Fujita Yuya, Khoo Hui Ming, Hirayama Miki, Kawahara Masaaki, Koyama Yoshihiro, Tarewaki Hiroyuki, Arisawa Atsuko, Yanagisawa Takufumi, Tani Naoki, Oshino Satoru, Lemieux Louis, Kishima Haruhiko
Department of Neurosurgery, Osaka University Graduate School of Medicine, Suita, Japan.
Department of Radiology, Osaka University Hospital, Suita, Japan.
Front Neurosci. 2022 Jun 23;16:921922. doi: 10.3389/fnins.2022.921922. eCollection 2022.
The unsurpassed sensitivity of intracranial electroencephalography (icEEG) and the growing interest in understanding human brain networks and ongoing activities in health and disease have make the simultaneous icEEG and functional magnetic resonance imaging acquisition (icEEG-fMRI) an attractive investigation tool. However, safety remains a crucial consideration, particularly due to the impact of the specific characteristics of icEEG and MRI technologies that were safe when used separately but may risk health when combined. Using a clinical 3-T scanner with body transmit and head-receive coils, we assessed the safety and feasibility of our icEEG-fMRI protocol.
Using platinum and platinum-iridium grid and depth electrodes implanted in a custom-made acrylic-gel phantom, we assessed safety by focusing on three factors. First, we measured radio frequency (RF)-induced heating of the electrodes during fast spin echo (FSE, as a control) and the three sequences in our icEEG-fMRI protocol. Heating was evaluated with electrodes placed orthogonal or parallel to the static magnetic field. Using the configuration with the greatest heating observed, we then measured the total heating induced in our protocol, which is a continuous 70-min icEEG-fMRI session comprising localizer, echo-planar imaging (EPI), and magnetization-prepared rapid gradient-echo sequences. Second, we measured the gradient switching-induced voltage using configurations mimicking electrode implantation in the frontal and temporal lobes. Third, we assessed the gradient switching-induced electrode movement by direct visual detection and image analyses.
On average, RF-induced local heating on the icEEG electrode contacts tested were greater in the orthogonal than parallel configuration, with a maximum increase of 0.2°C during EPI and 1.9°C during FSE. The total local heating was below the 1°C safety limit across all contacts tested during the 70-min icEEG-fMRI session. The induced voltage was within the 100-mV safety limit regardless of the configuration. No gradient switching-induced electrode displacement was observed.
We provide evidence that the additional health risks associated with heating, neuronal stimulation, or device movement are low when acquiring fMRI at 3 T in the presence of clinical icEEG electrodes under the conditions reported in this study. High specific absorption ratio sequences such as FSE should be avoided to prevent potential inadvertent tissue heating.
颅内脑电图（icEEG）具有无与伦比的敏感性，且人们对理解人类脑网络以及健康和疾病状态下的持续活动兴趣日增，这使得同时进行icEEG与功能磁共振成像采集（icEEG-fMRI）成为一种颇具吸引力的研究工具。然而，安全性仍是一个关键考量因素，尤其是因为icEEG和MRI技术各自使用时是安全的，但联合使用时可能会对健康构成风险，这归因于它们的特定特性。我们使用一台带有体部发射和头部接收线圈的临床3-T扫描仪，评估了我们的icEEG-fMRI方案的安全性和可行性。
我们使用植入定制丙烯酸凝胶模型中的铂和铂铱网格电极及深度电极，通过关注三个因素来评估安全性。首先，我们在快速自旋回波（FSE，作为对照）以及我们的icEEG-fMRI方案中的三个序列期间，测量电极的射频（RF）感应加热情况。在电极与静磁场正交或平行放置时评估加热情况。使用观察到加热最显著的配置，然后我们测量了我们方案中诱导的总加热量，该方案是一个持续70分钟的icEEG-fMRI检查，包括定位像、回波平面成像（EPI）和磁化准备快速梯度回波序列。其次，我们使用模拟额叶和颞叶电极植入的配置测量梯度切换感应电压。第三，我们通过直接视觉检测和图像分析评估梯度切换引起的电极移动。
平均而言，在测试的icEEG电极触点上，RF感应局部加热在正交配置中比平行配置更大，在EPI期间最大增加0.2°C，在FSE期间最大增加1.9°C。在70分钟的icEEG-fMRI检查期间，所有测试触点的总局部加热均低于1°C的安全限值。无论配置如何，感应电压均在100-mV的安全限值内。未观察到梯度切换引起的电极位移。
我们提供的证据表明，在本研究报告的条件下，在存在临床icEEG电极的情况下于3 T进行fMRI采集时，与加热、神经元刺激或设备移动相关的额外健康风险较低。应避免使用高比吸收率序列，如FSE，以防止潜在的意外组织加热。
