title: Breathheld autocalibrated phase-contrast imaging.
abstract: OBJECTIVE
  To compare generalized autocalibrating partially parallel acquisitions (GRAPPA), modified sensitivity encoding (mSENSE), and SENSE in phase-contrast magnetic resonance imaging (PC-MRI) applications.
  
  
  METHODS
  Aliasing of the torso can occur in PC-MRI applications. If the data are further undersampled for parallel imaging, SENSE can be problematic in correctly unaliasing signals due to coil sensitivity maps that do not match that of the aliased volume. Here, a method for estimating coil sensitivities in flow applications is described. Normal volunteers (n = 5) were scanned on a 1.5 T MRI scanner and underwent PC-MRI scans using GRAPPA, mSENSE, SENSE, and conventional PC-MRI acquisitions. Peak velocity and flow through the aorta and pulmonary artery were evaluated.
  
  
  RESULTS
  Bland-Altman statistics for flow in the aorta and pulmonary artery acquired with mSENSE and GRAPPA methods (R = 2 and R = 3 cases) have comparable mean differences to flow acquired with conventional PC-MRI. GRAPPA and mSENSE PC-MRI have more robust measurements than SENSE when there is aliasing artifact caused by insufficient coil sensitivity maps. For peak velocity, there are no considerable differences among the mSENSE, GRAPPA, and SENSE reconstructions and are comparable to conventional PC-MRI.
  
  
  CONCLUSIONS
  Flow measurements of images reconstructed with autocalibration techniques have comparable agreement with conventional PC-MRI and provide robust measurements in the presence of wraparound.
authors.affiliation: Department of Radiology, Stanford University, Stanford, California 94305, USA. calvinlew@gmail.com
authors.forename: Calvin
authors.initials: C
authors.lastname: Lew
authors.forename: Marcus T
authors.initials: MT
authors.lastname: Alley
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Spielman
authors.forename: Roland
authors.initials: R
authors.lastname: Bammer
authors.forename: Frandics P
authors.initials: FP
authors.lastname: Chan
mesh_terms: D000465:Algorithms; D001011:Aorta / Q000473:pathology; D002138:Calibration; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015233:Models, Statistical; D011651:Pulmonary Artery / Q000473:pathology; D012119:Respiration