Rapid B1 mapping using orthogonal, equal-amplitude radio-frequency pulses.
Rapid B1 mapping using orthogonal, equal-amplitude radio-frequency pulses.
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DOI：
10.1002/mrm.23051
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发表时间：
2012-03
影响因子：
3.3
通讯作者：
Chang YV
中科院分区：
文献类型：
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作者：
Chang YV
我们提出了一种新的基于相位的方法来映射发射机线圈的射频场(B1)的三维幅度。该方法利用了绕正交轴旋转之间的非对易关系。我们在目前的工作中实现了这一原理，得到了最终磁化的相位与翻转角之间的简单关系。在这项研究中，我们关注的是小于90°的翻转角度。与现有的B1映射方案相比，该方法具有快速、易实现的特点。映射序列可以通过向规则的3D梯度回波(GE)序列添加与激励RF脉冲具有相同翻转角但在相位上正交的磁化准备RF脉冲来简单地获得。这种方法能够在一分钟内用不大于60°的翻转角生成可靠的B1场图。我们表明，它对T1、小的化学位移和轻微的背景不均匀性是健壮的。该方法尤其适用于长T1、超极化气体成像等情况下的B1标测。基于震级的方法不容易应用的地方。文中还给出了用该方法计算翻转角映射图的噪声。
We present a new phase-based method for mapping the amplitude of the radio-frequency (RF) field (B1) of a transmitter coil in 3-dimension. This method exploits the non-commutation relation between rotations about orthogonal axes. Our implementation of this principle in the current work results in a simple relation between the phase of the final magnetization and the flip angle. In this study we focus on flip angles less than 90°. Compared to the existing B1 mapping schemes, our method is rapid and easy to implement. The mapping sequence can be simply obtained by adding to a regular 3D gradient-echo (GE) sequence a magnetization preparation RF pulse of the same flip angle but orthogonal in phase to the excitation RF pulse. This method is demonstrated capable of generating reliable maps of the B1 field within one minute using flip angles no larger than 60°. We show that it is robust against T1, small chemical shift and mild background inhomogeneity. This method may especially be suitable for B1 mapping in situations (e.g., long-T1, hyperpolarized-gas imaging, etc.) where magnitude-based methods are not readily applicable. A noise calculation of the flip angle map using this method is also presented.