C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
Magn Reson Med. 2022 Feb;87(2):872-883. doi: 10.1002/mrm.29005. Epub 2021 Sep 14.
Current challenges of in vivo CEST imaging include overlapping signals from different pools. The overlap arises from closely resonating pools and/or the broad magnetization transfer contrast (MTC) from macromolecules. This study aimed to evaluate the feasibility of variable delay multipulse (VDMP) CEST to separately assess solute pools with different chemical exchange rates in the human brain in vivo, while mitigating the MTC.
VDMP saturation buildup curves were simulated for amines, amides, and relayed nuclear Overhauser effect. VDMP data were acquired from glutamate and bovine serum albumin phantoms, and from six healthy volunteers at 7T. For the in vivo data, MTC removal was performed via a three-pool Lorentzian fitting. Different B amplitudes and mixing times were used to evaluate CEST pools with different exchange rates.
The results show the importance of removing MTC when applying VDMP in vivo and the influence of B for distinguishing different pools. Finally, the optimal B and mixing times to effectively saturate slow- and fast-exchanging components are also reported. Slow-exchanging amides and rNOE components could be distinguished when using B = 1 μT and t = 10 ms and 40 ms, respectively. Fast-exchanging components reached the highest saturation when using a B = 2.8 μT and t = 0 ms.
VDMP is a powerful CEST-editing tool, exploiting chemical exchange-rate differences. After MTC removal, it allows separate assessment of slow- and fast-exchanging solute pools in in vivo human brain.
目前活体 CEST 成像面临的挑战包括来自不同池的重叠信号。这种重叠来自于紧密共振的池和/或来自大分子的宽磁化转移对比度（MTC）。本研究旨在评估可变延迟多脉冲（VDMP）CEST 的可行性，以分别评估体内人脑不同化学交换率的溶质池，同时减轻 MTC 的影响。
为胺、酰胺和中继核奥弗豪瑟效应模拟了 VDMP 饱和积累曲线。在 7T 下从谷氨酸和牛血清白蛋白模型以及六名健康志愿者中获取 VDMP 数据。对于体内数据，通过三池洛伦兹拟合去除 MTC。使用不同的 B 幅度和混合时间来评估具有不同交换率的 CEST 池。
结果表明，在体内应用 VDMP 时去除 MTC 的重要性以及 B 对区分不同池的影响。最后，还报告了有效饱和慢交换和快交换成分的最佳 B 和混合时间。当使用 B = 1 μT 和 t = 10 ms 和 40 ms 时，可以区分慢交换酰胺和 rNOE 成分。当使用 B = 2.8 μT 和 t = 0 ms 时，快交换成分达到最高饱和。
VDMP 是一种强大的 CEST 编辑工具，利用化学交换率差异。去除 MTC 后，它允许分别评估体内人脑的慢交换和快交换溶质池。
