Alecci M, Collins C M, Smith M B, Jezzard P
Centre for Functional Magnetic Resonance Imaging of the Brain, Department of Clinical Neurology, John Radcliffe Hospital, University of Oxford, Headington, Oxford, UK.
Magn Reson Med. 2001 Aug;46(2):379-85. doi: 10.1002/mrm.1201.
The RF B(1) distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B(1) distortion at high field can be explained with 3D full-Maxwell calculations. It was found that the B(1) distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z-axis the B(1) distribution is determined mainly by the coil geometry. In the transverse plane, the region of B(1) uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B(1) uniformity was 9 cm with phantoms and 7 cm in the head.
使用配备鸟笼线圈的3T磁共振成像（MRI）系统，对幻影模型和志愿者头部中的射频B(1)分布进行了理论和实验研究。数值模拟与实验结果的一致性表明，高场下的B(1)畸变可用三维全麦克斯韦计算来解释。研究发现，横向平面中的B(1)分布强烈依赖于样品的介电特性。我们表明，这是射频穿透效应与射频驻波效应相结合的结果。相比之下，沿鸟笼线圈z轴，B(1)分布主要由线圈几何形状决定。在横向平面中，B(1)均匀性区域（在最大值的10%以内），油中为15厘米，蒸馏水中为6厘米，盐水中为11厘米，头部中为10厘米。沿z轴，幻影模型中的B(1)均匀性为9厘米，头部中为7厘米。
