Data from: Investigation of parallel radiofrequency transmission for the reduction of heating in long conductive leads in 3 tesla magnetic resonance imaging

Deep Brain Stimulation (DBS) is increasingly used to treat a variety of brain diseases by sending electrical impulses to deep brain nuclei through long, electrically conductive leads. Magnetic resonance imaging (MRI) of patients pre- and post-implantation is desirable to target and position the implant, to evaluate possible side-effects and to examine DBS patients who have other health conditions. Although MRI is the preferred modality for pre-operative planning, MRI post-implantation is limited due to the risk of high local power deposition, and therefore tissue heating, at the tip of the lead. The localized power deposition arises from currents induced in the leads caused by coupling with the radiofrequency (RF) transmission field during imaging. In the present work, parallel RF transmission (pTx) is used to tailor the RF electric field to suppress coupling effects. Electromagnetic simulations were performed for three pTx coil configurations with 2, 4, and 8-elements, respectively. Optimal input voltages to minimize coupling, while maintaining RF magnetic field homogeneity, were determined for all configurations using a Nelder-Mead optimization algorithm. Resulting electric and magnetic fields were compared to that of a 16-rung birdcage coil. Experimental validation was performed with a custom-built 4-element pTx coil. In simulation, 95-99% reduction of the electric field at the tip of the lead was observed between the various pTx coil configurations and the birdcage coil. Maximal reduction in E-field was obtained with the 8-element pTx coil. Magnetic field homogeneity was comparable to the birdcage coil for the 4- and 8-element pTx configurations. In experiment, a temperature increase of 2±0.15°C was observed at the tip of the wire using the birdcage coil, whereas negligible increase (0.2±0.15°C) was observed with the optimized pTx system. Although further research is required, these initial results suggest that the concept of optimizing pTx to reduce DBS heating effects holds considerable promise.

脑深部电刺激（Deep Brain Stimulation, DBS）正愈发广泛地应用于多种脑部疾病的治疗，其通过细长的导电电极向脑深部核团递送电脉冲。为实现植入物精准靶向与定位、评估潜在不良反应，以及对合并其他健康问题的DBS患者进行影像学检查，对植入术前及术后的患者开展磁共振成像（Magnetic Resonance Imaging, MRI）是十分必要的。尽管MRI是术前规划的首选影像学手段，但术后MRI的应用却受到限制：这是由于电极尖端存在局部高功率沉积的风险，进而引发组织加热问题。此类局部功率沉积源于成像过程中，电极与射频（Radio Frequency, RF）发射场耦合所诱导的电极内电流。本研究采用并行射频发射（Parallel RF Transmission, pTx）技术对RF电场进行调控，以抑制上述耦合效应。我们针对分别包含2、4、8个通道的三类pTx线圈配置开展了电磁仿真。通过内尔德-米德（Nelder-Mead）优化算法，我们为所有配置求解出了在维持RF磁场均匀性的前提下最小化耦合效应的最优输入电压。将仿真得到的电场与磁场结果与16环鸟笼线圈的结果进行对比。我们使用定制的4通道pTx线圈完成了实验验证。仿真结果显示，相较于鸟笼线圈，各类pTx线圈配置均可使电极尖端的电场强度降低95%~99%，其中8通道pTx线圈可实现最大的电场衰减幅度。4通道与8通道pTx配置的磁场均匀性与鸟笼线圈相当。实验结果表明，采用鸟笼线圈时，导线尖端的温度升高幅度为2±0.15℃；而经优化后的pTx系统仅引发可忽略不计的温度升高（0.2±0.15℃）。尽管仍需开展进一步研究，但这些初步结果表明，通过优化pTx技术以降低DBS相关加热效应的理念，具备可观的应用前景。