title: Improvements in parallel imaging accelerated functional MRI using multiecho echo-planar imaging.
abstract: Multiecho echo-planar imaging (EPI) was implemented for blood-oxygenation-level-dependent functional MRI at 1.5 T and compared to single-echo EPI with and without parallel imaging acceleration. A time-normalized breath-hold task using a block design functional MRI protocol was carried out in combination with up to four echo trains per excitation and parallel imaging acceleration factors R = 1-3. Experiments were conducted in five human subjects, each scanned in three sessions. Across all reduction factors, both signal-to-fluctuation-noise ratio and the total number of activated voxels were significantly lower using a single-echo EPI pulse sequence compared with the multiecho approach. Signal-to-fluctuation-noise ratio and total number of activated voxels were also considerably reduced for nonaccelerated conventional single-echo EPI when compared to three-echo measurements with R = 2. Parallel imaging accelerated multiecho EPI reduced geometric distortions and signal dropout, while it increased blood-oxygenation-level-dependent signal sensitivity all over the brain, particularly in regions with short underlying T*(2). Thus, the presented method showed multiple advantages over conventional single-echo EPI for standard blood-oxygenation-level-dependent functional MRI experiments.
authors.affiliation: Lucas Center, Department of Radiology, Stanford University, Stanford, California, USA.
authors.forename: Heiko
authors.initials: H
authors.lastname: Schmiedeskamp
authors.forename: Rexford D
authors.initials: RD
authors.lastname: Newbould
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Pisani
authors.forename: Stefan
authors.initials: S
authors.lastname: Skare
authors.forename: Gary H
authors.initials: GH
authors.lastname: Glover
authors.forename: Klaas P
authors.initials: KP
authors.lastname: Pruessmann
authors.forename: Roland
authors.initials: R
authors.lastname: Bammer
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001931:Brain Mapping / Q000379:methods*; D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods