Lee K J, Barber D C, Paley M N, Wilkinson I D, Papadakis N G, Griffiths P D
Department of Academic Radiology, Royal Hallamshire Hospital, University of Sheffield, Sheffield, UK.
Magn Reson Med. 2002 Apr;47(4):812-7. doi: 10.1002/mrm.10101.
This work describes the use of a method, based on the projection onto convex sets (POCS) algorithm, for reduction of the N/2 ghost in echo-planar imaging (EPI). In this method, ghosts outside the parent image are set to zero and a model k-space is obtained from the Fourier transform (FT) of the resulting image. The zeroth- and first-order phase corrections for each line of the original k-space are estimated by comparison with the corresponding line in the model k-space. To overcome problems of phase wrapping, the first-order phase corrections for the lines of the original k-space are estimated by registration with the corresponding lines in the model k-space. It is shown that applying these corrections will result in a reduction of the ghost, and that iterating the process will result in a convergence towards an image in which the ghost is minimized. The method is tested on spin-echo EPI data. The results show that the method is robust and remarkably effective, reducing the N/2 ghost to a level nearly comparable to that achieved with reference scans.
这项工作描述了一种基于凸集投影（POCS）算法的方法在回波平面成像（EPI）中减少N/2鬼影的应用。在该方法中，父图像之外的鬼影被设置为零，并从所得图像的傅里叶变换（FT）获得一个模型k空间。通过与模型k空间中的相应行进行比较，估计原始k空间每行的零阶和一阶相位校正。为了克服相位缠绕问题，通过与模型k空间中的相应行配准来估计原始k空间各行的一阶相位校正。结果表明，应用这些校正将减少鬼影，并且迭代该过程将导致收敛到鬼影最小化的图像。该方法在自旋回波EPI数据上进行了测试。结果表明，该方法稳健且非常有效，将N/2鬼影减少到几乎与参考扫描所达到的水平相当的程度。
