Medical Physics Group, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University Jena, Philosophenweg 3, 07743 Jena, Germany.
University Clinic and Outpatient Clinic for Radiology, Department for Radiation Medicine, University Hospital Halle (Saale), Ernst-Grube-Str. 40, 06120 Halle (Saale), Germany.
Neuroimage Clin. 2022;35:103059. doi: 10.1016/j.nicl.2022.103059. Epub 2022 May 28.
Quantitative susceptibility mapping (QSM) has been successfully applied to study changes in deep grey matter nuclei as well as in lesional tissue, but its application to white matter has been complicated by the observed orientation dependence of gradient echo signal. The anisotropic susceptibility tensor is thought to be at the origin of this orientation dependence, and magnetic susceptibility anisotropy (MSA) derived from this tensor has been proposed as a marker of the state and integrity of the myelin sheath and may therefore be of particular interest for the study of demyelinating pathologies such as multiple sclerosis (MS). Reconstruction of the susceptibility tensor, however, requires repeated measurements with multiple head orientations, rendering the approach impractical for clinical applications. In this study, we combined single-orientation QSM with fibre orientation information to assess apparent MSA in three white matter tracts, i.e., optic radiation (OR), splenium of the corpus callosum (SCC), and superior longitudinal fascicle (SLF), in two cohorts of 64 healthy controls and 89 MS patients. The apparent MSA showed a significant decrease in optic radiation in the MS cohort compared with healthy controls. It decreased in the MS cohort with increasing lesion load in OR and with disease duration in the splenium. All of this suggests demyelination in normal appearing white matter. However, the apparent MSA observed in the SLF pointed to potential systematic issues that require further exploration to realize the full potential of the presented approach. Despite the limitations of such single-orientation ROI-specific estimation, we believe that our clinically feasible approach to study degenerative changes in WM is worthy of further investigation.
定量磁化率映射（QSM）已成功应用于研究深部灰质核以及病变组织的变化，但由于梯度回波信号的观察到的各向异性，其在白质中的应用变得复杂。各向异性磁化率张量被认为是这种各向异性的起源，并且从该张量导出的磁化率各向异性（MSA）被提出作为髓鞘状态和完整性的标志物，因此可能特别适合研究脱髓鞘病变，如多发性硬化症（MS）。然而，磁化率张量的重建需要使用多个头方向进行重复测量，这使得该方法在临床应用中不切实际。在这项研究中，我们将单方向 QSM 与纤维方向信息相结合，以评估三个白质束（即视辐射（OR）、胼胝体压部（SCC）和上纵束（SLF））中的表观 MSA 在两个队列的 64 名健康对照者和 89 名 MS 患者中。与健康对照组相比，MS 队列中的视辐射中的表观 MSA 明显降低。在 OR 中，随着病变负荷的增加，在 SCC 中，随着疾病持续时间的增加，表观 MSA 减少。所有这些都表明正常外观的白质中有脱髓鞘。然而，在 SLF 中观察到的表观 MSA 表明存在潜在的系统问题，需要进一步探索以实现所提出方法的全部潜力。尽管这种单方向 ROI 特定估计存在局限性，但我们相信，我们对 WM 退行性变化进行研究的临床可行方法值得进一步研究。
