Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
CorTec GmbH, Freiburg, Germany.
Neuroimage. 2022 Dec 1;264:119691. doi: 10.1016/j.neuroimage.2022.119691. Epub 2022 Nov 12.
Many neurological disorders are analyzed and treated with implantable electrodes. Many patients with such electrodes have to undergo MRI examinations - often unrelated to their implant - at the risk of radio-frequency induced heating. The number of electrode contact sites of these implants keeps increasing due to improvements in manufacturing and computational algorithms. Electrode grids with multiple receive channels couple to the RF fields present in MRI, but, due to their proximity, a combination of leads has a coupling response which is not a superposition of the individual leads' response. To investigate the problem of RF-induced heating of coupled multi-lead implants, temperature mapping was performed on a set of intra-cranial electroencephalogram (icEEG) electrode grid prototypes with increasing number of contact sites (1-16). Additionally, electric field measurements were used to investigate the radio-frequency heating characteristics of the implants in different media combinations, simulating the device being partially immersed inside the patient. MR measurements show RF-induced heating up to 19.6 K for the single electrode, reducing monotonically with larger number of contact sites to a minimum of 0.9 K for the largest grid. The SAR calculated from temperature measurements agrees well with electric field mapping: The same trend is visible for different insertion lengths, however, the energy dissipated by the whole implant varies with the grid size and insertion length. Thus, in the tested circumstances, a larger electrode number either reduced or had a similar risk of RF induced heating, indicating, that the size of electrode grids is a design parameter, which can be used to change an implants RF response and in turn to reduce the risk of RF induced heating and improve the safety of patient with neuro-implants undergoing MRI examinations.
许多神经疾病都可以通过植入式电极进行分析和治疗。许多带有此类电极的患者都必须接受磁共振成像（MRI）检查，而这些检查通常与他们的植入物无关，但会有射频感应加热的风险。由于制造和计算算法的改进，这些植入物的电极接触点数量不断增加。具有多个接收通道的电极网格与 MRI 中存在的射频场耦合，但由于它们的接近，导联的组合具有不是单个导联响应的叠加的耦合响应。为了研究射频感应加热的问题，对具有不同数量接触点（1-16）的一组颅内脑电图（icEEG）电极网格原型进行了温度映射。此外，还使用电场测量来研究不同介质组合中植入物的射频加热特性，模拟装置部分浸入患者体内。MR 测量显示单个电极的射频感应加热高达 19.6 K，随着接触点数量的增加而单调降低，最大网格的最小加热值为 0.9 K。从温度测量计算的 SAR 与电场映射吻合良好：不同插入长度也可见相同趋势，然而，整个植入物耗散的能量随网格尺寸和插入长度而变化。因此，在所测试的情况下，更大的电极数量要么降低了，要么具有类似的射频感应加热风险，这表明电极网格的大小是一个设计参数，可用于改变植入物的射频响应，从而降低射频感应加热的风险，并提高接受 MRI 检查的神经植入患者的安全性。
