Chang Hing-Chiu, Chen Nan-Kuei
Department of Diagnostic Radiology, The University of Hong Kong, Hong Kong; Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States.
Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States.
Magn Reson Imaging. 2016 Sep;34(7):974-9. doi: 10.1016/j.mri.2016.04.017. Epub 2016 Apr 22.
Diffusion-weighted imaging (DWI) obtained with interleaved echo-planar imaging (EPI) pulse sequence has great potential of characterizing brain tissue properties at high spatial-resolution. However, interleaved EPI based DWI data may be corrupted by various types of aliasing artifacts. First, inconsistencies in k-space data obtained with opposite readout gradient polarities result in Nyquist artifact, which is usually reduced with 1D phase correction in post-processing. When there exist eddy current cross terms (e.g., in oblique-plane EPI), 2D phase correction is needed to effectively reduce Nyquist artifact. Second, minuscule motion induced phase inconsistencies in interleaved DWI scans result in image-domain aliasing artifact, which can be removed with reconstruction procedures that take shot-to-shot phase variations into consideration. In existing interleaved DWI reconstruction procedures, Nyquist artifact and minuscule motion-induced aliasing artifact are typically removed subsequently in two stages. Although the two-stage phase correction generally performs well for non-oblique plane EPI data obtained from well-calibrated system, the residual artifacts may still be pronounced in oblique-plane EPI data or when there exist eddy current cross terms. To address this challenge, here we report a new composite 2D phase correction procedure, which effective removes Nyquist artifact and minuscule motion induced aliasing artifact jointly in a single step. Our experimental results demonstrate that the new 2D phase correction method can much more effectively reduce artifacts in interleaved EPI based DWI data as compared with the existing two-stage artifact correction procedures. The new method robustly enables high-resolution DWI, and should prove highly valuable for clinical uses and research studies of DWI.
采用交错回波平面成像（EPI）脉冲序列获得的扩散加权成像（DWI）在以高空间分辨率表征脑组织特性方面具有巨大潜力。然而，基于交错EPI的DWI数据可能会受到各种类型的混叠伪影的影响。首先，具有相反读出梯度极性的k空间数据中的不一致会导致奈奎斯特伪影，通常在后期处理中通过一维相位校正来减少。当存在涡流交叉项时（例如在斜平面EPI中），需要二维相位校正来有效减少奈奎斯特伪影。其次，交错DWI扫描中微小运动引起的相位不一致会导致图像域混叠伪影，可以通过考虑逐次相位变化的重建程序来消除。在现有的交错DWI重建程序中，奈奎斯特伪影和微小运动引起的混叠伪影通常分两个阶段依次去除。尽管两阶段相位校正对于从校准良好的系统获得的非斜平面EPI数据通常表现良好，但在斜平面EPI数据中或存在涡流交叉项时，残留伪影可能仍然很明显。为了应对这一挑战，我们在此报告一种新的复合二维相位校正程序，该程序可以在单个步骤中联合有效去除奈奎斯特伪影和微小运动引起的混叠伪影。我们的实验结果表明，与现有的两阶段伪影校正程序相比，新的二维相位校正方法可以更有效地减少基于交错EPI的DWI数据中的伪影。新方法有力地实现了高分辨率DWI，并且对于DWI的临床应用和研究应该具有很高的价值。
