Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kgs Lyngby, Denmark; Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark; Sino-Danish Center for Education and Research, Aarhus, Denmark; University of Chinese Academic of Sciences, Beijing, 100049, China.
Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark; High-Field Magnetic Resonance Center, Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany.
Brain Stimul. 2021 May-Jun;14(3):488-497. doi: 10.1016/j.brs.2021.02.019. Epub 2021 Mar 9.
Transcranial electric stimulation during MR imaging can introduce safety issues due to coupling of the RF field with the stimulation electrodes and leads.
To optimize the stimulation setup for MR current density imaging (MRCDI) and increase maximum stimulation current, a new low-conductivity (σ = 29.4 S/m) lead wire is designed and tested.
The antenna effect was simulated to investigate the effect of lead conductivity. Subsequently, specific absorption rate (SAR) simulations for realistic lead configurations with low-conductivity leads and two electrode types were performed at 128 MHz and 298 MHz being the Larmor frequencies of protons at 3T and 7T. Temperature measurements were performed during MRI using high power deposition sequences to ensure that the electrodes comply with MRI temperature regulations.
The antenna effect was found for copper leads at ¼ RF wavelength and could be reliably eliminated using low-conductivity leads. Realistic lead configurations increased the head SAR and the local head SAR at the electrodes only minimally. The highest temperatures were measured on the rings of center-surround electrodes, while circular electrodes showed little heating. No temperature increase above the safety limit of 39 °C was observed.
Coupling to the RF field can be reliably prevented by low-conductivity leads, enabling cable paths optimal for MRCDI. Compared to commercial copper leads with safety resistors, the low-conductivity leads had lower total impedance, enabling the application of higher currents without changing stimulator design. Attention must be paid to electrode pads.
由于射频场与刺激电极和导联的耦合，经颅电刺激在磁共振成像（MR）期间会引发安全问题。
为了优化磁共振电流密度成像（MRCDI）的刺激设置并增加最大刺激电流，设计并测试了一种新的低电导率（σ=29.4 S/m）导联线。
模拟天线效应以研究导联电导率的影响。随后，在 128 MHz 和 298 MHz 下对具有低电导率导联和两种电极类型的真实导联构型进行了比吸收率（SAR）模拟，这两个频率分别为 3T 和 7T 质子的拉莫尔频率。使用高功率沉积序列在 MRI 期间进行温度测量，以确保电极符合 MRI 温度规定。
在¼射频波长处发现了铜导联的天线效应，使用低电导率导联可以可靠地消除该效应。真实导联构型仅使头部 SAR 和电极处的局部头部 SAR 略有增加。在中心-环绕电极的环上测量到了最高温度，而圆形电极几乎没有发热。未观察到超过 39°C 安全限值的温度升高。
低电导率导联可可靠地防止与射频场的耦合，从而为 MRCDI 实现最佳的电缆路径。与带安全电阻的商业铜导联相比，低电导率导联的总阻抗更低，允许在不改变刺激器设计的情况下应用更高的电流。应注意电极片。
