Low-leakage wide-access magnet for MRI

Momy, A.; Taquin, J.

doi:10.1109/20.649897

Cited by 10 publications

(11 citation statements)

References 12 publications

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“…in which V e is the volume of the element and 2,3,4) are the algebraic complements of the ith-line elements in the determinant of Eq.…”

Section: Governing Equationsmentioning

confidence: 99%

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Characterization and reduction of X‐gradient induced eddy currents in a NdFeB magnetic resonance imaging magnet‐3D finite element method‐based numerical studies

Li¹,

Xia²,

F³

et al. 2011

Concepts Magn Reson

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ABSTRACT:In permanent magnetic resonance imaging (MRI) systems, pulsed gradient fields induce strong eddy currents in the conducting structures of the magnet. The gradient field for image encoding is perturbed by these eddy currents, thus leading to MR image distortions. The conventional approach for the reduction of the eddy current effects is to employ passive shielding (an eddy current board). However, the analysis of the passive shielding structure is typically nonoptimal. In this article, a comprehensive 3D finite element method (FEM) model for the characterization of eddy currents in the ferromagnetic materials of the magnet is developed, which is helpful for the evaluation of the shielding effects and the improvement of passive shielding designs. During the numerical analyses, the eddy current source was introduced through X-gradient coils, nonlinearity, and the anisotropy of the laminated silicon steel structure was considered, with the selection of a penalty factor in the FEM governing equations being also detailed. Based on the simulations results, suggestions have been made for passive shielding designs.

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“…in which V e is the volume of the element and 2,3,4) are the algebraic complements of the ith-line elements in the determinant of Eq.…”

Section: Governing Equationsmentioning

confidence: 99%

“…The permanent-magnet (PM) type of MRI system had been developed because of its advantages of a small leakage flux and a low operating cost (1)(2)(3)(4)(5)(6). Compared with other materials, NdFeB magnetic material has high capability in magnetic energy storage (7,8).…”

Section: Introductionmentioning

confidence: 99%

Characterization and reduction of X‐gradient induced eddy currents in a NdFeB magnetic resonance imaging magnet‐3D finite element method‐based numerical studies

Li¹,

Xia²,

F³

et al. 2011

Concepts Magn Reson

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show abstract

“…The target volume of interest is taken to be a 40 cm DSV at isocenter. The gradient of the objective function with respect to the design variables is therefore defined as (10) for which each of the partial derivatives is approximated using a forward finite-difference approximation: (11) where is a small perturbation, chosen as 0.1 mm. Each of the two objective function terms in the numerator of (11) corresponds to a particular design for which a FEM analysis is performed and the integral in (9) over the entire volume calculated.…”

Section: Nonlinear Optimization Algorithmmentioning

confidence: 99%

“…Consequently, resistive coil magnets are sometimes selected as an alternative to superconducting systems when field strengths less than 0.5 T are acceptable. Similar efforts to optimize resistive magnets have lead to more compact and open designs with suitable field uniformity and power consumption [11]- [14]. These systems are less expensive and simpler to construct than superconducting magnets, however they still require dedicated cooling and power systems and demand significant ongoing maintenance.…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Nonaxisymmetric Pole Piece Shape Optimization for Biplanar Permanent-Magnet MRI Systems

Tadic

Fallone

2011

IEEE Trans. Magn.

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The pole pieces of a permanent-magnet system for magnetic resonance imaging (MRI) are optimized for maximum magnetic field homogeneity in the imaging volume. Axisymmetric and nonaxisymmetric optimized pole piece designs based on the same geometrical parameterization are presented. The optimization algorithm demonstrated is based on field calculations by the three-dimensional finiteelement method and takes into account the nonlinearity of the magnetic materials involved. The necessity of the nonaxisymmetric design in obtaining suitable field homogeneity over a large imaging volume is demonstrated through comparison of various pole piece designs for a novel biplanar permanent-magnet assembly with reduced pole dimensions as required in the development of an integrated linear accelerator and MRI system for real-time image-guided adaptive radiotherapy. The sensitivity of the field inhomogeneities to geometrical variations in the nonaxisymmetric design surface is explored and statistical parameters quantifying this sensitivity are approximated.

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“…The permanent magnet (PM) type of MRI system had been developed because of their advantages of small leakage flux and low operating cost [1][2][3][4][5][6]. In a whole-body PM MRI systems, the magnets are assembled with ferromagnetic materials, such as pole pieces and the yoke.…”

Section: Introductionmentioning

confidence: 99%

Finite element analysis of gradient z-coil induced eddy currents in a permanent MRI magnet

Xia

Chen

et al. 2011

Journal of Magnetic Resonance

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Low-leakage wide-access magnet for MRI

Cited by 10 publications

References 12 publications

Characterization and reduction of X‐gradient induced eddy currents in a NdFeB magnetic resonance imaging magnet‐3D finite element method‐based numerical studies

Characterization and reduction of X‐gradient induced eddy currents in a NdFeB magnetic resonance imaging magnet‐3D finite element method‐based numerical studies

Three-Dimensional Nonaxisymmetric Pole Piece Shape Optimization for Biplanar Permanent-Magnet MRI Systems

Finite element analysis of gradient z-coil induced eddy currents in a permanent MRI magnet

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