Bencsik M, Bowtell R, Bowley R M
School of Physics and Astronomy, University of Nottingham, UK.
Phys Med Biol. 2002 Feb 21;47(4):557-76. doi: 10.1088/0031-9155/47/4/302.
A homogeneous spherical volume conductor is used as a model system for the purpose of calculating electric fields induced in the human head by externally applied time-varying magnetic fields. We present results for the case where magnetic field gradient coils, used in magnetic resonance imaging (MRI), form the magnetic field, and we use these data to put limits on the rates of gradient change with time needed to produce nerve stimulation. The electric field is calculated analytically for the case of ideal longitudinal and transverse linear field gradients. We also show results from computer calculations yielding the electric field maps in a sphere when the field gradients are generated by a real MRI gradient coil set. In addition, the effect of shifting the sphere within each gradient coil volume is investigated. Numerical analysis shows similar results when applied to a model human head.
为了计算外部施加的随时间变化的磁场在人头部感应产生的电场，使用了一个均匀的球形体积导体作为模型系统。我们给出了磁共振成像（MRI）中使用的磁场梯度线圈形成磁场时的结果，并利用这些数据来限制产生神经刺激所需的梯度随时间的变化率。对于理想的纵向和横向线性场梯度情况，电场通过解析计算得出。当由实际的MRI梯度线圈组产生场梯度时，我们还展示了计算机计算得出的球体中电场图的结果。此外，还研究了球体在每个梯度线圈体积内移动的影响。数值分析表明，将其应用于人体头部模型时会得到类似的结果。
