Mapping B1-induced eddy current effects near metallic structures in MR images: A comparison of simulation and experiment
Mapping B1-induced eddy current effects near metallic structures in MR images: A comparison of simulation and experiment
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DOI：
10.1016/j.jmr.2014.10.016
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发表时间：
2015-01-01
影响因子：
2.2
通讯作者：
Balcom, B. J.
中科院分区：
文献类型：
--
作者：
Vashaee, S.;Goora, F.;Balcom, B. J.
金属结构的磁共振成像（MRI）在医学和非医学领域非常常见。金属结构通过三种机制引起MRI图像失真：（1）通过磁化率失配引起的静态场失真，（2）由切换磁场梯度引起的涡流和（3）射频（RF）引起的涡流。采用T-1增强的单点斜坡成像（SPRITE）MRI测量在很大程度上不受磁化率和梯度诱导涡流伪影的影响。因此，可以隔离金属物体对RE场的影响。RE场影响磁共振（MR）信号的激励和检测。这是具有挑战性的与传统的MRI方法，它不能很容易地分开的三个effects.RF诱导的MRI伪影进行了实验研究，在2.4 T通过分析周围的两个几何形状相同的金属带铝和铅的图像失真。将条带浸入掺有造影剂的琼脂凝胶中，并采用锥形SPRITE序列成像。采用纯相位编码SPRITE的B-1映射法测量金属条周围的B-1场。模拟了电化学研究中所用的金属电极的几何形状，并对两种金属条中的射频场感应涡流进行了研究。RE模拟结果与实验结果吻合较好。实验和模拟结果表明，金属对周围空间的B-1分布和B-1振幅有显著影响。金属的导电性具有最小的影响。(C)2014 Elsevier Inc. All rights reserved.
Magnetic resonance imaging (MRI) in the presence of metallic structures is very common in medical and non-medical fields. Metallic structures cause MRI image distortions by three mechanisms: (1) static field distortion through magnetic susceptibility mismatch, (2) eddy currents induced by switched magnetic field gradients and (3) radio frequency (RF) induced eddy currents. Single point ramped imaging with T-1 enhancement (SPRITE) MRI measurements are largely immune to susceptibility and gradient induced eddy current artifacts. As a result, one can isolate the effects of metal objects on the RE field. The RE field affects both the excitation and detection of the magnetic resonance (MR) signal. This is challenging with conventional MRI methods, which cannot readily separate the three effects.RF induced MRI artifacts were investigated experimentally at 2.4 T by analyzing image distortions surrounding two geometrically identical metallic strips of aluminum and lead. The strips were immersed in agar gel doped with contrast agent and imaged employing the conical SPRITE sequence. B-1 mapping with pure phase encode SPRITE was employed to measure the B-1 field around the strips of metal. The strip geometry was chosen to mimic metal electrodes employed in electrochemistry studies.Simulations are employed to investigate the RF field induced eddy currents in the two metallic strips. The RE simulation results are in good agreement with experimental results. Experimental and simulation results show that the metal has a pronounced effect on the B-1 distribution and B-1 amplitude in the surrounding space. The electrical conductivity of the metal has a minimal effect. (C) 2014 Elsevier Inc. All rights reserved.