Vanderbilt University Institute of Imaging Science, Nashville, Tennessee.
Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee.
Magn Reson Med. 2018 Dec;80(6):2609-2617. doi: 10.1002/mrm.27365. Epub 2018 May 25.
To test the ability of a novel pulse sequence applied in vivo at 3 Tesla to separate the contributions to the water signal from amide proton transfer (APT) and relayed nuclear Overhauser enhancement (rNOE) from background direct water saturation and semisolid magnetization transfer (MT). The lack of such signal source isolation has confounded conventional chemical exchange saturation transfer (CEST) imaging.
We quantified APT and rNOE signals using a chemical exchange rotation transfer (CERT) metric, MTR . A range of duty cycles and average irradiation powers were applied, and results were compared with conventional CEST analyses using asymmetry (MTR ) and extrapolated magnetization transfer (EMR).
Our results indicate that MTR is more specific than MTR and, because it requires as few as 3 data points, is more rapid than methods requiring a complete Z-spectrum, such as EMR. In white matter, APT (1.5 ± 0.5%) and rNOE (2.1 ± 0.7%) were quantified by using MTR with a 30% duty cycle and a 0.5-µT average power. In addition, our results suggest that MTR is insensitive to B inhomogeneity, further magnifying its speed advantage over CEST metrics that require a separate B measurement. However, MTR still has nontrivial sensitivity to B inhomogeneities.
We demonstrated that MTR is an alternative metric to evaluate APT and rNOE, which is fast, robust to B inhomogeneity, and easy to process.
测试一种新的脉冲序列在 3T 下体内应用的能力，以分离酰胺质子转移 (APT) 和中继核奥弗豪瑟增强 (rNOE) 对背景直接水饱和和半固态磁化转移 (MT) 的贡献。缺乏这种信号源分离一直困扰着传统的化学交换饱和转移 (CEST) 成像。
我们使用化学交换旋转转移 (CERT) 度量，MTR 来量化 APT 和 rNOE 信号。应用了一系列占空比和平均辐照功率，并将结果与使用不对称性 (MTR) 和外推磁化转移 (EMR) 的传统 CEST 分析进行比较。
我们的结果表明，MTR 比 MTR 更具特异性，并且由于它只需要 3 个数据点，因此比需要完整 Z 谱的方法（如 EMR）更快。在白质中，使用占空比为 30%和平均功率为 0.5-µT 的 MTR 可以量化 APT（1.5±0.5%）和 rNOE（2.1±0.7%）。此外，我们的结果表明，MTR 对 B 不均匀性不敏感，进一步放大了其相对于需要单独 B 测量的 CEST 度量的速度优势。然而，MTR 对 B 不均匀性仍然具有相当大的敏感性。
我们证明了 MTR 是评估 APT 和 rNOE 的替代度量，它快速、对 B 不均匀性具有鲁棒性且易于处理。
