Department of Electrical and Computer Engineering and the Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA.
IEEE Trans Biomed Eng. 2012 Dec;59(12):3365-71. doi: 10.1109/TBME.2012.2208965. Epub 2012 Aug 23.
In high-field magnetic resonance imaging (MRI) systems, B₀ fields of 7 and 9.4 T, the RF field shows greater inhomogeneity compared to clinical MRI systems with B₀ fields of 1.5 and 3.0 T. In multichannel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the nonuniformity of the RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected region of interest. The pseudoinverse method has also been used to find a solution. The simulation results for 9.4- and 7-T MRI systems are discussed in detail for the head model. Variation of the simulation results in a 9.4-T system with the number of RF coil elements for different positions of the regions of interest in a spherical phantom are also discussed. Experimental results were obtained in a phantom in the 9.4-T system and are compared to the simulation results and the specific absorption rate has been evaluated.
在高磁场磁共振成像（MRI）系统中，B₀场为 7 和 9.4 T，与 B₀场为 1.5 和 3.0 T 的临床 MRI 系统相比，RF 场的不均匀性更大。在多通道 RF 线圈中，可以独立控制每个线圈元件的幅度和相位，以减少 RF 场的不均匀性。凸优化技术已被用于通过迭代解来获得选定感兴趣区域的均匀性的最佳激励参数。也使用了伪逆方法来找到解决方案。详细讨论了用于头部模型的 9.4-T 和 7-T MRI 系统的模拟结果。还讨论了在球形体模中不同感兴趣区域位置的情况下，9.4-T 系统中 RF 线圈元件数量的变化对模拟结果的影响。在 9.4-T 系统的体模中获得了实验结果，并将其与模拟结果进行了比较，评估了比吸收率。
