title: Referenceless reconstruction of spatiotemporally encoded imaging data: principles and applications to real-time MRI.
abstract: OBJECTIVE
  Ultrafast sequences based on "Hybrid" spatiotemporal encoding (SPEN) replace echo-planar imaging's phase encoding "blips," while retaining a k-space readout acquisition. Hardware imperfections during acquisition may lead to ghosts and striped artifacts along the SPEN dimension; akin to echo-planar imaging's Nyquist ghosts, but weaker. A referenceless method to eliminate these artifacts in Hybrid SPEN is demonstrated.
  
  
  METHODS
  Owing to its encoding in direct space, rather than reciprocal space, undersampling in SPEN does not generate an echo-planar-imaging-like aliasing, but instead lowers the spatial resolution. Hybrid SPEN data can be split into two undersampled signals: a reference one comprised of the odd-echos, and an even-echo set that has to be "corrected" for consistency with the former. A simple way of implementing such a correction that enables a joint high-resolution reconstruction is proposed.
  
  
  RESULTS
  The referenceless algorithm is demonstrated with various examples, including oblique scans, large in vivo datasets from real-time dynamic contrast-enhanced perfusion experiments, and human brain imaging.
  
  
  CONCLUSIONS
  The referenceless correction enables robust single-scan imaging under changing conditions-such as patient motion and changes in shimming over time-without the need of ancillary navigators. This opens new options for real-time MRI and interactive scanning.
authors.affiliation: Chemical Physics Department, Weizmann Institute of Science, Rehovot, Israel, 76100.
authors.forename: Amir
authors.initials: A
authors.lastname: Seginer
authors.forename: Rita
authors.initials: R
authors.lastname: Schmidt
authors.forename: Avigdor
authors.initials: A
authors.lastname: Leftin
authors.forename: Eddy
authors.initials: E
authors.lastname: Solomon
authors.forename: Lucio
authors.initials: L
authors.lastname: Frydman
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D003199:Computer Systems; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D009716:Numerical Analysis, Computer-Assisted; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D062211:Spatio-Temporal Analysis
keywords: dynamic contrast-enhanced magnetic resonance imaging; real-time magnetic resonance imaging; referenceless reconstruction; spatiotemporal encoding