1H/13C磁共振人工电磁媒质性能与兼容性研究

   本文在磁共振人工电磁媒质这一磁共振学科与电磁材料学科的交叉领域，通过对现有磁共振双频人工电磁媒质的分析，发现现有双频人工电磁媒质存在工作频率不可调、工作原理（电激励）不适于磁共振环境的问题，随后提出了一种基于磁响应的1H/13C双频人工电磁媒质结构。并通过引入外加电容元件，改善了传统人工电磁媒质设计中对结构自身电容需求极高的问题，同时获得了对结构谐振频率的宽频调整能力。

   在仿真设计部分，提出了一种基于电容近似估计的外加电容容值计算方法，利用此方法，仅通过一次迭代即可将结构调整至目标共振频率，调整后实际共振频率与目标值误差不超过1%。此外，通过对人工电磁媒质与磁共振线圈的异同点分析，提出了一种用于人工电磁媒质仿真的软件仿真方法。并通过对1H/13C双频人工电磁媒质的实测结果，发现在相同目标频率下仿真与实际外加电容容值差异不超过4.3%，证明了此仿真方法可较准确的模拟实际人工电磁媒质共振频率。

   在线圈的人工电磁媒质兼容性测试部分，分别测试了1H/13C双频人工电磁媒质距射频发射、接收线圈不同距离、角度下对线圈的传输增益、反射系数的影响。发现距离越近、人工电磁媒质平面与线圈平面角度越小，人工电磁媒质与射频发射、接收线圈间的耦合效果越强。这种耦合可使人工电磁媒质发挥其作为负载的作用，进而改善线圈匹配状态；但过强的耦合也可能会导致线圈出现谐振频率偏移、匹配变差等问题。在1H/13C双频人工电磁媒质成像实验部分，分别探究了1H/13C双频人工电磁媒质对13C波谱成像与1H成像效果的影响与机理。结果显示1H/13C双频人工电磁媒质对13C波谱成像有较好的信号增幅效果，最高信号增幅超过30倍。而在1H频率下的测试则显示，其对1H成像的信噪比也有较强的增幅效果，增幅最强处的图像信噪比提升了近6倍。

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