Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Germany.
High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.
Magn Reson Med. 2019 Aug;82(2):693-705. doi: 10.1002/mrm.27762. Epub 2019 Apr 19.
To mitigate inhomogeneity in quantitative CEST MRI at ultra-high magnetic field strengths (B ≥ 7 Tesla) using a parallel transmit system.
Multiple interleaved mode saturation employs interleaving of 2 complementary phase sets during the saturation pulse train. Phase differences of 45° (first mode) and 90° (second mode) between 2 adjacent transmitter coil channels are used. The influence of the new saturation scheme on the CEST contrast was analyzed using Bloch-McConnell simulations. The presented method was verified in phantom and in vivo measurements of the healthy human brain. The relayed nuclear Overhauser effect was evaluated, and the inverse magnetic transfer ratio metric was calculated. Results were compared to a published correction method. All measurements were conducted on a whole-body 7 Tesla MRI system using an 8 transmitter and 32 receiver channel head coil.
Simulations showed that the inverse magnetic transfer ratio metric contrast of relayed nuclear Overhauser effect shows a smaller dependency on the relative amplitudes of the 2 different modes than the contrasts of Cr and amide proton transfer. Measurements of an egg white phantom showed markedly improved homogeneity compared to the uncorrected inverse magnetic transfer ratio metric (relayed nuclear Overhauser effect) images and slightly improved results compared to corrected images. In vivo multiple interleaved mode saturation images showed similar contrast compared to corrected images.
Multiple interleaved mode saturation can be used as a simple method to mitigate inhomogeneity effects in CEST MRI at ultra-high magnetic field strengths. Compared to previous correction methods, acquisition time can be reduced because an additional scan, usually required for correction, can be omitted.
在超高磁场强度（B≥7 特斯拉）下使用并行传输系统减轻定量 CEST MRI 的不均匀性。
多交错模式饱和在饱和脉冲序列期间交错使用 2 个互补的相位集。使用两个相邻发射线圈通道之间的 45°（第一模式）和 90°（第二模式）的相位差。使用 Bloch-McConnell 模拟分析了新饱和方案对 CEST 对比度的影响。在健康人脑的体模和体内测量中验证了所提出的方法。评估了中继核奥弗豪瑟效应，并计算了逆磁转移比度量。结果与已发表的一种校正方法进行了比较。所有测量均在全身 7 特斯拉 MRI 系统上进行，使用 8 个发射和 32 个接收通道头部线圈。
模拟表明，与 Cr 和酰胺质子转移的对比度相比，中继核奥弗豪瑟效应的逆磁转移比度量对比度对 2 种不同模式的相对幅度的依赖性较小。蛋清体模的测量结果表明，与未校正的逆磁转移比度量（中继核奥弗豪瑟效应）图像相比，均匀性得到了显著改善，与校正图像相比，结果略有改善。体内多交错模式饱和图像与校正图像的对比度相似。
多交错模式饱和可作为一种简单的方法，用于减轻超高磁场强度下 CEST MRI 的不均匀性效应。与以前的校正方法相比，可以减少采集时间，因为可以省略通常用于校正的附加扫描。
