Irfanoglu M O, Walker L, Sammet S, Pierpaoli C, Machiraju R
Computer Sciences and Engineering Department, The Ohio State University, USA.
Med Image Comput Comput Assist Interv. 2011;14(Pt 2):174-81. doi: 10.1007/978-3-642-23629-7_22.
In this paper, we propose a novel method for correcting the geometric distortions in diffusion weighted images (DWI) obtained with echo planar imaging (EPI) protocol. Our EPI distortion correction approach employs a deformable registration framework with the B-splines transformation, where the control point distributions are non-uniform and functions of the expected norm of the spatial distortions. In our framework, the amount of distortions are first computed by estimating the B(0) fieldmap from an initial segmentation of a distortion-free structural image and tissue susceptibility models. Fieldmap estimates are propagated to obtain expected spatial distortion maps, which are used in the sampling of active B-spline control points. This transformation is flexible in locations with large distortion expectations, yet with relatively few degrees-of-freedom and does not suffer from local optima convergence and hence does not distort anatomically salient locations. Results indicate that with the proposed correction scheme, tensor derived scalar maps and fiber tracts of the same subject computed from data acquired with different phase encoding directions provide better coherency and consistency compared traditional registration based approaches.
在本文中，我们提出了一种新颖的方法，用于校正采用回波平面成像（EPI）协议获取的扩散加权图像（DWI）中的几何失真。我们的EPI失真校正方法采用了带有B样条变换的可变形配准框架，其中控制点分布是非均匀的，并且是空间失真预期范数的函数。在我们的框架中，首先通过从无失真结构图像的初始分割和组织磁化率模型估计B(0)场图来计算失真量。场图估计值被传播以获得预期的空间失真图，该图用于活动B样条控制点的采样。这种变换在具有大失真预期的位置处具有灵活性，但自由度相对较少，并且不会受到局部最优收敛的影响，因此不会扭曲解剖学上显著的位置。结果表明，使用所提出的校正方案，从以不同相位编码方向采集的数据计算得到的同一受试者的张量衍生标量图和纤维束，与传统的基于配准的方法相比，具有更好的一致性和连贯性。
