Biomedical Applications of Vibration and Acoustics in Therapy, Bioeffect and Modeling
11 Acoustic Noise in MRI Scanners
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Magnetic resonance imaging (MRI) technology has significantly changed the way modern medical research and clinical diagnostic work is conducted. It provides the ability to obtain detailed pictures from within a living body in a non-intrusive manner. However, the acoustic noise generated (primarily by the gradient coil) during the imaging process presents significant problems for patients (heightened anxiety), health care workers (temporary and permanent hearing impairment), and medical research and diagnostic personnel (disturbed brain activation). The acoustic noise levels in the next generation of ultra-high magnetic-field-strength scanning systems currently being delivered to hospitals and research institutions are known to exceed the ability of existing sound abatement methods to bring the noise generated to within acceptable levels. This chapter describes much of the work done so far to characterize the acoustic noise generated and emitted by scanners during the scanning process. The work described includes preliminary and advanced experimental measurements of the acoustic noise that exists inside and around MRI scanners during scanning, various types of modeling (empirical, computational, and analytical) that have been used to predict the acoustic noise, and techniques currently being used to reduce the acoustic noise levels.