Asymmetric MRI Magnet Design Using a Hybrid Numerical Method

Zhao, Huawei; Crozier, Stuart; Doddrell, David M.

doi:10.1006/jmre.1999.1924

Cited by 36 publications

(22 citation statements)

References 21 publications

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“…Next generation magnets came with the concept of active shielding where the stray field is less than 4 G (in regions at least 4 m away from the iso-center) either by using ferromagnetic materials [11] or using coaxial coils carrying current in the opposite direction [12]. Different methods are used to design magnets of highly homogeneous field, based on stochastic optimization [20], matrix subset selection [21], inverse approach [22], hybrid numerical methods [23] and methods for permanent magnet design [24].…”

Section: Magnet Design and Modelingmentioning

confidence: 99%

Comprehensive Analysis of Lenz Effect on the Artificial Heart Valves During Magnetic Resonance Imaging

Golestanirad¹,

Dlala²,

Wright³

et al. 2012

PIER

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Abstract-This work presents results of a comprehensive analysis of the Lenz effect due to motion of artificial heart valves during magnetic resonance imaging. The interaction of rotating metallic heart valves with magnetic fields is studied by performing a time-domain analysis of the corresponding electromagnetic problem. We applied the finite element method (FEM) to solve the T − Ω formulation of Maxwell equations in two cases: first, for metallic disks located in the high intensity homogenous field of the magnet iso-center, and second, disks located in the non-uniform fringe field of the bore entrance. We showed that for valves with full solid disks (such as Starr-Edwards 6500) located in the magnet iso-center, the magnitude of adverse forces can be comparable to the forces applied by the beating heart. However, for rings which consist of multiply connected conductive regions, skin effect and proximity effect counteract, which leads to a diminished magnetic force. Results of this study show that mechanical heart valves with strengthening rings may be considered safe even under ultra-high imaging conditions with field intensities as high as 10 T. However, heart valves with full conducting disks should be considered as a contraindication to MR imaging.

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Section: Magnet Design and Modelingmentioning

confidence: 99%

Comprehensive Analysis of Lenz Effect on the Artificial Heart Valves During Magnetic Resonance Imaging

Golestanirad¹,

Dlala²,

Wright³

et al. 2012

PIER

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“…The superconducting magnet has an asymmetric coil structure for realizing this configuration. Feasibility of asymmetric coil structures was discussed in previous papers [6], [7], but MRI magnet with such coil structures has never been fabricated, as far as we know.…”

Section: Introductionmentioning

confidence: 97%

Fabrication of an MRI Model Magnet With an Off-Centered Distribution of Homogeneous Magnetic Field Zone

Sekino

Ohsaki

Wada

et al. 2010

IEEE Trans. Appl. Supercond.

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Magnetic resonance imaging (MRI) requires a highly homogenous magnetic field zone which usually appears at the center of the MRI magnet coil. If this homogeneous zone is allowed to occur at an off-centered position along the coil axis, quite new applications of MRI may be possible. In order to examine this idea, we fabricate a model magnet consisting of several NbTi coils and generating a vertical magnetic field of 0.77 T; coil outer diameter is 307 mm, coil length 191 mm, designed field homogeneity 5 ppm @ 35 mm DSV, and the location of homogeneous field zone 29.4 mm off-centered along the vertical coil axis. As an example of application of this type of MRI, we will discuss about a functional-MRI-based Benton visual retention test which is currently adopted on dementia. This test requires patients to carry out some work like drawing, so that they need some field of vision while sitting in the magnet. The off-centered homogeneous field zone is expected to provide the necessary field of vision.

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“…We have recently introduced our version of the concept of asymmetric clinical MR magnet systems. 7,8 For asymmetric magnet systems to be useful as a clinical system, asymmetric shim fields must be implemented, and in this work we describe a design methodology for provision of asymmetric zonal shim coils.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric zonal shim coils for magnetic resonance applications

Forbes

Crozier

2001

Medical Physics

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A method is presented for the systematic design of asymmetric zonal shim coils for magnetic resonance applications. Fourier-series methods are used to represent the magnetic field inside and outside a circular cylinder of length 2L and radius a. The current density on the cylinder is also represented using Fourier series. Any desired field can be specified in advance on the cylinder's radius, over some nonsymmetric portion pL

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Asymmetric MRI Magnet Design Using a Hybrid Numerical Method

Cited by 36 publications

References 21 publications

Comprehensive Analysis of Lenz Effect on the Artificial Heart Valves During Magnetic Resonance Imaging

Comprehensive Analysis of Lenz Effect on the Artificial Heart Valves During Magnetic Resonance Imaging

Fabrication of an MRI Model Magnet With an Off-Centered Distribution of Homogeneous Magnetic Field Zone

Asymmetric zonal shim coils for magnetic resonance applications

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