Robust 2D Phase Correction for Echo Planar Imaging Under a Tight Field-of-View
Robust 2D Phase Correction for Echo Planar Imaging Under a Tight Field-of-View
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DOI：
10.1002/mrm.22577
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发表时间：
2010-12-01
影响因子：
3.3
通讯作者：
Hinks, R. Scott
中科院分区：
文献类型：
--
作者：
Xu, Dan;King, Kevin F.;Hinks, R. Scott
奈奎斯特鬼影伪影是回波平面成像中的一个严重问题。这些伪影主要源于偶数和奇数回波图像之间的相位差，并且可以使用相位校正方法来消除或减少。常用的一维相位校正只能校正读出轴线上的相位差。因此，当沿读出和相位编码轴都存在相位差时，2D校正是必要的。然而，现有的2D方法有几个未解决的问题，影响了它们的实用性。这些问题包括未表征的噪声行为、未优化的相位估计导致的图像伪影、直接应用于部分k(Y)数据时的Gibbs振铃伪影，以及最严重的是紧视场(即，视场略小于物体大小)下的新图像伪影。所有这些问题都在本文中得到了解决。具体地，对噪声放大和相位估计误差的影响进行了理论分析，并研究了噪声和重影之间的权衡。在此基础上，提出了一种改进的多项式拟合法、联合零差处理和与小视场兼容的二维相位校正方法。各种结果表明，即使在倾斜扫描或交叉项涡流项显着的情况下，该方法也能稳健地生成没有奈奎斯特重影和其他图像伪影的图像。《医学杂志》：1800年-1813年。(C)2010年Wiley-Liss公司
Nyquist ghost artifacts are a serious issue in echo planar imaging. These artifacts primarily originate from phase difference between even and odd echo images and can be removed or reduced using phase correction methods. The commonly used 1D phase correction can only correct phase difference along readout axis. 2D correction is, therefore, necessary when phase difference presents along both readout and phase encoding axes. However, existing 2D methods have several unaddressed issues that affect their practicality. These issues include uncharacterized noise behavior, image artifact due to unoptimized phase estimation, Gibbs ringing artifact when directly applying to partial k(y) data, and most seriously a new image artifact under tight field-of-view (i.e., field-of-view slightly smaller than object size). All these issues are addressed in this article. Specifically, theoretical analysis of noise amplification and effect of phase estimation error is provided, and tradeoff between noise and ghost is studied. A new 2D phase correction method with improved polynomial fitting, joint homodyne processing and phase correction, compatibility with tight field-of-view is then proposed. Various results show that the proposed method can robustly generate images free of Nyquist ghosts and other image artifacts even in oblique scans or when cross-term eddy current terms are significant. Magn Reson Med 64:1800-1813, 2010. (C) 2010 Wiley-Liss, Inc.