Key Laboratory for Magnetic Resonance and Multimodality Imaging of Guangdong Province, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen University Town, Shenzhen, Guangdong, China.
F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
NMR Biomed. 2023 Jun;36(6):e4778. doi: 10.1002/nbm.4778. Epub 2022 Jun 20.
Magnetic resonance (MR) is a powerful technique for noninvasively probing molecular species in vivo but suffers from low signal sensitivity. Saturation transfer (ST) MRI approaches, including chemical exchange saturation transfer (CEST) and conventional magnetization transfer contrast (MTC), allow imaging of low-concentration molecular components with enhanced sensitivity using indirect detection via the abundant water proton pool. Several recent studies have shown the utility of chemical exchange relayed nuclear Overhauser effect (rNOE) contrast originating from nonexchangeable carbon-bound protons in mobile macromolecules in solution. In this review, we describe the mechanisms leading to the occurrence of rNOE-based signals in the water saturation spectrum (Z-spectrum), including those from mobile and immobile molecular sources and from molecular binding. While it is becoming clear that MTC is mainly an rNOE-based signal, we continue to use the classical MTC nomenclature to separate it from the rNOE signals of mobile macromolecules, which we will refer to as rNOEs. Some emerging applications of the use of rNOEs for probing macromolecular solution components such as proteins and carbohydrates in vivo or studying the binding of small substrates are discussed.
磁共振（MR）是一种强大的技术，可用于非侵入性地探测体内的分子种类，但信号灵敏度较低。饱和转移（ST）MRI 方法，包括化学交换饱和转移（CEST）和传统的磁化转移对比（MTC），允许使用通过丰富的水质子池进行间接检测来增强灵敏度，从而对低浓度的分子成分进行成像。最近的几项研究表明，源自溶液中可移动大分子中不可交换的碳结合质子的化学交换传递核 Overhauser 效应（rNOE）对比在水中的可用性饱和光谱（Z 谱）中。在本文中，我们描述了导致 rNOE 信号出现在水饱和谱（Z 谱）中的机制，包括来自可移动和不可移动分子源以及分子结合的机制。虽然很明显，MTC 主要是基于 rNOE 的信号，但我们继续使用经典的 MTC 命名法将其与可移动大分子的 rNOE 信号区分开来，我们将其称为 rNOEs。讨论了 rNOEs 在体内探测蛋白质和碳水化合物等生物大分子溶液成分或研究小分子底物结合的一些新兴应用。
