Background

Nuclear Magnetic Resonance (NMR) is extensively utilized in research as a non-invasive technique for investigating molecular structures and composite components. The spatiotemporal encoding (SPEN) technique effectively accelerates multi-dimensional NMR experiments. In ultrafast SPEN NMR, the acquired data are divided into odd and even segments corresponding to the positive and negative gradients during the decoding stage, respectively. However, the interlaced Fourier transform (FT) method used to reconstruct a full-width spectrum from these segments often suffers from severe noise contamination, necessitating the development of a more effective spectrum reconstruction method.

Results

In this work, we analyze the noise amplification effect of the interlaced FT and find that the noise is most significant in two edge regions of the spectrum along the indirect dimension due to the relatively small time offset differences between odd and even segments in those regions. Consequently, we develop an iterative optimization method to obtain the full-width spectrum while mitigating the noise. The proposed method incorporates the odd and even data segments into an objective function with sparsity regularization to simplify the spectrum, which is then refined iteratively during the optimization. As a result, the reconstructed spectrum is significantly cleaner and maintains the full spectral width. Experimental results demonstrate a remarkable improvement in the readability and interpretability of SPEN data, evidenced by clearer signal peaks and reduced background noise.

Significance

The proposed reconstruction method provides a reliable approach for processing SPEN 2D NMR data, effectively addressing the low sensitivity issue in the joint reconstruction on odd and even segments. Combining SPEN's ultrafast data acquisition with the proposed high-sensitivity spectrum reconstruction method enhances the utility of NMR for more accurate molecular structure analysis and component identification in composite samples, particularly promoting NMR research in rapid reaction systems.

中文翻译：

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超快时空编码 2D NMR 波谱的增强光谱重建

 背景

核磁共振 （NMR） 作为一种研究分子结构和复合成分的非侵入性技术，被广泛用于研究。时空编码 （SPEN） 技术有效地加速了多维 NMR 实验。在超快 SPEN NMR 中，采集的数据在解码阶段被分成分别对应于正梯度和负梯度的奇数和偶数段。然而，用于从这些段重建全宽频谱的隔行傅里叶变换 （FT） 方法经常受到严重的噪声污染，因此需要开发一种更有效的频谱重建方法。

 结果

在这项工作中，我们分析了隔行扫描 FT 的噪声放大效应，发现由于这些区域中奇数段和偶数段之间的时间偏移差异相对较小，因此沿间接维度的频谱的两个边缘区域的噪声最为显着。因此，我们开发了一种迭代优化方法，以获得全宽频谱，同时减轻噪声。所提出的方法将奇数和偶数数据段合并到一个目标函数中，并进行稀疏正则化以简化频谱，然后在优化过程中迭代优化。因此，重建的光谱明显更清晰，并保持了完整的光谱宽度。实验结果表明，SPEN 数据的可读性和可解释性得到了显着改善，更清晰的信号峰值和更低的背景噪声证明了这一点。

 意义

所提出的重建方法为处理 SPEN 2D NMR 数据提供了一种可靠的方法，有效地解决了奇数段和偶数段联合重建中的低灵敏度问题。将 SPEN 的超快数据采集与提出的高灵敏度光谱重建方法相结合，增强了 NMR 在复合材料样品中更准确地进行分子结构分析和成分鉴定的实用性，特别是促进了快速反应系统中的 NMR 研究。