title: Free-breathing phase contrast MRI with near 100% respiratory navigator efficiency using k-space-dependent respiratory gating.
abstract: OBJECTIVE
  To investigate the efficacy of a novel respiratory motion scheme, where only the center of k-space is gated using respiratory navigators, versus a fully respiratory-gated acquisition for three-dimensional flow imaging.
  
  
  METHODS
  Three-dimensional flow images were acquired axially using a gradient echo sequence in a volume, covering the ascending and descending aorta, and the pulmonary artery bifurcation in 12 healthy subjects (33.2 ± 15.8 years; five men). For respiratory motion compensation, two gating and tracking strategies were used with a 7-mm gating window: (1) All of k-space acquired within the gating window (fully gated) and (2) central k-space acquired within the gating window, and the remainder of k-space acquired without any gating (center gated). Each scan was repeated twice. Stroke volume, mean flow, peak velocity, and signal-to-noise-ratio measurements were performed both on the ascending and on the descending aorta for all acquisitions, which were compared using a linear mixed-effects model and Bland-Altman analysis.
  
  
  RESULTS
  There were no statistical differences between the fully gated and the center-gated strategies for the quantification of stroke volume, peak velocity, and mean flow, as well as the signal-to-noise-ratio measurements. Furthermore, the proposed center-gated strategy had significantly shorter acquisition time compared to the fully gated strategy (13:19 ± 3:02 vs. 19:35 ± 5:02, P < 0.001).
  
  
  CONCLUSIONS
  The proposed novel center-gated strategy for three-dimensional flow MRI allows for markedly shorter acquisition time without any systematic variation in quantitative flow measurements in this small group of healthy volunteers.
authors.affiliation: Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Akçakaya
authors.forename: Praveen
authors.initials: P
authors.lastname: Gulaka
authors.forename: Tamer A
authors.initials: TA
authors.lastname: Basha
authors.forename: Long H
authors.initials: LH
authors.lastname: Ngo
authors.forename: Warren J
authors.initials: WJ
authors.lastname: Manning
authors.forename: Reza
authors.initials: R
authors.lastname: Nezafat
mesh_terms: D000328:Adult; D001013:Aorta, Thoracic / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009038:Motion; D011651:Pulmonary Artery / Q000502:physiology*; D012119:Respiration; D059629:Signal-To-Noise Ratio; D013997:Time Factors
keywords: 3D flow; blood flow assessment; cardiac MR; gating efficiency; intra-scan variability; mean flow; phase contrast MR; respiratory navigators; stroke volume
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