Elimination of Nyquist ghosting caused by read-out to phase-encode gradient cross-terms in EPI.
Echo-planar imaging (EPI) commonly suffers from ghosting artifacts caused by zero- or first-order phase differences between the odd and even echoes that constitute an EPI dataset. Small-bore imaging systems with shielded gradients may suffer significantly from cross-term eddy currents due to the high degree of manufacturing precision required in such systems compared to larger whole-body coils. A Nyquist ghost caused by cross-term eddy current contributions from the read-out to the phase-encode axis was identified in a small-bore system and characterized using a modified EPI experiment and a computer simulation. The artifact was corrected for using both a postprocessing approach and compensation blips along the phase-encode axis. Correction using compensation blips proved to be a more effective strategy to reduce this artifact than the postprocessing method used.
Grieve
Stuart M
SM
MRC Biochemical and Clinical Magnetic Resonance Unit, Department of Biochemistry, University of Oxford, Headington, Oxford, UK.
Blamire
Andrew M
AM
Styles
Peter
P
D016477:Artifacts; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging