Abstract：
Quantitative Susceptibility Mapping (QSM) is a recent MRI-technique able to quantify the bulk magnetic susceptibility of myelin, iron, and calcium in the brain. Its variability across different acquisition parameters has prompted the need for standardisation across multiple centres and MRI vendors. However, a high level of agreement between repeated imaging acquisitions is equally important. With this study we aimed to assess the inter-scan repeatability of an optimised multi-echo GRE sequence in 28 healthy volunteers. We extracted and compared the susceptibility measures from the scan and rescan acquisitions across 7 bilateral brain regions (i.e., 14 regions of interest (ROIs)) relevant for neurodegeneration. Repeatability was first assessed while reconstructing QSM with a fixed number of echo times (i.e., 8). Excellent inter-scan repeatability was found for putamen, globus pallidus and caudate nucleus, while good performance characterised the remaining structures. An increased variability was instead noted for small ROIs like red nucleus and substantia nigra. Secondly, we assessed the impact exerted on repeatability by the number of echoes used to derive QSM maps. Results were impacted by this parameter, especially in smaller regions. Larger brain structures, on the other hand, showed more consistent performance. Nevertheless, with either 8 or 7 echoes we managed to obtain good inter-scan repeatability on almost all ROIs. These findings indicate that the designed acquisition/reconstruction protocol has wide applicability, particularly in clinical or research settings involving longitudinal acquisitions (e.g. rehabilitation studies).
摘要：
定量磁化率图（QSM）是一种最新的MRI技术，能够量化髓鞘的整体磁化率，铁,和大脑中的钙。它在不同采集参数之间的可变性促使需要在多个中心和MRI供应商之间进行标准化。然而,重复成像采集之间的高度一致性同样重要.通过这项研究，我们旨在评估28名健康志愿者中优化的多回波GRE序列的扫描间可重复性。我们从7个双侧大脑区域的扫描和重新扫描采集中提取并比较了易感性测量值(即，14个感兴趣区域(ROI))与神经变性相关。首先评估重复性，同时用固定数量的回声时间重建QSM(即，8).对于壳核，发现了极好的扫描间可重复性，苍白球和尾状核，而良好的性能表征其余的结构。相反，对于像红色核和黑质这样的小ROI，变异性增加。其次,我们通过用于导出QSM图的回波数量评估了对可重复性的影响.结果受此参数影响，尤其是在较小的地区。更大的大脑结构，另一方面,表现更加一致。然而，通过8或7个回波，我们能够在几乎所有ROI上获得良好的扫描间可重复性。这些发现表明，所设计的采集/重建协议具有广泛的适用性，特别是在涉及纵向采集的临床或研究环境中（例如康复研究）。
