Premium
BOLD contrast sensitivity enhancement and artifact reduction with multiecho EPI: Parallel‐acquired inhomogeneity‐desensitized fMRI
Author(s) -
Poser Benedikt A.,
Versluis Maarten J.,
Hoogduin Johannes M.,
Norris David G.
Publication year - 2006
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.20900
Subject(s) - echo planar imaging , contrast (vision) , artifact (error) , nuclear magnetic resonance , sensitivity (control systems) , blood oxygen level dependent , distortion (music) , voxel , physics , functional magnetic resonance imaging , computer science , artificial intelligence , magnetic resonance imaging , neuroscience , psychology , medicine , amplifier , optoelectronics , cmos , electronic engineering , engineering , radiology
Functional MRI (fMRI) generally employs gradient‐echo echo‐planar imaging (GE‐EPI) to measure blood oxygen level‐dependent (BOLD) signal changes that result from changes in tissue relaxation time T * 2between activation and rest. Since T * 2strongly varies across the brain and BOLD contrast is maximal only where the echo time (TE) equals the local T * 2 , imaging at a single TE is a compromise in terms of overall sensitivity. Furthermore, the long echo train makes EPI very sensitive to main field inhomogeneities, causing strong image distortion. A method is presented that uses accelerated parallel imaging to reduce image artifacts and acquire images at multiple TEs following a single excitation, with no need to increase TR. Sensitivity gains from the broadened T * 2coverage are optimized by pixelwise weighted echo summation based on local T * 2or contrast‐to‐noise ratio (CNR) measurements. The method was evaluated using an approach that allows differential BOLD CNR to be calculated without stimulation, as well as with a Stroop experiment. Results obtained at 3 T showed that BOLD sensitivity improved by 11% or more in all brain regions, with larger gains in areas typically affected by strong susceptibility artifacts. The use of parallel imaging markedly reduces image distortion, and hence the method should find widespread application in functional brain imaging. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.