Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.
NMR Biomed. 2022 Aug;35(8):e4722. doi: 10.1002/nbm.4722. Epub 2022 Mar 17.
Longitudinally orientated dipoles and microstrip antennas have both demonstrated superior results as RF transmit elements for body imaging at 7 T MRI, and are as of today the most commonly used transmit elements. In this study, the performances of the two antenna concepts were compared for use in local RF antenna arrays by numerical simulations. Antenna elements investigated are the fractionated dipole and the microstrip line with meander structures. Phantom simulations with a single antenna element were performed and evaluated with regard to specific absorption rate (SAR) efficiency in the center of the subject. Simulations of array configurations with 8 and 16 elements were performed with anatomical body models. Both antenna elements were combined with a loop coil to compare hybrid configurations. Singular value decomposition of the B fields, RF shimming, and calculation of the voxel-wise power and SAR efficiencies were performed in regions of interest with varying sizes to evaluate the transmit performance. The signal-to-noise ratio (SNR) was evaluated to estimate the receive performance. Simulated data show similar transmit profiles for the two antenna types in the center of the phantom (penetration depth > 20 mm). For body imaging, no considerable differences were determined for the different antenna configurations with regard to the transmit performance. Results show the advantage of 16 transmit channels compared with today's commonly used 8-channel systems (minimum RF shimming excitation error of 4.7% (4.3%) versus 2.7% (2.8%) for the 8-channel and 16-channel configurations with the microstrip antennas in a (5 cm) cube in the center of a male (female) body model). Highest SNR is achieved for the 16-channel configuration with fractionated dipoles. The combination of either fractionated dipoles or microstrip antennas with loop coils is more favorable with regard to the transmit performance compared with only increasing the number of elements.
纵向偶极子和微带天线都在 7T MRI 体成像的射频发射元件方面表现出了优异的性能，并且是迄今为止最常用的发射元件。在这项研究中，通过数值模拟比较了这两种天线概念在局部射频天线阵列中的性能。研究的天线元件是分段偶极子和具有曲折结构的微带线。对单个天线元件进行了幻影模拟，并根据在受检者中心的特定吸收率（SAR）效率进行了评估。使用解剖体模型对具有 8 个和 16 个元件的阵列配置进行了模拟。将两种天线元件与环形线圈组合以比较混合配置。在不同大小的感兴趣区域中进行了 B 场奇异值分解、RF 匀场以及体素级功率和 SAR 效率的计算，以评估发射性能。评估了信噪比（SNR）以估计接收性能。模拟数据显示，在幻影中心两种天线类型的发射特性相似（穿透深度> 20mm）。对于体成像，不同的天线配置在发射性能方面没有明显差异。结果表明，与当前常用的 8 通道系统相比，16 个发射通道具有优势（在男性（女性）体模型中心的（5cm）立方体内，微带天线的 8 通道和 16 通道配置的最小 RF 匀场激励误差分别为 4.7%（4.3%）和 2.7%（2.8%））。使用分段偶极子获得最高 SNR。与仅增加元件数量相比，分段偶极子或微带天线与环形线圈的组合在发射性能方面更有利。
