Vibration and Acoustic Noise Characterization of a Gradient Coil Insert in a                 4 T MRI

Mechefske, Chris K.; Yao, Guijin; Wang, Fenglin

doi:10.1177/1077546304040948

Cited by 10 publications

(10 citation statements)

References 9 publications

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“…(6) The modal shapes obtained using the thinwalled model also partly match and validate the results found by the authors in previous work (11)(12)(13)(14) using experimental and finite element based computational methods.…”

Section: Discussionsupporting

confidence: 87%

“…Previous work investigating the dynamic behavior of gradient coil cylinders has involved the finite ele-ment and boundary element approaches (11)(12)(13)(14). These studies revealed the complicated modal shapes and their corresponding natural frequencies associated with gradient coils in the low frequency range (Ͻ3000 Hz).…”

Section: Introductionmentioning

confidence: 98%

“…Acoustic noise reductions of up to 20 dB(A) were achieved. SPL characteristic predictions (7,8), vibroacoustic mechanism analysis (9,10), and structural modal analysis of gradient cylinders (11)(12)(13)(14) were also explored. These studies indicated that the SPLs and the frequency features of different MRI scanners depend not only on the pulse sequence employed but also depend greatly on the type of scanner, especially the gradient coil insert structure and supports.…”

Section: Introductionmentioning

confidence: 99%

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Modal analysis and testing of a thin-walled gradient coil cylinder model

Wang

Mechefske

2005

Concepts Magn. Reson.

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ABSTRACT:The high level of vibroacoustic noise generated during magnetic resonance imaging (MRI) can make the diagnostic process extremely uncomfortable. The vibration caused by the electromagnetic forces acting on the gradient cylinder is one of the main acoustic noise sources together with the vibration caused by RF shields and the warm bore. To help further the fundamental understanding of the dynamic behavior of gradient coil cylinders, a dynamic model based on thin shell theory is explored in this article. The source-path response of the vibroacoustic mechanism in and around the gradient coil is investigated from the viewpoint of structural dynamics. A thin elastic cylinder model is established in terms of forcing function, the governing equations, and the boundary conditions. Modal characteristics of the cylinder model are fully described, including bending modes, torsional modes, axial modes, and their natural frequencies. The basic modal components and the linear and nonlinear combinations are also analyzed. Experimental modal testing of a thin cylinder model demonstrates that the bending modes are dominated in the low frequency band. These modal results should help further the fundamental understanding of the complicated modal behavior of real gradient cylinders.

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Section: Discussionsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Modal analysis and testing of a thin-walled gradient coil cylinder model

Wang

Mechefske

2005

Concepts Magn. Reson.

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“…The rapid pulsed gradient currents produce powerful Lorentz forces acting on the gradient coil insert (5). By focusing on the vibro-acoustics of a 4-T MRI scanner, the surface vibrations of a gradient coil insert were predicted using a multilayered fi-nite element (FE) modeling method (7,8). The acoustic noise levels were calculated, measured, and verified in the 4-T MRI bore.…”

Section: Introductionmentioning

confidence: 99%

Modal analysis of a multilayered gradient coil insert in a 4‐T MRI scanner

Wang

Mechefske

2007

Concepts Magn Reson

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In ultrahigh field strength Magnetic Resonance Imaging (MRI), the pulsed electrical currents passing through gradient coil windings cause powerful alternating forces that act on the gradient coil structure and create structural vibration and consequential acoustic noise (as high as 130 dB). The dynamic response of the gradient coil cylinder largely determines the acoustic noise generated in terms of frequency components, sound pressure levels (SPL), and the spatial distribution within the bore of the scanner. The objective of this article is to characterize the dynamic behavior of a real (multilayered) gradient coil insert in a 4-T MRI scanner (from 200 to 3,000 Hz). The simply supported (assembly condition) and free-free (modal testing) condition are investigated in the dynamic analysis. In-situ vibration testing, modal testing, and numerical analyses are applied to uncover the dynamic features. The results indicate that bending modes in combination with different specific free-free and simply supported radial mode shapes provide the fundamental characteristics of the dynamic behavior of the gradient coil cylinder in the frequency range tested. The change in dominant bending mode as a function of scanning input frequency was also studied.

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“…In addition, similar to typical MRI systems, the faster the gradient current switches, the louder the noise will be [11,52,101,[130][131][132][133]140].…”

Section: Introductionmentioning

confidence: 99%

Gradient coil design and acoustic noise control in magnetic resonance imaging systems

Wang¹

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In magnetic resonance imaging (MRI), three-dimensional linearly varied magnetic field gradients are required in the imaging volume, for the encoding of the spatial information of the imaged object.The gradient magnetic field is generated by gradient coils, whose performance directly affects the final MR image quality. Modern MRI applications demand gradient coils to be designed with higher performance such as a faster slew rate for rapid imaging, and fewer system interactions to ensure distortion-free images.During MR imaging, the gradient coil current switches quickly and the alternating current under a strong magnetic field generates a large Lorentz force, thus increasing the vibrations and noise in the gradient assembly, and the vibrations can also transmit to other components in the system. Moreover, the gradient magnetic field induces eddy currents on the surrounding conductive materials, resulting in further mechanical vibration. The sound pressure level (SPL) of an MRI scanner very commonly exceeds 100 dB, which may be discomforting to patients. Therefore, an effective acoustic noise control is necessary for the MRI operation.This thesis attempts to design a novel gradient coil system in an MRI scanner with a particular focus on the investigation of an acoustic noise control scheme. A brief summary of the thesis work is as follows.(1) Gradient coil design A conventional cylindrical MRI scanner has a long patient bore, which may make some patients uneasy due to claustrophobia. In order to alleviate this, an asymmetric gradient coil was proposed to accommodate an asymmetric MRI magnet. The coil was designed with a number of features, for example, to enable the installation of the shim tray, the coil was configured with one end connected and the other end separated. The electromagnetic and acoustic performances were also improved compared with a conventional non-connected coil system.The stream function approach is commonly used in gradient coil design, but an issue with this design is a connection problem between coil loops. To eliminate the field errors due to the coil connections, this thesis proposed a novel spiral coil design scheme, including both transverse coils and a longitudinal coil. The proposed coil design method was not only able to improve the magnetic II performance of the coil, but also could integrate the cooling system into the coil design using hollow wires in the discrete wire space.Wire spacing is a major engineering problem in gradient coil design. Conventional gradient coils are designed with three primary layers and three shielding layers, and in general, primary transverse coils are located in two layers separated by a very dense wire structure. In this thesis, a novel gradient coil design strategy using a layer-sharing scheme was proposed. This design scheme mutually combined the x and y gradient coil layers, effectively utilizing the unoccupied or sparse coil-layer space. The new method was modelled in the case of an asymmetric head coil design, and enhanced coil performan...

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Vibration and Acoustic Noise Characterization of a Gradient Coil Insert in a 4 T MRI

Cited by 10 publications

References 9 publications

Modal analysis and testing of a thin-walled gradient coil cylinder model

Modal analysis and testing of a thin-walled gradient coil cylinder model

Modal analysis of a multilayered gradient coil insert in a 4‐T MRI scanner

Gradient coil design and acoustic noise control in magnetic resonance imaging systems

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