SAR and Power Implications of Different RF Shimming Strategies in the Pelvis for 7T MRI
SAR and Power Implications of Different RF Shimming Strategies in the Pelvis for 7T MRI
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DOI：
10.1002/jmri.21806
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发表时间：
2009-07-01
影响因子：
4.4
通讯作者：
Lagendijk, Jan J. W.
中科院分区：
文献类型：
--
作者：
van den Bergen, Bob;van den Berg, Cornelis A. T.;Lagendijk, Jan J. W.
目的：确定用于 7 T 身体成像的最佳射频 (RF) 匀场方法，该方法在目标区域内提供足够的 B-1(+) 激励，同时能量沉积 (SAR) 和功率需求尽可能低，并且不包含患者模型内的解剖特定电场信息，因为该信息在实践中不可用。材料和方法：使用有限差分时域 (FDTD) 模拟来评估身体线圈内骨盆的五种射频匀场策略。将结果与已知患者体内电场时可实现的理论上最佳解决方案进行比较。结果：大多数射频匀场策略都是成功的。然而，在不同的策略之间，观察到平均 SAR 降低有 2 倍的差异，局部最大 SAR 降低有 3 倍的差异，功率效率有 20 倍的差异。对于所使用的身体线圈和患者模型，相位匹配被发现是最有前途的射频匀场方法。结论：射频匀场可以在不知道电场的情况下降低精确患者模型中的 SAR 并提高功率效率。然而，选择正确的方法对于防止局部 SAR 沉积中的意外行为至关重要。
Purpose: To determine the best radiofrequency (RF) shimming method for 7 T body imaging that provides sufficient B-1(+) excitation inside the target region while energy deposition (SAR) and power demands are as low as possible and that does not incorporate anatomy specific electric field information inside the patient models, as this information is not available in practice.Materials and Methods: Finite difference time domain (FDTD) simulations were used to evaluate five RF shimming strategies for the pelvis inside a body coil. The results were compared to the theoretical best solution that could be achieved if the electric field inside the patient was known.Results: Most of the RF shimming strategies were successful. However, between the different strategies a factor of two difference in average SAR reduction, a factor of three difference in local maximum SAR reduction, and a factor of 20 difference in power efficiency was observed. Phase matching was found to be the most promising RF shimming method for the body coil used and patient models.Conclusion: RF shimming can reduce the SAR and improve power efficiency in an accurate patient model without knowing the electric field. However, choosing the right method is critical to prevent unexpected behavior in local SAR deposition.