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IEEE Symposium on Nuclear Science (NSS/MIC)

作者： K. Sourbelle G. Lauritsch K.C. Tam F. Noo W.A. Kalender Institute of Medical Physics University of Erlangen Erlangen Germany Siemens Medical Engineering Group Erlangen Germany Siemens Corporate Research Inc. Princeton NJ USA Institute of Electricity Montefïore University of Liège Liege Belgium

This paper investigates the performance of exact reconstruction algorithms for spiral cone-beam computed tomography. The authors compare two different approaches of exact algorithms: the first one is the Radon algorithm with explicit calculation of Radon data and subsequent direct inversion, the second approach is a reformulation of the Radon algorithm as a 3D filtered backprojection method. Both algorithms are able to reconstruct a region-of-interest (ROI) of a long object by using the local ROI technique. The filtered backprojection approach seems a convenient method since the projections can be processed sequentially. However, no other justified advantage has been pointed out up to now. The goal of this study is to identify which algorithm has the better performance with respect to image quality and practicability. The properties of the algorithms are analyzed. Image quality is evaluated regarding artifacts, spatial as well as contrast resolution, and noise properties. The 3D Point Spread Function (PSF) is examined for violations of isotropy and spatial invariance. In-plane and axial resolutions are derived from the in-plane modulation transfer function (MTF) and the slice sensitivity profile (SSP), respectively.

关键词： Spirals Computed tomography Image quality Detectors Image reconstruction Spatial resolution Biomedical imaging Physics Biomedical engineering reconstruction algorithms

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algorithms and basis functions in tomographic reconstruction of ionospheric electron density

Algorithms and basis functions in tomographic reconstruction...

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European Signal Processing Conference (EUSIPCO)

作者： Ersin Yavuz Feza Arıkan Orhan Arıkan Cemil B. Erol Finansal Teknoloji Hizmetleri A.S. Ziraat Bankasi Tandogan Ankara Turkey Electrical and Electronics Engineering Department Hacettepe University Ankara Turkey Electrical and Electronics Engineering Department Bilkent University Ankara Turkey TUBITAK UEKAE ÍLTAREN Ankara Turkey

Computerized ionospheric tomography (CIT) is a method to investigate ionosphere electron density in two or three dimensions. This method provides a flexible tool for studying ionosphere. Earth based receivers record signals transmitted from the GPS satellites and the computed pseudorange and phase values are used to calculate Total Electron Content (TEC). Computed TEC data and the tomographic reconstruction algorithms are used together to obtain tomographic images of electron density. In this study, a set of basis functions and reconstruction algorithms are used to investigate best fitting two dimensional tomographic images of ionosphere electron density in height and latitude for one satellite and one receiver pair. Results are compared to IRI-95 ionosphere model and both receiver and model errors are neglected.

关键词： Ionosphere Receivers Satellites reconstruction algorithms Polynomials Image reconstruction

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Direct adaptive algorithms for CT reconstruction

Direct adaptive algorithms for CT reconstruction

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IEEE International Symposium on Biomedical Imaging

作者： Joseph Shtok Michael Elad Michael Zibulevsky Computer Science Department Technion-Israel Institute of Technology Haifa Israel

ISBN: (纸本)9781424439317

This work concerns with linear and spatially-adaptive direct reconstruction algorithms for 2-D parallel-beam transmission tomography, extending the filtered back-projection (FBP). The standard apodized Ram-Lak filter kernel is replaced with a bank of statistically trained 2-D convolution kernels, leading to improved reconstruction results. Two types of filter training procedures are considered. The first deals with reconstruction from noisy and truncated projections in a predefined region of interest, for images from a known family. In the second algorithm, termed SPADES, the training aims at improving the impulse response properties of the overall projection-reconstruction scheme. In this algorithm, the degree of smoothing applied to the reconstructed image is spatially controlled by a switch rule. Both methods are shown by simulations to operate well and lead to substantially improved reconstruction results.

关键词： Adaptive algorithm Image reconstruction Computed tomography Kernel Adaptive filters reconstruction algorithms Iterative algorithms Nonlinear filters Convolution Switches

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Fast parallelizable algorithms for transmission image reconstruction

Fast parallelizable algorithms for transmission image recons...

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IEEE Symposium on Nuclear Science (NSS/MIC)

作者： J.A. Fessler E.P. Ficaro N.H. Clinthorne K. Lange University of Michigan Ann Arbor MI USA

Presents a new class of algorithm for penalized-likelihood reconstruction of attenuation maps from low-count transmission scans. The authors derive the algorithms by applying to the transmission log-likelihood a variation of the convexity technique developed by De Pierro for the emission case. The new algorithms overcome several limitations associated with previous algorithms. (1) Fewer exponentiations are required than in the transmission EM algorithm or in coordinate-ascent algorithms. (2) The algorithms intrinsically accommodate nonnegativity constraints, unlike many gradient-based methods. (3) The algorithms are easily parallelizable, unlike coordinate-ascent algorithms and perhaps line-search algorithms. The authors show that the algorithms converge faster than several alternatives, even on conventional workstations. They give examples from low-count PET transmission scans and from truncated fan-beam SPECT transmission scans.

关键词： Image reconstruction Positron emission tomography Statistical analysis Whole-body PET Attenuation measurement Workstations Availability Protocols reconstruction algorithms US Department of Energy

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Handling data redundancy in helical cone beam reconstruction with a cone-angle-based window function and its asymptotic approximation

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MEDICAL PHYSICS 2007年第6期34卷 1989-1998页

作者： Tang, Xiangyang Hsieh, Jiang GE Co Appl Sci Lab Milwaukee WI 53201 USA

A cone-angle-based window function is defined in this manuscript for image reconstruction using helical cone beam filtered backprojection (CB-FBP) algorithms. Rather than defining the window boundaries in a two-dimensional detector acquiring projection data for computed tomographic imaging, the cone-angle-based window function deals with data redundancy by selecting rays with the smallest cone angle relative to the reconstruction plane. To be computationally efficient, an asymptotic approximation of the cone-angle-based window function is also given and analyzed in this paper. The benefit of using such an asymptotic approximation also includes the avoidance of functional discontinuities that cause artifacts in reconstructed tomographic images. The cone-angle-based window function and its asymptotic approximation provide a way, equivalent to the Tam-Danielsson-window, for helical CB-FBP reconstruction algorithms to deal with data redundancy, regardless of where the helical pitch is constant or dynamically variable during a scan. By taking the cone-parallel geometry as an example, a computer simulation study is conducted to evaluate the proposed window function and its asymptotic approximation for helical CB-FBP reconstruction algorithm to handle data redundancy. The computer simulated Forbild head and thorax phantoms are utilized in the performance evaluation, showing that the proposed cone- angle-based window function and its asymptotic approximation can deal with data redundancy very well in cone beam image reconstruction from projection data acquired along helical source trajectories. Moreover, a numerical study carried out in this paper reveals that the proposed cone-angle-based window function is actually equivalent to the Tam-Danielsson-window, and rigorous mathematical proofs are being investigated. (c) 2007 American Association of Physicists in Medicine.

关键词： window function cone-beam volume CT helical CT CT reconstruction 3D reconstruction reconstruction algorithms

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Wobbling and LSF-based maximum likelihood expectation maximization reconstruction for wobbling PET

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RADIATION PHYSICS AND CHEMISTRY 2016年 121卷 1-9页

作者： Kim, Hang-Keun Son, Young-Don Kwon, Dae-Hyuk Joo, Yohan Cho, Zang-Hee Gachon Univ Dept Biomed Engn Gachon South Korea Gachon Univ Neurosci Res Inst Gachon South Korea Gwangju Inst Sci & Technol Dept Med Syst Engn Gwangju South Korea Seoul Natl Univ Adv Inst Convergence Technol Seoul 151 South Korea Univ Calif Irvine Radiol Sci & Psychiat & Human Behav Irvine CA 92697 USA

Positron emission tomography (PET) is a widely used imaging modality;however, the PET spatial resolution is not yet satisfactory for precise anatomical localization of molecular activities. Detector size is the most important factor because it determines the intrinsic resolution, which is approximately half of the detector size and determines the ultimate PET resolution. Detector size, however, cannot be made too small because both the decreased detection efficiency and the increased septal penetration effect degrade the image quality. A wobbling and line spread function (LSF)-based maximum likelihood expectation maximization (WL-MLEM) algorithm, which combined the MLEM iterative reconstruction algorithm with wobbled sampling and LSF-based deconvolution using the system matrix, was proposed for improving the spatial resolution of PET without reducing the scintillator or detector size. The new algorithm was evaluated using a simulation, and its performance was compared with that of the existing algorithms, such as conventional MLEM and LSF-based MLEM. Simulations demonstrated that the WL-MLEM algorithm yielded higher spatial resolution and image quality than the existing algorithms. The WL-MLEM algorithm with wobbling PET yielded substantially improved resolution compared with conventional algorithms with stationary PET. The algorithm can be easily extended to other iterative reconstruction algorithms, such as maximum a priori (MAP) and ordered subset expectation maximization (OSEM). The WL-MLEM algorithm with wobbling PET may offer improvements in both sensitivity and resolution, the two most sought-after features in PET design. (C) 2015 Published by Elsevier Ltd.

关键词： High-resolution imaging Iterative algorithms Positron emission tomography reconstruction algorithms

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FPGA-Based Short Horizon Integration Voltage reconstruction Method for Three-Level Neutral Point Clamped Inverter

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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 2021年第11期68卷 10412-10421页

作者： Diao, Naizhe Sun, Xianrui Song, Chonghui Zhang, Haifeng Northeastern Univ Coll Informat Sci & Engn Shenyang 110819 Peoples R China

In this article, a real-time short horizon integration voltage reconstruction method based on field programmable gate array (FPGA-based) is proposed for the three-level neutral point clamped (NPC) inverter. It uses real driving signals obtained by FPGA's internal signals to rebuild the inverter's phase voltages. First, auxiliary driving signals are rebuilt according to the phase-current directions. They differ from real driving signals in that the effects of operations such as adding the dead time (DT) and eliminating narrow pulses (NP) is removed. Then, the output voltage within each synchronous clock pulse is reconstructed by the integration of the instant voltage, which is computed by the dc-bus voltage and auxiliary switching states determined by auxiliary driving signals. The equivalent voltage in each switching period can also be obtained by the integration of the instant voltage. Compared with other methods, it is universally suitable for various pulsewidth modulation (PWM) methods regardless of whether the NP is eliminated or the DT is added in these PWM methods. Meanwhile, it ensures that the reconstructed voltage is consistent with the actual output voltage at a low cost. Its effectiveness is verified by simulations and experiments.

关键词： Switches Pulse width modulation reconstruction algorithms Reliability theory Observers Inverters Real-time systems Driving signals short horizon integration three-level neutral point clamped (NPC) inverter voltage reconstruction

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Fast algorithms for the reconstruction of images from hyperbolic systems

Fast algorithms for the reconstruction of images from hyperb...

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IEEE Conference on Decision and Control

作者： Laurence R. Riddle Howard L. Weinert Ship Acoustics Department David W. Taylor Naval Ship Research and Development Center Annapolis MD USA Department of Electrical Engineering and Computer Science Johns Hopkins University Baltimore MD USA

In this paper, we discuss efficient methods for reconstructing the state variables and inputs of certain hyperbolic systems. We assume that the hyperbolic system is characterized by a system of partial differential equations that it is operating in steady state, and that the observation interval is long enough to reliably compute the Fourier transform (or Fourier series if the data is periodic) with respect to time of the observations. We specifically discuss algorithms applicable to the 2-D wave equation with continuous observations over a rectangle, and a class of hyperbolic systems having one spatial dimension and point sensors placed on the system. It is shown that under realistic stability conditions, these reconstruction algorithms are well-posed. We also present a decentralized implementation of the one spatial dimension, point sensor reconstruction algorithm.

关键词： Image reconstruction Partial differential equations Fourier transforms Sensor systems Frequency estimation Signal processing algorithms reconstruction algorithms Electromagnetic waveguides DH-HEMTs Boundary conditions

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algorithms for signal reconstruction from short-time Fourier transform magnitude

Algorithms for signal reconstruction from short-time Fourier...

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International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： S. Nawab T. Quatieri Jae Lim Massachusetts Institute of Technology Lexington Massachusetts Lincoln Laboratory and Research Laboratory of Electronics Massachusetts Institute of Technology Lexington MA USA

We have previously established a number of conditions under which a real signal can be uniquely reconstructed from its STFT magnitude. For the STFT magnitude to be a practical signal representation, we need robust reconstruction algorithms. In this paper, we discuss such a class of algorithms within the framework of sequential extrapolation techniques. Such techniques reconstruct the short-time sections of a signal in an order determined by their positions on the time axis. We find that compared to direct reconstruction, the robust algorithms are less sensitive to roundoff errors. To further test the robustness of these algorithms, we applied them to STFT magnitudes which were purposely modified for accomplishing signal processing tasks such as noise reduction and time-scale modification of speech.

关键词： Signal reconstruction Fourier transforms Signal processing algorithms Noise robustness Signal representations reconstruction algorithms Extrapolation Roundoff errors Testing Noise reduction

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DATA-DEPENDENT BANDWIDTH SELECTION FOR EMISSION COMPUTED-TOMOGRAPHY reconstruction

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IEEE TRANSACTIONS ON MEDICAL IMAGING 1993年第2期12卷 167-172页

作者： PAWITAN, Y OSULLIVAN, F UNIV WASHINGTON DEPT STATSEATTLEWA 98195

At present, the choice of bandwidth in emission computed tomography (ECT) reconstruction is done by subjective means. Here we develop an automated objective selection technique for linear reconstruction algorithms such as filtered backprojection. The approach is based on the method of unbiased risk estimation. A set of 2-dimensional validation studies using computer simulated and physical phantom data from the Hoffman et al. [5] brain phantom are then carried out. These 2-dimensional studies incorporate measured corrections for object attenuation and lack of uniformity in detector sensitivity. We find that the unbiased risk approach works very well. Over a range of count rates and brain slice source distributions, the root mean square (rms) error of the fully automated reconstruction, with the data-dependent choice of bandwidth, is around 5 percent greater than the rms error for the reconstruction with an ideal choice of the bandwidth.

关键词： Bandwidth Computed tomography Imaging phantoms Electrical capacitance tomography reconstruction algorithms Nonlinear filters Physics computing Brain modeling Computational modeling Computer simulation

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