脑深部电刺激(DBS)方法对多种神经系统相关疾病具有良好疗效，也是迄今为止可以直接接触大脑深部组织并干预脑深部神经活动的主要技术手段。磁共振成像(MRI)技术对于大脑的结构和功能成像具有优越性能。这两种技术的结合对脑疾病的诊断、治疗及脑科学研究具有重要意义。但这两种技术之间的兼容性问题阻碍了它们的结合应用。尤其是DBS导线与MRI射频磁场相互作用所致的电极触点射频感应发热问题对植入DBS的患者带来了安全隐患，以致无法安全地进行MRI扫描。因此，解决DBS电极触点的MRI射频感应发热问题，成为了本文研究的目的和重点。本文深入研究了植入式导线在MRI射频磁场中的发热原理和规律。基于偶极子天线模型，通过数值模拟计算和体外实验验证分析了导线结构和尖端射频感应致热之间的关系，发现并证明了屏蔽层导线与裸露导线在天线性能上的等效性，提出使用良导体屏蔽层抑制导线尖端射频感应致热的方法。本文选用金属丝编织网作为DBS导线的屏蔽层，开展MRI相容DBS导线研发工作。通过体外实验证明金属网对电极触点发热具有良好抑制效果，具体分析了材料电导率、网格密度、连接方式等对抑制效果的影响。此外，分析了金属网疲劳性能的影响因素，采用热处理方法改善金属网的疲劳性能使其寿命提高至大于107。基于Pennes生物传热方程，对体外实验中DBS电极触点附近的射频感应温升规律进行研究，发现系统中一点温升与另一点电流密度平方之间的线性关系。据此提出判断温升数据测量可靠性及预测长时温升的新方法，实验证明该方法可行。本文的机理研究和技术验证为解决DBS和MRI组合应用的关键技术难点奠定了基础。本文基于此开展了体外验证和动物试验，证明在常规采用的1.5T和3T MRI环境中，电极触点的射频感应发热得到有效抑制。和现有的DBS装置相比，体外实验中的电极触点温升降幅在1.5T和3T MRI中分别可达88.0%和89.2%；在动物试验中，电极触点温升降幅分别为68.3%和42.9%。在取得可靠安全性前提下，MRI相容DBS导线进入了临床应用，分别在北京天坛医院、北京协和医院和山东大学齐鲁医院对首批10名入组患者完成植入手术。术后1个月的随访情况表明，搭配该型导线的MRI相容DBS系统既保持了原有的治疗功能，又可同时安全进行MRI扫描。该项新技术未来将惠及更多的医疗工作人员和患者，并为进一步开展脑科学研究提供了新的技术平台。
Deep brain stimulation (DBS) is used as a clinical treatment for various neurological disorders. It remains the main technology for directly contacting the deep brain tissues and modulating brain neural network activities. Magnetic resonance imaging (MRI) is advanced in structural and functional brain imaging. The combined application of DBS and MRI is a significant prospect in the field of diagnosing and treating brain disorders, as well as for brain science research. However, issues with compatibility have so far hindered the successful combined application of DBS and MRI, especially with radiofrequency (RF) induced heating at electrodes, which poses apparent dangers to DBS patients. In this thesis, we set out to find a method on how to resolve MRI RF-induced heating of DBS electrodes.Firstly, the principle and regularity of MRI RF-induced heating of implantable leads were researched thoroughly. Based on the dipole antenna model, a mathematical relationship between the lead structure and its heating effect in MRI was established. The mathematical relationship was demonstrated in numerical and in vitro experiments. The equivalence of an antenna effect between the bare and shielded conductor was discovered. From this finding, the addition of a conducting shielding layer on the surface was proposed as a solution for the RF-induced heating of implantable leads.Next, we developed a new-type of DBS lead with MRI-compatibility, where a metal wire mesh was applied as a conducting shielding layer. The effectiveness in heating reduction of the metal mesh shielding layer was demonstrated in in vitro experiments. The influence of electrical conductivity of material, mesh density, and the connection between mesh segments, were thoroughly analyzed. In addition, the influencing factors on the fatigue performance of the metal mesh were studied. It was found that the fatigue life of the metal mesh was improved significantly to a level of N > 107 through heat-treatment.Based on Pennes’ bioheat transfer equation, the laws on temperature rise around DBS electrodes were studied in in vitro experiments. A linear relationship was discovered between the electrical current density squared at one point and the temperature rise at another point. Consequently, a method for measured temperature data validation and predicting temperature rise was proposed. The feasibility of this method was then proved in in vitro experiments.In this thesis, the study of the underlying mechanism followed by technical validation provided the foundation for the combined application of DBS and MRI. From this initial research, in vitro and in vivo verification experiments were then conducted. The results showed that the heating at electrodes was effectively suppressed in MRI scans that used field strengths of 1.5 T and 3.0 T. In comparison to conventional DBS systems, the temperature rise in in vitro experiments were reduced by 88.0% and 89.2% in 1.5 T and 3.0 T MRI, respectively. The reductions of temperature rise in in vivo experiments were 68.3% and 42.9%, respectively.On the premise that the safety has been established, the metal mesh MRI-compatible DBS lead was applied in clinical practice. A total of 10 volunteers were recruited. Implanting operations were completed in Beijing Tian Tan Hospital, Peking Union Medical College Hospital, and Qilu Hospital of Shandong University. The first round of follow-up results proved that MRI-compatible DBS protected DBS patients from the MRI RF-induced heating, while maintaining successful treatment therapy. This has provided a new technical platform for more in-depth brain science research, and will benefit more doctors and patients in the future.
