A method to improve time resolution in 3D contrast-enhanced magnetic resonance angiography (CE-MRA) is proposed. A temporal basis based on prior knowledge of the contrast flow dynamics is applied to a sequence of imag...
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ISBN:
(纸本)9780819482969
A method to improve time resolution in 3D contrast-enhanced magnetic resonance angiography (CE-MRA) is proposed. A temporal basis based on prior knowledge of the contrast flow dynamics is applied to a sequence of imagereconstructions. In CE-MRA a contrast agent (gadolinium) is injected into a peripheral vein and MR data is acquired as the agent arrives in the arteries and then the veins of the region of clinical interest. The acquisition extends over several minutes. Information is effectively measured in 3D k-space (spatial frequency space) one line at-a-time. That line may be along a Cartesian grid line in k-space, a radial line or a spiral trajectory. A complete acquisition comprises many such lines but in order to improve temporal resolution, reconstructions are made from only partial sets of k-space data. By imposing a basis for the temporal changes, based on prior expectation of the smoothness of the changes in contrast concentration with time, it is demonstrated that a significant reduction in artifacts caused by the under-sampling of k-space can be achieved. The basis is formed from a set of gamma variate functions. Results are presented for a simulated set of 2D spiral-sampled CE-MRA data.
The approach to solving inverse problems of source identification in acoustics is proposed based on fuzzy relational calculus. The compositional rule of inference connects the real and observed fuzzy acoustic image us...
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ISBN:
(纸本)9783030542153;9783030542146
The approach to solving inverse problems of source identification in acoustics is proposed based on fuzzy relational calculus. The compositional rule of inference connects the real and observed fuzzy acoustic image using the relationship matrix, which reflects the degree of completeness of the microphone array measurement data. The fuzzy model of the acoustic field is based on 3D membership functions, for which the degree of membership decreases in proportion to the square of the distance to the source. The problem of reconstructing the acoustic field is formulated as the problem of inverse logical inference. The method for reconstructing the acoustic field fromincompletedata is proposed based on solving fuzzy relational equations. The problem consists in finding such a number of sound sources, their locations and powers, which minimize the difference between the model and observed fuzzy acoustic image. The solutions of the equation system represent the variants of the acoustic field reconstruction in the form of the main acoustic surface and a set of secondary acoustic surfaces. The main acoustic surface is generated by the least number of sources. The set of secondary acoustic surfaces represents the variants of the sound field reconstruction generated by the upper solutions for the number of sources. Since the sources distribution is completely determined by the properties of the solution set, the proposed approach allows avoiding the generation and selection of candidate sources, that provides simplification of the reconstruction process and reduction of time costs. The genetic and neural algorithm provides accurate and fast reconstruction of the acoustic field for an unknown number of sources and their configuration.
Multi-objective optimization reconstruction algorithm is one of the main methods to solve the limited angle imagereconstruction. However we have great difficulty in selecting the right parameter reasonably because th...
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ISBN:
(纸本)9781424451944
Multi-objective optimization reconstruction algorithm is one of the main methods to solve the limited angle imagereconstruction. However we have great difficulty in selecting the right parameter reasonably because there is not only one objective function. So we give a new method to choose the parameter which was called homotopy parameter based on the theory of homotopy in this paper. Finally, the simulations were carried out to verify the proposed strategy, and the simulation results show that this algorithm is superior to the conventional multi-objective optimization methods in many aspects, such as less reconstruction errors, higher smoothness and gray value resolution.
We propose an approach allowing significant reduction or even complete removal of artifacts that can appear in optoacoustic images acquired with limited number of transducers (missing detectors) due to incompletedata...
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ISBN:
(纸本)0819452289
We propose an approach allowing significant reduction or even complete removal of artifacts that can appear in optoacoustic images acquired with limited number of transducers (missing detectors) due to incompletedata. In optoacoustic tomography the image is reconstructed from a set of acoustic transducers located on the surface of tissue irradiated by a laser. The rigorous solution of the tomographic problem requires covering of the entire surface of the illuminated volume by an array of transducers. However, in practice, only portion of the surface is available. As a result of dataincompleteness, artifacts (usually looking like arc-shaped shadows extending from the bright objects) can appear. These artifacts limit the spatial resolution, degrade the image contrast and distort shapes of the reconstructed objects. The results of the numerical simulation, presented in this work, show that the intensity and the shape of the "arc-shadow" artifacts depend on the surface area of uncovered by the acoustic detectors. The cause of the artifacts appearance is the violation of the absorbed energy conservation by the imagereconstruction algorithm. Such explanation of this fact represents a key for removal of these artifacts. As presented in the paper, the intensity of the artifacts could be reduced by partial restoration of the missed transducers. In case of sufficient a priori information about number of objects, the proposed algorithm can be considered as the interpolation/extrapolation of the data or substitution of the missed signal by averaged real signal taking into account energy conservation. In a common case, the signals of virtual transducers are restored from the distorted image using the solution of the wave equation. Then the cleaned image is reconstructed from the complete set of signals combining real and virtual transducers. These operations can be repeated iteratively until artifacts become weak. The accuracy of the imagereconstruction depends on the number
Neuro-scientific studies are often aimed at imaging brain activity, which is time-locked to external stimuli. This provides the possibility to use statistical methods to extract even weak signal components, which occu...
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ISBN:
(纸本)9781628417661
Neuro-scientific studies are often aimed at imaging brain activity, which is time-locked to external stimuli. This provides the possibility to use statistical methods to extract even weak signal components, which occur with each stimulus. For electroencephalographic recordings this concept is limited by inevitable time jitter, which cannot be controlled in all cases. Our study is based on a cross-correlation analysis of trials to alignment trials based on the recorded data. This is demonstrated both with simulated signals and with clinical EEG data, which were recorded intracranially. Special attention is given to the evaluation of the time-frequency resolved phase-locking across multiple trails.
Binary tomography focuses on the problem of reconstructing homogeneous objects from a small number of their projections. In many applications, incomplete projection data holds insufficient information for the correct ...
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ISBN:
(纸本)9783319930008;9783319929996
Binary tomography focuses on the problem of reconstructing homogeneous objects from a small number of their projections. In many applications, incomplete projection data holds insufficient information for the correct reconstruction of the original object. In this paper, we provide an optimization based method to select the "most informative" projection set, using information of global uncertainty. Beside the projection data we assume no further knowledge of the image to be reconstructed. Still, we achieve approximately as accurate reconstruction results, as it is possible to gain with a former method that uses blueprint images to find the optimal set of projections. We give experimental results for validating our approach on artificial images of various structures.
We propose a nem Miller-Tikhonov restoration method where an a priori model of the solution is included. fn sharp contrast with fire classical method, this approach incorporates local informations. We show that the op...
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ISBN:
(纸本)0818681837
We propose a nem Miller-Tikhonov restoration method where an a priori model of the solution is included. fn sharp contrast with fire classical method, this approach incorporates local informations. We show that the optimal model can be directly calculated from the data or a priori given and adjusted by minimizing the reconstruction error.
We describe position-position-velocity data cubes derived from the star-forming interstellar medium (SFISM). The physical characteristics and evolution of the SFISM must be deduced from the incomplete information pres...
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ISBN:
(纸本)9781467325332;9781467325349
We describe position-position-velocity data cubes derived from the star-forming interstellar medium (SFISM). The physical characteristics and evolution of the SFISM must be deduced from the incomplete information present in the observed data. Astrophysicists can simulate the evolution of the SFISM from first principles but the standard comparisons of simulated data with observations do not completely describe the SFISM. Given the hierarchical structure present in the emission, we forward the use of Reeb graphs as a tool for comparing data cubes. We describe the computation of a Reeb graph and show that the properties encoded in the Reeb graph highlight the deficiencies of simulations at capturing the structure of the SFISM.
A novel tag completion algorithm is proposed in this paper, which is designed with the following features: 1) Low-rank and error s-parsity: the incomplete initial tagging matrix D is decomposed into the complete taggi...
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In this work, we analyze the imagereconstruction problem within the first order Rytov approximation and optimize the imagereconstruction by looking at the singular value spectrum of the "weight matrix". We...
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ISBN:
(纸本)0819447552
In this work, we analyze the imagereconstruction problem within the first order Rytov approximation and optimize the imagereconstruction by looking at the singular value spectrum of the "weight matrix". We show that the optimal data is from the tail of the temporal intensity autocorrelation curve by investigating the condition number. Furthermore, by doing a standard L-curve analysis, we find the optimal regularization constant (Tikhonov regularization). images from simulated data are shown to illustrate the advantage of the optimization process.
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