Evaluation of magnetic resonance imaging acoustic noise reduction technology by magnetic gradient waveform control

Abstract

Background: ComforTone is a noise reduction technology used in magnetic resonance imaging (MRI) systems; it suppresses acoustic noise by modifying pulse sequences, which appropriately changes the magnetic field gradient waveforms. Although ComforTone can be used to solve the acoustic noise problems that affect patients who are exposed to acoustic noise from MRI, to the best of our knowledge, the associated technical details have not been published and its effects on acoustic noise reduction remain unclear.

Purpose: To evaluate the efficacy of acoustic noise reduction and the impact of acoustic noise reduction technology involving magnetic field gradient waveform control on image quality.

Population: The study included 18 healthy volunteers (11 males and 7 females; median age, 34 years; age range, 24-51 years).

Field strength: 1.5 T Philips Ingenia using a SENSE head-spine coil.

Assessment: The sound pressure level (SPL) and 1/3 octave spectra of MRI acoustic noise with the human head positioned in the iso-center of the MRI system were measured for five different pulse sequences used in clinical MRI. This subjective evaluation of noise included 18 healthy volunteers. The degree of discomfort experienced by the subjects was measured using a visual analog scale. The image quality was assessed objectively and subjectively. For objective assessment, signal-to-noise ratio (SNR) and contrast-to -noise ratio (CNR) of diffusion-weighted images were measured; for subjective assessment, visual evaluation was performed by two radiologists.

Statistical tests: Data were analyzed using Welch's t-test, and a p value <0.05 defined significance.

Results: ComforTone could recognize a decrease in sound pressure, and the sound pressure of the acute high-frequency portion of the auditory characteristics was reduced. As reported by the subjects, discomfort caused by the sound pressure was significantly alleviated with ComforTone (p < 0.01). The sound pressure reduction in the high-frequency region with high audibility characteristics was recognized by ComforTone. The visual evaluation of the image quality of the diffusion-weighted images revealed that although there was no difference between SNR and CNR, the image quality was reduced by distortion artifacts.

Data conclusion: ComforTone reduced the SPL in the frequency range where auditory characteristics were sensitive, suggesting that ComforTone was useful for auditory protection and alleviation of discomfort in patients undergoing MRI. However, because magnetic field gradient waveform control is involved, such noise-reducing techniques should be used by considering their possible influence on the image quality.

Keywords: Acoustic noise; Electromagnetic force; Magnetic resonance imaging.