Andrew Hahn1, Andrew Nencka1, Daniel
Rowe, 1,2
1Biophysics, Medical College of
Wisconsin, Milwaukee, WI, United States; 2Mathematics, Statistics,
and Computer Science, Marquette University, Milwaukee, WI
Estimations
of main magnetic field inhomogeneity are often acquired for correction of
image warping in echo planar images (EPI) resulting from vulnerability to
off-resonance effects of EPI. Many
established methods exist for field estimation, one of which involves two EPI
acquisitions with different echo times.
The method is fast, easily implemented and can be performed in-line
with fMRI experiments. However,
inconsistencies in the MRI scanner hardware, specifically with the RF pulse,
as well as physiologic phenomena that alter the off-resonance characteristics
between image acquisitions such as motion or respiration can induce errors in
field maps estimated in this manner.