Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA.
Department of Electrical and Computer Engineering, Seoul National University, Gwanak-gu, Seoul 08826, Korea.
Sensors (Basel). 2021 Oct 30;21(21):7250. doi: 10.3390/s21217250.
For ultra-high field and frequency (UHF) magnetic resonance imaging (MRI), the associated short wavelengths in biological tissues leads to penetration and homogeneity issues at 10.5 tesla (T) and require antenna transmit arrays for efficiently generated 447 MHz B fields (defined as the transmit radiofrequency (RF) magnetic field generated by RF coils). Previously, we evaluated a 16-channel combined loop + dipole antenna (LD) 10.5 T head array. While the LD array configuration did not achieve the desired B efficiency, it showed an improvement of the specific absorption rate (SAR) efficiency compared to the separate 8-channel loop and separate 8-channel dipole antenna arrays at 10.5 T. Here we compare a 16-channel dipole antenna array with a 16-channel LD array of the same dimensions to evaluate B efficiency, 10 g SAR, and SAR efficiency. The 16-channel dipole antenna array achieved a 24% increase in B efficiency in the electromagnetic simulation and MR experiment compared to the LD array, as measured in the central region of a phantom. Based on the simulation results with a human model, we estimate that a 16-channel dipole antenna array for human brain imaging can increase B efficiency by 15% with similar SAR efficiency compared to a 16-channel LD head array.
对于超高磁场和频率（UHF）磁共振成像（MRI），生物组织中的相关短波长会导致在 10.5 特斯拉（T）下的穿透和均匀性问题，并且需要天线发射阵列来有效地产生 447 MHz B 场（定义为由 RF 线圈产生的发射射频（RF）磁场）。此前，我们评估了一个 16 通道组合环形+偶极子天线（LD）10.5 T 头阵列。虽然 LD 阵列配置并未达到所需的 B 效率，但与单独的 8 通道环形和单独的 8 通道偶极子天线阵列相比，它在 10.5 T 下显示出特定吸收率（SAR）效率的提高。在这里，我们比较了具有相同尺寸的 16 通道偶极子天线阵列和 16 通道 LD 阵列，以评估 B 效率、10 g SAR 和 SAR 效率。在电磁模拟和 MR 实验中，16 通道偶极子天线阵列与 LD 阵列相比，在体模中心区域测量的 B 效率提高了 24%。基于人体模型的模拟结果，我们估计对于人脑成像，与 16 通道 LD 头部阵列相比，16 通道偶极子天线阵列可以提高 15%的 B 效率，同时保持相似的 SAR 效率。
