title: Correction of phase offset errors in main pulmonary artery flow quantification.
abstract: OBJECTIVE
  To investigate whether an existing method for correction of phase offset errors in phase-contrast velocity quantification is applicable for assessment of main pulmonary artery flow with an MR scanner equipped with a high-power gradient system.
  
  
  METHODS
  The correction method consists of fitting a surface through the time average of stationary pixels of velocity-encoded phase images, and subtracting this surface from the velocity images. Pixels are regarded as stationary if their time standard deviation falls into the lowest percentile. Flow was measured in the main pulmonary artery of 15 subjects. Each measurement was repeated on a stationary phantom. The phase offset error in the phantom was used as a reference. Correction was applied with varying polynomial surface orders (0-5) and stationarity percentiles (5-50%). The optimal surface order and stationarity percentile were determined by comparing the fitted surface with the phantom.
  
  
  RESULTS
  Using a first-order surface and a (noncritical) 25% percentile, the correction method significantly reduced the phase offset error from 1.1 to 0.35 cm/second (RMS), which is equivalent to a reduction from 11% to 3.3% of mean volume flow. Phase error correction strongly affected stroke volume (range -11 to 26%).
  
  
  CONCLUSIONS
  The method significantly reduces phase offset errors in pulmonary artery flow.
authors.affiliation: Department of Physics and Medical Technology, VU University Medical Center, Institute for Cardiovascular Research, Amsterdam, The Netherlands. jw.lankhaar@vumc.nl
authors.forename: Jan-Willem
authors.initials: JW
authors.lastname: Lankhaar
authors.forename: Mark B M
authors.initials: MB
authors.lastname: Hofman
authors.forename: J Tim
authors.initials: JT
authors.lastname: Marcus
authors.forename: Jaco J M
authors.initials: JJ
authors.lastname: Zwanenburg
authors.forename: Theo J C
authors.initials: TJ
authors.lastname: Faes
authors.forename: Anton
authors.initials: A
authors.lastname: Vonk-Noordegraaf
mesh_terms: D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000175:diagnosis; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011651:Pulmonary Artery / Q000502:physiology*