title: Multi-VENC acquisition of four-dimensional phase-contrast MRI to improve precision of velocity field measurement.
abstract: OBJECTIVE
  The present study aims to improve precision of four-dimensional (4D) phase-contrast (PC) MRI technique by using multiple velocity encoding (VENC) parameters.
  
  
  METHODS
  The 3D flow fields in an in vitro stenosis phantom and an in vivo ascending aorta were determined using a 4D PC-MRI sequence with multiple VENC values. The velocity field obtained for large VENC was combined with that from small VENC, unless velocity data were lost by phase aliasing and phase dispersion. Noise levels of the combined velocity fields were compared with the increasing overlapping number of VENC parameters.
  
  
  RESULTS
  The phantom measurement showed that the multi-VENC acquisition reduced the noise levels in radial and axial velocities (> 24 cm/s at VENC = 300 cm/s) down to 0.80 ± 0.45 cm/s and 5.60 ± 2.63 cm/s, respectively. This increased the velocity-to-noise ratio (VNR) by approximately two-fold to six-fold depending on the locations. As a result, the multi-VENC measurement could visualize the low-velocity recirculating flows more clearly.
  
  
  CONCLUSIONS
  The multi-VENC measurement of 4D PC-MRI sequence increased the VNR distribution by reducing velocity noise. The improved VNR can be beneficial for investigating blood flow structures in a flow field with a high velocity dynamic range.
authors.affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang, 790-784, South Korea.
authors.forename: Hojin
authors.initials: H
authors.lastname: Ha
authors.affiliation: Asan Institute of Life Science, Asan Medical Center, University of Ulsan College of Medicine, Seoul, South Korea.
authors.forename: Guk Bae
authors.initials: GB
authors.lastname: Kim
authors.affiliation: Department of Cardiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, South Korea.
authors.forename: Jihoon
authors.initials: J
authors.lastname: Kweon
authors.affiliation: Department of Cardiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, South Korea.
authors.forename: Young-Hak
authors.initials: YH
authors.lastname: Kim
authors.affiliation: Department of Convergence Medicine, University of Ulsan College of Medicine, Asan Medical Center, Seoul, South Korea.|Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, South Korea.
authors.forename: Namkug
authors.initials: N
authors.lastname: Kim
authors.affiliation: Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, South Korea.
authors.forename: Dong Hyun
authors.initials: DH
authors.lastname: Yang
authors.affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang, 790-784, South Korea.
authors.forename: Sang Joon
authors.initials: SJ
authors.lastname: Lee
mesh_terms: D000368:Aged; D001011:Aorta / Q000000981:diagnostic imaging* / Q000473:pathology*; D001783:Blood Flow Velocity; D003251:Constriction, Pathologic; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio
keywords: 4D PC-MRI; VNR; ascending aorta; multiple VENC; phase-contrast magnetic resonance imaging; stenosis flow