Raaijmakers Alexander J E, Italiaander Michel, Voogt Ingmar J, Luijten Peter R, Hoogduin Johannes M, Klomp Dennis W J, van den Berg Cornelis A T
Department of Radiology, UMC Utrecht, Utrecht, The Netherlands.
MR Coils B.V, Drunen, The Netherlands.
Magn Reson Med. 2016 Mar;75(3):1366-74. doi: 10.1002/mrm.25596. Epub 2015 May 2.
Dipole antennas in ultrahigh field MRI have demonstrated advantages over more conventional designs. In this study, the fractionated dipole antenna is presented: a dipole where the legs are split into segments that are interconnected by capacitors or inductors.
A parameter study has been performed on dipole antenna length using numerical simulations. A subsequent simulation study investigates the optimal intersegment capacitor/inductor value. The resulting optimal design has been constructed and compared to a previous design, the single-side adapted dipole (SSAD) by simulations and measurements. An array of eight elements has been constructed for prostate imaging on four subjects (body mass index 20-27.5) using 8 × 2 kW amplifiers.
For prostate imaging at 7T, lowest peak local specific-absorption rate (SAR) levels are achieved if the antenna is 30 cm or longer. A fractionated dipole antenna design with inductors between segments has been chosen to achieve even lower SAR levels and more homogeneous receive sensitivities.
With the new design, good quality prostate images are acquired. SAR levels are reduced by 41% to 63% in comparison to the SSAD. Coupling levels are moderate (average nearest neighbor: -14.6 dB) for each subject and prostate B1+ levels range from 12 to 18 μT.
超高场磁共振成像中的偶极天线已展现出优于更传统设计的优势。在本研究中，提出了一种分段偶极天线：一种其臂被分割成通过电容器或电感器互连的段的偶极天线。
使用数值模拟对偶极天线长度进行了参数研究。随后的模拟研究调查了段间电容器/电感器的最佳值。构建了所得的最佳设计，并通过模拟和测量将其与先前的设计——单边适配偶极天线（SSAD）进行比较。使用8×2千瓦放大器为四名受试者（体重指数20 - 27.5）构建了一个八元阵列用于前列腺成像。
对于7T下的前列腺成像，如果天线长度为30厘米或更长，则可实现最低的峰值局部比吸收率（SAR）水平。已选择一种在段间带有电感器的分段偶极天线设计，以实现更低的SAR水平和更均匀的接收灵敏度。
采用新设计获得了高质量的前列腺图像。与SSAD相比，SAR水平降低了41%至63%。每个受试者的耦合水平适中（平均最近邻：-14.6 dB），前列腺B1 +水平范围为12至18μT。
