  To develop a tissue field filtering algorithm, called maximum Spherical Mean
Value (mSMV), for reducing shadow artifacts in quantitative susceptibility
mapping (QSM) of the brain without requiring brain tissue erosion.Residual
background field is a major source of shadow artifacts in QSM. The mSMV
algorithm filters large field values near the border, where the maximum value
of the harmonic background field is located. The effectiveness of mSMV for
artifact removal was evaluated by comparing with existing QSM algorithms in
numerical brain simulation as well as using in vivo human data acquired from 11
healthy volunteers and 93 patients. Numerical simulation showed that mSMV
reduces shadow artifacts and improves QSM accuracy. Better shadow reduction, as
demonstrated by lower QSM variation in the gray matter and higher QSM image
quality score, was also observed in healthy subjects and in patients with
hemorrhages, stroke and multiple sclerosis. The mSMV algorithm allows QSM maps
that are substantially equivalent to those obtained using SMV-filtered dipole
inversion without eroding the volume of interest.
