Relationship between magnetic field strength and magnetic-resonance-related acoustic noise levels

Abstract

The need for better signal-to-noise ratios and resolution has pushed magnetic resonance imaging (MRI) towards high-field MR-scanners for which only little data on MR-related acoustic noise production have been published. The purpose of this study was to validate the theoretical relationship of sound pressure level (SPL) and static magnetic field strength. This is relevant for allowing adequate comparisons of acoustic data of MR systems at various magnetic field strengths. Acoustic data were acquired during various pulse sequences at field strengths of 0.5, 1.0, 1.5 and 2.0 Tesla using the same MRI unit by means of a Helicon rampable magnet. Continuous-equivalent, i.e. time-averaged, linear SPLs and 1/3-octave band frequencies were recorded. Ramping from 0.5 to 1.0 Tesla and from 1.0 to 2.0 Tesla resulted in an SPL increase of 5.7 and 5.2 dB(L), respectively, when averaged over the various pulse sequences. Most of the acoustic energy was in the 1-kHz frequency band, irrespective of magnetic field strength. The relation between field strength and SPL was slightly non-linear, i.e. a slightly less increase at higher field strengths, presumably caused by the elastic properties of the gradient coil encasings.

Gradient and shim technologies for ultra high field MRI

“…(1) may be incomplete. Instead we now understand that there may be a nonlinear dependence on field strength (Moelker et al, 2003), leading to lower levels of vibration and acoustics than anticipated. This should alleviate some concerns and improve the prospects for clinical translation of UHF MR systems.…”

Quiet PROPELLER MRI Techniques Match the Quality of Conventional PROPELLER Brain Imaging Techniques

“…Noise tends to be enhanced by decreases in section thickness, FOV, TR, and TE. 5 Noise levels for clinical MR imaging pulse sequences run as high as 100 -120 dB, [19][20][21][22] levels capable of causing temporary or even permanent hearing loss if hearing protection is not properly applied.…”

Verbal Communication in MR Environments: Effect of MR System Acoustic Noise on Speech Understanding

“…Absolute speech levels can therefore be calculated by taking the absolute sound levels of the particular MR system into account. In addition, conclusions about absolute sound levels may be derived from cautious extrapolation of MR sound levels based on the linear relationship between magnetic field strength and sound pressure level (38).…”