Li Xu, van Zijl Peter C M
F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA; Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Magn Reson Med. 2014 Sep;72(3):610-9. doi: 10.1002/mrm.25322. Epub 2014 Jun 27.
An increasing number of studies show that magnetic susceptibility in white matter fibers is anisotropic and may be described by a tensor. However, the limited head rotation possible for in vivo human studies leads to an ill-conditioned inverse problem in susceptibility tensor imaging (STI). Here we suggest the combined use of limiting the susceptibility anisotropy to white matter and imposing morphology constraints on the mean magnetic susceptibility (MMS) for regularizing the STI inverse problem.
The proposed MMS regularized STI (MMSR-STI) method was tested using computer simulations and in vivo human data collected at 3T. The fiber orientation estimated from both the STI and MMSR-STI methods was compared to that from diffusion tensor imaging (DTI).
Computer simulations show that the MMSR-STI method provides a more accurate estimation of the susceptibility tensor than the conventional STI approach. Similarly, in vivo data show that use of the MMSR-STI method leads to a smaller difference between the fiber orientation estimated from STI and DTI for most selected white matter fibers.
The proposed regularization strategy for STI can improve estimation of the susceptibility tensor in white matter.
越来越多的研究表明，白质纤维中的磁化率是各向异性的，并且可以用张量来描述。然而，在活体人体研究中可能的头部旋转受限，导致在磁化率张量成像（STI）中出现病态反问题。在此，我们建议将磁化率各向异性限制在白质范围内，并对平均磁化率（MMS）施加形态学约束，以正则化STI反问题。
使用计算机模拟以及在3T下收集的活体人体数据，对所提出的MMS正则化STI（MMSR-STI）方法进行测试。将从STI和MMSR-STI方法估计得到的纤维方向与从扩散张量成像（DTI）得到的纤维方向进行比较。
计算机模拟表明，MMSR-STI方法比传统的STI方法能更准确地估计磁化率张量。同样，活体数据表明，对于大多数选定的白质纤维，使用MMSR-STI方法会使从STI估计的纤维方向与从DTI估计的纤维方向之间的差异更小。
所提出的STI正则化策略可以改善白质中磁化率张量的估计。
