多回波序列中优化的不均匀脉冲间隔可改善重聚焦
Optimized, Unequal Pulse Spacing in Multiple Echo Sequences Improves Refocusing
摘要：
最近的量子计算论文（G. S. Uhrig，Phys Rev Lett 98 100504（2007））分析导出的用于多自旋回波序列的最佳脉冲间隔，该序列被设计为去除耦合到浴的两级系统中的退相干。所谓的UDD序列中的间隔与Carr-Purcell-Meiboom-Gill（CPMG）多重自旋回波序列的传统等脉冲间隔有显着不同。UDD序列是为一个与磁共振无关的模型推导的，但最近在理论上被证明是更普遍的。在这里，我们表明，UDD序列具有理论优势的磁共振成像的结构化材料，如组织，在分隔和微结构化的环境中的扩散导致波动场的范围内的不同的时间尺度。我们还通过实验表明，无论是在切除的组织和活的小鼠肿瘤模型中，最佳UDD序列产生不同的T2加权对比度比CPMG序列具有相同数量的脉冲和总延迟，在大多数地区有很大的增强。
英文摘要：
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 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 timescales. We also show experimentally, both in excised tissue and in a live mouse tumor model, that optimal UDD sequences produce different T2-weighted contrast than do CPMG sequences with the same number of pulses and total delay, with substantial enhancements in most regions.
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