Collins C M, Li S, Smith M B
Department of Radiology, The Pennsylvania State University College of Medicine, Hershey Medical Center, 17033, USA.
Magn Reson Med. 1998 Dec;40(6):847-56. doi: 10.1002/mrm.1910400610.
Calculations of radiofrequency magnetic (B1) field and specific energy absorption rate (SAR) distributions in a sphere of tissue and a multi-tissue human head model in a 12-element birdcage coil are presented. The coil model is driven in linear and quadrature modes at 63, 175, 200, and 300 MHz. Plots of B1 field magnitude and SAR distributions, average SAR, maximum local SAR, and measures of B1 field homogeneity and signal-to-noise ratio are given. SAR levels for arbitrary pulse sequences can be estimated from the calculated data. Maximum local SAR levels are lower at lower frequencies, in quadrature rather than in linear coils, and in linear fields oriented posterior-to-anterior rather than left-to-right in the head. It should be possible to perform many experiments in the head at frequencies up to 300 MHz without exceeding standard limits for local or average SAR levels.
本文给出了在一个12单元鸟笼式线圈中，组织球体和多组织人体头部模型内射频磁场（B1）和比吸收率（SAR）分布的计算结果。该线圈模型在63、175、200和300 MHz频率下以线性和正交模式驱动。给出了B1场强和SAR分布、平均SAR、最大局部SAR以及B1场均匀性和信噪比的测量结果。可根据计算数据估算任意脉冲序列的SAR水平。在较低频率、正交线圈而非线性线圈中，以及头部中从后到前而非从左到右的线性场中，最大局部SAR水平较低。在高达300 MHz的频率下，应该可以在头部进行许多实验，而不会超过局部或平均SAR水平的标准限值。
