title: 3D multi-slab diffusion-weighted readout-segmented EPI with real-time cardiac-reordered K-space acquisition.
abstract: OBJECTIVE
  The aim of this study was to develop, implement, and demonstrate a three-dimensional (3D) extension of the readout-segmented echo-planar imaging (rs-EPI) sequence for diffusion imaging.
  
  
  METHODS
  Potential k-space acquisition schemes were assessed by simulating their associated spatial point spread functions. Motion-induced phase artifacts were also simulated to test navigator corrections and a real-time reordering of the k-space acquisition relative to the cardiac cycle. The cardiac reordering strategy preferentially chooses readout segments closer to the center of 3D k-space during diastole. Motion-induced phase artifacts were quantified by calculating the voxel-wise temporal variation in a set of repeated diffusion-weighted acquisitions. Based on the results of these simulations, a 2D navigated multi-slab rs-EPI sequence with real-time cardiac reordering was implemented. The multi-slab implementation enables signal-to-noise ratio-optimal repetition times of 1-2 s.
  
  
  RESULTS
  Cardiac reordering was validated in simulations and in vivo using the multi-slab rs-EPI sequence. In comparisons with standard k-space acquisitions, cardiac reordering was shown to reduce the variability due to motion-induced phase artifacts by 30-50%. High-resolution diffusion tensor imaging data acquired with the cardiac-reordered multi-slab rs-EPI sequence are presented.
  
  
  CONCLUSIONS
  A 3D multi-slab rs-EPI sequence with cardiac reordering has been demonstrated in vivo and is shown to provide high-quality 3D diffusion-weighted data sets.
authors.affiliation: FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: Frost
authors.forename: Karla L
authors.initials: KL
authors.lastname: Miller
authors.forename: Rob H N
authors.initials: RH
authors.lastname: Tijssen
authors.forename: David A
authors.initials: DA
authors.lastname: Porter
authors.forename: Peter
authors.initials: P
authors.lastname: Jezzard
mesh_terms: D000465:Algorithms; D003199:Computer Systems; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods / Q000592:standards*; D021621:Imaging, Three-Dimensional / Q000379:methods / Q000592:standards*; D016247:Information Storage and Retrieval / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D046032:Microscopy, Energy-Filtering Transmission Electron / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
keywords: 3D diffusion-weighting; cardiac synchronization; diffusion MR; diffusion tensor imaging; navigator correction; readout-segmented EPI