IEEE Trans Biomed Eng. 2019 Oct;66(10):2848-2854. doi: 10.1109/TBME.2019.2897029. Epub 2019 Feb 1.
To develop a novel radio-frequency (RF) concept for ultra-high field (UHF) human magnetic resonance imaging (MRI) based on a coaxial resonant cavity.
A two-channel slotted coaxial cavity RF applicator was designed for human head MRI at 9.4T. Physical dimensions made the proposed conducting structure resonant at the required frequency without tuning lumped elements. Numerical electromagnetic modeling was used to optimize the design. RF safety was assessed with two representative human body models. MR experiments on a 9.4T scanner included gradient echo images and mapping of a circularly polarized RF magnetic field in the human head phantom.
The simulations and the phantom MR experiments agreed both qualitatively and quantitatively. The design was relatively simple, robust and required only a few additional reactive elements for the applicator's input impedance matching. The transmit efficiency and homogeneity of the excitation field were only 20% and 4% lower compared to a conventional 8-channel head array.
The coaxial RF applicator was feasible for human MRI at UHF and required no lumped elements for its tuning. Imaging performance of the RF applicator was only moderately lower compared to the conventional transmit array, but would be sufficient to provide an anatomical reference for the heteronuclei MRI.
An alternative approach with the minimal involvement of lumped elements becomes feasible to design volume-type RF coils for UHF human MRI.
基于同轴谐振腔，开发一种用于超高场（UHF）人体磁共振成像（MRI）的新型射频（RF）概念。
设计了一种用于 9.4T 人体头部 MRI 的双通道开槽同轴腔 RF 发射器。物理尺寸使所提出的导电结构在无需调谐集总元件的情况下在所需频率下谐振。使用数值电磁建模对设计进行了优化。使用两个代表性人体模型评估了 RF 安全性。在 9.4T 扫描仪上进行的 MR 实验包括梯度回波图像以及在人体头部体模中对圆极化 RF 磁场的映射。
模拟和体模 MR 实验在定性和定量上均一致。该设计相对简单、稳健，仅需为发射器的输入阻抗匹配添加几个额外的电抗元件。与传统的 8 通道头部阵列相比，发射效率和激励场的均匀性仅低 20%和 4%。
同轴 RF 发射器可用于 UHF 人体 MRI，且无需调谐集总元件。与传统的发射阵列相比，RF 发射器的成像性能仅略低，但足以提供异核 MRI 的解剖参考。
对于 UHF 人体 MRI，设计容积式 RF 线圈的方法变得可行，其涉及的集总元件最少。
