title: Respiratory motion-resolved, self-gated 4D-MRI using rotating cartesian k-space (ROCK).
abstract: OBJECTIVE
  To propose and validate a respiratory motion resolved, self-gated (SG) 4D-MRI technique to assess patient-specific breathing motion of abdominal organs for radiation treatment planning.
  
  
  METHODS
  The proposed 4D-MRI technique was based on the balanced steady-state free-precession (bSSFP) technique and 3D k-space encoding. A novel rotating cartesian k-space (ROCK) reordering method was designed which incorporates repeatedly sampled k-space centerline as the SG motion surrogate and allows for retrospective k-space data binning into different respiratory positions based on the amplitude of the surrogate. The multiple respiratory-resolved 3D k-space data were subsequently reconstructed using a joint parallel imaging and compressed sensing method with spatial and temporal regularization. The proposed 4D-MRI technique was validated using a custom-made dynamic motion phantom and was tested in six healthy volunteers, in whom quantitative diaphragm and kidney motion measurements based on 4D-MRI images were compared with those based on 2D-CINE images.
  
  
  RESULTS
  The 5-minute 4D-MRI scan offers high-quality volumetric images in 1.2 × 1.2 × 1.6 mm3and eight respiratory positions, with good soft-tissue contrast. In phantom experiments with triangular motion waveform, the motion amplitude measurements based on 4D-MRI were 11.89% smaller than the ground truth, whereas a -12.5% difference was expected due to data binning effects. In healthy volunteers, the difference between the measurements based on 4D-MRI and the ones based on 2D-CINE were 6.2 ± 4.5% for the diaphragm, 8.2 ± 4.9% and 8.9 ± 5.1% for the right and left kidney.
  
  
  CONCLUSIONS
  The proposed 4D-MRI technique could provide high-resolution, high-quality, respiratory motion-resolved 4D images with good soft-tissue contrast and are free of the "stitching" artifacts usually seen on 4D-CT and 4D-MRI based on resorting 2D-CINE. It could be used to visualize and quantify abdominal organ motion for MRI-based radiation treatment planning.
authors.affiliation: Department of Radiological Sciences, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Han
authors.affiliation: Department of Radiological Sciences, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.|Department of Bioengineering, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.
authors.forename: Ziwu
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, University of California, 200 UCLA Medical Plaza Suite B265, Los Angeles, CA 90095, USA.|Physics and Biology in Medicine Graduate Program, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.
authors.forename: Minsong
authors.initials: M
authors.lastname: Cao
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, University of California, 200 UCLA Medical Plaza Suite B265, Los Angeles, CA 90095, USA.|Physics and Biology in Medicine Graduate Program, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.
authors.forename: Yingli
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, University of California, 200 UCLA Medical Plaza Suite B265, Los Angeles, CA 90095, USA.|Physics and Biology in Medicine Graduate Program, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Sheng
authors.affiliation: Department of Radiological Sciences, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.|Physics and Biology in Medicine Graduate Program, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA 90095, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Hu
mesh_terms: D016477:Artifacts; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009068:Movement; D019047:Phantoms, Imaging; D012119:Respiration; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D012399:Rotation
keywords: 4D-MRI; k-space binning; respiratory motion management; self-gating