title: Improved temporal resolution for functional studies with reduced number of segments with three-dimensional echo planar imaging.
abstract: OBJECTIVE
  To introduce a new k-space traversal strategy for segmented three-dimensional echo planar imaging (3D EPI) that encodes two partitions per radiofrequency excitation, effectively reducing the number excitations used to acquire a 3D EPI dataset by half.
  
  
  METHODS
  The strategy was evaluated in the context of functional MRI applications for: image quality compared with segmented 3D EPI, temporal signal-to-noise ratio (tSNR) (the ability to detect resting state networks compared with multislice two-dimensional (2D) EPI and segmented 3D EPI, and temporal resolution (the ability to separate cardiac- and respiration-related fluctuations from the desired blood oxygen level-dependent signal of interest).
  
  
  RESULTS
  Whole brain images with a nominal voxel size of 2 mm isotropic could be acquired with a temporal resolution under half a second using traditional parallel imaging acceleration up to 4× in the partition-encode direction and using novel data acquisition speed-up of 2× with a 32-channel coil. With 8× data acquisition speed-up in the partition-encode direction, 3D reduced excitations (RE)-EPI produced acceptable image quality without introduction of noticeable additional artifacts. Due to increased tSNR and better characterization of physiological fluctuations, the new strategy allowed detection of more resting state networks compared with multislice 2D-EPI and segmented 3D EPI.
  
  
  CONCLUSIONS
  3D RE-EPI resulted in significant increases in temporal resolution for whole brain acquisitions and in improved physiological noise characterization compared with 2D-EPI and segmented 3D EPI.
authors.affiliation: Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Department of Radiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Mayur
authors.initials: M
authors.lastname: Narsude
authors.forename: Wietske
authors.initials: W
authors.lastname: van der Zwaag
authors.forename: Tobias
authors.initials: T
authors.lastname: Kober
authors.forename: Rolf
authors.initials: R
authors.lastname: Gruetter
authors.forename: José P
authors.initials: JP
authors.lastname: Marques
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D059629:Signal-To-Noise Ratio; D013997:Time Factors
keywords: EPI; acceleration; functional MRI; k-space trajectory; physiological noise; pulse sequence; temporal SNR