1.5T下高介电材料几何结构对发射场影响的仿真研究

2022-06-14唐德港李红闯刘小玲李海东叶朝辉

波谱学杂志 2022年2期

关键词：方形磁共振线圈

唐德港，李红闯，刘小玲，石磊，李海东，叶朝辉，周欣*

唐德港1,2，李红闯1,2，刘小玲1,2，石磊1,2，李海东1,2，叶朝辉1,2，周欣1,2*

1. 波谱与原子分子物理国家重点实验室，武汉磁共振中心（中国科学院精密测量科学与技术创新研究院），湖北武汉 430071；2. 中国科学院大学，北京 100049

引言

1 HPMs几何结构对发射场影响的仿真研究

1.1 HPMs提高射频线圈发射效率的原理

将HPMs放置在成像物体ROI附近，在射频脉冲激励下，根据麦克斯韦全电流定律：

1.2 仿真模型及参数设置

图1 带有水模负载的鸟笼线圈仿真模型（对照组）．(a)仿真模型示意图；(b)水模内有限元网格剖分结果

在水模附近加入四种文献报道过的不同几何结构的高介电衬垫作为实验组，包括：（1）四等分圆筒状衬垫[30]；（2）对称环绕水模的四块方形衬垫[20]；（3）同侧三块方形衬垫[31]；（4）120°扇环柱状衬垫[32]．采用的HPMs厚度均为13 mm、长度均为71 mm．其中四等分圆筒状衬垫相邻单元间隙为3 mm；环绕四方块衬垫宽58 mm；同侧三方块衬垫宽34 mm，相邻两单元中心成60°夹角．衬垫材料为掺杂镐和铈的钛酸钡，首先将钛酸钡（Ba/Ti比为0.996）和高纯度的ZrO2、CeO2研磨混合，再在1 340°下高温烧结为陶瓷衬垫．衬垫相对介电常数设为4 500[20]，电导率为0.44 S/m．实验组水模均采用和对照组相同的网格剖分，以保证参数和电磁场的精确度和一致性，实验组水模仿真模型示意图如图2所示．

图2 不同几何结构的高介电衬垫（深灰色）的仿真模型示意图（隐藏线圈）．(a)无衬垫；(b)四等分圆筒状衬垫；(c)四块方形衬垫对称环绕水模；(d)同侧三块方形衬垫；(e) 120°扇环柱状衬垫

2 结果与讨论

2.1 HPMs几何结构对发射场的影响

图3 不同几何结构的高介电衬垫仿真模型水模中心横断面的发射效率h分布．(a)无衬垫；(b)四等分圆筒状衬垫；(c)四块方形衬垫对称环绕水模；(d)同侧三块方形衬垫；(e) 120°扇环柱状衬垫

表1 不同几何结构的高介电衬垫仿真模型ROI内的发射效率h均值与不均匀度（CV）

图4 不同几何结构的高介电衬垫仿真模型ROI内发射效率均值和不均匀度分析

2.2 理论分析

不同模型水模中心横断面沿轴方向中心线的发射效率分布如图5所示，可以看出，加入四等分圆筒状、环绕四方块、同侧三方块衬垫后，发射效率沿轴方向中心线分布都较为均匀．

图5 不同仿真模型水模中心横断面沿y轴方向中心线的发射效率分布（以中心为原点）

3 结论

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1,2，1,2，1,2，1,2，1,2，1,2，1,2*

1. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China

O482.53

10.11938/cjmr20212904

2021-04-01;

2021-05-15

国家重点研发计划(2016YFC1304702)；国家自然科学基金资助项目(82127802,81227902)；中国科学院战略性先导科技专项(XDB25000000)；广东省重点领域研发计划(2018B030333001)；湖北省科技重大专项(2021ACA013)；中国科学院磁共振技术联盟资助项目(2020GZL002).

* Tel: 027-87198802, E-mail: xinzhou@wipm.ac.cn.