Department of Chemistry, University of Miami, Coral Gables, FL 33124, USA.
J Magn Reson. 2011 Sep;212(1):186-96. doi: 10.1016/j.jmr.2011.06.026. Epub 2011 Jul 7.
In this work, average Hamiltonian theory is used to study selective excitation under a series of small flip-angle θ-pulses [θ≪π/3] applied either periodically [corresponding to the DANTE pulse sequence] or aperiodically to a spin-1/2 system. First, an average Hamiltonian description of the DANTE pulse sequence is developed that is valid for frequencies either at or very far from integer multiples of 1τ, where τ is the interpulse delay. For aperiodic excitation, a single resonance, νsel, can be selectively excited if the θ-pulse phases are modulated in concert with the interpulse delays. The conditions where average Hamiltonian theory can be accurately applied to describe the dynamics under aperiodic selective pulses, which are referred to as pseudorandom-DANTE or p-DANTE sequences, are similar to those found for the DANTE sequence. Signal averaging over different p-DANTE sequences improves the apparent selectivity at νsel by reducing the excitations at other frequencies. Experimental demonstrations of p-DANTE sequences and comparisons with the theory are presented.
在这项工作中，平均哈密顿理论被用于研究在一系列小翻转角θ脉冲（θ≪π/3）下的选择性激发，这些脉冲要么周期性地施加[对应于 DANTE 脉冲序列]，要么非周期性地施加到自旋 1/2 系统上。首先，开发了一种适用于 DANTE 脉冲序列的平均哈密顿描述，该描述在频率上既可以在整数倍 1τ处，也可以在非常远离 1τ的地方有效，其中 τ 是脉冲间延迟。对于非周期性激发，如果θ脉冲相位与脉冲间延迟协同调制，则可以选择性地激发单个共振νsel。平均哈密顿理论可以准确地应用于描述非周期性选择性脉冲下的动力学的条件，这些条件被称为伪随机 DANTE 或 p-DANTE 序列，与 DANTE 序列的条件相似。通过在不同的 p-DANTE 序列上进行信号平均，可以减少其他频率的激发，从而提高在 νsel 处的表观选择性。展示了 p-DANTE 序列的实验演示并与理论进行了比较。
