title: k-t GRAPPA accelerated four-dimensional flow MRI in the aorta: effect on scan time, image quality, and quantification of flow and wall shear stress.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the utility of k-t parallel imaging for accelerating aortic four-dimensional (4D)-flow MRI. The aim was to systematically investigate the impact of different acceleration factors and number of coil elements on acquisition time, image quality and quantification of hemodynamic parameters.
  
  
  METHODS
  k-t accelerated 4D-flow MRI (spatial/temporal resolution = 2.1 × 2.5 × 2.5 mm/40.0 ms) was acquired in 10 healthy volunteers with acceleration factors R = 3, 5, and 8 using 12- and 32-channel receiver coils. Results were compared with conventional parallel imaging (GRAPPA [generalized autocalibrating partial parallel acquisition], R = 2). Data analysis included radiological grading of three-dimensional blood flow visualization quality as well as quantification of blood flow, velocities and wall shear stress (WSS).
  
  
  RESULTS
  k-t GRAPPA significantly reduced scan time by 28%, 54%, and 68%, for R = 3, 5, and 8, respectively, while maintaining image quality as demonstrated by overall similar image quality grading. Significant differences in peak WSS (diff12ch = -5.9%, diff32ch = 18.5%) and mean WSS (diff32ch = 13.9%) were found at the descending aorta for both receiver coils for R = 5 (PWSS < 0.04). Peak velocity differed for R=8 at the aortic root (-7.4%) and descending aorta (-12%) with PpeakVelo < 0.03.
  
  
  CONCLUSIONS
  k-t GRAPPA acceleration with a 12- or 32-channel receiver coil and an acceleration of 3 or 5 can compete with a standard GRAPPA R = 2 acceleration.
authors.affiliation: Department of Radiology, Northwestern University, Chicago, Illinois, USA.
authors.forename: Susanne
authors.initials: S
authors.lastname: Schnell
authors.forename: Michael
authors.initials: M
authors.lastname: Markl
authors.forename: Pegah
authors.initials: P
authors.lastname: Entezari
authors.forename: Riti J
authors.initials: RJ
authors.lastname: Mahadewia
authors.forename: Edouard
authors.initials: E
authors.lastname: Semaan
authors.forename: Zoran
authors.initials: Z
authors.lastname: Stankovic
authors.forename: Jeremy
authors.initials: J
authors.lastname: Collins
authors.forename: James
authors.initials: J
authors.lastname: Carr
authors.forename: Bernd
authors.initials: B
authors.lastname: Jung
mesh_terms: D000328:Adult; D000465:Algorithms; D001011:Aorta / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology*; D055424:Cardiac-Gated Imaging Techniques / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D033081:Shear Strength
keywords: 4D-flow MRI; WSS; k-t GRAPPA; parallel imaging; quantification