Simultaneous B1+ homogenization and specific absorption rate hotspot suppression using a magnetic resonance phased array transmit coil
Simultaneous B1+ homogenization and specific absorption rate hotspot suppression using a magnetic resonance phased array transmit coil
复制标题
DOI：
10.1002/mrm.21149
复制
发表时间：
2007-03-01
影响因子：
3.3
通讯作者：
Lagendijk, Jan J. W.
中科院分区：
文献类型：
--
作者：
Van den Berg, Cornelis A. T.;Van den Bergen, Bob;Lagendijk, Jan J. W.
在高场磁共振成像中，B-1(+)的均匀性和比吸收率(SAR)沉积的严重问题给全身成像带来了巨大的挑战。在这项研究中，研究了相控阵发射线圈的潜力，以同时减少B-1(+)不均匀性和SAR沉积。通过对以128 MHz频率工作的相控阵TEM线圈进行电磁仿真来验证这一点，该线圈加载了两个不同的均匀椭圆体模和四个介电患者模型。结果表明，圆偏振射频场与椭圆和骨盆的波干涉产生了基本相同的B-1(+)和电场模式。特别是对于肥胖患者，这会导致大的B-1(+)不均匀和全球区域SAR沉积升高。结果表明，相控阵发射线圈可以减少这些现象。该技术在抑制SAR热点方面尤其成功，降幅高达50%。将椭圆的优化设置应用于患者模型，可得到与患者特定优化所获得的结果类似的结果。这表明通用的相位/幅度端口设置是可能的，不需要关于患者特定的射频场的预先信息。这种方案由于其同时的B-1(+)均质化和额外的SAR边缘，对于3T的全身成像将有许多好处。
In high-field MRI severe problems with respect to B-1(+) uniformity and specific absorption rate (SAR) deposition pose a great challenge to whole-body imaging. In this study the potential of a phased array transmit coil is investigated to simultaneously reduce B-1(+) nonuniformity and SAR deposition. This was tested by performing electromagnetic simulations of a phased array TEM coil operating at 128 MHz loaded with two different homogeneous elliptical phantoms and four dielectric patient models. It was shown that the wave interference of a circularly polarized RF field with an ellipse and a pelvis produces largely identical B-1(+) and electric field patterns. Especially for obese patients, this results in large B-1(+) nonuniformity and global areas with elevated SAR deposition. It is demonstrated that a phased array transmit coil can reduce these phenomena. The technique was especially successful in suppressing SAR hotspots with a decrease up to 50%. The application of optimized settings for an ellipse to the patient models leads to comparable results as obtained with the patient-specific optimizations. This suggests that generic phase/amplitude port settings are possible, requiring no preinformation about patient-specific RF fields. Such a scheme would, due to its simultaneous B-1(+) homogenization and extra SAR margin, have many benefits for whole-body imaging at 3 T.