Quantitative susceptibility mapping of the spine using in-phase echoes to initialize inhomogeneous field and R2*for the nonconvex optimization problem of fat-water separation
Quantitative susceptibility mapping of the spine using in-phase echoes to initialize inhomogeneous field and R2*for the nonconvex optimization problem of fat-water separation
复制标题
使用同相回波初始化非均匀场和 R2 的脊柱定量磁化率绘图，解决脂肪水分离的非凸优化问题
DOI：
10.1002/nbm.4156
复制
发表时间：
2019-08-19
影响因子：
2.9
通讯作者：
Wang, Yi
中科院分区：
文献类型：
--
作者：
Guo, Yihao;Liu, Zhe;Wang, Yi
从多回波梯度回波（GRE）序列的人体脊椎骨的定量磁化率映射（QSM）是具有挑战性的，因为椎骨中的脂肪和水的可比量使得难以解决非凸优化问题的脂肪-水分离（R2*-IDEAL）估计组织磁化率诱导的磁场。我们提出了一个同相（IP）回波初始化的R2*-理想的QSM在脊柱椎骨。招募10名健康人类受试者进行脊柱MRI。采用3D多回波GRE序列采集异相回波和IP回波。对于IP方法，通过分别拟合IP回波的幅度和相位估计的R2* 和场图用于初始化梯度搜索R2*-IDEAL以获得最终的R2*、场、水和脂肪图，并且最终的场图用于生成QSM。在模拟和体内数据上，将IP方法与现有的零方法（将场初始化为零）、VARPRO-GC（使用graphcuts的可变投影，但仍将场初始化为零）和SPURS（使用graphcuts进行初始化的同时相位展开和化学位移去除）进行比较。并将单峰脂肪模型与多峰脂肪模型进行了比较。单峰和多峰脂肪模型的QSM值无显著性差异，但不同初始化方法的QSM值有显著性差异。仿真结果表明，IP提供了最低的误差在字段地图。与Zero、VARPRO-GC和SPURS相比，所提出的IP方法在所有10名受试者中提供了显著改善的脊柱QSM。
Quantitative susceptibility mapping (QSM) of human spinal vertebrae from a multi-echo gradient-echo (GRE) sequence is challenging, because comparable amounts of fat and water in the vertebrae make it difficult to solve the nonconvex optimization problem of fat-water separation (R2*-IDEAL) for estimating the magnetic field induced by tissue susceptibility. We present an in-phase (IP) echo initialization of R2*-IDEAL for QSM in the spinal vertebrae. Ten healthy human subjects were recruited for spine MRI. A 3D multi-echo GRE sequence was implemented to acquire out-phase and IP echoes. For the IP method, the R2* and field maps estimated by separately fitting the magnitude and phase of IP echoes were used to initialize gradient search R2*-IDEAL to obtain final R2*, field, water, and fat maps, and the final field map was used to generate QSM. The IP method was compared with the existing Zero method (initializing the field to zero), VARPRO-GC (variable projection using graphcuts but still initializing the field to zero), and SPURS (simultaneous phase unwrapping and removal of chemical shift using graphcuts for initialization) on both simulation and in vivo data. The single peak fat model was also compared with the multi-peak fat model. There was no substantial difference on QSM between the single peak and multi-peak fat models, but there were marked differences among different initialization methods. The simulations demonstrated that IP provided the lowest error in the field map. Compared to Zero, VARPRO-GC and SPURS, the proposed IP method provided substantially improved spine QSM in all 10 subjects.