Shif Mark, Zur Yuval, Lupulescu Adonis, He Tian, Montrazi Elton T, Frydman Lucio
Chemical and Biological Physics Department, Weizmann Institute, Rehovot, Israel.
Insightec Ltd, Tirat Carmel, Israel.
Nat Commun. 2025 Jul 1;16(1):5745. doi: 10.1038/s41467-025-61215-0.
NMR acquisitions based on Ernst-angle excitations are widely used for maximizing spectral sensitivity without compromising bandwidth or resolution. However, if relaxation times T, T are long and similar, as is often the case in liquids, steady-state free-precession (SSFP) experiments could provide higher sensitivity per (SNR). Although strong offset dependencies and poor spectral resolutions have impeded SSFP's analytical applications, this study reexplores if, when and how can phase-incremented (PI) SSFP schemes overcome these drawbacks. It is found that PI-SSFP can indeed provide a superior SNR than Ernst-angle FT-NMR acquisitions, but that achieving this requires using relatively large flip angles. This, however, can restrict PI-SSFP's spectral resolution and lead to distorted line shapes; to deal with this we introduce here a new SSFP outlook that overcomes this dichotomy. This outlook also leads to a new processing pipeline for PI-SSFP acquisitions, providing high spectral resolution even when utilizing relatively the large flip angles. The enhanced SNR that the ensuing method can provide over FT-based NMR counterparts, is demonstrated with a series of C and N investigations on organic compounds.
基于恩斯特角激发的核磁共振采集被广泛用于在不影响带宽或分辨率的情况下最大化光谱灵敏度。然而，如果弛豫时间T1、T2较长且相近，液体中通常就是这种情况，稳态自由进动（SSFP）实验每单位时间可能会提供更高的灵敏度（信噪比）。尽管强烈的偏移依赖性和较差的光谱分辨率阻碍了SSFP的分析应用，但本研究重新探讨了相位递增（PI）SSFP方案是否、何时以及如何能够克服这些缺点。研究发现，PI-SSFP确实可以提供比恩斯特角傅里叶变换核磁共振采集更高的信噪比，但要实现这一点需要使用相对较大的翻转角。然而，这可能会限制PI-SSFP的光谱分辨率并导致线形失真；为了解决这个问题，我们在此引入一种新的SSFP视角，它克服了这种二分法。这种视角还引出了一种用于PI-SSFP采集的新处理流程，即使在使用相对较大翻转角时也能提供高光谱分辨率。通过对有机化合物进行一系列碳和氮研究，证明了该后续方法相对于基于傅里叶变换的核磁共振方法所能提供的增强信噪比。
