Medtronic, Inc., Minneapolis, Minnesota, USA.
Magn Reson Med. 2013 Jan;69(1):290-4. doi: 10.1002/mrm.24244. Epub 2012 Apr 3.
In numerical analyses of radiofrequency (RF) fields for MRI, RF power is often permitted to radiate out of the problem region. In reality, RF power will be confined by the magnet bore and RF screen enclosing the magnet room. We present numerical calculations at different frequencies for various surface and volume coils, with samples from simple spheres to the human body in environments from free space to a shielded RF room. Results for calculations within a limited problem region show radiated power increases with frequency. When the magnet room RF screen is included, nearly all the power is dissipated in the human subject. For limited problem regions, inclusion of a term for radiation loss results in an underestimation of transmit efficiency compared to results including the complete bore and RF screen. If the term for radiated power is not included, calculated coil efficiencies are slightly overestimated compared to the complete case.
在 MRI 的射频（RF）场的数值分析中，通常允许 RF 功率从问题区域辐射出来。但实际上，RF 功率将受到磁体孔和包围磁体室的 RF 屏蔽的限制。我们针对不同频率的各种表面和体积线圈进行了数值计算，样品从简单的球体到人体，环境从自由空间到屏蔽的 RF 房间。在有限的问题区域内的计算结果表明，辐射功率随频率增加而增加。当包括磁体室 RF 屏蔽时，几乎所有的功率都耗散在人体中。对于有限的问题区域，如果包括辐射损耗项，则与包括完整孔和 RF 屏蔽的结果相比，传输效率的计算会低估。如果不包括辐射功率项，则与完整情况相比，计算出的线圈效率会略有高估。
