Gradient-induced acoustic and magnetic field fluctuations in a 4T whole-body MR imager

Wu, Yuhua; Chronik, Blaine A.; Bowen, Chris V.; Mechefske, Chris K.; Rutt, Brian K.

doi:10.1002/1522-2594(200010)44:4<532::aid-mrm6>3.0.co;2-q

Cited by 59 publications

(56 citation statements)

References 8 publications

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“…As presented elsewhere (4,5,6), the major source of the spurious peaks present throughout the spectrum at discrete frequencies is the vibration of the gradient coils at acoustic frequencies activated during their switching immediately prior to data acquisition and/or the oscillation of the magnetic field. The latter may be seen then as a superimposition of a time dependent magnetic field B G (t) and a static magnetic field ( ).…”

Section: Frequency Modulations Of Signals In Localized Mr Spectroscopymentioning

confidence: 86%

“…However, these localized MR spectra acquired without solvent suppression can exhibit an ensemble of spurious peaks added to the metabolite resonances (3). According to the literature, the origin of these spurious peaks, called sidebands, might be the vibrations of the gradients at acoustic frequencies during data acquisition (4), the oscillation of the magnetic field ( ) (5), or a correlation between both gradient-induced acoustic vibrations and the oscillation of the ( ) field (6). Either one of these fluctuations induce a time-varying magnetic field, which causes a time domain signal phase contamination, manifested as signal frequency modulations.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Localized Proton Spectroscopy without Water Suppression: Removal of Gradient Induced Frequency Modulations by Modulus Signal Selection

Serrai

Clayton

Senhadji

et al. 2002

Journal of Magnetic Resonance

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are removed. This is demonstrated by processing proton MRS spectra acquired without water suppression collected from a phantom containing metabolites at concentrations comparable to those in human brain and from a human subject using two different localization methods (PRESS and Chemical Shift Imaging PRESS-(CSI)). The results obtained illustrate the ability of this approach to remove the spurious peaks. The corrected spectra can then be fit accurately. This is confirmed by the results obtained from both the relative and the absolute metabolites concentrations in phantoms and in-vivo.

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Section: Frequency Modulations Of Signals In Localized Mr Spectroscopymentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Localized Proton Spectroscopy without Water Suppression: Removal of Gradient Induced Frequency Modulations by Modulus Signal Selection

Serrai

Clayton

Senhadji

et al. 2002

Journal of Magnetic Resonance

View full text Add to dashboard Cite

show abstract

“…However, the generation of magnetic field gradients requires time-varying currents which, in the presence of a strong external magnetic field, can lead to a number of unwanted effects like eddy currents (1-3), gradient coil vibrations (4) and acoustic noise (5)(6)(7). Eddy currents are a manifestation of Faraday's law of induction in which a time-varying magnetic field will induce a current in any nearby conducting structure, like the cryostat.…”

Section: Introductionmentioning

confidence: 99%

Compensation of gradient-induced magnetic field perturbations

Nixon

McIntyre

Rothman

et al. 2008

Journal of Magnetic Resonance

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Pulsed magnetic field gradients are essential for MR imaging and localized spectroscopy applications. However, besides the desired linear field gradients, pulsed currents in a strong external magnetic field also generate unwanted effects like eddy currents, gradient coil vibrations and acoustic noise. While the temporal magnetic field perturbations associated with eddy currents lead to spectral line shape distortions and signal loss, the vibration-related modulations lead to anti-symmetrical sidebands of any large signal (i.e. water), thereby obliterating the signals from smaller signals (i.e. metabolites). Here the measurement, characterization and compensation of vibrations-related magnetic field perturbations is presented. Following a quantitative evaluation of the various temporal components of the main magnetic field, a digital B 0 magnetic field waveform is generated which reduces all temporal variations of the main magnetic field to within the spectral noise level.

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“…Moreover, the mechanical vibration transmitted from the gradient assembly can trigger fluctuations in the static magnetic field to some extent [65]. However, there are also other MRI systems which directly mount the gradient assembly to the floor [9,66].…”

Section: Gradient Assemblymentioning

confidence: 99%

“…It is well-known that the acoustic field of a MRI scanner varies spatially and is dependent on the types of sequences used [8,67,69,[126][127][128]. The correlation between gradient magnetic field fluctuations and the acoustic noise has also been investigated [65]. It is commonly recognized that the most of the noise is generated by the gradient coils [8,56,65,67,69,101,115,[126][127][128][129][130][131][132][133][134].…”

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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Gradient-induced acoustic and magnetic field fluctuations in a 4T whole-body MR imager

Cited by 59 publications

References 8 publications

Localized Proton Spectroscopy without Water Suppression: Removal of Gradient Induced Frequency Modulations by Modulus Signal Selection

Localized Proton Spectroscopy without Water Suppression: Removal of Gradient Induced Frequency Modulations by Modulus Signal Selection

Compensation of gradient-induced magnetic field perturbations

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

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