Jaffer F A, Wen H, Jezzard P, Balaban R S, Wolff S D
Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1061, USA.
J Magn Reson Imaging. 1997 Nov-Dec;7(6):1122-31. doi: 10.1002/jmri.1880070627.
Echo-planar imaging (EPI) is sensitive to motion despite its rapid data acquisition rate. Compared with traditional imaging techniques, it is more sensitive to motion or flow in the phase-encode direction, which can cause image artifacts such as ghosting, misregistration, and loss of spatial resolution. Consequently, EPI of dynamic structures (eg, the cardiovascular system) could benefit from methods that eliminate these artifacts. In this paper, two methods of artifact reduction for motion in the phase-encode direction are evaluated. First, the k-space trajectory is evaluated by comparing centric with top-down ordered sequences. Next, velocity gradient moment nulling (GMN) of the phase-encode direction is evaluated for each trajectory. Computer simulations and experiments in flow phantoms and rabbits in vivo show that uncompensated centric ordering produces the highest image quality. This is probably due to a shorter readout duration, which reduces T2* relaxation losses and off-resonance effects, and to the linear geometry of phantoms and vessels, which can obscure centric blurring artifacts.
回波平面成像（EPI）尽管数据采集速度很快，但对运动很敏感。与传统成像技术相比，它对相位编码方向上的运动或流动更敏感，这可能会导致图像伪影，如重影、配准错误和空间分辨率丧失。因此，动态结构（如心血管系统）的EPI可以受益于消除这些伪影的方法。本文评估了两种减少相位编码方向上运动伪影的方法。首先，通过比较中心排序与自上而下排序的序列来评估k空间轨迹。接下来，对每个轨迹评估相位编码方向的速度梯度矩归零（GMN）。计算机模拟以及在流动模型和活体兔中的实验表明，未补偿的中心排序产生的图像质量最高。这可能是由于读出持续时间较短，减少了T2*弛豫损失和失谐效应，以及模型和血管的线性几何结构，这可能会掩盖中心模糊伪影。
