Glover P M, Bowtell R
The Sir Peter Mansfield Magnetic Resonance, Centre School of Physics and Astronomy, University of Nottingham, NG7 2RD Nottingham, UK.
Phys Med Biol. 2008 Jan 21;53(2):361-73. doi: 10.1088/0031-9155/53/2/005. Epub 2007 Dec 28.
A dual dipole electric field probe has been used to measure surface electric fields in vivo on a human subject over a frequency range of 0.1-800 Hz. The low-frequency electric fields were induced by natural body movements such as walking and turning in the fringe magnetic fields of a 3 T magnetic resonance whole-body scanner. The rate-of-change of magnetic field (dB/dt) was also recorded simultaneously by using three orthogonal search coils positioned near to the location of the electric field probe. Rates-of-change of magnetic field for natural body rotations were found to exceed 1 T s(-1) near the end of the magnet bore. Typical electric fields measured on the upper abdomen, head and across the tongue for 1 T s(-1) rate of change of magnetic field were 0.15+/-0.02, 0.077+/-0.003 and 0.015+/-0.002 V m(-1) respectively. Electric fields on the abdomen and chest were measured during an echo-planar sequence with the subject positioned within the scanner. With the scanner rate-of-change of gradient set to 10 T m(-1) s(-1) the measured rate-of-change of magnetic field was 2.2+/-0.1 T s(-1) and the peak electric field was 0.30+/-0.01 V m(-1) on the chest. The values of induced electric field can be related to dB/dt by a 'geometry factor' for a given subject and sensor position. Typical values of this factor for the abdomen or chest (for measured surface electric fields) lie in the range of 0.10-0.18 m. The measured values of electric field are consistent with currently available numerical modelling results for movement in static magnetic fields and exposure to switched magnetic field gradients.
一种双偶极电场探头已被用于在0.1 - 800 Hz频率范围内测量人体受试者体内的表面电场。低频电场是由自然身体运动（如行走和在3 T磁共振全身扫描仪的边缘磁场中转身）感应产生的。通过使用位于电场探头位置附近的三个正交搜索线圈，还同时记录了磁场变化率（dB/dt）。发现在磁体孔末端附近，自然身体旋转时的磁场变化率超过1 T s⁻¹。对于1 T s⁻¹的磁场变化率，在上腹部、头部和舌面上测量的典型电场分别为0.15±0.02、0.077±0.003和0.015±0.002 V m⁻¹。在回波平面序列期间，当受试者位于扫描仪内时，测量了腹部和胸部的电场。将扫描仪的梯度变化率设置为10 T m⁻¹ s⁻¹时，测量到的磁场变化率为2.2±0.1 T s⁻¹，胸部的峰值电场为0.30±0.01 V m⁻¹。对于给定的受试者和传感器位置，感应电场的值可以通过一个“几何因子”与dB/dt相关联。腹部或胸部（对于测量的表面电场）这个因子的典型值在0.10 - 0.18 m范围内。电场的测量值与目前关于在静磁场中运动和暴露于切换磁场梯度的数值模拟结果一致。
