of static scatterers comparing to the dynamic ones in tissue causes significant error in results of temporal and spatial speckle contrast processing for the given camera exposure time. At the same time, the analysis of the spatial and temporal speckle contrast values, values of coefficient of speckle dynamics as well as results of Monte Carlo simulation of sampling volumes showed that presence of relatively thin static layer (up to 30% of all volume) cannot cause significant changes in results of laser speckle contrast imaging. The camera exposure time, as well as amount of frames for image processing can vary depending on the experiment goals. Finally, the proposed spatial and temporal algorisms of laser speckle contrast imaging were verified during transcranial visualization of the mouse brain vasculature.

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20

Puschmann, K. G., and C. Beck. "Application of speckle and (multi-object) multi-frame blind deconvolution techniques on imaging and imaging spectropolarimetric data." Astronomy & Astrophysics 533 (August 19, 2011): A21. http://dx.doi.org/10.1051/0004-6361/201116904.

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21

Tucker, David, and Lee C. Potter. "Speckle Suppression in Multi-Channel Coherent Imaging: A Tractable Bayesian Approach." IEEE Transactions on Computational Imaging 6 (2020): 1429–39. http://dx.doi.org/10.1109/tci.2020.3029385.

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22

Tong, Zhaomin, Feng Niu, Zequn Jian, Changyuan Sun, Yifei Ma, Mei Wang, Suotang Jia, and Xuyuan Chen. "Micro-refractive optical elements fabricated by multi-exposure lithography for laser speckle reduction." Optics Express 28, no. 23 (October 29, 2020): 34597. http://dx.doi.org/10.1364/oe.405622.

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23

Ramírez-San-Juan, J. C., Y. C. Huang, N. Salazar-Hermenegildo, R. Ramos-García, J. Muñoz-Lopez, and B. Choi. "Integration of image exposure time into a modified laser speckle imaging method." Physics in Medicine and Biology 55, no. 22 (November 3, 2010): 6857–66. http://dx.doi.org/10.1088/0031-9155/55/22/016.

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24

Wang, Chenge, Zili Cao, Xin Jin, Weihao Lin, Yang Zheng, Bixin Zeng, and M. Xu. "Robust quantitative single-exposure laser speckle imaging with true flow speckle contrast in the temporal and spatial domains." Biomedical Optics Express 10, no. 8 (July 17, 2019): 4097. http://dx.doi.org/10.1364/boe.10.004097.

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25

Chen, Hsi-Hsun, Vijay Raj Singh, and Yuan Luo. "Speckle-based volume holographic microscopy for optically sectioned multi-plane fluorescent imaging." Optics Express 23, no. 6 (March 9, 2015): 7075. http://dx.doi.org/10.1364/oe.23.007075.

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26

Yuan, Shuai, Anna Devor, David A. Boas, and Andrew K. Dunn. "Determination of optimal exposure time for imaging of blood flow changes with laser speckle contrast imaging." Applied Optics 44, no. 10 (April 1, 2005): 1823. http://dx.doi.org/10.1364/ao.44.001823.

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27

Hui, Liu, and Ye Xinhua. "A Novel Improved Multi-Point Matching Based Coronary Disease Quantitative Analysis for Speckle Tracking in Ultrasound Image." Journal of Medical Imaging and Health Informatics 10, no. 2 (February 1, 2020): 489–95. http://dx.doi.org/10.1166/jmihi.2020.2897.

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Ultrasonic imaging technology is one of the most direct and effective methods, which can prevent, treat cardiovascular disease, and it can make noninvasive observation and detection of cardiac motion. To calculate accurate myocardial motion parameters more directly, effectively and accurately, speckle tracking algorithm is put forward. However, the performance of speckle tracking is directly related to the diagnosis effect of coronary disease. Compared with the speckle tracking algorithm based on optical flow algorithm, the speckle tracking algorithm based on block matching algorithm has advantages of higher tracking accuracy and faster computation speed and better anti-interference immunity. According to the requirements of clinical application, the full search block matching algorithm whose accuracy is the highest is adopted as the basic algorithm of the speckle tracking algorithm. In paper, In view of the shortcomings of the full search block matching algorithm, the algorithm based on calculating tracking error is proposed. The speckle tracking algorithm based on calculating tracking error has good tracking results, which shows that this algorithm can effectively improve the applicability, stability and accuracy of tracking in different ultrasound images and multi-point tracking in the same ultrasound images.

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28

Kalchenko, Vyacheslav, Yuri Kuznetsov, Dina Preise, Igor Meglinski, and Alon Harmelin. "Ear swelling test by using laser speckle imaging with a long exposure time." Journal of Biomedical Optics 19, no. 6 (June 26, 2014): 060502. http://dx.doi.org/10.1117/1.jbo.19.6.060502.

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29

Bevilacqua, M., G. Di Leo, M. Landi, and A. Paolillo. "Multi-exposure imaging for measurements in rubber production." Measurement Science and Technology 24, no. 7 (June 12, 2013): 074014. http://dx.doi.org/10.1088/0957-0233/24/7/074014.

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30

Morgan, Andrew J., Kevin T. Murray, Harry M. Quiney, Saša Bajt, and Henry N. Chapman. "speckle-tracking: a software suite for ptychographic X-ray speckle tracking." Journal of Applied Crystallography 53, no. 6 (October 19, 2020): 1603–12. http://dx.doi.org/10.1107/s1600576720011991.

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In recent years, X-ray speckle-tracking techniques have emerged as viable tools for wavefront metrology and sample imaging applications. These methods are based on the measurement of near-field images. Thanks to their simple experimental setup, high angular sensitivity and compatibility with low-coherence sources, these methods have been actively developed for use with synchrotron and laboratory light sources. Not only do speckle-tracking techniques give the potential for high-resolution imaging, but they also provide rapid and robust characterization of aberrations of X-ray optical elements, focal spot profiles, and sample position and transmission properties. In order to realize these capabilities, software implementations are required that are equally rapid and robust. To address this need, a software suite has been developed for the ptychographic X-ray speckle-tracking technique, an X-ray speckle-based method suitable for highly divergent wavefields. The software suite is written in Python 3, with an OpenCL back end for GPU and multi-CPU core processing. It is accessible as a Python module, through the command line or through a graphical user interface, and is available as source code under Version 3 or later of the GNU General Public License.

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31

Wang, Chengming, Yi-Jing You, Shengnan Ai, Wenxin Zhang, Wenchao Liao, Xiao Zhang, Juicheng Hsieh, et al. "Multi-frame speckle reduction in OCT using supercontinuum pumped by noise-like pulses." Journal of Innovative Optical Health Sciences 12, no. 02 (March 2019): 1950009. http://dx.doi.org/10.1142/s1793545819500093.

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In most coherent imaging modality, speckle noise is a major cause that blurs the boundary of tissues and degrades the image contrast. By utilizing the unique properties of supercontinuum (SC) generated by noise-like pulses (NLPs) and a simple multi-frame averaging technique, we achieved significant speckle reduction in spectral domain optical coherence tomography (SD-OCT). We quantitatively compared the speckle of our proposed method with those of conventional swept source OCT (SS-OCT) and SD-OCT based on commercial light sources. The experimental results show that SC pumped by NLPs combined with noncoherent averaging method achieves better denoising performance in terms of contrast to noise ratio (CNR).

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32

Morgan, Andrew J., Kevin T. Murray, Mauro Prasciolu, Holger Fleckenstein, Oleksandr Yefanov, Pablo Villanueva-Perez, Valerio Mariani, et al. "Ptychographic X-ray speckle tracking with multi-layer Laue lens systems." Journal of Applied Crystallography 53, no. 4 (July 8, 2020): 927–36. http://dx.doi.org/10.1107/s1600576720006925.

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The ever-increasing brightness of synchrotron radiation sources demands improved X-ray optics to utilize their capability for imaging and probing biological cells, nano-devices and functional matter on the nanometre scale with chemical sensitivity. Hard X-rays are ideal for high-resolution imaging and spectroscopic applications owing to their short wavelength, high penetrating power and chemical sensitivity. The penetrating power that makes X-rays useful for imaging also makes focusing them technologically challenging. Recent developments in layer deposition techniques have enabled the fabrication of a series of highly focusing X-ray lenses, known as wedged multi-layer Laue lenses. Improvements to the lens design and fabrication technique demand an accurate, robust, in situ and at-wavelength characterization method. To this end, a modified form of the speckle tracking wavefront metrology method has been developed. The ptychographic X-ray speckle tracking method is capable of operating with highly divergent wavefields. A useful by-product of this method is that it also provides high-resolution and aberration-free projection images of extended specimens. Three separate experiments using this method are reported, where the ray path angles have been resolved to within 4 nrad with an imaging resolution of 45 nm (full period). This method does not require a high degree of coherence, making it suitable for laboratory-based X-ray sources. Likewise, it is robust to errors in the registered sample positions, making it suitable for X-ray free-electron laser facilities, where beam-pointing fluctuations can be problematic for wavefront metrology.

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33

Mohan, Nandigana Krishna. "The influence of multiple-exposure recording on curvature pattern using multi-aperture speckle shear interferometry." Optics Communications 186, no. 4-6 (December 2000): 259–63. http://dx.doi.org/10.1016/s0030-4018(00)01072-5.

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34

Dragojević, Tanja, Joseph L. Hollmann, Davide Tamborini, Davide Portaluppi, Mauro Buttafava, Joseph P. Culver, Federica Villa, and Turgut Durduran. "Compact, multi-exposure speckle contrast optical spectroscopy (SCOS) device for measuring deep tissue blood flow." Biomedical Optics Express 9, no. 1 (December 20, 2017): 322. http://dx.doi.org/10.1364/boe.9.000322.

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35

Spahr, Hendrik, Clara Pfäffle, Gereon Hüttmann, and Dierck Hillmann. "Artifacts in speckle tracking and multi-aperture Doppler OCT imaging of lateral motion." Optics Letters 44, no. 6 (March 5, 2019): 1315. http://dx.doi.org/10.1364/ol.44.001315.

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36

Singh, Garima, Raphaël Galicher, Pierre Baudoz, Olivier Dupuis, Manuel Ortiz, Axel Potier, Simone Thijs, and Elsa Huby. "Active minimization of non-common path aberrations in long-exposure imaging of exoplanetary systems." Astronomy & Astrophysics 631 (October 31, 2019): A106. http://dx.doi.org/10.1051/0004-6361/201936206.

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Context. Spectroscopy of exoplanets is very challenging because of the high star-planet contrast. A technical difficulty in the design of imaging instruments is the noncommon path aberrations (NCPAs) between the adaptive optics (AO) sensing and the science camera, which induce planet-resembling stellar speckles in the coronagraphic science images. In an observing sequence of several long exposures, quickly evolving NCPAs average out and leave behind an AO halo that adds photon noise to the planet detection. Static NCPA can be calibrated a posteriori using differential imaging techniques. However, NCPAs that evolve during the observing sequence do not average out and cannot be calibrated a posteriori. These quasi-static NCPAs are one of the main limitations of the current direct imaging instruments such as SPHERE, GPI, and SCExAO. Aims. Our aim is to actively minimize the quasi-static speckles induced in long-exposure images. To do so, we need to measure the quasi-static speckle field above the AO halo. Methods. The self-coherent camera (SCC) is a proven technique which measures the speckle complex field in the coronagraphic science images. It is routinely used on the THD2 bench to reach contrast levels of < 10−8 in the range 5 − 12 λ/D in space-related conditions. To test the SCC in ground conditions on THD2, we optically simulated the residual aberrations measured behind the SPHERE/VLT AO system under good observing conditions. Results. We demonstrate in the laboratory that the SCC can minimize the quasi-static speckle intensity in the science images down to a limitation set by the AO halo residuals. The SCC reaches 1σ raw contrast levels below 10−6 in the region 5 − 12 λ/D at 783.25 nm in our experiments. Conclusions. The results presented in this article reveal an opportunity for the current and future high-contrast imaging systems to adapt the SCC for real-time measurement and correction of quasi-static speckles in long-exposure science observations from the ground.

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37

Komatsu, Shinichi, Katsuto Sumi, and Hitoshi Ohzu. "Double exposure speckle technique for imaging system analysis and use in rod lens arrays." Applied Optics 28, no. 10 (May 15, 1989): 1869. http://dx.doi.org/10.1364/ao.28.001869.

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38

Hultman, Martin, Ingemar Fredriksson, Marcus Larsson, Atila Alvandpour, and Tomas Strömberg. "A 15.6 frames per second 1-megapixel multiple exposure laser speckle contrast imaging setup." Journal of Biophotonics 11, no. 2 (August 7, 2017): e201700069. http://dx.doi.org/10.1002/jbio.201700069.

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39

Wang, Yang, Dong Wen, Xiao Chen, Qin Huang, Ming Chen, Jinling Lu, and Pengcheng Li. "Improving the estimation of flow speed for laser speckle imaging with single exposure time." Optics Letters 42, no. 1 (December 21, 2016): 57. http://dx.doi.org/10.1364/ol.42.000057.

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Restrepo, John, Nelson Correa-Rojas, and Jorge Herrera-Ramirez. "Speckle Noise Reduction in Digital Holography Using a DMD and Multi-Hologram Resampling." Applied Sciences 10, no. 22 (November 22, 2020): 8277. http://dx.doi.org/10.3390/app10228277.

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Speckle noise is a well-documented problem on coherent imaging techniques like Digital Holography. A method to reduce the speckle noise level is presented, based on introducing a Digital Micromirror Device to phase modulate the illumination over the object. Multiple holograms with varying illuminations are recorded and the reconstructed intensities are averaged to obtain a final improved image. A simple numerical resampling scheme is proposed to further improve noise reduction. The obtained results demonstrate the effectiveness of the hybrid approach.

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Bos, S. P. "Vector speckle grid: instantaneous incoherent speckle grid for high-precision astrometry and photometry in high-contrast imaging." Astronomy & Astrophysics 638 (June 2020): A118. http://dx.doi.org/10.1051/0004-6361/202037957.

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Context. Photometric and astrometric monitoring of directly imaged exoplanets will deliver unique insights into their rotational periods, the distribution of cloud structures, weather, and orbital parameters. As the host star is occulted by the coronagraph, a speckle grid (SG) is introduced to serve as astrometric and photometric reference. Speckle grids are implemented as diffractive pupil-plane optics that generate artificial speckles at known location and brightness. Their performance is limited by the underlying speckle halo caused by evolving uncorrected wavefront errors. The speckle halo will interfere with the coherent SGs, affecting their photometric and astrometric precision. Aims. Our aim is to show that by imposing opposite amplitude or phase modulation on the opposite polarization states, a SG can be instantaneously incoherent with the underlying halo, greatly increasing the precision. We refer to these as vector speckle grids (VSGs). Methods. We derive analytically the mechanism by which the incoherency arises and explore the performance gain in idealised simulations under various atmospheric conditions. Results. We show that the VSG is completely incoherent for unpolarized light and that the fundamental limiting factor is the cross-talk between the speckles in the grid. In simulation, we find that for short-exposure images the VSG reaches a ∼0.3–0.8% photometric error and ∼3−10 × 10−3λ/D astrometric error, which is a performance increase of a factor ∼20 and ∼5, respectively. Furthermore, we outline how VSGs could be implemented using liquid-crystal technology to impose the geometric phase on the circular polarization states. Conclusions. The VSG is a promising new method for generating a photometric and astrometric reference SG that has a greatly increased astrometric and photometric precision.

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Guo, De Quan, Hong Yu Yang, Cong Yao Zhang, and Dong C. Liu. "Optimization of Ultrasonic Imaging Using Persistence and Filter Technology." Advanced Materials Research 716 (July 2013): 542–47. http://dx.doi.org/10.4028/www.scientific.net/amr.716.542.

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B-mode ultrasonic images are often pervaded by the electronics noise and speckle artifact, which may make the interpretation of medical images difficult. In this paper, a legible method for ultrasonic image is constructed and it can be effective to suppress the noise and improve the images quality. Dynamic persistence technology based on temporal multi-frames is utilized to smooth the electronics noise and even lower speckle artifact. To reduce computing complexity, a sum table method and conjugate direction search approaches are applied to speed up estimation of motion vector. The guided image filter strategy is used to enhance the contrast and detail resolution for the processed image by persistence. Experimental results show that the proposed method is effective to smooth noise and enhance contrast of ultrasound image in vivo.

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He, Jin, Hao Zhang, and Meng Zhu. "Calibration of Eddy Current Sensor Using Speckle Photography." Applied Mechanics and Materials 734 (February 2015): 79–83. http://dx.doi.org/10.4028/www.scientific.net/amm.734.79.

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Double exposure speckle is proposed to calibrate eddy current sensor in micro-displacement measurement for its simplicity, robustness and high resolution. The specklegram is taken as the vector of the displacement. The actual displacement of an object is calculated according to the speckle displacement on the spatial term, which is worked out according to the fringe spacing on the spectrum surface. A calibration system is proposed with proper speckle size and imaging magnification. Experiments showed that the accuracy of displacement measurement is 0.196um with an optical magnification 65.8. The calibration curve of the eddy current sensor is consistent with the result by a nanopositioning system.

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Koppelhuber, Alexander, and Oliver Bimber. "Multi-exposure color imaging with stacked thin-film luminescent concentrators." Optics Express 23, no. 26 (December 22, 2015): 33713. http://dx.doi.org/10.1364/oe.23.033713.

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Aikio, Mika, Hannu Lindström, Eveliina Juntunen, Kari Kataja, and Heimo Keränen. "Pulsed LED Illumination for High Speed Imaging." Key Engineering Materials 364-366 (December 2007): 827–31. http://dx.doi.org/10.4028/www.scientific.net/kem.364-366.827.

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High speed imaging with decent image quality is difficult because the available exposure times are very short, which leads to the usage of a large aperture. Unfortunately, large aperture also decreases the depth resolution of the system, which reduces the quality of the image. Thus the source of illumination has to be able to output a high amount of energy in a very short time so that the aperture requirement can be relaxed. There are only a few Xenon flash lamps that fulfill the requirement of sub-microsecond pulses, so the natural choice would be to use lasers. However, when the target surface is rough, high degree of coherence causes black and white interference patterns known as speckle. The sensor might register irradiance values from zero to saturated state. Needless to say, this reduces drastically the quality of the image. There is variety of techniques for speckle removal, ranging from chaotic laser states to digital signal processing [1-5]. In this paper we discuss an alternative, namely LEDs, for this kind of illumination. The authors have performed some experiments and theoretical modeling, and successfully demonstrated an illumination system based on LEDs that can output enough energy to enable imaging with pulse lengths of 100 ns.

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Zhu, Shuo, Enlai Guo, Qianying Cui, Lianfa Bai, Jing Han, and Dongliang Zheng. "Locating and Imaging through Scattering Medium in a Large Depth." Sensors 21, no. 1 (December 25, 2020): 90. http://dx.doi.org/10.3390/s21010090.

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Scattering medium brings great difficulties to locate and reconstruct objects especially when the objects are distributed in different positions. In this paper, a novel physics and learning-heuristic method is presented to locate and image the object through a strong scattering medium. A novel physics-informed framework, named DINet, is constructed to predict the depth and the image of the hidden object from the captured speckle pattern. With the phase-space constraint and the efficient network structure, the proposed method enables to locate the object with a depth mean error less than 0.05 mm, and image the object with an average peak signal-to-noise ratio (PSNR) above 24 dB, ranging from 350 mm to 1150 mm. The constructed DINet firstly solves the problem of quantitative locating and imaging via a single speckle pattern in a large depth. Comparing with the traditional methods, it paves the way to the practical applications requiring multi-physics through scattering media.

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Aloisio, Isobel A., David M. Paganin, Christopher A. Wright, and Kaye S. Morgan. "Exploring experimental parameter choice for rapid speckle-tracking phase-contrast X-ray imaging with a paper analyzer." Journal of Synchrotron Radiation 22, no. 5 (July 21, 2015): 1279–88. http://dx.doi.org/10.1107/s1600577515011406.

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Phase-contrast X-ray imaging using a paper analyzer enables the visualization of X-ray transparent biological structures using the refractive properties of the sample. The technique measures the sample-induced distortions of a spatially random reference pattern to retrieve quantitative sample information. This phase-contrast method is promising for biomedical application due to both a simple experimental set-up and a capability for real-time imaging. The authors explore the experimental configuration required to achieve robustness and accuracy in terms of (i) the paper analyzer feature size, (ii) the sample-to-detector distance, and (iii) the exposure time. Results using a synchrotron source confirm that the technique achieves accurate phase retrieval with a range of paper analyzers and at exposures as short as 0.5 ms. These exposure times are sufficiently short relative to characteristic physiological timescales to enable real-time dynamic imaging of living samples. A theoretical guide to the choice of sample-to-detector distance is also derived. While the measurements are specific to the set-up, these guidelines, the example speckle images, the strategies for analysis in the presence of noise and the experimental considerations and discussion will be of value to those who wish to use the speckle-tracking paper analyzer technique.

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Pan, Zhiyong, Mei Yu, Gangyi Jiang, Haiyong Xu, Zongju Peng, and Fen Chen. "Multi-exposure high dynamic range imaging with informative content enhanced network." Neurocomputing 386 (April 2020): 147–64. http://dx.doi.org/10.1016/j.neucom.2019.12.093.

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Lv, Wenzhi, Yang Wang, Xiao Chen, Xiaoxi Fu, Jinling Lu, and Pengcheng Li. "Enhancing vascular visualization in laser speckle contrast imaging of blood flow using multi-focus image fusion." Journal of Biophotonics 12, no. 1 (September 14, 2018): e201800100. http://dx.doi.org/10.1002/jbio.201800100.

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Wu, Xiaoying, Xianbin Wen, Haixia Xu, Liming Yuan, and Changlun Guo. "Multi-Feature Fusion and Adaptive Kernel Combination for SAR Image Classification." Applied Sciences 11, no. 4 (February 10, 2021): 1603. http://dx.doi.org/10.3390/app11041603.

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Synthetic aperture radar (SAR) image classification is an important task in remote sensing applications. However, it is challenging due to the speckle embedding in SAR imaging, which significantly degrades the classification performance. To address this issue, a new SAR image classification framework based on multi-feature fusion and adaptive kernel combination is proposed in this paper. Expressing pixel similarity by non-negative logarithmic likelihood difference, the generalized neighborhoods are newly defined. The adaptive kernel combination is designed on them to dynamically explore multi-feature information that is robust to speckle noise. Then, local consistency optimization is further applied to enhance label spatial smoothness during classification. By simultaneously utilizing adaptive kernel combination and local consistency optimization for the first time, the texture feature information, context information within features, generalized spatial information between features, and complementary information among features is fully integrated to ensure accurate and smooth classification. Compared with several state-of-the-art methods on synthetic and real SAR images, the proposed method demonstrates better performance in visual effects and classification quality, as the image edges and details are better preserved according to the experimental results.

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