Kimberly Brewer1,2, James Rioux1,2,
Martyn Klassen3, Chris Bowen1,4, Steven Beyea1,4
1Institute for Biodiagnostics
(Atlantic), National Research Council of Canada, Halifax, Nova Scotia,
Canada; 2Physics and Atmospheric Science, Dalhousie University, Halifax,
Nova Scotia, Canada; 3Robarts Research Institute, University of
Western Ontario, London, Ontario, Canada; 4Physics and Atmospheric
Science, Radiology and Biomedical Engineering, Dalhousie University, Halifax,
Nova Scotia, Canada
Spiral
pulse sequences are commonly used in fMRI, and spiral-in is known to be
considerably better than spiral-out at signal recovery in regions with strong
susceptibility field gradients. Previously proposed theories in the
literature do not address the probability of signal displacement or fully
explain all of the differences in signal recovery between spiral-out and
spiral-in. In the current work we demonstrate that the difference in image
intensity is not due to differences in signal displacement between spiral-in
and spiral-out, but rather the increased phase coherence of the displaced
pixels when using spiral-in.