The sound pressure recordings show a substantial dampening effect when using an acoustic hood (figure 3). Results Using different acoustic hoods the acoustic noise levels were reduced by 6-24dB on the A-weighted scale (figure 2) a 38mm small flexible hood reducing 6dB and a 104mm hood with isolating mat reducing 24dB. The acoustic hoods were constructed of acoustic foam rubber, 38-104mm, combined with a 4mm isolating mat and a closed exit in the back of the MR-scanner. Different combinations of materials were tested and several hoods were built to achieve a substantial dampening effect. The MR-scanner (Philips Intera 1.5T, Best, Holland) was tested for acoustic noise levels during 12 common pulse sequences. The measurement chain was calibrated with the TES-1356 Sound Level Calibrator (ISO-Tech, Taipei, Taiwan).
#NATUS MINIMUFFS SOFTWARE#
The DSSF3 software (Yoshimasa Electronic Inc., Tokyo, Japan) and Matlab 7.0 (Mathworks, Novi, Michigan) was used to record and analyze data. The acoustic noise was measured inside the MR-scanner tunnel using a microphone unit (type 4189, Brüel & Kjaer, Naerum, Dennmark) and a laptop with a soundcard (VX Pocket v2, Digigram, Montbonnot, France). The acoustic hood is placed inside the MR-scanner tunnel. Methods An acoustic hood of dampening material was built (figure 1). In addition, we have developed a new simple, safe and reliable method for reducing the acoustic noise. Usually, three passive attenuators are used: (1) a moldable dental putty, reducing more than 20dB and showing small image artifacts in our tests, (2) Natus minimuffs, reducing 7dB and (3) regular earmuffs, reducing 15-32dB, if fitted properly which is difficult on the small neonate.
The acoustic noise is clearly a risk factor in MRI and hearing protection must be used. Since hearing protection is difficult to fit properly on newborns there is also a risk of hearing loss. High acoustic noise levels during MRI can lead to anxiety, motion artifacts, and incomplete examinations due to newborns waking up. Studies have shown that newborns are likely to be more sensitive to acoustic noise than adults. Introduction The effect of acoustic noise during MRI is unclear and difficult to study in neonatal individuals.
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