在体评估脑起搏器电极MRI相容性的研究

Deep brain stimulation (DBS) is currently a hot topic in both clinic and basic research. However, the implantable lead would interact with the radio frequency (RF) field in magnetic resonance imaging (MRI), resulting in severe heating at the stimulating electrodes. This brings safety concerns to the patients. It not only hinders the diagnostic needs of the patients with MRI, but also denies the application of MRI to study the brain network after stimulation. Previously, the National Natural Science Fund for Youth was granted, and a MRI compatible design of the lead was achieved by shielding with woven metal mesh. The RF heating was largely reduced. The first clinical trial in the world was conducted and broke the taboo by performing 3.0T MRI on the patients with DBS. However, the dilemma still exists that the RF heating cannot be detected and monitored in vivo. It was found from the previous study that the temperature rise curves were similar, implying that the local electric field and temperature distribution might be similar. Therefore, the project is to verify this law through simulation and experiment study, and based on it to develop a magnetic resonance thermometry that can measure the RF heating in vivo noninvasively. Next, a method is to be found to predict and monitor the RF heating of the lead in vivo. This work is a blank both home and abroad. Together with MRI compatible design, the MRI compatibility problem of the lead should be perfectly solved. It will populate the application of DBS under MRI, and is of great clinical value and significant research meaning.

脑起搏器是目前临床应用和基础研究的热点，但植入电极会在核磁（MRI）下与射频磁场耦合，而在前端触点产生严重的发热，带来安全隐患。这制约了植入患者用MRI诊断，也妨碍了应用MRI研究脑起搏器刺激后的大脑网络。前期在青年基金的支持下从电极MRI相容性设计出发，提出包裹以及编织屏蔽方法，极大降低了电极射频温升，并国际首次突破脑起搏器3.0T高场MRI禁忌，开展了全球第一个临床试验。但仍面临电极在体温升无法检测和监控的困境。前期发现电极触点温升曲线具有相似性，即电极局部感生电磁场与温度分布变化规律相似，因此拟通过仿真和体模、动物试验对此深入研究并作为基础，结合MRI温度敏感参数，研究可无创对电极测温的核磁测温法，并开发电极在体温升的预测监控方法。该项工作目前在国内外是一项空白，与电极设计结合，将完善解决电极MRI相容性问题，使脑起搏器在MRI下广泛应用，具有重大临床应用价值和研究意义。

脑起搏器通过向植入在大脑特定靶点的电极发送电脉冲来调节大脑功能，不仅成为多种脑疾病的首选外科疗法，也为研究大脑提供了有力工具。磁共振影像技术既是临床中的主要诊断手段，也是研究脑科学的主要方法。不仅越来越多的脑起搏器植入患者在临床中需要磁共振扫描，两者结合也能为研究脑科学和脑疾病提供新的机遇。但脑起搏器电极在磁共振射频磁场中的发热问题这一发展。由于射频温升情况极为复杂，临床中的精准评估面临困难。实时、在体的电极温升检测能为患者提供最大的安全保障，但尚无合适的方法。..本项目提出采用质子共振频率（PRF）方法，针对电极伪影干扰、单点测量精度不足以及测温与工作扫描异步等挑战开展了研究。首先揭示了电极尖端电磁场和温度场分布的相似性规律，为PRF测量奠定了基础。进而从电极伪影的电磁机制出发，揭示了在伪影干扰下的PRF相位差信号的统计性质，提出单次测量即可估计参数的建模方法，从而可以综合利用多点的温升分布提高精度。最后提出了最大似然估计框架，解决了降温段测量反求最大温升和小温升的可靠判定等问题，形成了脑起搏器电极射频温升无创检测的完整方法。..本项目成果使得植入脑起搏器的患者能够更安全、更有效的扫描磁共振，不仅满足了患者的疾病诊断需求，而且还极大促进了脑起搏器和磁共振结合进行脑疾病和脑科学的研究，对深入认识大脑、更好的治疗脑疾病有重要意义。同时，本项目方法还能拓展到其他植入式医疗器械上，成为保障磁共振安全的一种通用方法。本方法已在我国首个3T磁共振兼容脑起搏器临床试验中得到了应用，保障了植入脑起搏器后扫查3T磁共振的14名帕金森病患者的安全。