Baron Corey A, Beaulieu Christian
Department of Biomedical Engineering, Faculty of Medicine and Dentistry, Room 1098 Research Transition Facility, University of Alberta, Edmonton, Alberta, Canada.
Magn Reson Med. 2016 Mar;75(3):1166-74. doi: 10.1002/mrm.25705. Epub 2015 Apr 28.
A readout-segmented method for acquiring robust GRAPPA calibration data for echo-planar imaging (EPI) was proposed and compared with two previous methods, including the gold standard interleaved approach and a single shot method with halved phase encode resolution.
The readout-segmented and single shot techniques acquire adjacent phase encode lines in the same shot to obtain the calibration data, rather than interleaving of lines between shots, to decrease sensitivity to motion. Additionally, it uses multiple segments with shortened frequency encode extent to match the phase encode bandwidth to the undersampled data, which decreases sensitivity to B0 inhomogeneity. The three methods were tested using simulations and EPI scans of the brain in healthy volunteers.
The interleaved approach exhibited high sensitivity to motion, while residual undersampling artifacts remained in the single shot method due to mismatch of B0 inhomogeneity between the calibration and undersampled data. The readout segmented method exhibited no such errors, having 30% lower ghosting intensity than the single shot method and 90% lower ghosting intensity than the interleaved approach in moving subjects.
Artifacts from B0 inhomogeneity and motion during calibration scans for EPI GRAPPA can be mitigated with a readout segmented calibration scan.
提出一种读出分段方法，用于获取用于回波平面成像（EPI）的稳健GRAPPA校准数据，并与之前的两种方法进行比较，包括金标准交错方法和具有减半相位编码分辨率的单次激发方法。
读出分段技术和单次激发技术在同一次激发中采集相邻的相位编码线以获得校准数据，而不是在不同激发之间交错采集线，以降低对运动的敏感性。此外，它使用具有缩短频率编码范围的多个段来使相位编码带宽与欠采样数据相匹配，这降低了对B0不均匀性的敏感性。使用模拟和对健康志愿者大脑的EPI扫描测试了这三种方法。
交错方法对运动表现出高敏感性，而由于校准数据和欠采样数据之间B0不均匀性不匹配，单次激发方法中仍存在残留的欠采样伪影。读出分段方法没有此类误差，在运动受试者中，其重影强度比单次激发方法低30%，比交错方法低90%。
对于EPI GRAPPA校准扫描期间的B0不均匀性和运动产生的伪影，可以通过读出分段校准扫描来减轻。
