IEEE Trans Med Imaging. 2015 Feb;34(2):531-40. doi: 10.1109/TMI.2014.2361764. Epub 2014 Oct 8.
Quantitative susceptibility mapping (QSM) is a magnetic resonance imaging technique that reveals tissue magnetic susceptibility. It relies on having a high quality field map, typically acquired with a relatively long echo spacing and long final TE. Applications of QSM outside the brain require the removal of fat contributions to the total signal phase. However, current water/fat separation methods applied on typical data acquired for QSM suffer from three issues: inadequacy when using large echo spacing, over-smoothing of the field maps and high computational cost. In this paper, the general phase wrap and chemical shift problem is formulated using a single species fitting and is solved using graph cuts with conditional jump moves. This method is referred as simultaneous phase unwrapping and removal of chemical shift (SPURS). The result from SPURS is then used as the initial guess for a voxel-wise iterative decomposition of water and fat with echo asymmetric and least-squares estimation (IDEAL). The estimated 3-D field maps are used to compute QSM in body regions outside of the brain, such as the liver. Experimental results show substantial improvements in field map estimation, water/fat separation and reconstructed QSM compared to two existing water/fat separation methods on 1.5T and 3T magnetic resonance human data with long echo spacing and rapid field map variation.
定量磁敏感图（QSM）是一种揭示组织磁敏感性的磁共振成像技术。它依赖于高质量的磁场图，通常通过相对较长的回波间隔和长的最终 TE 来获取。QSM 在脑外的应用需要去除总信号相位中的脂肪贡献。然而，目前应用于典型 QSM 数据的水/脂分离方法存在三个问题：在使用大回波间隔时不充分、场图过度平滑和计算成本高。在本文中，使用单物种拟合来公式化一般的相位缠绕和化学位移问题，并使用具有条件跳跃移动的图切割来解决。这种方法被称为同时相位解缠和化学位移去除（SPURS）。然后，将 SPURS 的结果用作基于回波不对称和最小二乘估计（IDEAL）的体素分解水和脂肪的初始猜测。使用估计的 3D 磁场图在脑外的身体区域（如肝脏）计算 QSM。实验结果表明，与在具有长回波间隔和快速磁场图变化的 1.5T 和 3T 磁共振人体数据上的两种现有水/脂分离方法相比，在磁场图估计、水/脂分离和重建的 QSM 方面有了显著的改进。
