Effects of receive-only inserts on specific absorption rate, B1 (+) field, and Tx coil performance.
Effects of receive-only inserts on specific absorption rate, B1 (+) field, and Tx coil performance.
复制标题
DOI：
10.1002/jmri.24152
复制
发表时间：
2014-02
期刊：
影响因子：
--
通讯作者：
Ibrahim TS
中科院分区：
文献类型：
--
作者：
Krishnamurthy N;Zhao T;Ibrahim TS
为了评估不同的圆柱形和紧密协调接收阵列设计对7特斯拉纯发射头线圈的自旋激发和比吸收率(SAR)的影响。我们建立了不同接收阵列结构的FDTD模型。采用不同铜迹宽的圆柱形紧密贴合头盔阵列；数值模拟中使用了一个瞬变电磁发射线圈模型和两个头部模型。对TX线圈耦合进行了实验测量，并用FDTD建模进行了验证。改变阵列模型中回路的铜迹线宽度会导致射频吸收的细微变化(<；5%)。在仅植入Rx的头部模型中，观察到了SAR分布的变化。对于2−T的脑部，不同组织的峰值SAR值增加(μ1至+15%)，头部模型中1W前向功率的总吸收率在仅植入Rx的头部增加了5%至21%。不同Rx插件的RF吸收变化表明，即使在B1+和Tx线圈端口之间的耦合变化很小的情况下，Tx线圈的RF辐射也会发生变化。在仅存在Rx-插入物的情况下，观察到局部/全局SAR的变化以及B1+场分布的细微变化。因此，在评估SAR和设计用于7 T MRI的垫片和/或TX-SENSE的RF发射脉冲波形参数时，需要结合仅接收阵列效应。
To evaluate the effect of different cylindrical and close conforming receive only array designs on spin excitation and specific absorption rate (SAR) of a 7 Tesla transmit only head coil. We developed FDTD models of different receive only array geometries. Cylindrical and close fitting helmet arrays with varying copper trace widths; a TEM Tx coil model and two head models were used in numerical simulations. Tx coil coupling was experimentally measured and validated with FDTD modeling. Changing copper trace width of loops in array models caused subtle changes in RF absorption (<5%). Changes in SAR distribution were observed in the head models with Rx-only inserts. Peak SAR increased (−1 to +15%) in different tissues for a mean B1+ in the brain of 2 μT. Total absorption in the head models for 1 Watt forward power increased (5 to 21%) in the heads with Rx-only inserts. Changes in RF absorption with different Rx-inserts indicate a change in RF radiation of the Tx coil even when changes in B1+ and coupling between ports of Tx coil were minimal. Changes in local/global SAR and subtle changes in B1+ field distributions were observed with the presence of Rx-only inserts. Thus, incorporation of the receive-only array effects are needed when evaluating SAR and designing RF transmit pulse waveform parameters for shimming and/or Tx-SENSE for 7 T MRI.