Technical Note MRI Acoustic Noise Can Harm Experimental and Companion Animals Amanda M. Lauer, PhD, 1 AbdEl-Monem M. El-Sharkawy, PhD, 2 Dara L. Kraitchman, VMD, PhD, 2,3 and William A. Edelstein, PhD 2 * Purpose: To assess possible damage to the hearing of ex- perimental and companion animal subjects of magnetic resonance imaging (MRI) scans. Materials and Methods: Using animal hearing threshold data and sound level measurements from typical MRI pulse sequences, we estimated ‘equivalent loudness’ experienced by several experimental and companion animals commonly sub- jects of MRI scans. We compared the equivalent loudness and exam duration to safe noise standards set by the National Insti- tute for Occupational Safety and Health (NIOSH). Results: Monkeys, dogs, cats, pigs, and rabbits are fre- quently exposed to equivalent loudness levels during MRI scans beyond what is considered safe for human expo- sure. The sensitive frequency ranges for rats and mice are shifted substantially upward and their equivalent loud- ness levels fall within the NIOSH safe zone. Conclusion: MRI exposes many animals to levels of noise and duration that would exceed NIOSH human exposure limits. Researchers and veterinarians should use hearing protection for animals during MRI scans. Experimental research animals used in MRI studies are frequently kept and reimaged, and hearing loss could result in changed behavior. Damage to companion animals’ hearing could make them less sensitive to commands and generally worsen interactions with family members. Much quieter MRI scanners would help decrease stress and potential harm to scanned animals, normalize physiology during MRI, and enable MRI of awake animals. Key Words: health and safety; acoustic noise; animal MRI; companion animals; veterinary MRI J. Magn. Reson. Imaging 2012; 36:743–747. V C 2012 Wiley Periodicals, Inc. VERTEBRATE ANIMAL magnetic resonance imaging (MRI) is an important part of medical research, and veterinary MRI of companion animals is increasing. Human subjects are customarily provided with hear- ing protection against the loud, potentially damaging acoustic noise produced by MRI scanners (1); this is generally not done for animal MRI subjects. Hearing damage can interfere with physiological functions and consequent quality of life for research or companion animals (2). We investigate possible hearing damage to unprotected animals. Pulsed gradients are basic to the MRI process, and the concomitant pulsed Lorentz forces applied to the gradient coils, gradient coil assembly, and metal cryo- stat situated in a static magnetic field produce vibra- tions that result in intense acoustic noise (1). This noise has been a problem for decades and constitutes a safety concern for patients, physicians, and health workers in the vicinity of MR imagers (3,4). Following the introduction of clinical 1.5 T (and now 3 T) superconducting imaging magnets, increasingly powerful gradient electronics, and dense, multiplanar and multiecho pulse sequences, MRI systems now generate continuous acoustic noise with intensities in excess of 100 dB (5), well into the range of potential hearing damage as delineated by NIOSH (6). MRI acoustic noise is at levels sufficient to cause discom- fort and possible damage to human hearing (5,7,8), is a cause of patient distress (9), and interferes with functional MRI (fMRI) and interventional MRI (10,11). A lot of animal MRI is done in human clinical sys- tems. In addition, small-bore MRI systems specifically designed for animal imaging have acoustic noise as loud as that in human systems (2), as animal MRI systems have equally powerful current pulses and of- ten use higher static magnetic fields (leading to stron- ger Lorentz forces) than are the norm for human sys- tems (12). The intense acoustic noise generated for animal MRI systems again creates a health risk for operators and researchers and, obviously, for animal imaging subjects, which often are not fitted for hear- ing protection (2). Acoustic noise prevents an important area of animal MRI research, namely, MRI applied to conscious ani- mals. While MRI is not in and of itself painful, intense acoustic noise would be painful to a conscious Additional Supporting Information may be found in the online version of this article. 1 Otolaryngology-HNS, Johns Hopkins School of Medicine, Baltimore, Maryland, USA. 2 Russell H. Morgan Department of Radiology and Radiological Science/MRI Division, Johns Hopkins School of Medicine, Baltimore, Maryland, USA.. 3 Department of Molecular and Comparative Pathobiology, Johns Hopkins School of Medicine, Baltimore, Maryland, USA. *Address reprint requests to: W.A.E., Department of Radiology, MRI Division, Johns Hopkins School of Medicine, 600 North Wolfe St., Park 328, Baltimore, MD 21287. E-mail: w.edelstein@gmail.com Received August 16, 2011; Accepted March 5, 2012. DOI 10.1002/jmri.23653 View this article online at wileyonlinelibrary.com. JOURNAL OF MAGNETIC RESONANCE IMAGING 36:743–747 (2012) CME V C 2012 Wiley Periodicals, Inc. 743