Nuclear Overhauser enhancement (NOE) imaging in the human brain at 7T.
Nuclear Overhauser enhancement (NOE) imaging in the human brain at 7T.
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DOI：
10.1016/j.neuroimage.2013.03.047
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发表时间：
2013-08-15
期刊：
影响因子：
5.7
通讯作者：
van Zijl, Peter C. M.
中科院分区：
文献类型：
--
作者：
Jones, Craig K.;Huang, Alan;Xu, Jiadi;Edden, Richard A. E.;Schaer, Michael;Hua, Jun;Oskolkov, Nikita;Zaca, Domenico;Zhou, Jinyuan;McMahon, Michael T.;Pillai, Jay J.;van Zijl, Peter C. M.
关键词：
化学交换饱和转移（CEST）是一种磁化转移（MT）技术，通过水信号间接检测可交换质子池。CEST MRI主要集中在CEST光谱中来自水的可交换质子低场（较高频率）的信号上。低功率射频（RF）脉冲可以缓慢地使质子饱和，而传统的基于半固体的MT造影剂（MTC）的干扰最小。当这样做时，饱和转移信号从水的高场显现出来，这是不可交换的脂肪族和烯属质子的频率范围。这种信号的可见性表明存在水信号的中继传递机制，而它们的有限宽度反映了这些信号可能是由于移动的溶质。在蛋白质体模和人脑中显示，这些信号比常规CEST以移动的大分子（如蛋白质/肽和脂质）中分子内核奥弗豪泽增强（NOE）效应的典型速率建立得更慢。这些基于NOE的饱和转移信号显示pH依赖性，表明该过程是高分辨率NMR蛋白质研究中众所周知的交换中继NOE的逆，因此是中继NOE CEST过程。当用低功率脉冲CEST方法研究6名正常志愿者时，中继NOE CEST效应大约是CEST效应低场的两倍，并且在白色物质中比灰质中大。这种来自水的NOE对比高场提供了一种研究组织中移动的大分子的方法。关于肿瘤患者的第一个数据显示，中继NOE和CEST酰胺质子信号减少，导致磁化传递比不对称性增加，从而深入了解先前报道的酰胺质子转移（APT）在肿瘤中的作用。
Chemical exchange saturation transfer (CEST) is a magnetization transfer (MT) technique to indirectly detect pools of exchangeable protons through the water signal. CEST MRI has focused predominantly on signals from exchangeable protons downfield (higher frequency) from water in the CEST spectrum. Low power radiofrequency (RF) pulses can slowly saturate protons with minimal interference of conventional semi-solid based MT contrast (MTC). When doing so, saturation-transfer signals are revealed upfield from water, which is the frequency range of non-exchangeable aliphatic and olefinic protons. The visibility of such signals indicates the presence of a relayed transfer mechanism to the water signal, while their finite width reflects that these signals are likely due to mobile solutes. It is shown here in protein phantoms and the human brain that these signals build up slower than conventional CEST, at a rate typical for intramolecular nuclear Overhauser enhancement (NOE) effects in mobile macromolecules such as proteins/peptides and lipids. These NOE-based saturation transfer signals show a pH dependence, suggesting that this process is the inverse of the well-known exchange-relayed NOEs in high resolution NMR protein studies, thus an relayed-NOE CEST process. When studying 6 normal volunteers with a low-power pulsed CEST approach, the relayed-NOE CEST effect was about twice as large as the CEST effects downfield and larger in white matter than gray matter. This NOE contrast upfield from water provides a way to study mobile macromolecules in tissue. First data on a tumor patient show reduction in both relayed NOE and CEST amide proton signals leading to an increase in magnetization transfer ratio asymmetry, providing insight into previously reported amide proton transfer (APT) effects in tumors.
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