利用迭代软阈值方法抑制恒时演化类核磁共振实验中的采样截断伪峰

采样截断,即信号衰减殆尽之前结束采样,会在核磁共振(NMR)谱图中引入振荡状伪峰,进而影响谱图质量.在多维核磁共振实验中,为减少实验时间并为后续脉冲序列保留自旋相干,采样必然在信号衰减完毕之前结束,因此采样截断在所难免.变迹法(窗函数法)可以抑制采样截断造成的伪峰,但会导致谱峰增宽.线性预测也有助于减小截断伪峰.采样截断最严重的场合,是在恒时演化类实验中.这类实验的间接维演化时间固定,因此间接维采样信号强度没有表观衰减.本研究提出的迭代软阈值方法(Iterative Soft Thresholding,IST)虽然因为调节参数困难而在一般场合中应用受限,但恒时演化类(Constant time,CT)NMR实验的间接维信号缺没有表观衰减,这为IST处理参数设置提供了简化条件.本研究通过数据模拟和实验数据,证明了IST是抑制CT-NMR实验中采样截断伪峰的有效方法,并与其它相关方法进行了对比.

Suppress Sampling Truncation Artifacts in Constant-time Type Nuclear Magnetic Resonance Experiments Using Iterative Soft Thresholding Method

Sampling truncation, i. e. sampling ends before signal decays to zero, introduces wiggle-like artifacts that impair the quality of nuclear magnetic resonance ( NMR) spectra. In multidimensional ( mD) NMR experiments, the first few hundred or less data points are commonly sampled in the indirect dimension, and the truncation is unavoidable. Apodization can suppress truncation artifacts with cost of line-broadening. Linear prediction is also beneficial to the reduction of truncation artifacts. The worst situation is in the constant time ( CT) type experiments, where the signal doesn ' t decay at all in the CT evolution dimension. In this contribution we proposed that, although iterative soft thresholding ( IST) was rarely used due to the difficult parameter tuning, it was particularly suitable to suppress the truncation artifacts in the CT type NMR experiments. The simulation and experiments were performed to show the performance of this method. And the processing result was compared with a method proposed recently.