Searched for: author:"Webb, A."
(1 - 12 of 12)
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O’Reilly, Thomas (author), Teeuwisse, Wouter M. (author), de Gans, D.H. (author), Koolstra, Kirsten (author), Webb, A. (author)
Purpose: To design a low-cost, portable permanent magnet-based MRI system capable of obtaining in vivo MR images within a reasonable scan time. Methods: A discretized Halbach permanent magnet array with a clear bore diameter of 27 cm was designed for operation at 50 mT. Custom-built gradient coils, RF coil, gradient amplifiers, and RF...
journal article 2021
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De Vos, Bart (author), Fuchs, P.S. (author), O'Reilly, Thomas (author), Webb, A. (author), Remis, R.F. (author)
In this article, we design and construct gradient coils for a Halbach permanent-magnet array magnetic resonance (MR) scanner. The target field method, which is widely applied for the case of axial static magnetic fields, has been developed for a transverse static magnetic field as produced by a Halbach permanent-magnet array. Using this...
journal article 2020
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van der Weerd, Louise (author), Lefering, A.J.E. (author), Webb, A. (author), Egli, Ramon (author), Bossoni, Lucia (author)
Iron accumulation in the brain is a phenomenon common to many neurodegenerative diseases, perhaps most notably Alzheimer’s disease (AD). We present here magnetic analyses of post-mortem brain tissue of patients who had severe Alzheimer’s disease, and compare the results with those from healthy controls. Isothermal remanent magnetization...
journal article 2020
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Webb, A. (author), Cesar Garcia, P.S. (author)
We uncover how geographically distributed players of tabletop role-playing games engage narrative, ludic, and social aspects of play. Our existing understandings of tabletop role-playing games are centered around co-located play on physical tabletops. Yet, online play is increasingly popular. We interviewed 14 players, experienced with online...
conference paper 2019
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van Gemert, J.H.F. (author), Brink, Wyger M. (author), Remis, R.F. (author), Webb, A. (author)
PURPOSE: One of the main concerns in fetal MRI is the radiofrequency power that is absorbed both by the mother and the fetus. Passive shimming using high permittivity materials in the form of "dielectric pads" has previously been shown to increase the formula presented efficiency and homogeneity in different applications, while reducing the...
journal article 2019
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Leijsen, R.L. (author), Brink, Wyger M. (author), Remis, R.F. (author), Webb, A. (author)
Model-based electrical properties tomography (EPT; [1,2]) reconstruction with 3-D Contrast Source Inversion-EPT (CSI-EPT; [3,4]) has high potential, but is inherently sensitive to small errors in the model used. Here we assess its sensitivity to errors in the incident electromagnetic (EM) fields due to coupling of the coil to the sample (loading...
conference paper 2019
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Leijsen, R.L. (author), Fuchs, P.S. (author), Brink, Wyger (author), Webb, A. (author), Remis, R.F. (author)
The main objective of electrical-property tomography (EPT) is to retrieve dielectric tissue parameters from B <sub>1</sub> <sup>+</sup> data as measured by a magnetic-resonance (MR) scanner. This is a so-called hybrid inverse problem in which data are defined inside the reconstruction domain of interest. In this paper, we discuss recent and...
journal article 2019
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Leijsen, R.L. (author), van den Berg, Cornelis (author), Webb, A. (author), Remis, R.F. (author), Mandija, Stefano (author)
Magnetic resonance electrical properties tomography (MR-EPT) is a technique used to estimate the conductivity and permittivity of tissues from MR measurements of the transmit magnetic field. Different reconstruction methods are available; however, all these methods present several limitations, which hamper the clinical applicability. Standard...
journal article 2019
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Koolstra, K. (author), van Gemert, J.H.F. (author), Börnert, Peter (author), Webb, A. (author), Remis, R.F. (author)
Purpose: Design of a preconditioner for fast and efficient parallel imaging (PI) and compressed sensing (CS) reconstructions for Cartesian trajectories. Theory: PI and CS reconstructions become time consuming when the problem size or the number of coils is large, due to the large linear system of equations that has to be solved in l<sub>1<...
journal article 2019
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van Gemert, Jeroen (author), Brink, Wyger (author), Webb, A. (author), Remis, R.F. (author)
Purpose: High-permittivity materials in the form of flexible “dielectric pads” have proved very useful for addressing RF inhomogeneities in high field MRI systems. Finding the optimal design of such pads is, however, a tedious task, reducing the impact of this technique. We present an easy-to-use software tool which allows researchers and...
journal article 2019
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van Gemert, J.H.F. (author), Brink, W.M. (author), Webb, A. (author), Remis, R.F. (author)
Inhomogeneities in the transmit radio frequency magnetic field ( {\text{B}}-{1}^{+} ) reduce the quality of magnetic resonance (MR) images. This quality can be improved by using high-permittivity pads that tailor the {\text{B}}-{1}^{+} fields. The design of an optimal pad is application-specific and not straightforward and would therefore...
journal article 2018
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Leijsen, R.L. (author), Brink, Wyger M. (author), van den Berg, Cornelis A.T. (author), Webb, A. (author), Remis, R.F. (author)
Contrast source inversion &amp;#x2013; electrical properties tomography (CSI-EPT) is an iterative reconstruction method to retrieve the electrical properties (EPs) of tissues from MR data. The method is based on integral representations of the electromagnetic (EM) field and has been shown to allow EP reconstructions of small structures as...
journal article 2018
Searched for: author:"Webb, A."
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