Vaidya Manushka V, Deniz Cem M, Collins Christopher M, Sodickson Daniel K, Lattanzi Riccardo
Center for Advanced Imaging Innovation and Research and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 First Ave, Fourth Floor, New York, NY, 10016, USA.
The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, 550 First Avenue, New York, NY, 10016, USA.
MAGMA. 2018 Jun;31(3):355-366. doi: 10.1007/s10334-017-0657-5. Epub 2017 Nov 6.
To use high-permittivity materials (HPM) positioned near radiofrequency (RF) surface coils to manipulate transmit/receive field patterns.
A large HPM pad was placed below the RF coil to extend the field of view (FOV). The resulting signal-to-noise ratio (SNR) was compared with that of other coil configurations covering the same FOV in simulations and experiments at 7 T. Transmit/receive efficiency was evaluated when HPM discs with or without a partial shield were positioned at a distance from the coil. Finally, we evaluated the increase in transmit homogeneity for a four-channel array with HPM discs interposed between adjacent coil elements.
Various configurations of HPM increased SNR, transmit/receive efficiency, excitation/reception sensitivity overlap, and FOV when positioned near a surface coil. For a four-channel array driven in quadrature, shielded HPM discs enhanced the field below the discs as well as at the center of the sample as compared with other configurations with or without unshielded HPM discs.
Strategically positioning HPM at a distance from a surface coil or array can increase the overlap between excitation/reception sensitivities, and extend the FOV of a single coil for reduction of the number of channels in an array while minimally affecting the SNR.
使用位于射频（RF）表面线圈附近的高介电常数材料（HPM）来操控发射/接收场型。
在RF线圈下方放置一个大的HPM垫以扩展视野（FOV）。在7T的模拟和实验中，将由此产生的信噪比（SNR）与覆盖相同FOV的其他线圈配置的信噪比进行比较。当有或没有部分屏蔽的HPM圆盘与线圈保持一定距离放置时，评估发射/接收效率。最后，我们评估了在相邻线圈元件之间插入HPM圆盘的四通道阵列的发射均匀性增加情况。
当HPM位于表面线圈附近时，其各种配置可提高SNR、发射/接收效率、激发/接收灵敏度重叠以及FOV。对于以正交方式驱动的四通道阵列，与有或没有未屏蔽HPM圆盘的其他配置相比，屏蔽的HPM圆盘增强了圆盘下方以及样品中心处的场。
将HPM与表面线圈或阵列保持一定距离进行策略性定位，可以增加激发/接收灵敏度之间的重叠，并扩展单个线圈的FOV，从而减少阵列中的通道数量，同时对SNR的影响最小。
