Numerical Analysis of Human Sample Effect on RF Penetration and Liver MR Imaging at Ultrahigh Field.
Numerical Analysis of Human Sample Effect on RF Penetration and Liver MR Imaging at Ultrahigh Field.
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DOI：
10.1002/cmr.b.20209
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发表时间：
2011-10
期刊：
影响因子：
--
通讯作者：
Zhang X
中科院分区：
文献类型：
--
作者：
Pang Y;Wu B;Wang C;Vigneron DB;Zhang X
磁共振成像（MRI）可以为肝脏疾病提供有临床价值的图像，已成为评估肝脏病变最有前途的无创方法之一。为了促进超高场人体肝脏 MRI，在这项工作中，利用有限差分时域数值分析研究和评估了 7 特斯拉 (7T) 超高场下导电和高介电人体中的射频穿透行为。研究表明，在7T超高场的脑成像中，“介电共振”效应在其他因素中占主导地位，导致B1穿透力提高；而在肝脏成像中，由于肝脏的几何形状不规则，“介电共振”效应不易建立，导致与大脑相比，B1 穿透力降低或图像覆盖范围有限。因此，尽管由于所需的高频而使线圈设计变得更具挑战性，但有必要构建大尺寸线圈以具有更深的穿透力以对人体肝脏进行成像。基于这项研究，设计并构建了工作在 300 MHz 范围内的平分微带线圈。然后使用 7T 全身 MR 扫描仪上的专用射频线圈从健康志愿者那里获取轴向、矢状和冠状方向的三维体内肝脏图像。
Magnetic resonance imaging (MRI) can provide clinically-valuable images for hepatic diseases and has become one of the most promising noninvasive methods in evaluating liver lesions. To facilitate the ultrahigh field human liver MRI, in this work, the RF penetration behavior in the conductive and high dielectric human body at the ultrahigh field of 7 Tesla (7T) is investigated and evaluated using the finite-difference time-domain numerical analysis. The study shows that in brain imaging at the ultrahigh field of 7T, the “dielectric resonance” effect dominates among other factors, resulting in improved B1 penetration; while in liver imaging, due to its irregular geometry of the liver, the “dielectric resonance” effect is not readily to be established, leading to a reduced B1 penetration or limited image coverage comparing to that in the brain. Therefore, it is necessary to build a large size coil to have deeper penetration to image human liver although the coil design may become more challenging due to the required high frequency. Based on this study, a bisected microstrip coil operating at 300 MHz range is designed and constructed. Three-dimensional in vivo liver images in axial, sagittal and coronal orientations are then acquired from healthy volunteers using this dedicated RF coil on a 7T whole body MR scanner.
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