Acoustic noise during functional magnetic resonance imaging
Acoustic noise during functional magnetic resonance imaging
复制标题
DOI：
10.1121/1.1310190
复制
发表时间：
2000-10-01
影响因子：
2.4
通讯作者：
Kiang, NYS
中科院分区：
文献类型：
--
作者：
Ravicz, ME;Melcher, JR;Kiang, NYS
功能性磁共振成像（fMRI）能够定位人类受试者的大脑激活部位。对于听觉系统的研究，fMRI过程中产生的声学噪声会通过引入不受控制的外来声音来干扰对这种激活的评估。作为降低功能磁共振成像噪声的第一步，本文描述了两个具有不同静态磁场强度的成像仪在典型功能磁共振成像研究条件下存在的噪声的时间和频谱特征。在1.5 tesla (T)和3-T成像仪中，峰值噪声水平分别为123和138 dB / 20 mu Pa。噪声频谱（在与最高振幅噪声相一致的10 ms窗口内计算）显示1.5 t成像仪在1 kHz处（115 dB SPL）和3-T成像仪在1.4 kHz处（131 dB SPL）有一个显著的最大值。最强烈噪声分量的频率含量和时序表明，噪声主要是由成像脉冲序列中的读出梯度引起的。梯度活动停止后，噪声在背景水平以上持续300-500 ms，表明成像仪中的共振结构或成像仪室内的噪声混响也是因素。梯度噪声波形重复性好。此外，成像仪永磁体的冷却剂泵和室内空气处理系统是持续噪声的来源，其水平和频率都低于梯度线圈噪声。对噪声的来源和特征的了解使我们能够研究控制噪声的一般方法，这些方法可以用于减少功能磁共振成像过程中不必要的噪声。(C) 2000美国声学学会。[s0001 - 4966(00) 04610 - 5]。
Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For studies of the auditory system, acoustic noise generated during fMRI can interfere with assessments of this activation by introducing uncontrolled extraneous sounds. As a first step toward reducing the noise during fMRI, this paper describes the temporal and spectral characteristics of the noise present under typical fMRI study conditions for two imagers with different static magnetic field strengths. Peak noise levels were 123 and 138 dB re 20 mu Pa in a 1.5-tesla (T) and a 3-T imager, respectively. The noise spectrum (calculated over a 10-ms window coinciding with the highest-amplitude noise) showed a prominent maximum at 1 kHz for the 1.5-T imager (115 dB SPL) and at 1.4 kHz for the 3-T imager (131 dB SPL). The frequency content and timing of the most intense noise components indicated that the noise was primarily attributable to the readout gradients in the imaging pulse sequence. The noise persisted above background levels for 300-500 ms after gradient activity ceased, indicating that resonating structures in the imager or noise reverberating in the imager room were also factors. The gradient noise waveform was highly repeatable. In addition, the coolant pump for the imager's permanent magnet and the room air-handling system were sources of ongoing noise lower in both level and frequency than gradient coil noise. Knowledge of the sources and characteristics of the noise enabled the examination of general approaches to noise control that could be applied to reduce the unwanted noise during fMRI sessions. (C) 2000 Acoustical Society of America. [S0001-4966(00)04610-5].