Searched for: author%3A%22Webb%2C+A.%22
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de Vos, B. (author), Remis, R.F. (author), Webb, A. (author)
MRI systems have a thin conducting layer placed between the gradient and RF coils, this acts as a shield at the RF-frequency, minimizing noise coupled into the experiment, and decreasing the coupling between the RF and gradient coils. Ideally, this layer should be transparent to the gradient fields to reduce eddy currents. In this work the...
journal article 2024
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de Vos, B. (author), Remis, R.F. (author), Webb, A. (author)
Objective: Low-cost low-field point-of-care MRI systems are used in many different applications. System design has correspondingly different requirements in terms of imaging field-of-view, spatial resolution and magnetic field strength. In this work an iterative framework has been created to design a cylindrical Halbach-based magnet along...
journal article 2023
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Brink, Wyger M. (author), Remis, R.F. (author), Webb, A. (author)
Purpose: High permittivity dielectric pads are known to be effective for tailoring the RF field and improving image quality in high field MRI. Despite a number of studies reporting benign specific absorption rate (SAR) effects, their “universal” safety remains an open concern. In this work, we evaluate the impact of the insulation material in...
journal article 2023
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de Vos, B. (author), Remis, R.F. (author), Webb, A. (author)
Purpose: Concomitant gradient fields have been extensively studied at clinical field strengths. However, their effects have not yet been modeled for low-field point-of-care (POC) systems. The purpose of this work is to characterize the effects associated with concomitant fields for POC Halbach-array-based systems. Methods: The concomitant...
journal article 2023
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de Leeuw den Bouter, M.L. (author), Ippolito, G. (author), O’Reilly, T. P.A. (author), Remis, R.F. (author), van Gijzen, M.B. (author), Webb, A. (author)
Low-field MRI scanners are significantly less expensive than their high-field counterparts, which gives them the potential to make MRI technology more accessible all around the world. In general, images acquired using low-field MRI scanners tend to be of a relatively low resolution, as signal-to-noise ratios are lower. The aim of this work is...
journal article 2022
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Kalisvaart, Gijsbert M. (author), van Velden, Floris H.P. (author), Hernández-Girón, Irene (author), Meijer, Karin M. (author), Ghesquiere-Dierickx, Laura M.H. (author), Brink, Wyger M. (author), Webb, A. (author), de Geus-Oei, Lioe-Fee (author), Slump, Cornelis H. (author), Kuznetsov, D.V. (author), Schaart, D.R. (author), Grootjans, Willem (author)
Background: Accuracy and precision assessment in radiomic features is important for the determination of their potential to characterize cancer lesions. In this regard, simulation of different imaging conditions using specialized phantoms is increasingly being investigated. In this study, the design and evaluation of a modular multimodality...
journal article 2022
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Brink, Wyger M. (author), Yousefi, Sahar (author), Bhatnagar, Prernna (author), Remis, R.F. (author), Staring, M. (author), Webb, A. (author)
Purpose: Parallel RF transmission (PTx) is one of the key technologies enabling high quality imaging at ultra-high fields (≥7T). Compliance with regulatory limits on the local specific absorption rate (SAR) typically involves over-conservative safety margins to account for intersubject variability, which negatively affect the utilization of...
journal article 2022
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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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Leijsen, R.L. (author), Brink, W. (author), An, X. (author), Webb, A. (author), Remis, R.F. (author)
A new local method for magnetic resonance electrical properties tomography (EPT), dubbed transverse-EPT (T-EPT), is introduced. This approach iteratively optimizes the dielectric properties (conductivity and permittivity) and the z-component of the electric field strength, exploiting the locally E-polarized field structure typically present...
journal article 2021
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de Vos, B. (author), Parsa, Javad (author), Abdulrazaq, Zaynab (author), Teeuwisse, Wouter M. (author), Van Speybroeck, Camille D.E. (author), de Gans, D.H. (author), Remis, R.F. (author), O’Reilly, Tom (author), Webb, A. (author)
Low-field permanent magnet-based MRI systems are finding increasing use in portable, sustainable and point-of-care applications. In order to maximize performance while minimizing cost many components of such a system should ideally be designed specifically for low frequency operation. In this paper we describe recent developments in...
journal article 2021
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Koolstra, Kirsten (author), Börnert, Peter (author), Lelieveldt, B.P.F. (author), Webb, A. (author), Dzyubachyk, Oleh (author)
Objective: To visualize the encoding capability of magnetic resonance fingerprinting (MRF) dictionaries. Materials and methods: High-dimensional MRF dictionaries were simulated and embedded into a lower-dimensional space using t-distributed stochastic neighbor embedding (t-SNE). The embeddings were visualized via colors as a surrogate for...
journal article 2021
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Leijsen, R.L. (author), Brink-van Caspel, W.M. (author), At Van Den Berg, Cornelis (author), Webb, A. (author), Remis, R.F. (author)
Electrical properties tomography (EPT) is an imaging method that uses a magnetic resonance (MR) system to non-invasively determine the spatial distribution of the conductivity and permittivity of the imaged object. This manuscript starts by providing clear definitions about the data required for, and acquired in, EPT, followed by comprehensively...
journal article 2021
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Hendriks, P. (author), Berkhout, W. E.M. (author), Kaanen, C.I. (author), Sluijter, J.H. (author), Visser, I. J. (author), van den Dobbelsteen, J.J. (author), de Geus-Oei, L. F. (author), Webb, A. (author), Burgmans, M.C. (author)
Purpose: To investigate the performance of two microwave ablation (MWA) systems regarding ablation volume, ablation shape and variability. Materials and Methods: In this ex vivo study, the Emprint and Amica MWA systems were used to ablate porcine livers at 4 different settings of time and power (3 and 5 minutes at 60 and 80 Watt). In total,...
journal article 2021
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Vroegindeweij, Lena H.P. (author), Bossoni, Lucia (author), Boon, Agnita J.W. (author), Wilson, J. H.Paul (author), Bulk, Marjolein (author), Labra Muñoz, J. (author), Huber, M. (author), Webb, A. (author), van der Weerd, Louise (author)
Aims: Aceruloplasminemia is an ultra-rare neurodegenerative disorder associated with massive brain iron deposits, of which the molecular composition is unknown. We aimed to quantitatively determine the molecular iron forms in the aceruloplasminemia brain, and to illustrate their influence on iron-sensitive MRI metrics. Methods: The...
journal article 2021
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Leijsen, Reijer L. (author), Brink, Wyger M. (author), Webb, A. (author), Remis, R.F. (author)
Three-dimensional contrast source inversion-electrical properties tomography (3-D CSI-EPT) is an iterative reconstruction method that estimates the electrical properties of tissue from transmit field magnetic resonance data. However, in order to bring 3-D CSI-EPT into practice for complex tissue structures and to understand the origin and...
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, Pablo (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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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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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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