BOLD contrast sensitivity enhancement and artifact reduction with multiecho EPI: Parallel-acquired inhomogeneity-desensitized fMRI

• Published in: Magnetic resonance in medicine Vol. 55; no. 6; pp. 1227 - 1235
• Main Authors: Poser, Benedikt A., Versluis, Maarten J., Hoogduin, Johannes M., Norris, David G.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.06.2006
• Subjects: Adult; Algorithms; BOLD CNR; BOLD sensitivity; Brain - anatomy & histology; Brain - metabolism; Brain Mapping - methods; Echo-Planar Imaging - methods; Female; fMRI; Humans; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Magnetic Resonance Imaging - methods; Male; multiecho EPI; Oxygen - metabolism; parallel imaging; Reproducibility of Results; Sensitivity and Specificity
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.20900

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 *2 between activation and rest. Since T *2 strongly 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 *2 coverage are optimized by pixelwise weighted echo summation based on local T *2 or 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.