有源植入式医疗器械和磁共振成像技术分别在神经系统疾病的治疗和诊断上发挥着不可替代的作用，二者的结合应用具有重大的临床价值和科研价值。然而由于潜在的安全性问题，植入了有源植入式医疗器械的患者通常被限制或禁止磁共振扫描。特别是对于有长导线的植入物，导线会吸收射频能量，在尖端产生高能量沉积，给患者带来不可逆损伤，影响最恶劣、情况最复杂，这一问题被称为射频致热问题。要系统、准确地评估有源植入物的射频热效应，需要建立植入物准确的射频耦合模型，这是保证患者进行安全、高效的磁共振扫查的重要基础。传递函数方法是近年来被广泛使用的建立植入物射频耦合模型的一种方法，如何有效获取传递函数是该领域研究的重要问题。本文针对现有研究的不足，提出了包含端部电极、植入物整体结构、射频环境的一整套电磁建模体系，对应传递函数的影响因素、建模方法和验证手段。可以在体模实验中高效、准确地获取植入物的传递函数。本文开展了以下工作：分析了电极在植入物射频致热效应中的三方面的影响；针对现有电极评价参数单一的问题，提出了电极射频敏感度和电极温升系数的概念来描述电极的射频接收性能和发热情况，证明了使用电极周围散射场可以对其相关的能量传输过程进行分析；确定了电极模拟计算的范式，阐明了电极触点面积对射频致热温升影响的原因。针对现有传递函数建模与验证耦合的问题，从电磁学基本原理出发进行了理论推导，提出了近场显著激励的概念用于传递函数独立测量，并提出了差分方法构造了该激励，在模拟计算实验中验证了差分测量理论的正确性；基于测量理论搭建了传递函数的移动源测量系统、平衡差分源测量系统、多源差分测量系统，首次实现了独立于射频致热实验的传递函数确定。提出了根据实测射频场进行数值模型优化，以构建射频线圈数字孪生的方法；在商用磁共振系统上进行了实施和验证，同时将该系统中的射频场建立成合格的射频测试环境，研究成果应用于有源植入物磁共振相容的欧盟CE认证；最后在该测试环境中对端部电极计算和差分方法进行了综合应用实验验证。
Active implantable medical devices (AIMDs) and magnetic resonance imaging (MRI) technology play indispensable roles in the therapy and diagnosis of neurological disorders, respectively. The combined use of these two technologies holds significant clinical and research value. However, patients with active implants are often restricted or prohibited from scanning due to potential safety concerns. Radiofrequency (RF) induced heating is one of the key issues. Especially for AIMDs with elongated conducting leads, the power deposition concentrated at the lead tip may cause irreversible damage to the patient. To systematically and accurately assess the RF-induced effect of AIMDs, an electromagnetic (EM) modelling analysis of the various factors involved is required. In the case of AIMD, it is the creation of accurate RF coupling models, which is the foundation for safe and efficient MR scanning for patients.Transfer function (TF) method is a widely used method to establish RF coupling model of AIMDs in recent years. How to obtain the TF effectively is an important issue for research in this field. Aiming at the shortcomings of the existing research, this paper proposes a complete set of EM modeling system including the end electrode, the overall implant, and the RF environment, which allows efficiently and accurately obtain the TF of the implant in vitro phantom study.The following work has been carried out in this paper:The influence of the electrode in three main aspects of the RF-induced heating study is analyzed. The concepts of electrode sensitivity and electrode temperature rise coefficient are proposed to describe the receiving and transmitting features of the electrode, and it is demonstrated that the power transmission through the electrode is analyzable with the help of electrode sensitivity. The electrode paradigm for simulation is determined. The effect of electrode area on RF induced heating is clarified.To solve problem of coupling between TF modeling and validation, theoretical derivation based on the basic principles of electromagnetism is carried out. The sense of near-field significant excitation is proposed and the differential method is proposed to construct such an excitation. The correctness of the differential measurement theory is verified in simulation study. Based on this theory, a translational excitation measurement system, a balanced differential measurement system, and a multi-excitation differential measurement system are constructed. It is the first EM modeling method independent of RF exposure experiments.A numerical model method based on measured RF field distribution is proposed to construct the digital twin of the birdcage RF coil. It is implemented and validated on a commercial MRI system, making it a qualified RF test environment. This test environment is applied to the CE certification of the MRI compatibility of AIMDs. Finally, a combined application of the electrode sensitivity simulation and differential methods is validated in this test environment.
