Increasing the oscillation frequency of strong magnetic fields above 101 kHz significantly raises peripheral nerve excitation thresholds
Increasing the oscillation frequency of strong magnetic fields above 101 kHz significantly raises peripheral nerve excitation thresholds
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DOI：
10.1118/1.3702775
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发表时间：
2012-05-01
期刊：
影响因子：
3.8
通讯作者：
Reilly, J. Patrick
中科院分区：
文献类型：
--
作者：
Weinberg, Irving N.;Stepanov, Pavel Y.;Reilly, J. Patrick
目的：当磁场的最大偏移（Δ B）高于频率依赖性阈值水平时，时变磁场可能导致令人不快的外周神经刺激（PNS）[P.曼斯菲尔德和P. R.哈维，梅森。29，746-758（1993）]。临床和研究磁共振成像（MRI）梯度系统的设计旨在通过遵守基于临床试验制定的法规和指南来避免此类生物效应。这些试验通常采用正弦波形，测试人类对频率在0.5和10 kHz之间的磁场的反应。Irnich和F.施密特，梅森。33，619-623（1995），T. F. Budinger等人，J.计算机协助。托莫格15，909-914（1991）和D. J. Schaefer等人，J.磁共振Imaging 12，20-29（2000）]。使用生理模型外推频率高于10 kHz的PNS阈值[J. P. Reilly等人，IEEE生物医学学报BME-32（12），1001-1011（1985）]。本研究提供了人类PNS阈值振荡磁场刺激从2到183 kHz的实验数据。采用正弦波形有几个原因：（1）便于与使用正弦波的早期报告进行比较，（2）因为用于广义波形的快速梯度硬件的现有设计者（例如，例如，在一个实施例中，包括梯形脉冲）已经采用四分之一正弦波谐振电路来减少脉冲波形的上升和下降时间，以及（3）因为正弦曲线通常用于快速脉冲序列（例如，例如，在一个实施例中，螺旋扫描）[S.诺瓦克，美国S.专利5，245，287（1993年9月14日）和K. F. King和D. J. Schaefer，J. Magn. Reson. Imaging 12，164-170（2000）].方法：进行IRB批准的前瞻性临床试验，涉及26名成人，其中一个手腕暴露于频率为2至183 kHz且振幅高达0.4 T的衰减正弦磁场脉冲。假暴露（即，结果：对于2、25、59、101和183 kHz的0.4 T脉冲，（84.6%）、24（92.3%）、15（57.7%）、2（7.7%），1（3.8%）的受试者。PNS的概率，由于短暂的双相时变正弦磁场的磁偏移高达0.4 T的显着降低，在101 kHz以上。这种现象可能在动态场景中有特殊用途（例如，例如，在一个实施例中，心脏成像）和研究具有短衰减时间的过程（例如，例如，在一个实施例中，电子顺磁共振成像、骨和固体成像）。该研究表明，人类和临床前MRI系统的新设计可能在临床实践和科学研究中有用。(C)2012年美国医学物理学家协会。[http：//dx.doi.org/10.1118/1.3702775]
Purpose: A time-varying magnetic field can cause unpleasant peripheral nerve stimulation (PNS) when the maximum excursion of the magnetic field (Delta B) is above a frequency-dependent threshold level [P. Mansfield and P. R. Harvey, Magn. Reson. Med. 29, 746-758 (1993)]. Clinical and research magnetic resonance imaging (MRI) gradient systems have been designed to avoid such bioeffects by adhering to regulations and guidelines established on the basis of clinical trials. Those trials, generally employing sinusoidal waveforms, tested human responses to magnetic fields at frequencies between 0.5 and 10 kHz [W. Irnich and F. Schmitt, Magn. Reson. Med. 33, 619-623 (1995), T. F. Budinger et al., J. Comput. Assist. Tomogr. 15, 909-914 (1991), and D. J. Schaefer et al., J. Magn. Reson. Imaging 12, 20-29 (2000)]. PNS thresholds for frequencies higher than 10 kHz had been extrapolated, using physiological models [J. P. Reilly et al., IEEE Trans. Biomed. Eng. BME-32(12), 1001-1011 (1985)]. The present study provides experimental data on human PNS thresholds to oscillating magnetic field stimulation from 2 to 183 kHz. Sinusoidal waveforms were employed for several reasons: (1) to facilitate comparison with earlier reports that used sine waves, (2) because prior designers of fast gradient hardware for generalized waveforms (e. g., including trapezoidal pulses) have employed quarter-sine-wave resonant circuits to reduce the rise- and fall-times of pulse waveforms, and (3) because sinusoids are often used in fast pulse sequences (e. g., spiral scans) [S. Nowak, U. S. patent 5,245,287 (14 September 1993) and K. F. King and D. J. Schaefer, J. Magn. Reson. Imaging 12, 164-170 (2000)].Methods: An IRB-approved prospective clinical trial was performed, involving 26 adults, in which one wrist was exposed to decaying sinusoidal magnetic field pulses at frequencies from 2 to 183 kHz and amplitudes up to 0.4 T. Sham exposures (i.e., with no magnetic fields) were applied to all subjects.Results: For 0.4 T pulses at 2, 25, 59, 101, and 183 kHz, stimulation was reported by 22 (84.6%), 24 (92.3%), 15 (57.7%), 2 (7.7%), and 1 (3.8%) subjects, respectively.Conclusions: The probability of PNS due to brief biphasic time-varying sinusoidal magnetic fields with magnetic excursions up to 0.4 T is shown to decrease significantly at and above 101 kHz. This phenomenon may have particular uses in dynamic scenarios (e. g., cardiac imaging) and in studying processes with short decay times (e. g., electron paramagnetic resonance imaging, bone and solids imaging). The study suggests the possibility of new designs for human and preclinical MRI systems that may be useful in clinical practice and scientific research. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.3702775]