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https://www.readbyqxmd.com/read/27926748/fast-and-robust-estimation-of-ophthalmic-wavefront-aberrations
#1
Keith Dillon
No abstract text is available yet for this article.
December 1, 2016: Journal of Biomedical Optics
https://www.readbyqxmd.com/read/27921187/rotor-tracking-using-phase-of-electrograms-recorded-during-atrial-fibrillation
#2
Caroline H Roney, Chris D Cantwell, Norman A Qureshi, Rasheda A Chowdhury, Emmanuel Dupont, Phang Boon Lim, Edward J Vigmond, Jennifer H Tweedy, Fu Siong Ng, Nicholas S Peters
Extracellular electrograms recorded during atrial fibrillation (AF) are challenging to interpret due to the inherent beat-to-beat variability in amplitude and duration. Phase mapping represents these voltage signals in terms of relative position within the cycle, and has been widely applied to action potential and unipolar electrogram data of myocardial fibrillation. To date, however, it has not been applied to bipolar recordings, which are commonly acquired clinically. The purpose of this study is to present a novel algorithm for calculating phase from both unipolar and bipolar electrograms recorded during AF...
December 5, 2016: Annals of Biomedical Engineering
https://www.readbyqxmd.com/read/27918800/special-section-guest-editorial-adaptive-optics-and-wavefront-control-for-biological-systems
#3
Thomas G Bifano, Joel A Kubby, Sylvain Gigan
No abstract text is available yet for this article.
December 1, 2016: Journal of Biomedical Optics
https://www.readbyqxmd.com/read/27918353/removal-and-repositioning-of-intracorneal-ring-segments-improving-corneal-topography-and-clinical-outcomes-in-keratoconus-and-ectasia
#4
Kahei Chan, Peter S Hersh
PURPOSE: To evaluate the efficacy of removal and relocation of intracorneal ring segments for improving outcomes in treatment of keratoconus and corneal ectasia. METHODS: This is a retrospective case series conducted at a cornea and refractive surgery subspecialty practice setting. Patients with previous insertion of 2 intracorneal ring segments underwent surgical removal and repositioning of segments because of unsatisfactory visual and topographic outcomes. The principal outcomes included uncorrected and corrected visual acuities, manifest refraction, topography-derived maximum keratometry (Kmax), inferior-superior topography power difference (I - S), and higher-order aberration profile derived from wavefront analysis...
December 1, 2016: Cornea
https://www.readbyqxmd.com/read/27917909/apparent-negative-reflection-with-the-gradient-acoustic-metasurface-by-integrating-supercell-periodicity-into-the-generalized-law-of-reflection
#5
Bingyi Liu, Wenyu Zhao, Yongyuan Jiang
As the two dimensional version of the functional wavefront manipulation metamaterial, metasurface has become a research hot spot for engineering the wavefront at will with a subwavelength thickness. The wave scattered by the gradient metasurface, which is composed by the periodic supercells, is governed by the generalized Snell's law. However, the critical angle that derived from the generalized Snell's law circles the domain of the incident angles that allow the occurrence of the anomalous reflection and refraction, and no free space scattering waves could exist when the incident angle is beyond the critical angle...
December 5, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27916845/measurement-of-m%C3%A2-curve-for-asymmetric-beams-by-self-referencing-interferometer-wavefront-sensor
#6
Yongzhao Du
For asymmetric laser beams, the values of beam quality factor M x 2 and M y 2 are inconsistent if one selects a different coordinate system or measures beam quality with different experimental conditionals, even when analyzing the same beam. To overcome this non-uniqueness, a new beam quality characterization method named as M²-curve is developed. The M²-curve not only contains the beam quality factor M x 2 and M y 2 in the x-direction and y-direction, respectively; but also introduces a curve of M x α 2 versus rotation angle α of coordinate axis...
November 29, 2016: Sensors
https://www.readbyqxmd.com/read/27916567/fluorescent-visualization-of-cellular-proton-fluxes
#7
Lejie Zhang, Karl Bellve, Kevin Fogarty, William R Kobertz
Cells use plasma membrane proton fluxes to maintain cytoplasmic and extracellular pH and to mediate the co-transport of metabolites and ions. Because proton-coupled transport often involves movement of multiple substrates, traditional electrical measurements provide limited information about proton transport at the cell surface. Here we visualize voltage-dependent proton fluxes over the entire landscape of a cell by covalently attaching small-molecule fluorescent pH sensors to the cell's glycocalyx. We found that the extracellularly facing sensors enable real-time detection of proton accumulation and depletion at the plasma membrane, providing an indirect readout of channel and transporter activity that correlated with whole-cell proton current...
November 14, 2016: Cell Chemical Biology
https://www.readbyqxmd.com/read/27913343/a-frequency-shift-method-to-measure-shear-wave-attenuation-in-soft-tissues
#8
Simon Bernard, Siavash Kazemirad, Guy Cloutier
In vivo quantification of shear wave attenuation in soft tissues may help to better understand human tissue rheology and lead to new diagnostic strategies. Attenuation is difficult to measure in acoustic radiation force elastography because the shear wave amplitude decreases due to a combination of diffraction and viscous attenuation. Diffraction correction requires assuming a cylindrical wavefront and an isotropic propagation medium, which may not be the case in some applications. In this study, the frequency shift method, used in ultrasound imaging and seismology, was adapted for shear wave attenuation measurement in elastography...
December 1, 2016: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
https://www.readbyqxmd.com/read/27908063/simulation-study-of-axial-ultrasonic-wave-propagation-in-heterogeneous-bovine-cortical-bone
#9
Toshiho Hata, Yoshiki Nagatani, Koki Takano, Mami Matsukawa
The effect of the heterogeneity of the long cortical bone is an important factor when applying the axial transmission technique. In this study, the axial longitudinal wave velocity distributions in specimens from the mid-shaft of a bovine femur were measured, in the MHz range. Bilinear interpolation and the piecewise cubic Hermite interpolating polynomial method were used to construct three-dimensional (3D) axial velocity models with a resolution of 40 μm. By assuming the uniaxial anisotropy of the bone and using the results of previous experimental studies [Yamato, Matsukawa, Yanagitani, Yamazaki, Mizukawa, and Nagano (2008b)...
November 2016: Journal of the Acoustical Society of America
https://www.readbyqxmd.com/read/27906655/methodology-considerations-in-phase-mapping-of-human-cardiac-arrhythmias
#10
Ramya Vijayakumar, Sunil K Vasireddi, Phillip S Cuculich, Mitchell N Faddis, Yoram Rudy
BACKGROUND: Phase analysis of cardiac arrhythmias, particularly atrial fibrillation, has gained interest because of the ability to detect organized stable drivers (rotors) and target them for therapy. However, the lack of methodology details in publications on the topic has resulted in ongoing debate over the phase mapping technique. By comparing phase maps and activation maps, we examined advantages and limitations of phase mapping. METHODS AND RESULTS: Seven subjects were enrolled...
November 2016: Circulation. Arrhythmia and Electrophysiology
https://www.readbyqxmd.com/read/27906321/dm-lcwfc-based-adaptive-optics-system-for-large-aperture-telescopes-imaging-from-visible-to-infrared-waveband
#11
Fei Sun, Zhaoliang Cao, Yukun Wang, Caihua Zhang, Xingyun Zhang, Yong Liu, Quanquan Mu, Li Xuan
Almost all the deformable mirror (DM) based adaptive optics systems (AOSs) used on large aperture telescopes work at the infrared waveband due to the limitation of the number of actuators. To extend the imaging waveband to the visible, we propose a DM and Liquid crystal wavefront corrector (DM/LCWFC) combination AOS. The LCWFC is used to correct the high frequency aberration corresponding to the visible waveband and the aberrations of the infrared are corrected by the DM. The calculated results show that, to a 10 m telescope, DM/LCWFC AOS which contains a 1538 actuators DM and a 404 × 404 pixels LCWFC is equivalent to a DM based AOS with 4057 actuators...
November 28, 2016: Optics Express
https://www.readbyqxmd.com/read/27906275/near-core-structure-of-a-propagating-optical-vortex
#12
Priyanka Lochab, P Senthilkumaran, Kedar Khare
We study the propagation of a charge-1 vortex beam using the angular spectrum method. While vortex beams are commonly assumed to have a helical wavefront, it is well known that the phase of the vortex in the near-core region varies arbitrarily quickly. In order to explain the wavefront behavior in the near-core region, ideas such as evanescent fields or superoscillatory functions have been used before. Our study using the angular spectrum method can inherently take into account the propagating as well as evanescent spatial frequencies and is able to provide the detailed wavefront structure as the vortex wavefront evolves...
December 1, 2016: Journal of the Optical Society of America. A, Optics, Image Science, and Vision
https://www.readbyqxmd.com/read/27906262/light-field-and-holographic-three-dimensional-displays-invited
#13
Masahiro Yamaguchi
A perfect three-dimensional (3D) display that satisfies all depth cues in human vision is possible if a light field can be reproduced exactly as it appeared when it emerged from a real object. The light field can be generated based on either light ray or wavefront reconstruction, with the latter known as holography. This paper first provides an overview of the advances of ray-based and wavefront-based 3D display technologies, including integral photography and holography, and the integration of those technologies with digital information systems...
December 1, 2016: Journal of the Optical Society of America. A, Optics, Image Science, and Vision
https://www.readbyqxmd.com/read/27906249/zonal-wavefront-sensing-with-enhanced-spatial-resolution
#14
Biswajit Pathak, Bosanta R Boruah
In this Letter, we introduce a scheme to enhance the spatial resolution of a zonal wavefront sensor. The zonal wavefront sensor comprises an array of binary gratings implemented by a ferroelectric spatial light modulator (FLCSLM) followed by a lens, in lieu of the array of lenses in the Shack-Hartmann wavefront sensor. We show that the fast response of the FLCSLM device facilitates quick display of several laterally shifted binary grating patterns, and the programmability of the device enables simultaneous capturing of each focal spot array...
December 1, 2016: Optics Letters
https://www.readbyqxmd.com/read/27906228/holographic-imaging-with-a-hard-x-ray-nanoprobe-ptychographic-versus-conventional-phase-retrieval
#15
A-L Robisch, J Wallentin, A Pacureanu, P Cloetens, T Salditt
We have performed near-field x-ray imaging with simultaneous object and probe reconstruction. By an advanced ptychographic algorithm based on longitudinal and lateral translations, full-field images of nanoscale objects are reconstructed with quantitative contrast values, along with the extended wavefronts used to illuminate the objects. The imaging scheme makes idealizing assumptions on the probe obsolete, and efficiently disentangles phase shifts related to the object from the imperfections in the illumination...
December 1, 2016: Optics Letters
https://www.readbyqxmd.com/read/27898448/laser-vision-correction-in-treating-myopia
#16
Germano Leal Ehlke, Ronald R Krueger
Myopia is a generally benign refractive error with an increasing prevalence worldwide. It can be corrected temporarily with glasses and contact lenses and permanently with laser vision correction. The 2 main procedures currently being performed for myopia correction are photorefractive keratectomy and laser-assisted in situ keratomileusis. Each technique has its advantages, but they appear to yield similar visual outcomes 1 year after surgery. Laser vision correction for myopia was considered a paradigm shift because healthy eyes could now undergo a surgical procedure to permanently and safely correct the error by altering the center of the cornea, which was previously off limits because of the potential for loss of transparency...
November 2016: Asia-Pacific Journal of Ophthalmology
https://www.readbyqxmd.com/read/27897976/test-of-the-practicality-and-feasibility-of-edof-empowered-image-sensors-for-long-range-biometrics
#17
Sheng-Hsun Hsieh, Yung-Hui Li, Chung-Hao Tien
For many practical applications of image sensors, how to extend the depth-of-field (DoF) is an important research topic; if successfully implemented, it could be beneficial in various applications, from photography to biometrics. In this work, we want to examine the feasibility and practicability of a well-known "extended DoF" (EDoF) technique, or "wavefront coding," by building real-time long-range iris recognition and performing large-scale iris recognition. The key to the success of long-range iris recognition includes long DoF and image quality invariance toward various object distance, which is strict and harsh enough to test the practicality and feasibility of EDoF-empowered image sensors...
November 25, 2016: Sensors
https://www.readbyqxmd.com/read/27896533/characteristics-of-higher-order-aberrations-and-anterior-segment-tomography-in-patients-with-pathologic-myopia
#18
Kaori Kasahara, Naoyuki Maeda, Takashi Fujikado, Makoto Tomita, Muka Moriyama, Mutsumi Fuchihata, Kyoko Ohno-Matsui
PURPOSE: To investigate prospectively the characteristics in the higher-order aberrations and anterior segment tomography in patients with pathologic myopia. METHODS: One hundred and twelve consecutive highly myopic patients (mean age 43.4 ± 9.3 years, spherical equivalent of refractive error ≥8 D and an axial length ≥26.5 mm) were studied. Thirty-seven emmetropic individuals (mean age 37.0 ± 14.5 years, spherical equivalent of refractive error ≤ ±1 D) were analyzed as controls...
November 28, 2016: International Ophthalmology
https://www.readbyqxmd.com/read/27893094/comparison-of-patient-specific-computational-modeling-predictions-and-clinical-outcomes-of-lasik-for-myopia
#19
Ibrahim Seven, Ali Vahdati, Vinicius Silbiger De Stefano, Ronald R Krueger, William J Dupps
Purpose: To assess the predictive accuracy of simulation-based LASIK outcomes. Methods: Preoperative and 3-month post-LASIK tomographic data from 20 eyes of 12 patients who underwent wavefront-optimized LASIK for myopia were obtained retrospectively. Patient-specific finite element models were created and case-specific treatment settings were simulated. Simulated keratometry (SimK) values and the mean tangential curvature of the central 3 mm (Kmean) were obtained from the anterior surfaces of the clinical tomographies, and computational models were compared...
November 1, 2016: Investigative Ophthalmology & Visual Science
https://www.readbyqxmd.com/read/27892454/miniature-optical-planar-camera-based-on-a-wide-angle-metasurface-doublet-corrected-for-monochromatic-aberrations
#20
Amir Arbabi, Ehsan Arbabi, Seyedeh Mahsa Kamali, Yu Horie, Seunghoon Han, Andrei Faraon
Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They are poised to revolutionize optics by enabling complex low-cost systems where multiple metasurfaces are lithographically stacked and integrated with electronics. For imaging applications, metasurface stacks can perform sophisticated image corrections and can be directly integrated with image sensors. Here we demonstrate this concept with a miniature flat camera integrating a monolithic metasurface lens doublet corrected for monochromatic aberrations, and an image sensor...
November 28, 2016: Nature Communications
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