title: k-t accelerated aortic 4D flow MRI in under two minutes: Feasibility and impact of resolution, k-space sampling patterns, and respiratory navigator gating on hemodynamic measurements.
abstract: OBJECTIVE
  To assess the performance of highly accelerated free-breathing aortic four-dimensional (4D) flow MRI acquired in under 2 minutes compared to conventional respiratory gated 4D flow.
  
  
  METHODS
  Eight k-t accelerated nongated 4D flow MRI (parallel MRI with extended and averaged generalized autocalibrating partially parallel acquisition kernels [PEAK GRAPPA], R = 5, TRes = 67.2 ms) using four ky-kzCartesian sampling patterns (linear, center-out, out-center-out, random) and two spatial resolutions (SRes1 = 3.5 × 2.3 × 2.6 mm3, SRes2 = 4.5 × 2.3 × 2.6 mm3) were compared in vitro (aortic coarctation flow phantom) and in 10 healthy volunteers, to conventional 4D flow (16 mm-navigator acceptance window; R = 2; TRes = 39.2 ms; SRes = 3.2 × 2.3 × 2.4 mm3). The best k-t accelerated approach was further assessed in 10 patients with aortic disease.
  
  
  RESULTS
  The k-t accelerated in vitro aortic peak flow (Qmax), net flow (Qnet), and peak velocity (Vmax) were lower than conventional 4D flow indices by ≤4.7%, ≤ 11%, and ≤22%, respectively. In vivo k-t accelerated acquisitions were significantly shorter but showed a trend to lower image quality compared to conventional 4D flow. Hemodynamic indices for linear and out-center-out k-space samplings were in agreement with conventional 4D flow (Qmax ≤ 13%, Qnet ≤ 13%, Vmax ≤ 17%, P > 0.05).
  
  
  CONCLUSIONS
  Aortic 4D flow MRI in under 2 minutes is feasible with moderate underestimation of flow indices. Differences in k-space sampling patterns suggest an opportunity to mitigate image artifacts by an optimal trade-off between scan time, acceleration, and k-space sampling. Magn Reson Med 79:195-207, 2018. © 2018 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: Emilie
authors.initials: E
authors.lastname: Bollache
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Barker
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: Ryan Scott
authors.initials: RS
authors.lastname: Dolan
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: James C
authors.initials: JC
authors.lastname: Carr
authors.affiliation: Department of Radiology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Pim
authors.initials: P
authors.lastname: van Ooij
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: Rouzbeh
authors.initials: R
authors.lastname: Ahmadian
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: Alex
authors.initials: A
authors.lastname: Powell
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Collins
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.|Department of Diagnostic and Interventional Radiology, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Geiger
authors.affiliation: Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.|Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, Illinois, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Markl
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001011:Aorta / Q000000981:diagnostic imaging* / Q000473:pathology; D001017:Aortic Coarctation / Q000000981:diagnostic imaging / Q000601:surgery; D016477:Artifacts; D002138:Calibration; D005260:Female; D064368:Healthy Volunteers; D006439:Hemodynamics; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013997:Time Factors; D016277:Ventricular Function, Left
keywords: 4D flow magnetic resonance imaging; aortic hemodynamics; k-space sampling; k-t acceleration; navigator gating; short scan time