title: Velocity encoding with the slice select refocusing gradient for faster imaging and reduced chemical shift-induced phase errors.
abstract: OBJECTIVE
  To investigate a novel phase-contrast MRI velocity-encoding technique for faster imaging and reduced chemical shift-induced phase errors.
  
  
  METHODS
  Velocity encoding with the slice select refocusing gradient achieves the target gradient moment by time shifting the refocusing gradient, which enables the use of the minimum in-phase echo time (TE) for faster imaging and reduced chemical shift-induced phase errors. Net forward flow was compared in 10 healthy subjects (N = 10) within the ascending aorta (aAo), main pulmonary artery (PA), and right/left pulmonary arteries (RPA/LPA) using conventional flow compensated and flow encoded (401 Hz/px and TE = 3.08 ms) and slice select refocused gradient velocity encoding (814 Hz/px and TE = 2.46 ms) at 3 T.
  
  
  RESULTS
  Improved net forward flow agreement was measured across all vessels for slice select refocused gradient compared to flow compensated and flow encoded: aAo vs. PA (1.7% ± 1.9% vs. 5.8% ± 2.8%, P = 0.002), aAo vs. RPA + LPA (2.1% ± 1.7% vs. 6.0% ± 4.3%, P = 0.03), and PA vs. RPA + LPA (2.9% ± 2.1% vs. 6.1% ± 6.3%, P = 0.04), while increasing temporal resolution (35%) and signal-to-noise ratio (33%).
  
  
  CONCLUSIONS
  Slice select refocused gradient phase-contrast MRI with a high receiver bandwidth and minimum in-phase TE provides more accurate and less variable flow measurements through the reduction of chemical shift-induced phase errors and a reduced TE/repetition time, which can be used to increase the temporal/spatial resolution and/or reduce breath hold durations.
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California, USA; Biomedical Physics Interdepartmental Program, University of California, Los Angeles, California, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Middione
authors.forename: Richard B
authors.initials: RB
authors.lastname: Thompson
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Ennis
mesh_terms: D000465:Algorithms; D001011:Aorta; D016477:Artifacts; D001783:Blood Flow Velocity; D003951:Diagnostic Errors / Q000517:prevention & control; D064368:Healthy Volunteers; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D011651:Pulmonary Artery; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio
keywords: chemical shift; flow quantification; phase-contrast MRI; velocity encoding