Department of Integrated Health Sciences, Nagoya University Graduate School of Medicine, Japan; Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Japan.
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Neurology, Nagoya City University Graduate School of Medical Sciences, Japan.
Neuroimage. 2024 Aug 1;296:120676. doi: 10.1016/j.neuroimage.2024.120676. Epub 2024 Jun 7.
To separate the contributions of paramagnetic and diamagnetic sources within a voxel, a magnetic susceptibility source separation method based solely on gradient-echo data has been developed. To measure the opposing susceptibility sources more accurately, we propose a novel single-orientation quantitative susceptibility mapping method with adaptive relaxometric constant estimation (QSM-ARCS) for susceptibility source separation. Moreover, opposing susceptibilities and their anisotropic effects were determined in healthy volunteers in the white matter. Multiple spoiled gradient echo and diffusion tensor imaging of ten healthy volunteers was obtained using a 3 T magnetic resonance scanner. After the opposing susceptibility and fractional anisotropy (FA) maps had been reconstructed, the parametric maps were spatially normalized. To evaluate the agreements of QSM-ARCS against the susceptibility source separation method using R2 and R2* maps (χ-separation) by Bland-Altman plots, the opposing susceptibility values were measured using white and deep gray matter atlases. We then evaluated the relationships between the opposing susceptibilities and FAs in the white matter and used a field-to-fiber angle to assess the fiber orientation dependencies of the opposing susceptibilities. The susceptibility maps in QSM-ARCS were successfully reconstructed without large artifacts. In the Bland-Altman analyses, the opposing QSM-ARCS susceptibility values excellently agreed with the χ-separation maps. Significant inverse and proportional correlations were observed between FA and the negative and positive susceptibilities estimated by QSM-ARCS. The fiber orientation dependencies of the negative susceptibility represented a nonmonotonic feature. Conversely, the positive susceptibility increased linearly with the fiber angle with respect to the B0 field. The QSM-ARCS could accurately estimate the opposing susceptibilities, which were identical values of χ-separation, even using gradient echo alone. The opposing susceptibilities might offer direct biomarkers for assessment of the myelin and iron content in glial cells and, through the underlying magnetic sources, provide biologic insights toward clinical transition.
为了在体素内分离顺磁和抗磁性源的贡献，开发了一种仅基于梯度回波数据的磁化率源分离方法。为了更准确地测量相反的磁化率源，我们提出了一种新颖的单方向定量磁化率映射方法，具有自适应弛豫常数估计（QSM-ARCS）用于磁化率源分离。此外，在健康志愿者的白质中确定了相反的磁化率及其各向异性效应。使用 3T 磁共振扫描仪对 10 名健康志愿者进行了多次扰动脉冲梯度回波和弥散张量成像。在重建了相反的磁化率和各向异性分数（FA）图后，对参数图进行了空间归一化。为了通过 Bland-Altman 图评估 QSM-ARCS 与使用 R2 和 R2* 图（χ-分离）的磁化率源分离方法的一致性，使用白质和深部灰质图谱测量了相反的磁化率值。然后，我们评估了白质中相反磁化率与 FA 之间的关系，并使用场到纤维角评估了相反磁化率的纤维方向依赖性。在没有大伪影的情况下成功重建了 QSM-ARCS 的磁化率图。在 Bland-Altman 分析中，QSM-ARCS 的相反磁化率值与 χ-分离图极好地一致。FA 与 QSM-ARCS 估计的负磁化率和正磁化率之间存在显著的反相关和比例关系。负磁化率的纤维方向依赖性呈非单调特征。相反，正磁化率随纤维角相对于 B0 场线性增加。即使仅使用梯度回波，QSM-ARCS 也可以准确估计相反的磁化率，其值与 χ-分离相同。相反的磁化率可能为评估神经胶质细胞的髓鞘和铁含量提供直接的生物标志物，并通过潜在的磁源为临床转化提供生物学见解。
