Janssen Arno M, Oostendorp Thom F, Stegeman Dick F
Department of Neurology/Clinical Neurophysiology, Radboud University Nijmegen Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Reinier Postlaan 4, 6525 CG, Nijmegen, The Netherlands,
Med Biol Eng Comput. 2014 Oct;52(10):873-83. doi: 10.1007/s11517-014-1190-6. Epub 2014 Aug 28.
Many human cortical regions are targeted with transcranial magnetic stimulation (TMS). The stimulus intensity used for a certain region is generally based on the motor threshold stimulation intensity determined over the motor cortex (M1). However, it is well known that differences exist in coil-target distance and target site anatomy between cortical regions. These differences may well make the stimulation intensity derived from M1 sub-optimal for other regions. Our goal was to determine in what way the induced electric fields differ between cortical target regions. We used finite element method modeling to calculate the induced electric field for multiple target sites in a realistic head model. The effects on the electric field due to coil-target distance and target site anatomy have been quantified. The results show that a correction based on the distance alone does not correctly adjust the induced electric field for regions other than M1. In addition, a correction based solely on the TMS-induced electric field (primary field) does not suffice. A precise adjustment should include coil-target distance, the secondary field caused by charge accumulation at conductivity discontinuities and the direction of the field relative to the local cerebrospinal fluid-grey matter boundary.
许多人类皮质区域都接受经颅磁刺激(TMS)。用于特定区域的刺激强度通常基于在运动皮层(M1)上确定的运动阈值刺激强度。然而,众所周知,不同皮质区域之间的线圈与靶点距离和靶点部位解剖结构存在差异。这些差异很可能使源自M1的刺激强度对其他区域而言并非最优。我们的目标是确定皮质靶点区域之间感应电场的差异方式。我们使用有限元方法建模,在逼真的头部模型中计算多个靶点部位的感应电场。已对线圈与靶点距离和靶点部位解剖结构对电场的影响进行了量化。结果表明,仅基于距离进行校正并不能正确调整除M1之外其他区域的感应电场。此外,仅基于TMS感应电场(主电场)进行校正也不够。精确的调整应包括线圈与靶点距离、电导率不连续处电荷积累所产生的次级电场以及电场相对于局部脑脊液 - 灰质边界的方向。