Characterization of Acoustic Noise and Magnetic Field Fluctuations in a 4 T Whole-Body Mri Scanner

Mechefske, Chris K.; Wu, Yuhua; Rutt, Brian K.

doi:10.1006/mssp.2000.1383

Cited by 8 publications

(8 citation statements)

References 7 publications

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“…Finite-element analysis (FEA) as well as vibro-acoustic computational methods have also been used to estimate the acoustic noise distribution of the gradient coil during scanning [17,18]. However, not all these models were verified through experimental testing.…”

mentioning

confidence: 99%

Characterization of vibration and acoustic noise in a gradient-coil insert

Yao

Mechefske

Rutt

2004

MAGMA

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High-speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite-element (FE) model was developed using the dimensional design specifications of an available gradient-coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data. A computational acoustic noise model was then developed based on the validated FE model. The validation of the finite-element analysis results was done using experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient-coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing with the gradient-coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient-coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately.

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mentioning

confidence: 99%

Characterization of vibration and acoustic noise in a gradient-coil insert

Yao

Mechefske

Rutt

2004

MAGMA

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“…2, to explore the most effective stiffening pattern. In general, the rib stiffening has three types of effects on the gradient coil vibration: [1] it reduces the forced response amplitude in the stiffness control region of the gradient coil (below the first structure resonance) due to the increased structure rigidity of the coil; [2] it increases the frequency range of forced response of the gradient coil; and [3] it reduces the total number of modes in a given frequency range and minimizes the chance of the structure being excited resonantly by an operating input sequence. These are illustrated in details in the following discussions.…”

Section: Effects Of Rib Stiffeners To the Natural Vibration Of The Grmentioning

confidence: 99%

“…The high acoustic noise level in and around a gradient coil can cause difficulties in verbal communication, heightened anxiety, and temporary hearing loss, and even permanent hearing impairment of patients (1). Vibration of gradient coils also affects the image quality in functional magnetic resonance imaging (2,3). Work has been undertaken in the last few decades aimed at reducing the noise of MRI scanners, which has resulted in substantial reduction of the MRI noise.…”

Section: Introductionmentioning

confidence: 99%

Reducing MRI gradient coil vibration with rib stiffeners

Lin

O’Shea

Mechefske

2009

Concepts Magn Reson

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This work investigates the effect of rib stiffeners on the free and forced vibration of a gradient coil in a magnetic resonance imaging (MRI) scanner. Several reinforcement schemes are studied in this article. One scheme utilizes the existing holes in the gradient coil structure (typically reserved for magnetic shims) to produce the reinforcement. Nonferrous, nonmagnetic carbon fiber rib stiffeners are employed to fill these holes in several ways to strengthen a gradient coil. Another scheme replaces the inner half of the gradient coil material with a grid of interconnected axial and circumferential rib stiffeners. It is found that the structural stiffness of the gradient coil increases substantially when the coil is reinforced by carbon fiber rib stiffeners. The reinforcement affects the noise and vibration response of the gradient coil structure in the following ways. It increases the frequency range of forced response of the gradient coil at low frequencies due to the increased resonant frequency of the fundamental mode of the coil. Second, it reduces the forced response amplitude of the coil structure (which is governed by the structural stiffness of the coil). Thirdly, it reduces the number of natural modes in the low and medium frequency range and therefore lessens the chance of the coil structure being excited resonantly by magnetic resonance signal acquisition sequences. It is shown that gradient coils modeled by solid finite element models have higher stiffness along the coil's circumference and lower stiffness in the axial direction than those using shell finite element models.

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“…Finite element analysis (FEA) as well as vibro-acoustic computational methods have also been used to estimate the acoustic noise distribution of the gradient coil during scanning [14,10]. However, not all the models were verified through experimental testing.…”

Section: Introductionmentioning

confidence: 99%