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Conference on Medical Imaging - Physics of Medical Imaging

作者： Zhang, Guozhi Stratis, Andreas Marshall, Nicholas Bosmans, Hilde Univ Hosp Leuven B-3000 Leuven Belgium

ISBN: (数字)9781510616363

ISBN: (纸本)9781510616363

The in-plane modulation transfer function (MTF) for multi-slice computed tomography (CT) can be found by scanning a phantom with cylindrical contrast inserts and making use of the circular edges presented in reconstructed axial images. Pixel data across the edge are used to establish an edge spread function, which is then used to obtain the line spread function and finally the MTF. A crucial step in this approach is to accurately locate the centroid of the circular region. Since the ESF is usually established in subpixel scale, slight deviation of the centroid may result in large errors. It has been a common practice to apply a preset threshold and calculate the center of mass in the binary output on each individual slice. It has also been suggested to locate the centroid on each slice by maximizing the sum of pixel values lying under a predefined template. In this paper, we propose a new algorithm based on registering the entire cylindrical object in 3D space. In a test on a high-noise low-contrast edge, both the threshold and the maximization algorithm showed scattered distribution of centroids across consecutive slices, resulting in underestimation of the MTF up to 10% at intermediate frequencies. In comparison, the method based on 3D registration has been found more robust to noise and the centroid locations are more consistent in the longitudinal direction. It is therefore recommended to use the proposed algorithm for centroid determination in evaluating the MTF with a circular edge in CT images.

关键词： Computed tomography image quality modulation transfer function centroid algorithm

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New Location algorithm with Primary User Based on Scatter Information in Cognitive Radio

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WIRELESS PERSONAL COMMUNICATIONS 2021年第2期119卷 1845-1867页

作者： Ye, Dan Natl Taiwan Univ Dept Comp Sci & Informat Engn Taipei 106 Taiwan

In cognitive radio network, if cognitive user conflicts with primary user during the spectrum sensing, it should concede avoiding the effect of communication with primary user. The paper initiates a new sensing methodology using scatter information around mobile users to locate primary user. The multi-group TOA (Time of Arrival) and AOA (Angle of Arrival) provided by two base stations are measured based on the single reflect statistics channel model under NLOS (Non-line-of-sight) environment. An innovative location algorithm, proposed in this paper, which combines neural network with the weighted centroid algorithm to achieve primary user's location. The proposed algorithm can make great improvement on the location accuracy by effectively mitigating NLOS error in cognitive radio networks. Another contribution of the proposed algorithm is the benefit to the cognitive performance, which can be characterized by the probability of spectrum coexistence. The results under different simulation circumstances illustrate that the current location algorithm improves detection performance and location performance to obtain more exact probability of spectrum coexistence.

关键词： Cognitive radio Wireless location Scatter Neural network centroid algorithm

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centroids computation and point spread function analysis for reverse Hartmann test

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OPTICS COMMUNICATIONS 2017年 387卷 328-337页

作者： Zhao, Zhu Hui, Mei Liu, Ming Dong, Liquan Kong, Linqqin Zhao, Yuejin Beijing Inst Technol Sch Optoelect Beijing Key Lab Precis Optoelect Measurement Inst Beijing 100081 Peoples R China

This paper studies the point spread function (PSF) and centroids computation methods to improve the performance of reverse Hartmann test (RHT) in poor conditions, such as defocus, background noise, etc. In the RHT, we evaluate the PSF in terms of Lommel function and classify it as circle of confusion (CoC) instead of Airy disk. Approximation of a CoC spot with Gaussian or super-Gaussian profile to identify its centroid forms the basis of centroids algorithm. It is also effective for fringe pattern while the segmental fringe is served as a 'spot' with an infinite diameter in one direction. RHT experiments are conducted to test the fitting effects and centroiding performances of the methods with Gaussian and super-Gaussian approximations. The fitting results show that the super-Gaussian obtains more reasonable fitting effects. The super-Gauss orders are only slightly larger than 2 means that the CoC has a similar profile with Airy disk in certain conditions. The results of centroids computation demonstrate that when the signal to noise ratio (SNR) is falling, the centroid computed by super-Gaussian method has a less shift and the shift grows at a slower pace. It implies that the super-Gaussian has a better anti-noise capability in centroid computation.

关键词： Point spread function Circle of confusion centroid algorithm Gaussian and super-Gaussian approximations Reverse Hartmann test

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Development of a Fine Digital Sun Sensor for STSAT-2

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INTERNATIONAL JOURNAL OF AERONAUTICAL AND SPACE SCIENCES 2012年第2期13卷 260-265页

作者： Rhee, Sung-Ho Lyou, Joon Korea Adv Inst Sci & Technol Satellite Technol Res Ctr Taejon 305701 South Korea Chungnam Natl Univ Dept Elect Engn Taejon 305764 South Korea

Satellite devices for fine attitude control of the Science & Technology Satellite-2 (STSAT-2). Based on the mission requirements of STSAT-2, the conventional analog-type sun sensors were found to be inadequate, motivating the development of a compact, fast and fine digital sun sensor (FDSS). The FDSS uses a CMOS image sensor and has an accuracy of less than 0.03degrees, an update rate of 5Hz and a weight of less than 800g. A pinhole-type aperture is substituted for the optical lens to minimize its weight. The target process speed is obtained by utilizing the Field Programmable Gate Array (FPGA), which acquires images from the CMOS sensor, and stores and processes the image data. The sensor accuracy is maintained by a rigorous centroid algorithm. This paper describes the FDSS designs, realizations, tests and calibration results.

关键词： STSAT-2 FDSS CMOS-image sensor(CIS) Pinhole-type aperture centroid algorithm

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Bio-inspired coupled oscillatory phase reset control system applied to movement in an underwater vehicle

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ROBOTICS AND AUTONOMOUS SYSTEMS 2014年第2期62卷 257-266页

作者： Porras, A. Llinas, R. NYU Sch Med Dept Neurosci & Physiol New York NY 10016 USA

The present hardware circuit was designed as a fast and energy efficient motor control system based on cerebellar oscillatory neuron activity and network dynamics. Specifically, a hardware model of the olivo-cerebellar dynamics controlling vertebrate motor coordination is used to control movement in an underwater robotic vehicle. Single shot oscillatory phase resetting is used for instantaneous motor plant reorganization based on incoming sensory information. Such a rapid feedback mode, which is rapid enough to prevent animals from falling when they stumble, has been previously described in biological and mathematical papers (Pellionisz and Llinas, 1979, Velarde et al., 2002, 2004). In the present control system, the direction of the vehicle displacement is captured by a camera, and transformed into a phase shift modulation of sets of oscillatory elements that embody internal dynamics. This design provides a novel real time control platform for robotic control in three dimensions. (C) 2013 Elsevier B.V. All rights reserved.

关键词： Underwater vehicle Olivo-cerebellar system Inferior olive centroid algorithm Motor-controllers Phase modulation Sine wave generator Step motor Pattern generator CMUcam2

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Exact tests for comparing two paired proportions with incomplete data

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BIOMETRICAL JOURNAL 2004年第1期46卷 72-82页

作者： Tang, ML Tang, NS Harvard Univ Sch Med Channing Lab Dept Med Cambridge MA 02138 USA Yunnan Univ Ctr Appl Stat Kunming 650091 Peoples R China

Various asymptotic test procedures have been developed previously for testing the equality of two binomial proportions with partially incomplete paired data. Test procedures that discard incomplete observations have been shown to be less powerful than those procedures that utilize all available observations. On the other hand, asymptotic test procedures that utilize all available observations may not be reliable in small-sample problems or sparse data structures. In this article, unconditional exact test procedures are proposed for testing the equality of two paired binomial proportions with partially incomplete paired data under a random mechanism. The proposed unconditional exact test methods are illustrated with real data from a neurological study. Empirical studies are conducted to investigate the performance of these and other test procedures with respect to size and power.

关键词： asymptotic test centroid algorithm incomplete data paired binary data unconditional exact test

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Determination of the dependence of the error in measuring displacements by optoelectronic instruments with multielement radiation receivers on the signal-to-noise ratio

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MEASUREMENT TECHNIQUES 2012年第5期55卷 563-567页

作者： Soldatov, V. P. Moscow State Univ Geodesy & Cartog MIIGAiK Moscow Russia

A new simplified approach to establishing an approximate functional relation between the error in measuring displacements by optoelectronic instruments with multielement radiation receivers and the signal-to-noise ratio is considered. The approximate formulas obtained can be used for images with small dimensions both for accurate and energy calculations of such instruments.

关键词： centroid algorithm displacement signal-to-noise ratio multielement radiation receiver

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Hough transform used on the spot-centroiding algorithm for the Shack-Hartmann wavefront sensor

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OPTICAL ENGINEERING 2016年第1期55卷 1-9页

作者： Chia, Chou-Min Huang, Kuang-Yuh Chang, Elmer Natl Taiwan Univ Dept Mech Engn 1Sect 4Roosevelt Rd Taipei 10617 Taiwan Genius Elect Opt Co Cent Taiwan Sci Pk 1Keya E Rd Taichung 42882 Taiwan

An approach to the spot-centroiding algorithm for the Shack-Hartmann wavefront sensor (SHWS) is presented. The SHWS has a common problem, in that while measuring high-order wavefront distortion, the spots may exceed each of the subapertures, which are used to restrict the displacement of spots. This artificial restriction may limit the dynamic range of the SHWS. When using the SHWS to measure adaptive optics or aspheric lenses, the accuracy of the traditional spot-centroiding algorithm may be uncertain because the spots leave or cross the confined area of the subapertures. The proposed algorithm combines the Hough transform with an artificial neural network, which requires no confined subapertures, to increase the dynamic range of the SHWS. This algorithm is then explored in comprehensive simulations and the results are compared with those of the existing algorithm. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： Shack-Hartmann wavefront sensor artificial neural network Hough transform centroid algorithm

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High-frequency estimation of the ultrasonic attenuation coefficient slope obtained in human skin:: Simulation and in vivo results

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ULTRASOUND IN MEDICINE AND BIOLOGY 1999年第3期25卷 421-429页

作者： Guittet, C Ossant, F Remenieras, JP Pourcelot, L Berson, M Fac Med INSERM U316 F-37032 Tours France Fac Med GIP ULTRASONS F-37032 Tours France

In vivo ultrasonic characterization of the skin was performed at 40 MHz by estimating the slope of the attenuation coefficient in the human dermis. The centroid algorithm was first tested on simulated backscattered RF lines with a second-order autoregressive model to carry out the spectral analysis. A relative error of less than 8.5% and a relative precision of less than 6% were predicted for a 2-mm tissue thickness and for temporal window sizes ranging from 0.25 to 0.45 mu s. In vivo measurements performed on 138 healthy volunteers yielded values of the attenuation coefficient slope ranging from 0.8 to 3.6 dB/cm MHz. A decrease was observed with advancing age, but no significant difference appeared between men and women. The results from this study suggest that this acoustic parameter shows the effect of the ageing process on normal skin tissue in vivo. (C) 1999 World Federation for Ultrasound in Medicine & Biology.

关键词： tissue characterization ultrasound high-resolution attenuation coefficient slope simulations centroid algorithm in vivo skin dermatology ageing process

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ACQUISITION BY STARING FOCAL-PLANE ARRAYS - PIXEL GEOMETRY-EFFECTS

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OPTICAL ENGINEERING 1993年第11期32卷 2649-2656页

作者： IFTEKHARUDDIN, KM KARIM, MA Univ. of Dayton (USA) Univ. of Dayton (USA)

Spatial averaging techniques have been used to compare signal acquisition (i.e., detectivity performance) of hexagonally sampled equivalent-area rectangular, hexagonal, and rhombic pixel arrays. In the absence of noise, rhombic focal-plane arrays (FPAs) are found to be associated with a modulation transfer function, which is almost identical to that of the rectangular FPA. However, while detecting noisy signals, the probability density function of the detected signal of the rhombic FPA is found to be smaller than that of hexagonal FPA, but higher than that of the rectangular FPA. At large noise variances, all three staring arrays perform almost the same in acquisition of signal.

关键词： ACQUISITION TRACKING POINTING MODULATION TRANSFER FUNCTION FOCAL-PLANE ARRAYS SPATIAL AVERAGING TECHNIQUE centroid algorithm PROBABILITY DENSITY FUNCTION RANDOM VARIABLES

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