Continuous-wave saturation considerations for efficient xenon depolarization
Continuous-wave saturation considerations for efficient xenon depolarization
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DOI：
10.1002/nbm.3307
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发表时间：
2015-06-01
影响因子：
2.9
通讯作者：
Schroeder, Leif
中科院分区：
文献类型：
--
作者：
Kunth, Martin;Witte, Christopher;Schroeder, Leif
超极化NMR与化学交换饱和转移（Hyper-CEST）的结合是一种强大的NMR技术，可使用RF饱和脉冲检测高度稀释浓度的NMR结合位点。至关重要的是，产生最大Hyper-CEST效应的饱和脉冲强度和持续时间的组合是先验未知的。与质子MRI中的CEST相比，其中系统在长饱和时间内达到稳态，Hyper-CEST具有最佳饱和时间，即饱和时间更短或更长会降低Hyper-CEST效应。在这里，我们推导出这个最佳饱和脉冲长度的表达式。我们还发现，对应于5倍的超CEST交换率k（BA）（即，B-1=5 k（BA）/，旋磁比为k-129）的脉冲强度B-1直接生成96%的最大超CEST对比度，而无需进一步优化，同时保持光谱选择性。作为同时优化Hyper-CEST响应的幅度和宽度的措施，我们发现了对应于乘以交换率的最佳饱和脉冲强度，即B1 =。当检测到极低的主体浓度时，最佳饱和时间的表达式简化为接近自由电子的纵向弛豫时间。版权所有（c）2015约翰威利父子有限公司
The combination of hyperpolarized Xe with chemical exchange saturation transfer (Hyper-CEST) is a powerful NMR technique to detect highly dilute concentrations of Xe binding sites using RF saturation pulses. Crucially, that combination of saturation pulse strength and duration that generates the maximal Hyper-CEST effect is a priori unknown. In contrast to CEST in proton MRI, where the system reaches a steady-state for long saturation times, Hyper-CEST has an optimal saturation time, i.e.saturating for shorter or longer reduces the Hyper-CEST effect. Here, we derive expressions for this optimal saturation pulse length. We also found that a pulse strength, B-1, corresponding to five times the Xe exchange rate, k(BA) (i.e.B-1=5 k(BA)/ with the gyromagnetic ratio of Xe-129, ), generates directly and without further optimization 96% of the maximal Hyper-CEST contrast while preserving spectral selectivity. As a measure that optimizes the amplitude and the width of the Hyper-CEST response simultaneously, we found an optimal saturation pulse strength corresponding to times the Xe exchange rate, i.e.B1=. When extremely low host concentration is detected, then the expression for the optimum saturation time simplifies as it approaches the longitudinal relaxation time of free Xe. Copyright (c) 2015 John Wiley & Sons, Ltd.