Motion robust GRAPPA for echo-planar imaging.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
Artifacts from B0 inhomogeneity and motion during calibration scans for EPI GRAPPA can be mitigated with a readout segmented calibration scan.
Department of Biomedical Engineering, Faculty of Medicine and Dentistry, Room 1098 Research Transition Facility, University of Alberta, Edmonton, Alberta, Canada.
Corey A
CA
Baron
Department of Biomedical Engineering, Faculty of Medicine and Dentistry, Room 1098 Research Transition Facility, University of Alberta, Edmonton, Alberta, Canada.
Christian
C
Beaulieu
D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D002138:Calibration; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008954:Models, Biological; D009068:Movement / Q000502:physiology; D019047:Phantoms, Imaging
EPI; GRAPPA; calibration; echo-planar; parallel imaging