title: Radial k-t SPIRiT: autocalibrated parallel imaging for generalized phase-contrast MRI.
abstract: OBJECTIVE
  To extend SPIRiT to additionally exploit temporal correlations for highly accelerated generalized phase-contrast MRI and to compare the performance of the proposed radial k-t SPIRiT method relative to frame-by-frame SPIRiT and radial k-t GRAPPA reconstruction for velocity and turbulence mapping in the aortic arch.
  
  
  METHODS
  Free-breathing navigator-gated two-dimensional radial cine imaging with three-directional multi-point velocity encoding was implemented and fully sampled data were obtained in the aortic arch of healthy volunteers. Velocities were encoded with three different first gradient moments per axis to permit quantification of mean velocity and turbulent kinetic energy. Velocity and turbulent kinetic energy maps from up to 14-fold undersampled data were compared for k-t SPIRiT, frame-by-frame SPIRiT, and k-t GRAPPA relative to the fully sampled reference.
  
  
  RESULTS
  Using k-t SPIRiT, improvements in magnitude and velocity reconstruction accuracy were found. Temporally resolved magnitude profiles revealed a reduction in spatial blurring with k-t SPIRiT compared with frame-by-frame SPIRiT and k-t GRAPPA for all velocity encodings, leading to improved estimates of turbulent kinetic energy.
  
  
  CONCLUSIONS
  k-t SPIRiT offers improved reconstruction accuracy at high radial undersampling factors and hence facilitates the use of generalized phase-contrast MRI for routine use.
authors.affiliation: Imaging Sciences and Biomedical Engineering, King's College, London, United Kingdom; Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
authors.forename: Claudio
authors.initials: C
authors.lastname: Santelli
authors.forename: Tobias
authors.initials: T
authors.lastname: Schaeffter
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kozerke
mesh_terms: D001013:Aorta, Thoracic / Q000033:anatomy & histology*; D002138:Calibration; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D012680:Sensitivity and Specificity
keywords: autocalibration; iterative reconstruction; parallel imaging; phase-contrast; turbulent kinetic energy; velocity mapping