An inverse approach to the design of MRI main magnets

Thompson, Michael; Brown, Robert W.; Srivastava, Vishnu C.

doi:10.1109/20.272522

Cited by 40 publications

(18 citation statements)

References 9 publications

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“…For example, the finite-element method has been used for studying MRI devices made of permanent magnets [14]. Furthermore, some original methods have been proposed for designing MRI structures made of permanent magnets [15] by employing inverse methods [16]. All these studies deal with the optimization of the static field produced by permanent magnets or currents in coils.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Field in Mri Yokeless Devices: Analytical Approach

Ravaud¹,

Lemarquand²

2009

PIER

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Abstract-This paper presents a three-dimensional analytical expressions for studying the static magnetic field produced by Magnetic Resonance Imaging structures. This medical imaging technique uses a very high and uniform magnetic field produced by ring permanent magnets with rotating polarizations. However, the manufacturing of such ring permanent magnets is difficult to realize. Consequently, such ring permanent magnets are replaced by assemblies of tile permanent magnets uniformly magnetized. Unfortunately, the magnetic field produced by these tile permanent magnets uniformly magnetized is both less important and less uniform than the one produced by an idealized ring permanent magnet. We propose in this paper to study the influence of the number of tile permanent magnets used on the magnetic field properties.

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Section: Introductionmentioning

confidence: 99%

Magnetic Field in Mri Yokeless Devices: Analytical Approach

Ravaud¹,

Lemarquand²

2009

PIER

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“…Thompson et al [5] have considered several functionals that can lead to viable designs for MRI systems. Those constraints correspond to internal moments nulled at a given position on the surface of the diameter sphere volume (DSV) and the requirement that the magnetic field (stray field) at one or two locations outside the magnet be restricted to 5 Gauss.…”

Section: Introductionmentioning

confidence: 99%

“…In recent years, the trends in industry have been toward shorter cylindrical MRI machines, in order to increase patient comfort [1,2]. Previous design work has included a Monte Carlo method [3,4], functional (or inverse) methods [5,6], annealing methods [7,8], "hybrid" methods [9,10,11], and a genetic algorithm approach [12,13]. In general, the Monte Carlo, annealing, and genetic algorithm methods need extensive computing power in order to search through a larger parameter space.…”

Section: Introductionmentioning

confidence: 99%

Design of actively shielded main magnets: an improved functional method

Cheng

Eagan

Brown

et al. 2003

Magn Reson Mater Phy

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An improved functional approach for designing MRI (magnetic resonance imaging) main magnets with active shielding is presented. By nulling one or two external moments as well as a certain series of internal moments of the magnetic field, new designs with improved shielding in combination with or without shorter magnet lengths are obtained. The improved method can be employed to design short and practical superconducting magnets at any given field strength. The resulting designs yield the desired field homogeneity inside the region of interest without using superconducting shim coils. This approach requires only a modest amount of computing power. One of the design steps, a contour plot of the continuous current solutions, can be utilized to study stretch goals for favorable design parameters.

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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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An inverse approach to the design of MRI main magnets

Cited by 40 publications

References 9 publications

Magnetic Field in Mri Yokeless Devices: Analytical Approach

Magnetic Field in Mri Yokeless Devices: Analytical Approach

Design of actively shielded main magnets: an improved functional method

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

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