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Segmented RF shield design to minimize eddy currents for low-field Halbach MRI systems.

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Bibliographic Details
Title:	Segmented RF shield design to minimize eddy currents for low-field Halbach MRI systems.
Authors:	de Vos, Bart^1,2 (AUTHOR) b.de_vos@lumc.nl, Remis, Rob² (AUTHOR), Webb, Andrew^1,2 (AUTHOR)
Source:	Journal of Magnetic Resonance. May2024, Vol. 362, pN.PAG-N.PAG. 1p.
Subjects:	Eddies, Magnetic resonance imaging, Noise measurement, Radio frequency, Work design, Time management
Abstract:	MRI systems have a thin conducting layer placed between the gradient and RF coils, this acts as a shield at the RF-frequency, minimizing noise coupled into the experiment, and decreasing the coupling between the RF and gradient coils. Ideally, this layer should be transparent to the gradient fields to reduce eddy currents. In this work the design of such a shield, specifically for low-field point-of-care Halbach based MRI devices, is discussed. A segmented double layer shield is designed and constructed based on eddy current simulations. Subsequently, the performance of the improved shield is compared to a reference shield by measuring the eddy current decay times as well as using noise measurements. A maximum reduction factor of 2.9 in the eddy current decay time is observed. The segmented shield couples in an equivalent amount of noise when compared to the unsegmented reference shield. Turbo spin echo images of a phantom and the brain of a healthy volunteer show improvements in terms of blurring using the segmented shield. [Display omitted] • Segmented shield improves eddy current characteristics while keeping shielding properties. • Shield designed for solenoidal radio frequency transmit/receive coils. • Eddy current simulations with and without segmentation. • Noise measurements with and without segmented shield. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	MRI systems have a thin conducting layer placed between the gradient and RF coils, this acts as a shield at the RF-frequency, minimizing noise coupled into the experiment, and decreasing the coupling between the RF and gradient coils. Ideally, this layer should be transparent to the gradient fields to reduce eddy currents. In this work the design of such a shield, specifically for low-field point-of-care Halbach based MRI devices, is discussed. A segmented double layer shield is designed and constructed based on eddy current simulations. Subsequently, the performance of the improved shield is compared to a reference shield by measuring the eddy current decay times as well as using noise measurements. A maximum reduction factor of 2.9 in the eddy current decay time is observed. The segmented shield couples in an equivalent amount of noise when compared to the unsegmented reference shield. Turbo spin echo images of a phantom and the brain of a healthy volunteer show improvements in terms of blurring using the segmented shield. [Display omitted] • Segmented shield improves eddy current characteristics while keeping shielding properties. • Shield designed for solenoidal radio frequency transmit/receive coils. • Eddy current simulations with and without segmentation. • Noise measurements with and without segmented shield. [ABSTRACT FROM AUTHOR]
ISSN:	10907807
DOI:	10.1016/j.jmr.2024.107669