More Shashikant R, Lim Teik C, Li Mingfeng, Holland Christy K, Boyce Suzanne E, Lee Jing-Huei
Department of Mechanical, Industrial and Nuclear Engineering, University of Cincinnati, Cincinnati, OH 45267, USA.
J Magn Reson Imaging. 2006 Mar;23(3):388-97. doi: 10.1002/jmri.20526.
To quantify the acoustic noise characteristics of a 4 Tesla MRI scanner, and determine the effects of structural acoustics and gradient pulse excitations on the sound field so that feasible noise control measures can be developed.
Acoustic noise emissions were measured in the ear and mouth locations of a typical adult. The sound pressure measurements were acquired simultaneously with the electrical current signals of the gradient pulses. Two forms of gradient waveforms (impulsive and operating pulses) were studied.
The sound pressure levels (SPLs) emitted by the MRI scanner operating in echo-planar imaging (EPI) mode were in the range of 120-130 decibels. Three types of sound pressure responses were observed in the EPI sequences: 1) harmonic, 2) nonharmonic, and 3) broadband. The frequency-encoding gradient pulses were the most dominant and produced generally odd-number harmonics and nonharmonics. The phase-encoding gradient pulses generated mostly even-number harmonics, and the slice-selection gradient pulses produced primarily a broadband spectrum.
The operating condition acoustic spectrum can be predicted from the magnet-structural acoustic transfer functions, which are independent of imaging sequences. This finding is encouraging because it shows that it is possible to treat such noises with an active noise control application.
量化4特斯拉磁共振成像（MRI）扫描仪的声学噪声特性，确定结构声学和梯度脉冲激励对声场的影响，以便制定可行的噪声控制措施。
在典型成年人的耳部和口腔位置测量声学噪声排放。声压测量与梯度脉冲的电流信号同时采集。研究了两种形式的梯度波形（脉冲式和工作脉冲）。
在回波平面成像（EPI）模式下运行的MRI扫描仪发出的声压级（SPL）在120 - 130分贝范围内。在EPI序列中观察到三种类型的声压响应：1）谐波，2）非谐波，3）宽带。频率编码梯度脉冲最为主要，通常产生奇数谐波和非谐波。相位编码梯度脉冲主要产生偶数谐波，而层面选择梯度脉冲主要产生宽带频谱。
运行条件下的声谱可以通过磁体 - 结构声学传递函数来预测，该函数与成像序列无关。这一发现令人鼓舞，因为它表明可以通过有源噪声控制应用来处理此类噪声。
