Performance of Shielded Electromagnet-Evaluation Under Low-Frequency Excitation

Bringout, Gaël; Gräfe, Ksenija; Buzug, Thorsten M.

doi:10.1109/tmag.2014.2329396

Cited by 6 publications

(3 citation statements)

References 6 publications

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“…The mechanical surfaces of the 2 coils were predetermined to be on the inner and outer surface of a tiered cylinder former designed to fit snuggly inside the magnet (length = 42.7 cm, diameter 1 = 34.8 cm, diameter 2 = 26.4 cm). The current stream functions of the coils were optimized on a 20 cm diameter ROI using a stream function BEM solver based on a published toolbox 43 . The achievable current density at the truncated end of the coil (shoulder side) is limited by practical density of the windings in this area which proved to be the main constraint limiting the coil’s efficiency and linearity.…”

Section: Methodsmentioning

confidence: 99%

A portable scanner for magnetic resonance imaging of the brain

et al. 2020

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Access to scanners for magnetic resonance imaging (MRI) is typically limited by cost and by infrastructure requirements. Here, we report the design and testing of a portable prototype scanner for brain MRI that uses a compact and lightweight permanent rare-earth magnet with a built-in readout field gradient. The 122-kg low-field (80 mT) magnet uses has a Halbach-cylinder design that results in minimal stray field and requires neither cryogenics nor external power. The built-in magnetic-field gradient reduces the reliance on high-power gradient drivers, lowering the overall requirements for power and cooling, and reducing acoustic noise. Imperfections in the encoding fields are mitigated with a generalized iterative image-reconstruction technique that leverages prior characterization of the field patterns. In healthy adult volunteers, the scanner can generate T 1 -weighted, T 2 -weighted and proton-density-weighted brain images with a spatial resolution of 2.2 × 1.3 × 6.8 mm 3 . Future versions of the scanner could improve the accessibility of brain MRI at the point of care, particularly for critically ill patients.

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Section: Methodsmentioning

confidence: 99%

A portable scanner for magnetic resonance imaging of the brain

et al. 2020

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“…Additionally, in our experience, weak unshielded gradient coils do not produce significant eddy current effects if placed either inside or outside an NdFeB magnet. The gradient winding patterns were designed using a modified Boundary Element Method Stream Function (BEM‐SF) solver with L2‐regularization. Single‐sided gradients, like single‐sided magnets, have a natural decrease in field amplitude moving away from the structure.…”

Section: Methodsmentioning

confidence: 99%

The MR Cap: A single‐sided MRI system designed for potential point‐of‐care limited field‐of‐view brain imaging

McDaniel

Cooley

Stockmann

et al. 2019

Magnetic Resonance in Med

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Purpose:The size, cost, and siting requirements of conventional MRI systems limit their availability and preclude usage as monitoring or point-of-care devices. To address this, we developed a lightweight MRI for point-of-care brain imaging over a reduced field of view (FOV). Methods: The B 0 magnet was designed with a genetic algorithm optimizing homogeneity over a 3 × 8 × 8 cm FOV and a built-in gradient for slice selection or readout encoding. An external pair of gradient coils enables phase encoding in the other two directions and a radiofrequency (RF) coil provides excitation and detection. The system was demonstrated with high-resolution 1D "depth profiling" and 3D phantom imaging. Results: The lightweight B 0 magnet achieved a 64-mT average field over the imaging region at a materials cost of <$450 USD. The weight of the magnet, gradient, and RF coil was 8.3 kg. Depth profiles were obtained at high resolution (0.89 mm) and multislice rapid acquisition with refocused echoes (RARE) images were obtained with a resolution ~2 mm in-plane and ~6-mm slice thickness, each in an imaging time of 11 min. Conclusion: The system demonstrates the feasibility of a lightweight brain MRI system capable of 1D to 3D imaging within a reduced FOV. The proposed system is low-cost and small enough to be used in point-of-care applications. K E Y W O R D S accessible MRI, low-cost MRI, point of care, portable MRI | INTRODUCTIONMagnetic resonance imaging (MRI) has become a routine part of clinical medicine, especially for neuroimaging. However, expense, size, and siting requirements impose limitations on how conventional MRI scanners can be used within the health-care system. Installation of a whole-body MR scanner or even a head-only-type device using a conventional superconducting magnet entails a dedicated space, special infrastructure, and safety requirements, such as a 5-gauss exclusion area, high-power electrical supply, cooling system, and shielded room. These prerequisites preclude the use of MRI in many settings, such as rural or developingworld clinics that might not possess this infrastructure. F I G U R E 2 A, Illustration showing approximate desired magnet shape, ROI, and B 0 axis. B, Section of Halbach sphere magnet that approximates the desired magnet shape and B 0 direction. C, Discretized Halbach sphere section that approximates the continuous magnet design as an assembly of magnet blocks. D, Optimized discrete block magnet design. ROI, region of interest

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“…a) Electronic mail: rasmus.zetter@aalto.fi Similar methods have also been used in plasma physics (Abe et al, 2003). More recently, the same principles have been used in the design of coils for transcranial magnetic stimulation (TMS) (Koponen et al, 2017;Cobos Sánchez et al, 2018) as well as magnetic nanoparticle imaging (Bringout, Grafe, and Buzug, 2015).…”

Section: Introductionmentioning

confidence: 99%

Magnetic-field modeling with surface currents: Implementation and usage of bfieldtools

Zetter,

Mäkinen,

Iivanainen

et al. 2020

Preprint

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We present a novel open-source Python software package, bfieldtools, for magneto-quasistatic calculations with current densities on surfaces of arbitrary shape. The core functionality of the software relies on a stream-function representation of surface-current density and its discretization on a triangle mesh. Although this stream-function technique is well-known in certain fields, to date the related software implementations have not been published or have been limited to specific applications. With bfieldtools, we aimed to produce a general, easy-to-use and well-documented open-source software. The software package is written purely in Python; instead of explicitly using lower-level languages, we address computational bottlenecks through extensive vectorization and use of the NumPy library. The package enables easy deployment, rapid code development and facilitates application of the software to practical problems. In this paper, we describe the software package and give an extensive demonstration of its use with an emphasis on one of its main applications -coil design.

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Performance of Shielded Electromagnet-Evaluation Under Low-Frequency Excitation

Cited by 6 publications

References 6 publications

A portable scanner for magnetic resonance imaging of the brain

A portable scanner for magnetic resonance imaging of the brain

The MR Cap: A single‐sided MRI system designed for potential point‐of‐care limited field‐of‐view brain imaging

Magnetic-field modeling with surface currents: Implementation and usage of bfieldtools

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