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291.
Pollakrit Toonkum 《Ultrasonics》2011,51(2):136-147
This paper presents a new three-dimensional (3D) ultrasound reconstruction algorithm for generation of 3D images from a series of two-dimensional (2D) B-scans acquired in the mechanical linear scanning framework. Unlike most existing 3D ultrasound reconstruction algorithms, which have been developed and evaluated in the freehand scanning framework, the new algorithm has been designed to capitalize the regularity pattern of the mechanical linear scanning, where all the B-scan slices are precisely parallel and evenly spaced. The new reconstruction algorithm, referred to as the Cyclic Regularized Savitzky-Golay (CRSG) filter, is a new variant of the Savitzky-Golay (SG) smoothing filter. The CRSG filter has been improved upon the original SG filter in two respects: First, the cyclic indicator function has been incorporated into the least square cost function to enable the CRSG filter to approximate nonuniformly spaced data of the unobserved image intensities contained in unfilled voxels and reduce speckle noise of the observed image intensities contained in filled voxels. Second, the regularization function has been augmented to the least squares cost function as a mechanism to balance between the degree of speckle reduction and the degree of detail preservation. The CRSG filter has been evaluated and compared with the Voxel Nearest-Neighbor (VNN) interpolation post-processed by the Adaptive Speckle Reduction (ASR) filter, the VNN interpolation post-processed by the Adaptive Weighted Median (AWM) filter, the Distance-Weighted (DW) interpolation, and the Adaptive Distance-Weighted (ADW) interpolation, on reconstructing a synthetic 3D spherical image and a clinical 3D carotid artery bifurcation in the mechanical linear scanning framework. This preliminary evaluation indicates that the CRSG filter is more effective in both speckle reduction and geometric reconstruction of 3D ultrasound images than the other methods. 相似文献
292.
Percival F. Almoro Giancarlo PedriniPhanindra N. Gundu Wolfgang OstenSteen G. Hanson 《Optics and Lasers in Engineering》2011,49(2):252-257
A phase retrieval technique for enhanced wavefront reconstruction using random phase modulation and a phase diffuser is proposed. The speckle field generated is sampled at multiple axially displaced planes and the speckle patterns are used in an iterative algorithm based on the optical wave propagation in free space. The presentation of this technique is carried out using two setups. In the first setup, a diffuser plate is placed at the image plane of a metallic test object. The benefit of randomizing the phase of the object wave is the enhanced intensity recording due to high dynamic range of the diffusely scattered beam. The use of demagnification optics will also allow the investigations of relatively large objects. In the second setup, a transparent object is illuminated using a wavefront with random phase and constant amplitude by positioning the phase diffuser close to the object. The benefit of phase-only modulation is the increased resolution of the phase structures of the transparent test objects. 相似文献
293.
In this paper, digital speckle correlation is used in the measurement of Ti alloy compression and tension test. The key technologies applied in the measurement are discussed in detail, including camera calibration with telephoto lens and digital image correlation in large deformation. Single camera self-calibration algorithm based on photogrammetry is proposed. In the algorithm, the interior parameters of camera are estimated without calibrated object, using the bundle adjustment technique, so the 3-D coordinates of calibration target points are not needed in advance to get a reliable camera calibration result. An updating reference image scheme could be employed to deal with large deformation situation. A large deformation measurement scheme, updating reference image scheme, is proposed in this paper. The un-deformed image is used as reference in correlation at first. Only for extremely large deformation field, in which iteration of correlation is not convergent, the reference image is updated to the image of previous deformed stage. Using this method, not only extremely large deformation can be measured successfully but also the accumulated error could be controlled. The 75 mm lens is calibrated in the measurement and compared the result with extensometer and un-calibrated image. Experimental results show that up to 150% tensile deformation and 50% compression deformation can be measured successfully. 相似文献
294.
295.
On the specific experience of national metrology institutes (NMIs) with national accreditation bodies (NABs) 总被引:1,自引:1,他引:0
Janko Drnovsek 《Accreditation and quality assurance》2008,13(6):321-325
The following paper addresses the experience of certain national metrology institutes (NMIs) with national accreditation bodies
(NABs), in particular in small countries with emerging economies in new EU or candidate member states. Specific cases have
been analysed primarily in some Central and South-East European countries. NABs under consideration are, in principle, members
of European Co-operation for Accreditation (EA). EA cross-frontier policy in these cases will be discussed and resulting dilemmas
outlined. Focus will be given to the problems of NMIs also performing calibrations, commercial calibration laboratories, and
their relations with NABs. Due to numerous problems of smaller NABs, cross-frontier policy should stimulate cooperation between
foreign and local accreditation bodies not only at the request of the calibration laboratory or some other conformity assessment
body, but at the request of the local accreditation body in order to provide the best service for their local economy. As
a solution to the accreditation problems, this paper proposes a process of gradual formation of a common European pool of
experts, real-life common practices and, finally, maybe even some form of joint European accreditation service.
The opinions expressed in the paper are personal statements of the author, and do not necessarily reflect the official opinions
of the institutions of the author.
Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher. 相似文献
296.
Nicolas Gurineau Sylvain Rommeluere Emmanuel Di Mambro Isabelle Ribet Jrme Primot 《Comptes Rendus Physique》2003,4(10):1175-1185
During the last decade, amazing advances in microelectronics have led to the development of large infrared focal plane arrays (IRFPAs) with a high density of pixels per square centimetre. Bispectral and soon multispectral detectors are now under development. In order to follow or even anticipate this race for spatial and spectral resolution, new techniques of characterisation have been developed in our laboratory, allowing the measurement of the spatial and spectral responses of a hundred of thousands pixels forming the IRFPA. Thus, a test bench for the measurement of hyperspectral cartographies has been realised. The principle of measurement and experimental results will be presented. For the measurement of spatial responses, the projection of targets that illuminate the entire surface of the IRFPA and contain sub-pixel details is required in order to extract the line (or spot) spread function of every pixel. For this, non-imaging techniques of projection based on the self-imaging property of periodic targets have been elaborated. The first results and the potential of this original approach will be discussed. To cite this article: N. Guérineau et al., C. R. Physique 4 (2003). 相似文献
297.
We examine the problem of quantitative chemical measurement for well-identified substances, discuss the quantity called ‘amount
of substance’, the means of expressing it, and its physical SI unit the mole. The everyday quantity which is a number of entities
may be measured by the performance of two operations (identification and counting), the results of which may be communicated
with two items of information (their name and the number of entities). We distinguish nominal, ordinal, interval and ratio
scales of measurement and apply these to counting, referring to ordinal and cardinal numbers and Helmholtz’ analysis of measurement.
Counting may be by direct serial numeration, direct parallel numeration, or comparative numeration. We discuss the limitations
of serial numeration, the possibilities of parallel numeration, and the advantages of comparative numeration where a unit
for counting in multiples (such as the analyst’s mole) may be used to define a scale on which equal numbers of objects correspond
to equal values of some other physical quantity. We conclude that the numeration of very large numbers of objects is readily
achieved but with unavoidable uncertainty, using operations which compare numbers of entities either to numbers of other entities
or to some other quantity which accurately models numbers of entities. 相似文献
298.
Y.H. Huang S.Y. HungFarrokh Janabi-Sharifi W. WangY.S. Liu 《Optics and Lasers in Engineering》2012,50(4):534-539
The rapid progress of modern manufacturing and inspection technologies has posed stringent requirements on optical techniques for vibration characterization and dynamic testing. Due to its simplicity, accuracy and whole-field characters, laser speckle interferometry has served as one of the major techniques for dynamic measurement. In this paper, a two-step phase shifting method is developed for quantitative speckle phase measurement, which helps to eliminate the specklegrams needed for phase evaluation and facilitate dynamic measurement. Unlike previously reported two-step methods using fringe patterns with known phase shift of π/2, a small unknown phase shift is employed instead in the proposed method, which eliminates the need for phase shifting devices. Further investigation shows that small phase shifts are preferable over large phase shifts in this method. Shearographic experiments conducted have demonstrated the effectiveness of the proposed technique. 相似文献