The use of active noise control (ANC) to reduce acoustic noise generated during MRI scanning: Some initial results

doi:10.1016/S0730-725X(96)00337-2

Magnetic Resonance Imaging

Volume 15, Issue 3, 1997, Pages 319-322

https://doi.org/10.1016/S0730-725X(96)00337-2 Get rights and content

Abstract

MRI scanning generates high levels of acoustic noise that cannot only pose a safety hazard, but also impair communication between staff and patient. In this article we present active noise control (ANC) techniques that introduce antiphase noise to destructively interfere with the MRI noise and with the aim of producing a zone of quiet around the patient's ears. Using noise recorded from a 1.0 Tesla midfield MR scanner the acoustic noise generated by three standard MR imaging sequences was replayed to a real time two channel ANC system. The results obtained show a useful attenuation of low-frequency periodic acoustic noise components. Therefore, in combination with standard passive ear protection, this suggests that MR generated acoustic noise can be effectively attenuated at both low and high frequencies leading to improved patient comfort.

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Therefore, acoustic noise generated during MRI acquisition may cause discomfort in patients undergoing MRI. Although various techniques have been developed to mitigate acoustic noise [8–16], increasing levels of acoustic noise with the development of high-field MRI systems and ultrafast MRI scanning highlight the urgent need to improve acoustic noise reduction in MRI. The Japan Society for Occupational Health recommendations regarding hearing protection as part of occupational health [28] presents permissible noise standards, which are converted with the octave band level allowed for each frequency and the A characteristic equivalent noise level.
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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.
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.
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We developed a simple and low-cost system for patient distraction using visual computer animations that were synchronized to the MRI scanner's acoustic noise during the MRI exam. The system was implemented on a 3T MRI system and tested in 28 pediatric patients with bipolar disorder. The patients were randomized to receive noise-synchronized animations in the form of abstract animations in addition to music (n = 13, F/M = 6/7, age = 10.9 ± 2.5 years) or, as a control, receive only music (n = 15, F/M = 7/8, age = 11.6 ± 2.3 years). After completion of the scans, all subjects answered a questionnaire about their scan experience and the perceived scan duration.
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Numerous studies on the tonotopic organisation of auditory cortex in humans have employed a wide range of neuroimaging protocols to assess cortical frequency tuning. In the present functional magnetic resonance imaging (fMRI) study, we made a systematic comparison between acquisition protocols with variable levels of interference from acoustic scanner noise. Using sweep stimuli to evoke travelling waves of activation, we measured sound-evoked response signals using sparse, clustered, and continuous imaging protocols that were characterised by inter-scan intervals of 8.8, 2.2, or 0.0 s, respectively. With regard to sensitivity to sound-evoked activation, the sparse and clustered protocols performed similarly, and both detected more activation than the continuous method. Qualitatively, tonotopic maps in activated areas proved highly similar, in the sense that the overall pattern of tonotopic gradients was reproducible across all three protocols. However, quantitatively, we observed substantial reductions in response amplitudes to moderately low stimulus frequencies that coincided with regions of strong energy in the scanner noise spectrum for the clustered and continuous protocols compared to the sparse protocol. At the same time, extreme frequencies became over-represented for these two protocols, and high best frequencies became relatively more abundant. Our results indicate that although all three scanning protocols are suitable to determine the layout of tonotopic fields, an exact quantitative assessment of the representation of various sound frequencies is substantially confounded by the presence of scanner noise. In addition, we noticed anomalous signal dynamics in response to our travelling wave paradigm that suggest that the assessment of frequency-dependent tuning is non-trivially influenced by time-dependent (hemo)dynamics when using sweep stimuli.

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Original contributionThe use of active noise control (ANC) to reduce acoustic noise generated during MRI scanning: Some initial results

Abstract

Clin. Radiol.

Reduction of sound levels with anti-noise in MR imaging

Radiology

Acoustic analysis of gradient coil noise in MR imaging

Radiology

Acoustic noise levels during magnetic resonance imaging scanning at 1,5 T

Br. J. Radiol.

Measurement of acoustic noise during MR Imaging: Evaluation of six “Worst-case” pulse sequences

Radiology

Potential hearing loss resulting from MR imaging

Radiology

Original contribution
The use of active noise control (ANC) to reduce acoustic noise generated during MRI scanning: Some initial results