Compact MRI Magnet Design by Stochastic Optimization

Crozier, Stuart; Doddrell, David M.

doi:10.1006/jmre.1997.1200

Cited by 51 publications

(19 citation statements)

References 22 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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“…In terms of these common factors of design and other more specific application-related limitations, optimization methods used previously can be grouped into two categories: methods that search a large parameter space from which an optimal superconducting coil configuration is obtained (4-7), or ones wherein predefined constraints are used as part of the optimization strategy to speed up the calculation of a solution, while allowing for more stable convergence toward the optimal solution (8)(9)(10). In the first case, generally large computational resources are required to establish coil arrangements, whereas in the second case, a priori knowledge incorporated into the optimization strategy provides methods that converge fast, given that the seed data has been accurately formulated.…”

Section: Introductionmentioning

confidence: 99%

Minimum stored energy MRI superconducting magnets: From low to high field

Vegh

Tieng

Brereton

2009

Concepts Magn Reson

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The aim of this article is to describe superconducting magnet coil arrangements from low to high field, particularly from 1T to 7T, within the context of the minimum stored energy designs. The findings illustrate that at low field, the maximum peak magnetic fields are located away from the most inner coils of the magnet configuration, whereas in high field designs, the maximum peak magnetic fields are created on coils lying on the inner diameter of the magnet bore. This becomes a critical aspect of any high field design, since there appears to be much less freedom of design at higher fields, due to the inherent limitations posed by peak magnetic fields on superconductors. Our findings also indicate that at low fields, 3T and less, reverse current coils can be used to shorten superconducting magnets, whereas at high field, above 3T, this is not necessarily the case, due to the large peak fields produced between adjacent, alternating current coils.

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“…Optimization methods previously employed may be considered as one of two general approaches: either where a broad parameter space is searched for an optimal coil layout [2][3][4][5], or where initial constraints are placed on the optimization strategy to enable the calculation of a solution either more efficiently, or in a more convergent and stable manner [6][7][8]. The former tends to be associated with optimization strategies that require large computational resources, and the latter tends to achieve magnet coil layouts faster given favourable initial coil layout approximation or seed data.…”

Section: Introductionmentioning

confidence: 99%