Sharma Samir D, Artz Nathan S, Hernando Diego, Horng Debra E, Reeder Scott B
Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
Magn Reson Med. 2015 Feb;73(2):597-604. doi: 10.1002/mrm.25163. Epub 2014 Feb 28.
The purpose of this work was to improve the robustness of existing chemical shift encoded water-fat separation methods by incorporating object-based information of the B0 field inhomogeneity.
The primary challenge in water-fat separation is the estimation of phase shifts that arise from B0 field inhomogeneity, which is composed of the background field and susceptibility-induced field. The susceptibility-induced field can be estimated if the susceptibility distribution is known or can be approximated. In this work, the susceptibility distribution is approximated from the source images using the known susceptibility values of water, fat, and air. The field estimate is then demodulated from the source images before water-fat separation.
Chemical shift encoded source images were acquired in anatomical regions that are prone to water-fat swaps. The images were processed using algorithms from the ISMRM Fat-Water Toolbox, with and without the object-based field map information. The estimates were compared to examine the benefit of using the object-based field map information.
Multiple cases are shown in which water-fat swaps were avoided by using the object-based information of the B0 field map.
Object-based information of the B0 field may improve the robustness of existing chemical shift encoded water-fat separation methods.
本研究的目的是通过纳入基于对象的B0场不均匀性信息来提高现有化学位移编码水脂分离方法的稳健性。
水脂分离的主要挑战在于估计由B0场不均匀性引起的相移，B0场不均匀性由背景场和磁化率诱导场组成。如果已知或可以近似磁化率分布，则可以估计磁化率诱导场。在本研究中，利用水、脂肪和空气的已知磁化率值从源图像中近似得到磁化率分布。然后在水脂分离之前从源图像中解调场估计值。
在容易发生水脂交换的解剖区域采集化学位移编码源图像。使用ISMRM脂肪-水工具箱中的算法对图像进行处理，分别采用和不采用基于对象的场图信息。比较估计结果以检验使用基于对象的场图信息的益处。
展示了多个通过使用基于对象的B0场图信息避免水脂交换的案例。
基于对象的B0场信息可能会提高现有化学位移编码水脂分离方法的稳健性。
