Comprehensive chemical exchange saturation transfer (CEST) MRI

该项目是“超高磁场定量MR生物特征快速测绘”研究单元的一部分。CEST MRI是一种具有光谱信息的成像方法，极大地受益于7 T时更高的信噪比和更高的光谱分辨率。7 T CEST具有丰富的化学相关贡献信息，如pH、肌酸、谷氨酸、磷酸肌酸、糖胺聚糖（GAG）、蛋白质/肽含量、蛋白质结构以及脂质含量。CEST已经在肿瘤、中风和神经退行性疾病的成像诊断中显示出有希望的结果。然而，CEST MRI实际上不是一种单一的方法，而是可以选择多种不同的选项来进行不同的CEST标记。根据各自质子群的交换速率和频移，最佳CEST标记是不同的，打开由三重给出的参数（饱和偏移量，饱和振幅和饱和时间）的整个空间。到目前为止，由于扫描时间的限制，在临床研究中只研究了这个参数空间中的一个点。这个项目的目标是以一种全面的方式覆盖这个CEST参数空间，以便在一次扫描中可以获得大多数CEST权重。由于最近在快速采集（快照CEST）、特征减少和可能减少饱和时间方面的进步，这将成为可能。结合与5534研究单元的其他项目合作开发的方法，如欠采样采集、均匀pTx饱和、运动稳定采集和深度学习技术，一种全面的CEST方法旨在涵盖大多数CEST标记，并且作为MR生物签名扫描的一部分，在最短的扫描时间内提供最大的组织信息。因此，我们扩展并加速了7 T的CEST MRI，以达到临床可行但全面的CEST扫描。全面的CEST将有利于RU的临床研究问题的假设是显而易见的，例如，对于乳腺组织癌症风险分层，酰胺CEST检测的年龄相关性以及与GAG含量的相关性表明有可能更详细地表征纤维腺组织微观结构。在肌肉组织中，透析后pH值和尿素引起的CEST变化是预期的。对于神经变性，一个关键指标是脂质，它被证明有助于rNOE CEST信号，但蛋白质聚集和变性过程也被证明导致可检测的CEST变化。设想的全面CEST扫描包括所有这些标签，并探索未知的标签制度，以产生进一步的假设。

This project is part of the research unit “Fast Mapping of Quantitative MR biosignatures at Ultra-high Magnetic Field”. It focuses on extending, accelerating, and improving chemical exchange saturation transfer (CEST) MRI at 7 T. CEST MRI is an imaging method with spectroscopic information that greatly benefits from increased SNR and increased spectral resolution at 7 T. 7 T CEST is rich in information on several chemically relevant contributions such as pH, creatine, glutamate, phosphocreatine, glycosaminoglycans (GAG), protein/peptide content, protein structure, as well as lipid content. CEST has already shown promising diagnostic results in imaging of tumors, stroke, and neurodegeneration. However, CEST MRI is actually not one single method, but rather a variety of different options can be chosen for different CEST labeling. Depending on the exchange rate and frequency shift of the respective proton group the optimal CEST labeling is different, opening a whole space of parameters given by the triple (saturation offset, saturation amplitude, and the saturation time). Most often until now due to scan time limitations, only one point in this parameter space is investigated in clinical studies. The goal of this project is to cover this CEST parameter space in a comprehensive manner, so that most CEST-weightings are available within one single scan. This will be possible due to recent advancements in fast acquisition (snapshot CEST), feature reduction, and possible reduction of saturation times. In combination with methods developed in collaboration with other projects of the research unit 5534, such as undersampled acquisition, homogeneous pTx saturation, motion stable acquisition, and deep learning techniques, a comprehensive CEST method is aimed at that covers most CEST labelings and - as part of the MR biosignature scan - provides maximum tissue information in minimal scan time. Thus, we both extend and accelerate CEST MRI at 7 T to reach a clinically feasible, but comprehensive CEST scan. Hypotheses that comprehensive CEST will yield benefits for the clinical research questions of the RU are evident, e.g. for breast tissue cancer risk stratification, the detected age correlation of amide CEST, as well as correlations with GAG content indicates a potential for more detailed characterization of fibroglandular tissue microstructure. In muscle tissue, pH and urea induced CEST changes upon dialysis are expected. For neurodegeneration, a key indicator are lipids, which were shown to contribute to the rNOE CEST signal, but also protein aggregation and denaturation processes where shown to lead to detectable CEST changes. The envisioned comprehensive CEST scan includes all these labelings and explores yet unknown labeling regimes to generate further hypotheses.