Khalighi Mohammad Mehdi, Rutt Brian K, Kerr Adam B
Global Applied Science Laboratory, GE Healthcare, Menlo Park, California, USA.
Magn Reson Med. 2013 Sep;70(3):829-35. doi: 10.1002/mrm.24507. Epub 2012 Oct 5.
The Bloch-Siegert (B-S) B1+ mapping method has been shown to be fast and accurate, yet it suffers from high Specific Absorption Rate (SAR) and moderately long echo time. An adiabatic RF pulse design is introduced here for optimizing the off-resonant B-S RF pulse to achieve more B-S B1+ measurement sensitivity for a given pulse width. The extra sensitivity can be used for higher angle-to-noise ratio B1+ maps or traded off for faster scans. Using numerical simulations and phantom experiments, it is shown that a numerically optimized 2-ms adiabatic B-S pulse is 2.5 times more efficient than a conventional 6-ms Fermi-shaped B-S pulse. The adiabatic B-S pulse performance is validated in a phantom, and in vivo brain B1+ mapping at 3T and 7T are shown.
布洛赫-西格特（B-S）B1+映射方法已被证明快速且准确，但它存在比吸收率（SAR）高和回波时间适中较长的问题。本文引入了一种绝热射频脉冲设计，用于优化失谐的B-S射频脉冲，以便在给定脉冲宽度下实现更高的B-S B1+测量灵敏度。额外的灵敏度可用于获得更高的B1+图角度噪声比，或用于换取更快的扫描速度。通过数值模拟和体模实验表明，数值优化的2毫秒绝热B-S脉冲比传统的6毫秒费米形状B-S脉冲效率高2.5倍。绝热B-S脉冲性能在体模中得到验证，并展示了在3T和7T下的体内脑B1+映射。
