Correction for geometric distortion and N/2 ghosting in EPI by phase labeling for additional coordinate encoding (PLACE)
Correction for geometric distortion and N/2 ghosting in EPI by phase labeling for additional coordinate encoding (PLACE)
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DOI：
10.1002/mrm.21187
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发表时间：
2007-04-01
影响因子：
3.3
通讯作者：
Ye, Frank Q.
中科院分区：
文献类型：
--
作者：
Xiang, Qing-San;Ye, Frank Q.
回波平面成像（EPI）容易受到几何失真和N/2重影的影响。这些文物可以用直观的k-t空间工具进行分析，在这里，我们提出了一个简单的方法来校正。在稍微修改的附加EPI采集中，我们通过向相位编码（PE）梯度添加一个小区域来对具有k（y）移位的k-t空间进行采样。在物理上，添加的梯度区域在对象上创建相对相位斜坡，并直接将每个体素的未失真原始y坐标编码为两个失真复杂图像之间的相位差，这种方法称为“用于附加坐标编码的相位标记”（PLACE）。然后，相位信息用于将误映射的信号映射回其原始位置，以进行几何和强度校正。扩展的复数据矩阵的平滑有效地降低了微分相位图中的噪声，并允许亚像素扭曲。还可以对两个采集的图像进行平均以有效地抑制N/2重影。两种伪影的有效校正可以通过三次采集来实现。这些采集还可以用作参考扫描，以校正时间序列中所有图像上的几何失真和/或N/2个重影伪影。该技术已在体模和动物研究中得到成功证明。
Echo-planar imaging (EPI) is vulnerable to geometric distortion and N/2 ghosting. These artifacts can be analyzed with an intuitive k-t space tool, and here we propose a simple method for their correction. In a slightly modified additional EPI acquisition, we sample the k-t space with a shift in k(y) by adding a small area to the phase-encoding (PE) gradient. Physically, the added gradient area creates a relative phase ramp across the object and directly encodes the undistorted original y-coordinate of each voxel into a phase difference between two distorted complex images, in a method called "phase labeling for additional coordinate encoding" (PLACE). The phase information is then used to map the mismapped signals back to their original locations for geometric and intensity correction. Smoothing of expanded complex data matrix effectively reduces noise in the differential phase map and allows subpixel warping. The two acquired images can also be averaged to effectively suppress the N/2 ghost. Efficient correction for both artifacts can be achieved with three acquisitions. These acquisitions can also serve as reference scans to correct for geometric distortion and/or N/2 ghost artifacts on all images in a time series. The technique was successfully demonstrated in phantom and animal studies.