Storey Pippa, Chen Qun, Li Wei, Edelman Robert R, Prasad Pottumarthi V
Department of Radiology, MRI Research, Evanston Hospital, vanston Northwestern Healthcare, Evanston, Illinois 60201, USA.
Magn Reson Med. 2002 Dec;48(6):1028-36. doi: 10.1002/mrm.10314.
Band artifacts due to bulk motion were investigated in images acquired with fast gradient echo sequences. A simple analytical calculation shows that the width of the artifacts has a square-root dependence on the velocity of the imaged object, the time taken to acquire each line of k-space and the field of view in the phase-encoding direction. The theory furthermore predicts that the artifact width can be reduced using parallel imaging by a factor equal to the square root of the acceleration parameter. The analysis and results are presented for motion in the phase- and frequency-encoding directions and comparisons are made between sequential and centric ordering. The theory is validated in phantom experiments, in which bulk motion is simulated in a controlled and reproducible manner by rocking the scan table back and forth along the bore axis. Preliminary cardiac studies in healthy human volunteers show that dark bands may be observed in the endocardium in images acquired with nonsegmented fast gradient echo sequences. The fact that the position of the bands changes with the phase-encoding direction suggests that they may be artifacts due to motion of the heart walls during the image acquisition period.
在使用快速梯度回波序列采集的图像中，研究了由整体运动引起的带状伪影。一个简单的分析计算表明，伪影的宽度与成像物体的速度、采集k空间每条线所需的时间以及相位编码方向上的视野呈平方根依赖关系。该理论进一步预测，使用并行成像可以将伪影宽度减小到等于加速参数平方根的倍数。给出了相位编码和频率编码方向上运动的分析和结果，并对顺序排序和中心排序进行了比较。该理论在体模实验中得到了验证，在体模实验中，通过沿磁体孔轴前后摇动扫描台，以可控且可重复的方式模拟整体运动。对健康人类志愿者的初步心脏研究表明，在使用非分段快速梯度回波序列采集的图像中，在心内膜可能会观察到暗带。这些带的位置随相位编码方向而变化，这一事实表明它们可能是由于图像采集期间心脏壁的运动而产生的伪影。
