Reducing MRI gradient coil vibration with rib stiffeners

Abstract

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.

Acoustic Noise and Magnetic Resonance Imaging: A Narrative/Descriptive Review

“…The ear is not uniformly sensitive over the hearing range (see Fig. 1)—peak sensitivity is in the range of 2–5 kHz 12 . Sensitivity is also age dependent.…”

A numerical study of the acoustic radiation due to eddy current-cryostat interactions

“…Here the SPL for a specific frequency was averaged through the FE nodes in the patient bore by Eq. (10), where N is the node quantity and p 0 is the referential sound pressure (In the acoustic industry, for the investigation of the noise or acoustic wave propagation in air, the level of 2 9 10 À5 Pa is usually adopted as a reference sound pressure). The overall averaged SPLs were calculated by Eq.…”

“…Other methods, such as the acoustic liners, rib stiffeners and damping materials, have also been proposed. [9][10][11][12] Aside from these passive methods, an active vibration-offset method using actuators mounted on the gradient assembly was also reported. 13 Noise reduction through optimized gradient coil design has also been carried out.…”

“…In addition, the vacuum device takes up some very precious space inside a MRI bore. Other methods, such as the acoustic liners, rib stiffeners and damping materials, have also been proposed . Aside from these passive methods, an active vibration‐offset method using actuators mounted on the gradient assembly was also reported .…”

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

“…Mounting the gradient assembly independently on the floor [9,66] or reducing the eddy currents [10,35] can restrain the vibration of some structures, such as the cryostat or RF coils, thus reducing the SPL. Rib stiffeners can help reinforce the gradient assembly, so the response amplitude will be reduced [71]. By mounting supports between the gradient assembly and the main magnet, the mechanical resonance modes of the MRI system can be adjusted, thereby reducing the loud regions of the acoustic field [72].…”