Counter S A, Olofsson A, Borg E, Bjelke B, Häggström A, Grahn H F
Department of Neurology, Harvard University Biological Laboratories, Cambridge, Massachusetts 01238, USA.
Acta Otolaryngol. 2000 Sep;120(6):739-43. doi: 10.1080/000164800750000270.
High intensity acoustic noise is an undesirable side-effect in magnetic resonance imaging (MRI) that can cause discomfort and hearing loss in patients and may be an impediment in functional MRI (fMRI) studies of the auditory system. Experimental MRI systems with high magnetic field strengths may generate acoustic noise of higher sound pressure levels (SPLs) than conventional 1.0 and 1.5 T clinical systems. We measured the SPL and spectral content of the acoustic noise generated by the Bruker Biospect 47/40 4.7 T experimental MRI system during scanning sequences commonly used in animal testing. Each sequence generated acoustic noise of high SPL, rapid pulse rates, amplitude-modulated pulse envelopes and multi-peaked spectra. The rapid acquisition with enhancement sequence with a 0.25 mm slice thickness generated SPLs of up to 129 dB peak SPL and 130 dB (A). Fourier analysis of the spectral content of the acoustic noise generated by each MRI sequence showed a wide band of acoustic energy with spectral peaks from 0.2-5 kHz. The intense MRI acoustic impulse noise generated by the 4.7 T system may cause masking of stimuli used in fMRI of the auditory cortex, reduce the hearing acuity of experimental animals and present a risk for unprotected human ears.
高强度声学噪声是磁共振成像（MRI）中一种不良的副作用，它会给患者带来不适并导致听力损失，而且在听觉系统的功能磁共振成像（fMRI）研究中可能会成为一个障碍。具有高磁场强度的实验性MRI系统可能会产生比传统1.0和1.5 T临床系统声压级（SPL）更高的声学噪声。我们测量了布鲁克Biospect 47/40 4.7 T实验性MRI系统在动物测试常用扫描序列期间产生的声学噪声的声压级和频谱内容。每个序列都产生了高声压级、快速脉冲率、调幅脉冲包络和多峰频谱的声学噪声。使用0.25 mm层厚的快速采集增强序列产生的峰值声压级高达129 dB，A声级为130 dB。对每个MRI序列产生的声学噪声频谱内容进行傅里叶分析，结果显示存在一个宽带声能，频谱峰值在0.2 - 5 kHz之间。4.7 T系统产生的强烈MRI声学脉冲噪声可能会掩盖听觉皮层fMRI中使用的刺激，降低实验动物的听力敏锐度，并对未受保护的人耳构成风险。
