Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts, USA.
Department of Radiology, 3rd Affiliated Hospital, Zhengzhou University, Henan, China.
Magn Reson Med. 2017 Dec;78(6):2307-2314. doi: 10.1002/mrm.26959. Epub 2017 Oct 13.
Chemical exchange saturation transfer (CEST) MRI has shown promise in tissue characterization in diseases like stroke and tumor. However, in vivo CEST imaging such as amide proton transfer (APT) MRI is challenging because of concomitant factors such as direct water saturation, macromolecular magnetization transfer, and nuclear overhauser effect (NOE), which lead to a complex contrast in the commonly used asymmetry analysis (MTRasym). Here, we propose a direct saturation-corrected CEST (DISC-CEST) analysis for simplified decoupling and quantification of in vivo CEST effects.
CEST MRI and relaxation measurements were carried out on a classical 2-pool creatine-gel CEST phantom and normal rat brains (N = 6) and a rat model of glioma (N = 8) at 4.7T. The proposed DISC-CEST quantification was carried out and compared with conventional MTRasym and the original three-offset method.
We demonstrated that the DISC-CEST contrast in the phantom had much stronger correlation with MTRasym than the three-offset method, which showed substantial underestimation. In normal rat brains, the DISC-CEST approach revealed significantly stronger APT effect in gray matter and higher NOE effect in white matter. Furthermore, the APT and NOE maps derived from DISC-CEST showed significantly higher APT effect in the tumors than contralateral normal tissue but no apparent difference in NOE.
The proposed DISC-CEST method, by correction of nonlinear direct water saturation effect, serves as a promising alternative to both the commonly used MTRasym and the simplistic three-offset analyses. It provides simple yet reliable in vivo CEST quantification such as APT and NOE mapping in brain tumor, which is promising for clinical translation. Magn Reson Med 78:2307-2314, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
化学交换饱和传递（CEST）MRI 在中风和肿瘤等疾病的组织特征方面显示出良好的效果。然而，由于直接水饱和、大分子磁化转移和核奥弗豪瑟效应（NOE）等伴随因素，活体 CEST 成像（如酰胺质子转移（APT）MRI）具有挑战性，这导致在常用的不对称分析（MTRasym）中产生复杂的对比。在这里，我们提出了一种直接饱和校正的 CEST（DISC-CEST）分析方法，用于简化活体 CEST 效应的解耦和定量。
在 4.7T 上对经典的 2 池肌酸凝胶 CEST 幻影和正常大鼠脑（N=6）和大鼠胶质瘤模型（N=8）进行了 CEST MRI 和弛豫测量。进行了所提出的 DISC-CEST 定量，并与常规 MTRasym 和原始三偏移方法进行了比较。
我们证明，幻影中的 DISC-CEST 对比与 MTRasym 具有更强的相关性，而三偏移方法则显示出明显的低估。在正常大鼠脑中，DISC-CEST 方法显示灰质中 APT 效应明显增强，白质中 NOE 效应更高。此外，来自 DISC-CEST 的 APT 和 NOE 图显示肿瘤中的 APT 效应明显高于对侧正常组织，但 NOE 没有明显差异。
所提出的 DISC-CEST 方法通过校正非线性直接水饱和效应，是常用的 MTRasym 和简单的三偏移分析的一种很有前途的替代方法。它提供了简单而可靠的活体 CEST 定量，如脑肿瘤中的 APT 和 NOE 映射，这对于临床转化很有希望。磁共振医学 78：2307-2314，2017。© 2017 年国际磁共振学会。
