Axial Accuracy Research Articles

Noncontact common-path Fourier domain optical coherence tomography method for in vitro intraocular lens power measurement

We propose a novel common-path Fourier domain optical coherence tomography (CP-FD-OCT) method for noncontact, accurate, and objective in vitro measurement of the dioptric power of intraocular lenses (IOLs) implants. The CP-FD-OCT method principle of operation is based on simple two-dimensional scanning common-path Fourier domain optical coherence tomography. By reconstructing the anterior and posterior IOL surfaces, the radii of the two surfaces, and thus the IOL dioptric power are determined. The CP-FD-OCT design provides high accuracy of IOL surface reconstruction. The axial position detection accuracy is calibrated at 1.22 μm in balanced saline solution used for simulation of in situ conditions. The lateral sampling rate is controlled by the step size of linear scanning systems. IOL samples with labeled dioptric power in the low-power (5D), mid-power (20D and 22D), and high-power (36D) ranges under in situ conditions are tested. We obtained a mean power of 4.95/20.11/22.09/36.25 D with high levels of repeatability estimated by a standard deviation of 0.10/0.18/0.2/0.58 D and a relative error of 2/0.9/0.9/1.6%, based on five measurements for each IOL respectively. The new CP-FD-OCT method provides an independent source of IOL power measurement data as well as information for evaluating other optical properties of IOLs such as refractive index, central thickness, and aberrations.

Performance limits on three-dimensional particle localization in photon-limited microscopy

We present the performance limits on three-dimensional (3D) localization accuracy of currently used methods of wide-field superlocalization microscopy. The three methods investigated are double-helix microscopy, astigmatic imaging, and biplane detection. In the shot-noise limit, Cramer-Rao lower bound calculations show that, among these techniques, the double-helix microscope exhibits the best axial and 3D localization accuracy over short as well as long depth-of-field systems. The fundamental advantage of engineered point-spread function systems, like the double-helix, stems from the additional degrees of freedom available to control diffraction in three dimensions over variable regions of interest.

Combining multi-pulse excitation and chirp coding in contrast-enhanced ultrasound imaging

The development of techniques to separate the response of the contrast agent from that of the biological tissues is of great importance in ultrasound medical imaging. In the literature, one can find various solutions involving the use of multiple transmitted signals and the weighted sum of related echoes. In this paper, the combination of one of these multi-pulse techniques with a coded excitation is proposed and assessed. Coded excitation has been used mainly to increase the signal-to-noise ratio (SNR) and the penetration depth, provided that a matched filtering is applied in the reception chain. However, it has been shown that a signal with a long duration time also increases the backscattered echoes produced by the microbubbles and, consequently, the contrast-to-tissue ratio. Therefore, the implementation of a multi-pulse technique using a long coded pulse can yield a better contrast-to-tissue ratio and SNR. This paper investigates the combination of the linear chirp pulse with a multi-pulse technique based on the transmission of three pulses. The performance was evaluated using both simulated and real signals, assessing the improvement in the contrast-to-tissue ratio and SNR, the visual quality of the images obtained and the axial accuracy. A comparison with the same multi-pulse technique implemented using a traditional amplitude-modulated pulse revealed that the deployment of a chirp pulse produces several noticeable advantages and only a minor drawback.

Axial sub-nanometer accuracy in digital holographic microscopy

We present state-of-the-art dual-wavelength digital holographic microscopy (DHM) measurement on a calibrated 8.9 nm high chromium thin step sample and demonstrate sub-nanometer axial accuracy. By using a modified DHM reference calibrated hologram (RCH) reconstruction method, a temporal averaging procedure and a specific dual-wavelength DHM arrangement, it is shown that specimen topography can be measured with an accuracy, defined as the axial standard deviation, reduced to at least 0.9 nm. Indeed for the first time to the best of our knowledge, it is reported that averaging each of the two wavefronts recorded with real-time dual-wavelength DHM can provide up to 30% spatial noise reduction for the given configuration. Moreover, the presented experimental configuration achieves a temporal stability below 0.8 nm, thus paving the way to Angström range for dual-wavelength DHM.

In Vivo Imaging of the Fine Structure of Rhodamine-Labeled Macaque Retinal Ganglion Cells

The extent to which the fine structure of single ganglion cells, such as dendrites and axons, can be resolved in retinal images obtained from the living primate eye was investigated. Macaque retinal ganglion cells were labeled with retrograde transport of rhodamine dextran injected into the lateral geniculate nucleus. Fluorescence images of the ganglion cells were obtained in vivo with an adaptive optics scanning laser ophthalmoscope. Axons and dendritic arborization could be resolved in primate retinal ganglion cells in vivo, comparing favorably in detail with ex vivo confocal images of the same cells. The full width at half maximum of the transverse line spread function (LSF) was 1.6 microm, and that of the axial point spread function (PSF) was 115 microm. The axial positional accuracy of fluorescence-labeled objects was approximately 4 microm. This in vivo method applied to ganglion cells demonstrates that structures smaller than the somas of typical retinal cells can be accessible in living eyes. Similar approaches may be applied to image other relatively transparent retinal structures, providing a potentially valuable tool for microscopic examination of the normal and diseased living retina.

Influence of shot noise on phase measurement accuracy in digital holographic microscopy

Digital Holographic Microscopy (DHM) is a single shot interferometric technique, which provides quantitative phase images with subwavelength axial accuracy. A short hologram acquisition time (down to microseconds), allows DHM to offer a reduced sensitivity to vibrations, and real time observation is achievable thanks to present performances of personal computers and charge coupled devices (CCDs). Fast dynamic imaging at low-light level involves few photons, requiring proper camera settings (integration time and gain of the CCD; power of the light source) to minimize the influence of shot noise on the hologram when the highest phase accuracy is aimed. With simulated and experimental data, a systematic analysis of the fundamental shot noise influence on phase accuracy in DHM is presented.

SU‐FF‐I‐89: Performance Evaluation of a Unique Transrectal Ultrasound System

Purpose: To present a performance evaluation for a unique transrectal ultrasound probe for use in prostate seed implants. The ultrasound probe transducer moves inside the probe case while the case remains stationary. This allows imaging in different planes without moving the prostate. Sagittal and transverse plane imaging is available. Electronic longitudinal stepping and sagittal plane rotation of the transducer replaces manual/mechanical movement. Method and Materials: The ultrasound probe evaluated was the TargetScan® System from Envisioneering Medical Products (St. Louis, MO). Proper alignment of the needle template and software grid was verified, as well as electronic stepper position accuracy. Image quality was evaluated using a Multipurpose Tissue/Cyst Ultrasound Phantom (Nuclear Associates Model 84‐317). Tests included, maximum scanning depth, axial distance calibration accuracy, spatial resolution, high scatter resolution, low scatter resolution, superficial low scatter resolution, and dead zone region limit. All tests were performed with the probe immersed in a water medium. Both axial and sagittal scanning modes were tested. Results: Needle template/software grid coincidence (axial mode) was within 2mm, with most measurements being less than 1 mm. Longitudinal stepper accuracy was within 1mm. The following results apply to both sagittal and transverse scanning modes. Maximum scanning depth was approximately 60 mm in the medium. Axial distance accuracy was within 1 mm. Spatial resolution was 2mm axial, 3mm lateral. The 4 mm high and low scatter targets could be resolved. The 2 mm low scatter superficial targets could be resolved at the 2.2 cm and 4.4 cm depths for both sagittal and transverse modes. The dead zone limit was 2mm for both sagittal and transverse modes. Conclusion: The TargetScan® System has high image quality and transducer placement accuracy which makes it suitable for both diagnostic scanning as well as image guided prostate brachytherapy.

Cell refractive index tomography by digital holographic microscopy

For what we believe to be the first time, digital holographic microscopy is applied to perform optical diffraction tomography of a pollen grain. Transmission phase images with nanometric axial accuracy are numerically reconstructed from holograms acquired for different orientations of the rotating sample; then the three-dimensional refractive index spatial distribution is computed by inverse radon transform. A precision of 0.01 for the refractive index estimation and a spatial resolution in the micrometer range are demonstrated.

Anterior Vocal Commissure Invasion in Laryngeal Carcinoma Diagnosis

Laryngeal carcinoma involving anterior vocal commissure (AVC) represents a great challenge for staging and treatment. To compare laryngoscopy and computed tomography (CT) scan efficiency in staging tumors extending to the AVC. We also analyzed the helicoidal axial CT scan accuracy in recognizing this larynx subregion invasion. Fifty-two glottic and supraglottic laryngeal squamous cell carcinoma patients with tumoral extension to the AVC were prospectively studied from August 2001 to August 2003 at the National Cancer Institute (Rio de Janeiro, Brazil). All patients underwent videolaryngoscopic examination and direct laryngoscopy for lesion extension analysis and biopsy. After AVC helicoidal axial CT scan with sagittal and coronal 1.0 mm thick reconstruction, patients were submitted to surgical treatment. The same pathologist analyzed all surgical specimens. When compared with pathologic stage, clinical endoscopic classification was correct in 40.38% of cases (40% for T1, 29.41% for T2, 46.43% for T3, and 50% in T4). Helicoidal axial CT scan accuracy for AVC tumors was 75% (P = .0001), being more important for T2 (62.50%), T3 (73.91%), and T4 (88.24%) lesions. Identification of radiologic signs described as gross radiologic anterior commissure involvement (GRACI) increased radiologic image staging accuracy to over 96%. Endoscopic evaluation understaged tumors in all clinical stages but really T1. Helicoidal axial CT scan reformatted to 1.0 mm thick played an important role in correctly staging more advanced AVC laryngeal tumors. Radiologic signs, here identified as GRACI, may be very helpful for tomographic staging and patient treatment.

Digital holographic microscopy: a noninvasive contrast imaging technique allowing quantitative visualization of living cells with subwavelength axial accuracy

We have developed a digital holographic microscope (DHM), in a transmission mode, especially dedicated to the quantitative visualization of phase objects such as living cells. The method is based on an original numerical algorithm presented in detail elsewhere [Cuche et al., Appl. Opt. 38, 6994 (1999)]. DHM images of living cells in culture are shown for what is to our knowledge the first time. They represent the distribution of the optical path length over the cell, which has been measured with subwavelength accuracy. These DHM images are compared with those obtained by use of the widely used phase contrast and Nomarski differential interference contrast techniques.

Bore Reconstruction of Tubular Ducts From its Acoustic Input Impedance Curve

In order to get accurate bore information of tubular objects from acoustical input impedance measurements an optimization approach is proposed and investigated. The waveguide model used by the optimizer is reviewed and the impedance measurement setup is described. Reconstruction results are presented and discussed. Sensitivity of input impedance magnitude to bore variation indicates that axial accuracy can be improved without increasing the sampling rate. Advantages of the method are its increased numerical stability, its tolerance to white noise on top of measured data, no requirement to measure phase, and the fact that measured data need not to be contiguous in the frequency domain. Frequency bands which are difficult to measure can be omitted.

페룰 가공용 초정밀 무심 연삭기의 유정압 안내면 및 이송계에 대한 구조 특성 해석

This paper proposes the structural characteristic analysis and evaluation on the hydrostatic guide way and feeding system of a high-precision centerless grinder for machining ferrules. In order to realize the required accuracy of ferrules with sub-micron order, the axial stiffuess and motion accuracy of feeding system have to become higher level than those of existing centerless grinders. Under these points of view, the physical prototype of feeding system composed of steel bed, hydrostatic guide way and ballscrew feeding mechanism is designed and manufactured for trial. Experimental results show that the axial and vertical stiffuesses of the physical prototype are very low as compared with those design values. In this paper, to reveal the cause of these stiffuess difference, the structural deformations on the virtual prototype of feeding system are analyzed based on the fmite element method under experimental conditions. The simulated results illustrate that the deformation of front ballscrew support -bearing bracket is the main cause of reduction in the axial stiffness of feeding system, and the deflection of bed structure and the bending deformation of hydrostatic guide rails are the main causes of reduction in the vertical stiffness of feeding system.<br/>

Holographic particle image velocimetry: from film to digital recording

Holographic particle image velocimetry (HPIV) offers potentially the best solution to volumetric measurements of the three-dimensional velocity fields in complex flows. However, the traditional film-based HPIV measurement is rather cumbersome, limiting its use to only a handful of groups worldwide. The newly emerged digital HPIV revolutionizes flow measurement science by providing a practical 3D velocimetry tool. It commands simple hardware that is similar to regular two-dimensional particle image velocimetry (PIV), yet it provides continuous (time-series) three-dimensional, three-component flow field data. Not only is the need for chemical processing eliminated, but also the cumbersome optical reconstruction is completely replaced by numerical reconstruction algorithms. Several breakthroughs have led to the development of the first practical and integrated digital HPIV systems. To explain the transition from film to digital recording, fundamental issues in HPIV are reviewed in this paper. Axial accuracy in HPIV measurement is ultimately limited by an inherent depth-of-focus problem, while information capacity is limited by inherent speckle noise. Information capacity is an important concept in HPIV, comprising the maximum acceptable seeding density multiplied by the sample volume depth along the optic axis. Both the axial accuracy and the information capacity are limited by the effective hologram aperture. The pursuit of a large hologram aperture in the past has resulted in further complexity in film-based HPIV systems. Digital HPIV, on the other hand, enjoys great simplicity of implementation and operation. A digital HPIV is also far more compact and rugged compared to existing film-based HPIV systems, making it suitable for duplication and commercialization. However, since digital sensors suffer from inferior pixel resolutions compared to films, the effective hologram aperture is much smaller in digital HPIV than that achievable in film-based HPIV. Alleviating this problem, digital HPIV also presents new possibilities in data processing such as the use of the complex amplitude of the reconstructed light wave to improve depth sensitivity and signal-to-noise ratio. Two examples of digital HPIV systems and measurement results are given. We believe digital HPIV can revitalize holographic particle imaging and bring it into the mainstream in much the same way that digital PIV brought PIV into widespread use a decade ago.

STATIC AND DYNAMIC CHARACTERIZATION OF MEMS VIA ESPI

International Journal of Computational Engineering ScienceVol. 04, No. 03, pp. 467-470 (2003) Testing and CharacterisationNo AccessSTATIC AND DYNAMIC CHARACTERIZATION OF MEMS VIA ESPIAndreas H. Foitzik, Wolfgang Kaese, Thomas Vogt, Michael Sommerer, and Serguei ArkhipovAndreas H. FoitzikUniversity of Applied Sciences Esslingen, Department for Mechatronics, Robert-Bosch-Str. 1, D-73037 Goeppingen, Germany Search for more papers by this author , Wolfgang KaeseUniversity of Applied Sciences Esslingen, Department for Mechatronics, Robert-Bosch-Str. 1, D-73037 Goeppingen, Germany Search for more papers by this author , Thomas VogtUniversity of Applied Sciences Esslingen, Department for Automotive Technology, Esslingen, Germany Search for more papers by this author , Michael SommererUniversity of Applied Sciences Esslingen, Department for Automotive Technology, Esslingen, Germany Search for more papers by this author , and Serguei ArkhipovMOSCOW AVIATION INSTITUTE (MAI), MOSCOW, Russia Search for more papers by this author https://doi.org/10.1142/S1465876303001538Cited by:2 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractGenerally unaltered surfaces stemming from IC- or MEMS-production (Micro Electro Mechanical Systems) cannot be investigated with ESPI (Electronic Speckle Pattern Interferometry) due to the lack of any interference from the extremely flat surfaces of devices made of silicon. In order to enable ESPI for such devices additional "rough" layers can be added to the MEMS surfaces, while these relatively "thick" layers alter the mechanical properties of such small devices considerably. Utilizing a new surface preparation technique (Goeppingen Procedure®) allows to create a nm-sized roughness onto the surfaces of MEMS, thus enabling interference originating from such altered surfaces and subsequently allowing ESPI.Static ESPI on commercially available micro-sized tilt-sensors as well as read-write head of a hard disk drive showed that elastic deformations can be determined with a lateral accuracy in the μm-range and an axial accuracy in the nm-range, respectively. The static investigations allowed the identification of defect sensors in terms of quality assurance. Dynamic ESPI on MEMS showed different normal modes as well as the dynamic behaviour at the occurence of the first and the second harmonic.Keywords:MEMSESPI - Electronic Speckle Pattern InterferometryGoeppingen Procedure References J. A. Leendertz, J. Phys. E (Sci. Instrum.) 3, 214 (1970). Crossref, Google Scholar H. Marwitz , Praxis Holographie ( Expert-Verlag , 1990 ) . Google ScholarP. Aswendt and R. Höfling, Measurement 23, S. 205 (1998). Crossref, Google ScholarD. Holsteinet al., Composite Structures 40, S. 257 (1998). Crossref, Google Scholar K. Hariri , Bruchmechanisches Verhalten jungen Betons: Laser-Speckle-Interferometrie und Modellierung der Rißprozeßzone ( Techn. Univ. Braunschweig , 2000 ) . Google ScholarZ. Yanget al., Optics and Lasers in Engineering 28(6), 443 (1997). Google Scholar Höfling, R.; Aswendt, P.; Liebig, V.; Brückner, H.: Synthesis of experiment and simulation in speckle interferometry: a medical application; Akademie Verlag Series in Optical Metrology, Vol. 2, S. 261-268, Berlin 1996 . Google Scholar Foitzik, A.H.; Kümmel, M.; Schmid, M.; Kaese, W.; Vogt, T.; Groth, P.; "ESPI on MEMS", 13.Intern. Wissenschaftlich-technische Konferenz SENSOR 2001, Sudak/Krim 2001 . Google Scholar FiguresReferencesRelatedDetailsCited By 2An Experimental Study of the Vibrational Characteristics of a Diamond Circular Blade Using Electronic Speckle-Pattern Interferometry and FEMMykhaylo Tkach, Yurii Halynkin, Arkadii Proskurin, Irina Zhuk and Volodymyr Kluchnyk et al.15 May 2021 | Acta Mechanica et Automatica, Vol. 15, No. 1Electronic Speckle Pattern Interferometry for Vibrational Analysis of Cutting ToolsPiotr Mrozek, Ewa Mrozek and Andrzej Werner17 July 2018 | Acta Mechanica et Automatica, Vol. 12, No. 2 Recommended Vol. 04, No. 03 Metrics History KeywordsMEMSESPI - Electronic Speckle Pattern InterferometryGoeppingen ProcedurePDF download

２個の永久磁石を用いた顎運動計測システムの測定誤差解析

We developed a new system to capture jaw movement. It consists of two magnets and biaxial fluxgate sensors. A magnet is fixed to a tooth in the bottom jaw of the subject and another is fixed to the subject's forehead. The system can naturally detect movement of the jaw as a rigid body, because it does not require such attachments as a clutch inside the mouth or a magnetic field sensor array in contact with the head. In this paper, we investigate five error sources of the jaw-tracking system, using a jaw model, and report the achievement of a positional accuracy of 1.5 mm and an axial accuracy of 2 degrees. Positional accuracy within 2 mm is achieved as a rigid body.

Stiffness of geomaterials at very small strains

Experiments have been conducted in the triaxial apparatus to observe the behaviour at very small strains of three widely different natural materials: Bothkennar clay, London clay, and a high-porosity Chalk. Local strain measurements made using LVDTs were calibrated by a Fabry–Pérot laser interferometer. A displacement accuracy as high as ±0·027 μm was obtained, leading to an axial strain accuracy of the order of ±10−4%. Special care was taken to ensure that the rates of creep reduced to acceptably small levels before loading commenced. At very small strain levels the observed stress–strain behaviour appeared to be linear for all three materials. The extent of this linear behaviour was similar (0·002–0·003%) for all three materials, despite the maximum stiffness (Emax) ranging over two orders of magnitude. The initial influence of stress change and strain level on secant modulus was relatively small, with stiffnesses at 0·01% strain being of the order of 80–95% of Emax. Effects of loading path were observed, giving different rates of stiffness degradation as a function of strain, but recent stress history effects did not occur even though stress excursions went well beyond the range normally thought to induce plastic strains. Stiffnesses measured in the triaxial apparatus at very small strain levels were found to be similar to those obtained using field geophysical techniques, despite assumptions of isotropy, and the effects of sampling. The implications of these observations for practice are discussed.

Stiffness of geomaterials at very small strains

Experiments have been conducted in the triaxial apparatus to observe the behaviour at very small strains of three widely different natural materials: Bothkennar clay, London clay, and a high-porosity Chalk. Local strain measurements made using LVDTs were calibrated by a Fabry–Pérot laser interferometer. A displacement accuracy as high as ±0·027 μm was obtained, leading to an axial strain accuracy of the order of ±10−4%. Special care was taken to ensure that the rates of creep reduced to acceptably small levels before loading commenced. At very small strain levels the observed stress–strain behaviour appeared to be linear for all three materials. The extent of this linear behaviour was similar (0·002–0·003%) for all three materials, despite the maximum stiffness (Emax) ranging over two orders of magnitude. The initial influence of stress change and strain level on secant modulus was relatively small, with stiffnesses at 0·01% strain being of the order of 80–95% of Emax. Effects of loading path were observed, giving different rates of stiffness degradation as a function of strain, but recent stress history effects did not occur even though stress excursions went well beyond the range normally thought to induce plastic strains. Stiffnesses measured in the triaxial apparatus at very small strain levels were found to be similar to those obtained using field geophysical techniques, despite assumptions of isotropy, and the effects of sampling. The implications of these observations for practice are discussed.

Single nuclear pores visualized by confocal microscopy and image processing

How nuclear pore complexes, mediating the transport of nucleic acids, proteins, and metabolites between cell nucleus and cytoplasm, are arranged in the nuclear envelope is essentially unknown. Here we describe a method combining high-resolution confocal imaging with image processing and pattern recognition to visualize single nuclear pore complexes (120 nm diameter), determine their relative positions with nanometer accuracy, and analyze their distribution in situ. The method was tested by means of a model system in which the very same sample areas could be imaged by confocal and electron microscopy. It was thus found that single fluorescent beads of 105 nm nominal diameter could be localized with a lateral accuracy of <20 nm and an axial accuracy of approximately 20 nm. The method was applied to digitonin-permeabilized 3T3 cells, whose nuclear pore complexes were fluorescently labeled with the anti-nucleoporin antibody mAb414. Stacks of optical sections were generated by confocal imaging at high resolution. Herein the nuclear pore complexes appeared as bright diffraction-limited spots whose centers were localized by fitting them by three-dimensional gaussians. The nearest-neighbor distribution function and the pair correlation function were calculated and found to agree well with those of randomly distributed hard cylinders of 138 +/- 17 nm diameter, but not with those of randomly distributed points or nonrandomly distributed cylinders. This was supported by a cluster analysis. Implications for the direct observation of the transport of single particles and molecules through individual nuclear pore complexes are discussed.

Toolholder/Spindle Interfaces for CNC Machine Tools

The paper describes designs and tests of two novel toolholder/spindle interfaces. Interface WSU-1 provides improved axial and radial accuracy, higher stiffness, insensitivity to high rpm, and the potential for being used without keys, while being compatible with standard 7/24 spindles and toolholders. Interface WSU-2 is an inexpensive modification of the standard 7/24 interface with improved axial accuracy and stiffness characteristics. Cutting tests have confirmed the advantages of these interfaces.

An introduction to gyro optical pickoffs

An optical pickoff provides a uniquely satisfactory solution to the problem of sensing the attitude of aerostatic, electrostatic, and cryomagnetic field-suspended spherical-rotor gyros that are invariably operated in the space-fixed mode. The servos in gimbaled gyros are controlled by the optical pickoff to maintain the pickoff aligned with the rotor, usually parallel to the rotor spin axis. Autocollimation permits true angle sensing uninfluenced by rotor translation, but an autocollimating pickoff requires a flat mirror on the rotor and normal to its spin axis. Alternatively, in cases where the rotor surface must be perfectly spherical, an autoreflector viewing a variable reflectivity pattern at a pole is used to sense polar translation, which is proportional to the angular misalignment of a center-fixed rotor. Field-suspended, strap-down gyros, that invariably employ spherical rotors, utilize an orthogonal set of autoreflecting pickoffs to sense the transit of a rotor surface pattern and a computer to determine the orientation of the spin axis from the pickoff signals. Autocollimator accuracy is shown to fall in the y^ to 1 arc-sec region, whereas axial autoreflector accuracy is about 1 //in.; the strap-down readout system is capable of measuring with 10 to 100 arc-sec accuracy. Autocollimator and axial autoreflector accuracies are limited principally by the pickoffs themselves, whereas strap-down readout accuracy is restricted by the precision with which the sensing pattern can be applied to the rotor.