Herrmann Tim, Liebig Thorsten, Mallow Johannes, Bruns Christian, Stadler Jörg, Mylius Judith, Brosch Michael, Svedja Jan Taro, Chen Zhichao, Rennings Andreas, Scheich Henning, Plaumann Markus, Hauser Marcus J B, Bernarding Johannes, Erni Daniel
Institute of Biometrics and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany.
General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, and CENIDE-Center for Nanointegration Duisburg-Essen, Duisburg, Germany.
PLoS One. 2018 Jan 25;13(1):e0191719. doi: 10.1371/journal.pone.0191719. eCollection 2018.
Magnetic resonance imaging (MRI) at ultra-high fields (UHF), such as 7 T, provides an enhanced signal-to-noise ratio and has led to unprecedented high-resolution anatomic images and brain activation maps. Although a variety of radio frequency (RF) coil architectures have been developed for imaging at UHF conditions, they usually are specialized for small volumes of interests (VoI). So far, whole-body coil resonators are not available for commercial UHF human whole-body MRI systems. The goal of the present study was the development and validation of a transmit and receive system for large VoIs that operates at a 7 T human whole-body MRI system. A Metamaterial Ring Antenna System (MRAS) consisting of several ring antennas was developed, since it allows for the imaging of extended VoIs. Furthermore, the MRAS not only requires lower intensities of the irradiated RF energy, but also provides a more confined and focused injection of excitation energy on selected body parts. The MRAS consisted of several antennas with 50 cm inner diameter, 10 cm width and 0.5 cm depth. The position of the rings was freely adjustable. Conformal resonant right-/left-handed metamaterial was used for each ring antenna with two quadrature feeding ports for RF power. The system was successfully implemented and demonstrated with both a silicone oil and a water-NaCl-isopropanol phantom as well as in vivo by acquiring whole-body images of a crab-eating macaque. The potential for future neuroimaging applications was demonstrated by the acquired high-resolution anatomic images of the macaque's head. Phantom and in vivo measurements of crab-eating macaques provided high-resolution images with large VoIs up to 40 cm in xy-direction and 45 cm in z-direction. The results of this work demonstrate the feasibility of the MRAS system for UHF MRI as proof of principle. The MRAS shows a substantial potential for MR imaging of larger volumes at 7 T UHF. This new technique may provide new diagnostic potential in spatially extended pathologies such as searching for spread-out tumor metastases or monitoring systemic inflammatory processes.
超高场（UHF）磁共振成像（MRI），如7T，可提供更高的信噪比，并带来了前所未有的高分辨率解剖图像和脑激活图。尽管已开发出多种用于UHF条件下成像的射频（RF）线圈架构，但它们通常专门用于小感兴趣体积（VoI）。到目前为止，全身线圈谐振器尚未用于商用UHF人体全身MRI系统。本研究的目标是开发并验证一种用于大VoI的发射和接收系统，该系统在7T人体全身MRI系统上运行。开发了一种由多个环形天线组成的超材料环形天线系统（MRAS），因为它允许对扩展的VoI进行成像。此外，MRAS不仅需要较低强度的照射RF能量，还能在选定的身体部位提供更受限且聚焦的激发能量注入。MRAS由几个内径为50cm、宽度为10cm、深度为0.5cm的天线组成。这些环的位置可自由调节。每个环形天线使用共形谐振左右手超材料，带有两个用于RF功率的正交馈电端口。该系统已成功实现，并通过使用硅油和水-氯化钠-异丙醇体模以及通过获取食蟹猕猴的全身图像在体内进行了演示。通过获取猕猴头部的高分辨率解剖图像，证明了其在未来神经成像应用中的潜力。食蟹猕猴的体模和体内测量提供了高分辨率图像，其大VoI在xy方向上可达40cm，在z方向上可达45cm。这项工作的结果证明了MRAS系统用于UHF MRI作为原理验证的可行性。MRAS在7T UHF下对更大体积进行MR成像显示出巨大潜力。这项新技术可能在空间扩展的病理学中提供新的诊断潜力，例如寻找扩散的肿瘤转移或监测全身性炎症过程。
