Real-Time Shim Correction during Functional MRI Using a Volumetric Navigator
A Alhamud 1 , Paul Taylor 1,2 , Jia Fan 1 , Ernesta Meintjes 1 , and Andr J.W. van der Kouwe 3
Human Biology,MRC/UCT Medical Imaging
Research Unit, University of Cape Town, Cape Town,
Western Cape, South Africa,
Institute for Mathematical Sciences (AIMS), Western
Cape, South Africa,
General Hospital, Charlestown, Massachusetts, United
During fMRI acquisition, magnetic field inhomogeneities
may lead to severe signal dropouts and geometric
distortions in fMRI images. The inhomogeneities are
routinely minimized by shimming prior to fMRI scan.
However, factors, which may include breathing, heating
of the shim iron coils or subject motion, can alter the
static shim and affect the BOLD measures. The purpose of
this work is to introduce a technique to measure, report
and correct in real-time magnetic field distortions as
well as subject motion. This is achieved by acquiring
two volumetric navigators to track motion and produce a
field map after each fMRI volume acquisition.
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