Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Magn Reson Med. 2012 Oct;68(4):1048-55. doi: 10.1002/mrm.24420. Epub 2012 Jul 26.
Frequency-labeled exchange transfer is a promising MRI technique for labeling and detecting exchanging protons of low-concentration solutes through the water signal. Early frequency-labeled exchange studies have used off-resonance excitation-based labeling schemes that are well suited to study rapidly exchanging protons or molecules far from the water resonance (e.g., water in paramagnetic contrast agents) or slowly exchanging protons close to the water resonance (e.g., some amide protons). However, off-resonance labeling is not efficient for rapidly exchanging protons close to water. Here, we show that a new frequency-labeled exchange labeling scheme with excitation pulses applied on the water resonance gives much higher exchange contrast for rapidly exchanging protons resonating close to the water resonance frequency. This labeling scheme is particularly suited for studying rapidly exchanging hydroxyl, amine, and imino protons in diamagnetic chemical exchange saturation transfer agents.
频标交换转移是一种很有前途的 MRI 技术，可通过水信号对低浓度溶质的交换质子进行标记和检测。早期的频标交换研究使用了基于失谐激励的标记方案，这些方案非常适合研究快速交换的质子或远离水共振的分子（例如顺磁对比剂中的水），或者研究靠近水共振的缓慢交换的质子（例如一些酰胺质子）。然而，失谐标记对于靠近水的快速交换质子效率不高。在这里，我们展示了一种新的频标交换标记方案，该方案使用施加在水共振上的激发脉冲，对靠近水共振频率的快速交换质子产生更高的交换对比度。这种标记方案特别适合研究顺磁化学交换饱和转移试剂中快速交换的羟基、胺基和亚氨基质子。
