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- Fhager, Andreas, 1976, et al.
(författare)
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Methods for Dielectric Reconstruction in Microwave Tomography
- 2007
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Ingår i: The Second European Conference on Antennas and Propagation (EuCAP 2007), Nov. 11-16, Edinburgh, UK. - 0537-9989. - 9780863418426 ; , s. Tu1.7.5-
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Konferensbidrag (refereegranskat)abstract
- In this paper an iterative electromagnetic time-domain inversion algorithm is described and modified to include a priori data of the shape and dielectric properties of an object being imaged. The algorithm is based on solving the regular and the adjoint Maxwell's equations in order to compute gradients, which are used to update the dielectric profile with the conjugate-gradient method. As an alternative a global optimisation algorithm, the particle swarm optimisation method, has also been investigated. The results show that by exploiting a priori dielectric data in this way a significant improvement in the resolving ability can be obtained. Finally Tikonov and edge preserving regularisation has been investigated and a modified regularisation scheme, supporting the a priori data is suggested.
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| 2. |
- Edelvik, Fredrik, 1972, et al.
(författare)
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An improved method for dipole modeling in EEG-based source localization
- 2009
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Ingår i: International Federation for Medical and Biological Engineering Proceedings. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1680-0737. - 9783642038884 ; 25:9, s. 146-149
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Konferensbidrag (refereegranskat)abstract
- The inverse problem in EEG-based source localizationis to determine the location of the brain sources that areresponsible for the measured potentials at the scalp electrodes.The brain sources are usually modeled as current dipoles whichlead to a singularity in the right-hand side of the governing Poisson’sequation. Subtraction methods have been proposed as aremedy and in this paper an improved subtraction method formodeling the dipoles is presented. The accuracy is demonstratedfor radial and tangential sources in layered sphere models and isto the best of the authors’ knowledge superior to previous methodsfor superficial sources. An additional advantage is that itproduces a right hand side with few non-zeros which is beneficialfor efficient solution of the inverse problem.
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| 8. |
- Fhager, Andreas, 1976, et al.
(författare)
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Potential benefits of using a priori data in reconstruction algorithms for microwave tomography
- 2006
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Ingår i: Medicinteknikdagarna, 3-4 October 2006, Uppsala, Sweden.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Microwave tomography is rapidly developing into a promising imaging technique that could be useful in many different applications where a non-invasive detection of internal dielectric properties is required. Such a technique could for instance be useful in mammographical imaging for screening and follow up examinations of breast cancer tumours. Compared to x-ray mammography there is a potential significant benefit in using microwaves in the diagnosis of breast cancer tumours due to a significant contrast in the dielectric properties between tumour and surrounding tissue.Development of an efficient imaging reconstruction algorithm is a big challenge in the construction of an operational microwave tomograph. The algorithm has to be fast, accurate and robust. In this work results are presented showing how a priori dielectric data of the objects being reconstructed can be exploited to improve the convergence rate and the resolution of the reconstructed image. The work is based on a conjugate-gradient reconstruction algorithm and FDTD modelling of the electromagnetic wave propagation. For this work it has been modified to search for circular objects with given permittivity and conductivity. The results are promising and indicate that significantly improved reconstructions can be obtained. However to be practically viable further development of the algorithm need to be made in order to make it more robust and adaptive. Once that is made we plan to use this technique in a prototype that will be evaluated for clinical breast cancer imaging.
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| 10. |
- Hosseinzadegan, Samar, 1987, et al.
(författare)
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A discrete dipole approximation solver based on the COCG-FFT algorithm and its application to microwave breast imaging
- 2019
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Ingår i: International Journal of Antennas and Propagation. - : Hindawi Limited. - 1687-5869 .- 1687-5877. ; 2019
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Tidskriftsartikel (refereegranskat)abstract
- We introduce the discrete dipole approximation (DDA) for efficiently calculating the two-dimensional electric field distribution for our microwave tomographic breast imaging system. For iterative inverse problems such as microwave tomography, the forward field computation is the time limiting step. In this paper, the two-dimensional algorithm is derived and formulated such that the iterative conjugate orthogonal conjugate gradient (COCG) method can be used for efficiently solving the forward problem. We have also optimized the matrix-vector multiplication step by formulating the problem such that the nondiagonal portion of the matrix used to compute the dipole moments is block-Toeplitz. The computation costs for multiplying the block matrices times a vector can be dramatically accelerated by expanding each Toeplitz matrix to a circulant matrix for which the convolution theorem is applied for fast computation utilizing the fast Fourier transform (FFT). The results demonstrate that this formulation is accurate and efficient. In this work, the computation times for the direct solvers, the iterative solver (COCG), and the iterative solver using the fast Fourier transform (COCG-FFT) are compared with the best performance achieved using the iterative solver (COCG-FFT) in C++. Utilizing this formulation provides a computationally efficient building block for developing a low cost and fast breast imaging system to serve under-resourced populations.
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