Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
Magn Reson Med. 2019 Apr;81(4):2315-2329. doi: 10.1002/mrm.27555. Epub 2018 Oct 26.
To develop a prospective baseline enhancement that compensates for intermingled background effects in Z-spectra to achieve sensitivity enhancement of peaks related to CEST and nuclear Overhauser effect.
An MRI sequence-specific compensation of background effects is achieved through variation of the pulsed saturation power, , with the chemical shift, . After a "scout acquisition" of a standard Z-spectrum, the background is modeled through an appropriate spin system. Subsequently, an optimization procedure yields values that compensate for background contributions yielding a flat baseline. Contributions from metabolites not considered in the optimization procedure are enhanced as distinct perturbations to the baseline. For experimental verification, mapping of the lactate concentration in the presence of cross-linked bovine serum albumin was performed in phantoms at 7 T. As proof of concept, explorative experiments were performed in healthy human subjects at 3 T.
Nuisance contributions from direct water saturation, macromolecular magnetization transfer, and exchanging background protons were successfully removed from the Z-spectrum in phantoms and in brain tissue. The lactate methyl, methine, and hydroxyl peaks were readily observable in vitro. The peak areas correlated linearly with known concentrations. Improvement of the detection limit was achieved by a sparse distribution of saturation frequencies, allowing for more efficient signal averaging.
An optimization framework for high-resolution metabolite mapping by means of CEST/nuclear Overhauser effect was developed. It offers full flexibility to select spin-pool moieties, whose influence on the Z-spectrum will be compensated. Deviations from this background model will provide a contrast at the respective offset frequencies.
开发一种前瞻性的基线增强方法，以补偿 Z 谱中混杂的背景效应，从而提高与 CEST 和核 Overhauser 效应相关的峰的灵敏度。
通过改变脉冲饱和功率 与化学位移 的比值，可以实现 MRI 序列特异性的背景效应补偿。在标准 Z 谱的“侦察采集”之后，通过适当的自旋系统对背景进行建模。随后，通过优化程序得到 值，以补偿背景贡献，从而获得平坦的基线。未在优化过程中考虑的代谢物的贡献会增强为基线的明显扰动。为了实验验证，在 7T 下的体模中进行了存在交联牛血清白蛋白的乳酸浓度的映射。作为概念验证，在 3T 下对健康人体进行了探索性实验。
直接水饱和、大分子磁化转移和交换背景质子的干扰贡献在体模和脑组织的 Z 谱中被成功去除。在体外，乳酸的甲基、亚甲基和羟基峰很容易观察到。峰面积与已知浓度呈线性相关。通过稀疏分布饱和频率来提高检测限，允许更有效地进行信号平均，从而实现了检测限的提高。
开发了一种基于 CEST/nuclear Overhauser 效应的高分辨率代谢物映射的优化框架。它提供了充分的灵活性来选择自旋池基团，其对 Z 谱的影响将得到补偿。偏离此背景模型将在相应的偏移频率处提供对比度。
