title: Multiplexed echo planar imaging for sub-second whole brain FMRI and fast diffusion imaging.
abstract: Echo planar imaging (EPI) is an MRI technique of particular value to neuroscience, with its use for virtually all functional MRI (fMRI) and diffusion imaging of fiber connections in the human brain. EPI generates a single 2D image in a fraction of a second; however, it requires 2-3 seconds to acquire multi-slice whole brain coverage for fMRI and even longer for diffusion imaging. Here we report on a large reduction in EPI whole brain scan time at 3 and 7 Tesla, without significantly sacrificing spatial resolution, and while gaining functional sensitivity. The multiplexed-EPI (M-EPI) pulse sequence combines two forms of multiplexing: temporal multiplexing (m) utilizing simultaneous echo refocused (SIR) EPI and spatial multiplexing (n) with multibanded RF pulses (MB) to achieve m×n images in an EPI echo train instead of the normal single image. This resulted in an unprecedented reduction in EPI scan time for whole brain fMRI performed at 3 Tesla, permitting TRs of 400 ms and 800 ms compared to a more conventional 2.5 sec TR, and 2-4 times reductions in scan time for HARDI imaging of neuronal fibertracks. The simultaneous SE refocusing of SIR imaging at 7 Tesla advantageously reduced SAR by using fewer RF refocusing pulses and by shifting fat signal out of the image plane so that fat suppression pulses were not required. In preliminary studies of resting state functional networks identified through independent component analysis, the 6-fold higher sampling rate increased the peak functional sensitivity by 60%. The novel M-EPI pulse sequence resulted in a significantly increased temporal resolution for whole brain fMRI, and as such, this new methodology can be used for studying non-stationarity in networks and generally for expanding and enriching the functional information.
authors.affiliation: Advanced MRI Technologies, Sebastopol, California, United States of America. david.feinberg@advancedmri.com
authors.forename: David A
authors.initials: DA
authors.lastname: Feinberg
authors.forename: Steen
authors.initials: S
authors.lastname: Moeller
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Smith
authors.forename: Edward
authors.initials: E
authors.lastname: Auerbach
authors.forename: Sudhir
authors.initials: S
authors.lastname: Ramanna
authors.forename: Matthias
authors.initials: M
authors.lastname: Gunther
authors.forename: Matt F
authors.initials: MF
authors.lastname: Glasser
authors.forename: Karla L
authors.initials: KL
authors.lastname: Miller
authors.forename: Kamil
authors.initials: K
authors.lastname: Ugurbil
authors.forename: Essa
authors.initials: E
authors.lastname: Yacoub
mesh_terms: D000465:Algorithms; D001921:Brain / Q000378:metabolism / Q000473:pathology; D001931:Brain Mapping / Q000379:methods; D004058:Diffusion; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D009474:Neurons / Q000378:metabolism; D019047:Phantoms, Imaging; D012044:Regression Analysis