Sun Hongfu, Kate Mahesh, Gioia Laura C, Emery Derek J, Butcher Kenneth, Wilman Alan H
Department of Biomedical Engineering, University of Alberta, Edmonton, Canada.
Division of Neurology, Department of Medicine, University of Alberta, Edmonton, Canada.
Magn Reson Med. 2016 Sep;76(3):781-91. doi: 10.1002/mrm.25919. Epub 2015 Sep 28.
To investigate gradient-echo phase errors caused by intracranial hemorrhage (ICH) of low signal magnitude, and propose methods to reduce artifacts from phase errors in quantitative susceptibility mapping (QSM) of ICH.
Two QSM methods are proposed: (1) mask-inversion that masks the phase of low signal magnitude regions, and (2) ICH magnetic dipole field isolation followed by susceptibility superposition using multiple boundaries for background field removal. The reconstruction methods were tested in eight subjects with ICH using standard single-echo susceptibility-weighted imaging at 1.5 Tesla with 40 ms echo time. Different phase unwrapping algorithms were also compared.
Significant phase errors were evident inside ICHs with low signal magnitude. The mask-inversion method recovered susceptibility of ICH in numerical simulation and minimized phase error propagation in patients with ICH. The additional superposed dipole inversion process substantially suppressed and constrained streaking artifacts in all subjects. Using the proposed superposition method, ICH susceptibilities measured from long and short echo times were similar. Laplacian based phase unwrapping substantially underestimated the ICH dipole field as compared to a path-based method.
The proposed methods of mask-inversion as well as ICH isolation and superposition can substantially reduce artifacts in QSM of ICH. Magn Reson Med 76:781-791, 2016. © 2015 Wiley Periodicals, Inc.
研究低信号强度颅内出血（ICH）引起的梯度回波相位误差，并提出减少ICH定量磁化率成像（QSM）中相位误差伪影的方法。
提出了两种QSM方法：（1）掩膜反转，即对低信号强度区域的相位进行掩膜；（2）ICH磁偶极场隔离，随后使用多个边界进行背景场去除的磁化率叠加。在8名患有ICH的受试者中，使用1.5特斯拉、回波时间为40毫秒的标准单回波磁化率加权成像对重建方法进行了测试。还比较了不同的相位展开算法。
在低信号强度的ICH内部，明显存在显著的相位误差。掩膜反转方法在数值模拟中恢复了ICH的磁化率，并将ICH患者中的相位误差传播降至最低。额外的叠加偶极反转过程在所有受试者中都显著抑制并限制了条纹伪影。使用所提出的叠加方法，从长回波时间和短回波时间测量的ICH磁化率相似。与基于路径的方法相比，基于拉普拉斯的相位展开大大低估了ICH偶极场。
所提出的掩膜反转以及ICH隔离和叠加方法可以显著减少ICH的QSM中的伪影。《磁共振医学》76:781 - 791，2016年。©2015威利期刊公司。
