Searched for: subject%3A%22Low%255C-Field%22
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Haasjes, Corné (author)
Ultrasound imaging is an important modality in ocular oncology, allowing for fast examination of the eye by the ophthalmologist themselves. It is clinically used to measure tumour sizes for treatment planning. However, ocular ultrasound is limited to two-dimensional imaging, and suffers from poor contrast between tumour and sclera, which...
master thesis 2022
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Aggariyo Wanagiri, Aggariyo (author)
Low field magnetic resonance imaging (MRI) scanners provide a unique low-cost alternative to conventional MRI scanners. Nevertheless, low-field scanners come with drawbacks such as reduced signal-to-noise ratio and resolution, and also distorted images caused by magnetic field inhomogeneity and non-linear gradient fields. Despite this, it still...
master thesis 2022
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Bekkering, Aleid (author)
MRI has been used worldwide as an imaging modality for decades due to its ability to distinguish between soft tissues. However, MRIs cannot be used in all situations due to their extensive hard- and software. For this reason, research in the field of low-field MRI has been conducted. Low-field MRI systems do not use superconducting magnets but...
master thesis 2022
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Nijsse, Hannah (author)
Low-field MRI is susceptible to temperature changes in magnet temperature, resulting in time-dependent inhomogeneities. This causes time-dependent phase shifts in the measured signal, leading to image distortions. In this project, a method is proposed to interleave short magnetic field (B0) mapping sequences in the target image acquisition for...
master thesis 2022
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Shan, X. (author), van Gijzen, M.B. (author)
We study efficient implicit methods to denoise low-field MR images using a nonlinear diffusion operator as a regularizer. This problem can be formulated as solving a nonlinear reaction–diffusion equation. After discretization, a lagged-diffusion approach is used which requires a linear system solve in every nonlinear iteration. The choice of...
journal article 2022
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van der Werff, Karen (author)
Magnetic Resonance Imaging (MRI) is a non-invasive, non-ionizing imaging modality that is commonly used in the clinic today. However, it is an expensive technique. The high purchase, operational and maintenance costs, as well as the need for trained staff with technical expertise, put this technique out of reach for a large part of the world...
master thesis 2021
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Oppelaar, Pieter (author)
In this report, the conversion from spin-echo signals, obtained with a low-field hand-held MRI scanner that was designed and built at the Leiden University, to images of the proton density within the sample is considered. This scanner does not make use of switchable gradient coils, but instead relies solely on the natural inhomogeneity of the...
bachelor thesis 2021
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Liesker, Bas (author)
Magnetic resonance imaging (MRI) scanners are a crucial diagnostic tool for radiologists. They are able to render two­ and three­dimensional images of the body without exposure to harmful radiation. MRI systems are, however, costly to build and maintain. This adversely impacts access to these scanners in developing regions. In an effort to...
master thesis 2021
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Yang, Jingbin (author), Sun, Zhenping (author), Yanliang, Ji (author), Li, Biyun (author), Pang, Min (author)
As an internal curing material, superabsorbent polymers (SAPs) can effectively reduce the risk of volume shrinkage of cement-based materials. By preparing the cement paste mixed with SAPs, the amount of pre-absorbed water and the water-cement ratio of paste on the water absorption-release behavior in the fresh cement paste were studied by using...
conference paper 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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Ahishakiye, Emmanuel (author), van Gijzen, M.B. (author), Shan, X. (author), Tumwiine, Julius (author), Obungoloch, Johnes (author)
Currently, many children with hydrocephalus in East Africa and other resource-constrained countries do not have access to Magnetic Resonance Imaging (MRI) scanners, the preferred imaging tool during the disease administration and treatment. Conventional MRI scanners are costly to buy and manage, which limits their utilization in low-income...
conference paper 2021
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de Leeuw den Bouter, M.L. (author), van Gijzen, M.B. (author), Remis, R.F. (author)
In this paper we present a magnetic resonance imaging (MRI) technique that is based on multiplicative regularization. Instead of adding a regularizing objective function to a data fidelity term, we multiply by such a regularizing function. By following this approach, no regularization parameter needs to be determined for each new data set...
journal article 2021
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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 Leeuw den Bouter, M.L. (author), van den Berg, P.M. (author), Remis, R.F. (author)
In this paper we discuss an imaging method when the object has known support and its spatial Fourier transform is only known on a certain k-space undersampled pattern. The simple conjugate gradient least squares algorithm applied to the corresponding truncated Fourier transform equation produces reconstructions that are basically of a similar...
journal article 2021
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Guo, Rui (author), Weingärtner, S.D. (author), Šiuryté, P. (author), T. Stoeck, Christian (author), Füetterer, Maximilian (author), E. Campbell-Washburn, Adrienne (author), Suinesiaputra, Avan (author), Jerosch-Herold, Michael (author), Nezafat, Reza (author)
Cardiovascular disease is the leading cause of death and a significant contributor of health care costs. Noninvasive imaging plays an essential role in the management of patients with cardiovascular disease. Cardiac magnetic resonance (MR) can noninvasively assess heart and vascular abnormalities, including biventricular structure/function,...
review 2021
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Ippolito, Giulia (author)
This work is part of the low-fieldMRI project, which aims to bring portable, affordable, low-fieldMRI scanners to low-income countries. Replacing the superconducting magnets of conventional scanners with standard ones can significantly reduce the costs, but it also has a negative impact on the Signal-to-Noise Ratio (SNR). In order to circumvent...
master thesis 2020
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Macarulla Rodriguez, M. (author)
Low-field Magnetic Resonance Imaging (LF MRI) is a cheap and safe technique to visualise the internal structure of the human body. Unlike other imaging techniques, Magnetic Resonance Imaging does not use ionising radiation to generate the images. Instead, it uses magnetic fields and radio waves which are nonthreatening to the health. The LF MRI...
master thesis 2020
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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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Ahishakiye, Emmanuel (author), van Gijzen, M.B. (author), Tumwiine, Julius (author), Obungoloch, Johnes (author)
Background: Magnetic resonance imaging (MRI) is a safe non-invasive and nonionizing medical imaging modality that is used to visualize the structure of human anatomy. Conventional (high-field) MRI scanners are very expensive to purchase, operate and maintain, which limit their use in many developing countries. This study is part of a project...
journal article 2020
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Ahishakiye, Emmanuel (author), van Gijzen, M.B. (author), Tumwiine, Julius (author), Obungoloch, Johnes (author)
Objective: Image denoising has been considered as a separate procedure from image reconstruction which could otherwise be combined with acquisition and reconstruction. This paper discusses a joint image reconstruction and denoising algorithm in low-field MRI using a dictionary learning approach. Method: Our proposed algorithm uses a two-level...
conference paper 2020
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