Summary: Technical Note
A Novel Object-Independent ``Balanced'' Reference
Scan for Echo-Planar Imaging
Scott B. Reeder, MD, PhD,1 Anthony Z. Faranesh, MSE,1 Ergin Atalar, PhD,2 and
Elliot R. McVeigh, PhD1,2
Interleaved echo-planar imaging (EPI) is susceptible to
significant ghosting artifacts, resulting primarily from sys-
tem time delays that cause data matrix misregistration.
Most EPI applications rely on ``reference scans'' to mea-
sure delays, and post-processing algorithms are used to
correct these errors. Unfortunately, delay estimates made
with most reference scan techniques are object dependent,
since they are biased by magnetic field inhomogeneities
and chemical shift. The current work describes the effects
of field inhomogeneities and their influence on system
time delay estimation. Subsequently, a new, object-inde-
pendent ``balanced'' reference method using two readout
echo trains is proposed for time delay measurements. J.
Magn. Reson. Imaging 1999;9:847852.
1999 Wiley-Liss, Inc.