Vanderbilt University Institute of Imaging Science, Nashville, TN 37232-2310, USA.
J Magn Reson. 2013 Jan;226:79-87. doi: 10.1016/j.jmr.2012.11.004. Epub 2012 Nov 17.
A new family of optimized encoding pulses for Bloch-Siegert (BS) |B(1)(+)| mapping is introduced, as well as an algorithm to design them. The pulses are designed by numerical maximization of BS sequence sensitivity, subject to constraints that ensure low on-resonance excitation. The pulses are in all cases characterized by a constant envelope and U-shaped frequency sweep. They are validated in simulations, 7T in vivo experiments, and an experiment to measure their on-resonance excitation, and are compared to a Fermi pulse conventionally used in the BS method. The pulses are shown to produce larger phase shifts in a shorter time and with lower on-resonance excitation than the Fermi pulse, which results in lower SAR and improved |B(1)(+)| accuracy in areas of the body with large main field inhomogeneities.
引入了一种新的 Bloch-Siegert (BS) |B(1)(+)| 映射优化编码脉冲家族，以及一种设计它们的算法。这些脉冲是通过数值最大化 BS 序列灵敏度设计的，同时满足确保低失谐激发的约束条件。在所有情况下，这些脉冲的特点都是包络恒定且频率扫描呈 U 形。它们在模拟、7T 体内实验以及测量其失谐激发的实验中得到了验证，并与 BS 方法中常用的 Fermi 脉冲进行了比较。结果表明，与 Fermi 脉冲相比，这些脉冲在更短的时间内产生更大的相位偏移，同时失谐激发更低，从而在主磁场不均匀性较大的身体部位降低 SAR 并提高 |B(1)(+)| 的准确性。
