title: K-t GRAPPA-accelerated 4D flow MRI of liver hemodynamics: influence of different acceleration factors on qualitative and quantitative assessment of blood flow.
abstract: OBJECTIVE
  We sought to evaluate the feasibility of k-t parallel imaging for accelerated 4D flow MRI in the hepatic vascular system by investigating the impact of different acceleration factors.
  
  
  METHODS
  k-t GRAPPA accelerated 4D flow MRI of the liver vasculature was evaluated in 16 healthy volunteers at 3T with acceleration factors R = 3, R = 5, and R = 8 (2.0 × 2.5 × 2.4 mm(3), TR = 82 ms), and R = 5 (TR = 41 ms); GRAPPA R = 2 was used as the reference standard. Qualitative flow analysis included grading of 3D streamlines and time-resolved particle traces. Quantitative evaluation assessed velocities, net flow, and wall shear stress (WSS).
  
  
  RESULTS
  Significant scan time savings were realized for all acceleration factors compared to standard GRAPPA R = 2 (21-71 %) (p < 0.001). Quantification of velocities and net flow offered similar results between k-t GRAPPA R = 3 and R = 5 compared to standard GRAPPA R = 2. Significantly increased leakage artifacts and noise were seen between standard GRAPPA R = 2 and k-t GRAPPA R = 8 (p < 0.001) with significant underestimation of peak velocities and WSS of up to 31 % in the hepatic arterial system (p <0.05). WSS was significantly underestimated up to 13 % in all vessels of the portal venous system for k-t GRAPPA R = 5, while significantly higher values were observed for the same acceleration with higher temporal resolution in two veins (p < 0.05).
  
  
  CONCLUSIONS
  k-t acceleration of 4D flow MRI is feasible for liver hemodynamic assessment with acceleration factors R = 3 and R = 5 resulting in a scan time reduction of at least 40 % with similar quantitation of liver hemodynamics compared with GRAPPA R = 2.
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, 737 N Michigan Avenue Suite 1600, Chicago, IL, 60611, USA, zoran.stankovic@northwestern.edu.
authors.forename: Zoran
authors.initials: Z
authors.lastname: Stankovic
authors.forename: Jury
authors.initials: J
authors.lastname: Fink
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Collins
authors.forename: Edouard
authors.initials: E
authors.lastname: Semaan
authors.forename: Maximilian F
authors.initials: MF
authors.lastname: Russe
authors.forename: James C
authors.initials: JC
authors.lastname: Carr
authors.forename: Michael
authors.initials: M
authors.lastname: Markl
authors.forename: Mathias
authors.initials: M
authors.lastname: Langer
authors.forename: Bernd
authors.initials: B
authors.lastname: Jung
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008099:Liver / Q000033:anatomy & histology / Q000502:physiology*; D008102:Liver Circulation / Q000502:physiology*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D015203:Reproducibility of Results; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods; D012680:Sensitivity and Specificity; D033081:Shear Strength / Q000502:physiology
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