Department of Chemistry and Center for Molecular and Biomolecular Imaging, Duke University, North Carolina 27708-0346, USA.
J Chem Phys. 2009 Nov 28;131(20):204510. doi: 10.1063/1.3263196.
A recent quantum computing paper (G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007)) analytically derived optimal pulse spacings for a multiple spin echo sequence designed to remove decoherence in a two-level system coupled to a bath. The spacings in what has been called a "Uhrig dynamic decoupling (UDD) sequence" differ dramatically from the conventional, equal pulse spacing of a Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo sequence. The UDD sequence was derived for a model that is unrelated to magnetic resonance, but was recently shown theoretically to be more general. Here we show that the UDD sequence has theoretical advantages for magnetic resonance imaging of structured materials such as tissue, where diffusion in compartmentalized and microstructured environments leads to fluctuating fields on a range of different time scales. We also show experimentally, both in excised tissue and in a live mouse tumor model, that optimal UDD sequences produce different T(2)-weighted contrast than do CPMG sequences with the same number of pulses and total delay, with substantial enhancements in most regions. This permits improved characterization of low-frequency spectral density functions in a wide range of applications.
最近的一篇量子计算论文（G. S. Uhrig，Phys. Rev. Lett. 98, 100504 (2007)）从理论上推导出了一种用于双态系统与浴体耦合的去相干多自旋回波序列的最佳脉冲间隔。这种被称为“Uhrig 动态解耦（UDD）序列”的脉冲间隔与传统的 Carr-Purcell-Meiboom-Gill（CPMG）多自旋回波序列的等脉冲间隔有很大的不同。UDD 序列是为一个与磁共振无关的模型推导出来的，但最近的理论研究表明它具有更广泛的适用性。在这里，我们证明了 UDD 序列在磁共振成像结构材料（如组织）方面具有理论优势，在这些材料中，分室和微结构环境中的扩散会导致在一系列不同的时间尺度上产生波动的场。我们还通过离体组织和活体小鼠肿瘤模型进行了实验验证，表明与具有相同脉冲数和总延迟的 CPMG 序列相比，最优的 UDD 序列会产生不同的 T2 加权对比，在大多数区域都有显著的增强。这使得在广泛的应用中可以更好地表征低频谱密度函数。
