Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
J Magn Reson. 2010 Dec;207(2):220-33. doi: 10.1016/j.jmr.2010.09.003. Epub 2010 Sep 15.
We apply optimal control theory (OCT) to the design of refocusing pulses suitable for the CPMG sequence that are robust over a wide range of B(0) and B(1) offsets. We also introduce a model, based on recent progress in the analysis of unitary dynamics in the field of quantum information processing (QIP), that describes the multiple refocusing dynamics of the CPMG sequence as a dephasing Pauli channel. This model provides a compact characterization of the consequences and severity of residual pulse errors. We illustrate the methods by considering a specific example of designing and analyzing broadband OCT refocusing pulses of length 10t(180) that are constrained by the maximum instantaneous pulse power. We show that with this refocusing pulse, the CPMG sequence can refocus over 98% of magnetization for resonance offsets up to 3.2 times the maximum RF amplitude, even in the presence of ±10% RF inhomogeneity.
我们将最优控制理论（OCT）应用于设计适用于 CPMG 序列的重聚焦脉冲，这些脉冲在宽范围的 B(0) 和 B(1) 偏移下具有鲁棒性。我们还引入了一种模型，该模型基于量子信息处理（QIP）领域中对幺正动力学分析的最新进展，将 CPMG 序列的多次重聚焦动力学描述为去相位 Pauli 通道。该模型紧凑地描述了残余脉冲误差的后果和严重程度。我们通过考虑一个特定的例子来说明设计和分析长度为 10t(180)的宽带 OCT 重聚焦脉冲的方法，这些脉冲受到最大瞬时脉冲功率的限制。我们表明，使用这个重聚焦脉冲，即使在存在 ±10% 的 RF 非均匀性的情况下，CPMG 序列也可以将共振偏移高达 3.2 倍最大 RF 幅度的磁化强度重新聚焦 98%以上。
