未屏蔽超低场MRI中人体耦合电场干扰的建模
Modeling of Human Body-coupled Electric Field Interference in Unshielded Ultra-Low Field MRI
AI总结：
本文提出了一种用于分析和抑制便携式超低场MRI中人体耦合电场干扰的集中参数电路模型，并通过电容低阻抗旁路实现3.5倍信噪比提升。
摘要：
便携式超低场MRI（ULF-MRI）系统在未屏蔽环境中运行时易受电磁干扰（EMI）影响。受检者处于成像区域时会导致噪声显著增加，但主导的耦合机制仍缺乏充分表征。我们开发了一个集中参数电路模型，用于耦合环境-人体-接收器系统。该模型表明，环境中的时变电场会在人体中产生共模电势，通过头部与接收线圈端子之间的电容不平衡转换为差分模式噪声，产生对受检者位置和几何形状的强依赖性。电路分析、模拟和受控实验支持该模型，预测的不平衡与测量噪声变化一致。基于此机制，我们实现了电容低阻抗旁路以钳制人体电势，使50 mT原型的信噪比（SNR）提高了约3.5倍。所提出的模型提供了一种紧凑的电路工具，用于分析和抑制便携式ULF-MRI中的人体耦合电场干扰。
英文摘要：
Portable ultra-low field MRI (ULF-MRI) systems operated in unshielded environments are susceptible to electromagnetic interference (EMI). Subject presence in the imaging region will lead to substantial noise increases, yet the dominant coupling mechanism remains insufficiently characterized. We develop a lumped-parameter circuit model of the coupled environment-body-receiver system. The model indicates that ambient time-varying electric fields induce a body common-mode potential, which is converted into differential-mode noise through capacitive imbalance between the head and the receive-coil terminals, yielding strong dependence on subject position and geometry. Circuit analysis, simulations, and controlled experiments support the model, with predicted imbalance consistent with measured noise variations. Guided by this mechanism, we implement a capacitive low-impedance bypass to clamp the body potential, achieving an approximately 3.5-fold SNR improvement on a 50 mT prototype. The proposed model offers a compact circuit-based tool for analyzing and mitigating human body-coupled electric-field interference in portable ULF-MRI.
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