唐德港，李紅闖，劉小玲，石 磊，李海東，葉朝輝，周 欣*

1.5T下高介電材料幾何結(jié)構(gòu)對(duì)發(fā)射場(chǎng)影響的仿真研究

唐德港1,2，李紅闖1,2，劉小玲1,2，石 磊1,2，李海東1,2，葉朝輝1,2，周 欣1,2*

1. 波譜與原子分子物理國(guó)家重點(diǎn)實(shí)驗(yàn)室，武漢磁共振中心（中國(guó)科學(xué)院精密測(cè)量科學(xué)與技術(shù)創(chuàng)新研究院），湖北 武漢 430071；2. 中國(guó)科學(xué)院大學(xué)，北京 100049

引 言

1 HPMs幾何結(jié)構(gòu)對(duì)發(fā)射場(chǎng)影響的仿真研究

1.1 HPMs提高射頻線圈發(fā)射效率的原理

將HPMs放置在成像物體ROI附近，在射頻脈沖激勵(lì)下，根據(jù)麥克斯韋全電流定律：

1.2 仿真模型及參數(shù)設(shè)置

圖1 帶有水模負(fù)載的鳥籠線圈仿真模型（對(duì)照組）．(a)仿真模型示意圖；(b)水模內(nèi)有限元網(wǎng)格剖分結(jié)果

在水模附近加入四種文獻(xiàn)報(bào)道過的不同幾何結(jié)構(gòu)的高介電襯墊作為實(shí)驗(yàn)組，包括：（1）四等分圓筒狀襯墊[30]；（2）對(duì)稱環(huán)繞水模的四塊方形襯墊[20]；（3）同側(cè)三塊方形襯墊[31]；（4）120°扇環(huán)柱狀襯墊[32]．采用的HPMs厚度均為13 mm、長(zhǎng)度均為71 mm．其中四等分圓筒狀襯墊相鄰單元間隙為3 mm；環(huán)繞四方塊襯墊寬58 mm；同側(cè)三方塊襯墊寬34 mm，相鄰兩單元中心成60°夾角．襯墊材料為摻雜鎬和鈰的鈦酸鋇，首先將鈦酸鋇（Ba/Ti比為0.996）和高純度的ZrO2、CeO2研磨混合，再在1 340°下高溫?zé)Y(jié)為陶瓷襯墊．襯墊相對(duì)介電常數(shù)設(shè)為4 500[20]，電導(dǎo)率為0.44 S/m．實(shí)驗(yàn)組水模均采用和對(duì)照組相同的網(wǎng)格剖分，以保證參數(shù)和電磁場(chǎng)的精確度和一致性，實(shí)驗(yàn)組水模仿真模型示意圖如圖2所示．

圖2 不同幾何結(jié)構(gòu)的高介電襯墊（深灰色）的仿真模型示意圖（隱藏線圈）．(a)無襯墊；(b)四等分圓筒狀襯墊；(c)四塊方形襯墊對(duì)稱環(huán)繞水模；(d)同側(cè)三塊方形襯墊；(e) 120°扇環(huán)柱狀襯墊

2 結(jié)果與討論

2.1 HPMs幾何結(jié)構(gòu)對(duì)發(fā)射場(chǎng)的影響

圖3 不同幾何結(jié)構(gòu)的高介電襯墊仿真模型水模中心橫斷面的發(fā)射效率h分布．(a)無襯墊；(b)四等分圓筒狀襯墊；(c)四塊方形襯墊對(duì)稱環(huán)繞水模；(d)同側(cè)三塊方形襯墊；(e) 120°扇環(huán)柱狀襯墊

表1 不同幾何結(jié)構(gòu)的高介電襯墊仿真模型ROI內(nèi)的發(fā)射效率h均值與不均勻度（CV）

圖4 不同幾何結(jié)構(gòu)的高介電襯墊仿真模型ROI內(nèi)發(fā)射效率均值和不均勻度分析

2.2 理論分析

不同模型水模中心橫斷面沿軸方向中心線的發(fā)射效率分布如圖5所示，可以看出，加入四等分圓筒狀、環(huán)繞四方塊、同側(cè)三方塊襯墊后，發(fā)射效率沿軸方向中心線分布都較為均勻．

圖5 不同仿真模型水模中心橫斷面沿y軸方向中心線的發(fā)射效率分布（以中心為原點(diǎn)）

3 結(jié)論

無

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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

A

10.11938/cjmr20212904

2021-04-01;

2021-05-15

國(guó)家重點(diǎn)研發(fā)計(jì)劃(2016YFC1304702)；國(guó)家自然科學(xué)基金資助項(xiàng)目(82127802,81227902)；中國(guó)科學(xué)院戰(zhàn)略性先導(dǎo)科技專項(xiàng)(XDB25000000)；廣東省重點(diǎn)領(lǐng)域研發(fā)計(jì)劃(2018B030333001)；湖北省科技重大專項(xiàng)(2021ACA013)；中國(guó)科學(xué)院磁共振技術(shù)聯(lián)盟資助項(xiàng)目(2020GZL002).

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