Dynamic distortion correction with standard single-echo EPI: development of the method for multi-channel coils at 7T and accuracy in the presence of substantial motion.
Barbara Dymerska 1 , Benedikt Poser 2 , Markus Barth 3 , Siegfried Trattnig 1 , and Simon Daniel Robinson 1
High Field MR Center, Department of
Biomedical Imaging and Image-guided Therapy, Medical
University of Vienna, Vienna, Vienna, Austria,
of Psychology and Neuroscience, Cognitive Neuroscience,
Maastricht University, Maastricht, Netherlands,
for Advanced Imaging, The University of Queensland,
Dynamic maps of B0 can be extracted from a time series
of standard, single-echo EPI by calculating the
echo-time-independent phase (or offset) from a
reference measurement and subtracting this from the
phase of each EPI. This yields a field map for each
volume. In this study we i) improve the SNR of the field
maps by using a GE rather than EPI reference scan and
ii) modify the method for multi-channel coils. In
experiments at 7 T we find that while B0 varies
dramatically with head motion, phase offsets remain
stable, allowing distortions to be accurately corrected.
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