Wang Jiun-Jie, Deichmann Ralf, Hsiao IngTsung, Liu HoLing, Wai YauYau, Wan YungLiang, Turner Robert, Ordidge Roger
Department of Medical Imaging and Radiological Sciences, ChangGung University, TaoYuan county 333, Taiwan.
Magn Reson Imaging. 2005 May;23(4):585-90. doi: 10.1016/j.mri.2005.02.005.
The multishot echo planar imaging sequence was often used in the high-resolution diffusion measurements. However, it is susceptible to motion artifacts because of the requirements of combining the raw data from different acquisitions into one complete k-space data set. Conventional solutions used cardiac gating but greatly extended the total acquisition time. Here we propose a selective averaging algorithm based on the information in the navigator echoes. The data were sampled continuously without cardiac gating. Contributions contaminated by motion were detected by a thresholding algorithm and were discarded during postprocessing. The data were then averaged in the modulus or complex format. Diffusion tensor imaging (DTI) data with isotropic spatial resolution were acquired in phantom as well as from two normal volunteers. The information in the navigator echoes proved to be a good indicator for the extent of motion contamination. Differences were noticed between modulus and complex averaging in DTI quantification, but both showed reduced artifact and improved signal-to-noise ratio.
多激发回波平面成像序列常用于高分辨率扩散测量。然而，由于需要将来自不同采集的原始数据组合成一个完整的k空间数据集，它容易受到运动伪影的影响。传统的解决方案采用心脏门控，但大大延长了总采集时间。在此，我们提出一种基于导航回波信息的选择性平均算法。数据在无心脏门控的情况下连续采样。通过阈值算法检测受运动污染的部分，并在后期处理中丢弃。然后对数据进行模或复数形式的平均。在体模以及两名正常志愿者身上采集了具有各向同性空间分辨率的扩散张量成像（DTI）数据。导航回波中的信息被证明是运动污染程度的良好指标。在DTI定量分析中，模平均和复数平均之间存在差异，但两者均显示伪影减少且信噪比提高。
