脑起搏器（Deep brain stimulation, DBS）是一种有效的脑疾病疗法与脑研究工具。它与磁共振成像（Magnetic resonance imaging, MRI）这一目前最流行的脑成像手段之间存在应用冲突，表现为DBS中的金属电极会吸收MRI中的射频磁场（B1）能量，使局部脑组织的温度升高（ΔT）带来热安全隐患。因此，确定DBS电极在脑内的温升水平，是保证植入者能够安全接受MRI检查的基础。目前对该问题的研究，在规律探索上，多局限于电极结构改进等方面，缺少对MRI线圈的关注；在温升评估上，虽已有传递函数法可对部分植入物的温升进行估计，但尚未有研究者应用于DBS电极，且往往局限于单一工程问题，对个中特性的把握不足。本文针对这一现状，在线圈对MRI温升的影响及规律研究、保证DBS电极热安全的MRI扫描条件的确定、传递函数法在拼接导线中的快速应用等方面开展工作，取得的主要结论及创新点如下：1） 搭建并验证了MRI温升评估的数值计算平台，发现了不同尺寸的线圈下，B1、电场、ΔT等物理量各自具备的分布相似性，提出并证明了以小区域的B1制定MRI安全扫描条件的优势，建立了升温过程的数学表述，论证了在电场分布相似时可由一点电场确定温升；2） 对多种植入环境下传递函数预测温升的方法有效性进行了验证，应用传递函数法得到了DBS电极在人体植入时的温升，设立植入路径的随机选取方法，统计了大量植入情形下的温升，确定了可保证DBS电极温升在阈值以下的MRI扫描条件；3） 推导并提出了两段拼接导线中各段传递函数的构成特征，创建了由已知的独段导线的传递函数，合成未知拼接导线的传递函数的理论方法，以数值计算及实验测量两种方式，分别对所建立的拼接合成理论进行了有效性的验证。以上工作在对DBS电极MRI温升规律的把握，以及热安全性评估方法的规范、优化等方面有着借鉴作用和现实意义。
As one of the most widely applied surgical neuromodulation techniques, the deep brain stimulation (DBS) has great medical and clinical potential for the treatment of neurological disorders. However, there are many restrictions in magnetic resonance imaging (MRI) for patients with DBS implants due to the hazard of a temperature rise (ΔT) in tissue caused from the interaction between the DBS and the radio frequency magnetic field (B1) transmitted by the MRI coil. Thus, an accurate understanding and estimation of the rising temperature become essential to make MRI accessible for patients with DBS implants. At present, most of the research attempts on this problem focused on the improvement of lead structure or some other things, and few attention was paid on MRI coils. Although there is a transfer function method to estimate the temperature rise of implants, it has not yet been applied to the DBS lead. Furthermore, it was often limited to solve engineering problems, and some characteristics remained covered. In view of this, (1) the regularity of coils' effects on MRI temperature rise, (2) the determination of MRI scanning conditions which is safety for patients with DBS, and (3) the easy application of transfer function in spliced leads are the major contributions of this thesis. The main conclusions and innovations are as follows: 1) A numerical calculation platform of MRI temperature rise is built and validated. The similarity of the distribution of the B1, electric field, ΔT among different sized coils is revealed. It is also found that the B1 in a small volume is a better control criterion in an MRI scan. The mathematical expression of the heating process is established, and it demonstrates that the temperature rise can be determined by the electric field on a single point when the electric field distribution is similar. 2) The effectiveness of predicting the temperature rise by the transfer function method is verified when some parameters are changed. The temperature rise of the DBS lead in the human body was obtained by using the transfer function method. The permitted MRI scan is determined by generating a large number of random routes and analyzing the temperature rise statistically. 3) The constituent features of the transfer function of the two-section splicing lead is deduced and presented. A theoretical method of synthesizing the transfer function of the spliced lead is created through the transfer function of the separate leads. By numerical calculation and experimental measurement, the validity of the established splice-synthesis theory was verified. The content in this thesis is important for the undarstanding of MRI temperature rise of the DBS lead. This thesis could help to standardize and optimize the safety assessment of MRI for patients with DBS.
