Acoustic noise during functional magnetic resonance imaging

Area of Science:

• Neuroimaging
• Auditory Neuroscience
• Biomedical Engineering

Background:

• Functional magnetic resonance imaging (fMRI) is crucial for localizing brain activity in humans.
• Acoustic noise from fMRI scanners poses a significant challenge for auditory system studies.
• Uncontrolled extraneous sounds interfere with accurate assessment of brain activation.

Purpose of the Study:

• To characterize the temporal and spectral properties of acoustic noise in fMRI.
• To identify the primary sources of noise during typical fMRI study conditions.
• To lay the groundwork for developing noise reduction techniques in fMRI.

Main Methods:

• Measured acoustic noise characteristics using two fMRI scanners with different magnetic field strengths (1.5-T and 3-T).
• Analyzed noise spectra over 10-ms windows during high-amplitude noise events.
• Identified noise sources including readout gradients, imager resonances, and environmental systems.

Main Results:

• Peak noise levels reached 123 dB (1.5-T) and 138 dB (3-T).
• Dominant noise frequencies were around 1 kHz (1.5-T) and 1.4 kHz (3-T), attributed to readout gradients.
• Noise persisted for 300-500 ms post-gradient activity, with contributions from resonating structures and environmental systems.

Conclusions:

• Readout gradients are the main contributors to intense, transient noise in fMRI.
• Persistent noise components suggest contributions from imager acoustics and room reverberation.
• Understanding noise characteristics is essential for designing effective noise control strategies for fMRI.