title: In vivo three-dimensional MR wall shear stress estimation in ascending aortic dilatation.
abstract: OBJECTIVE
  To estimate surface-based wall shear stress (WSS) and evaluate flow patterns in ascending aortic dilatation (AscAD) using a high-resolution, time-resolved, three-dimensional (3D), three-directional velocity encoded, radially undersampled phase contrast MR sequence (4D PC-MRI).
  
  
  METHODS
  4D PC-MRI was performed in 11 patients with AscAD (46.3 ± 22.0 years) and 10 healthy volunteers (32.9 ± 13.4 years) after written informed consent and institutional review board approval. Following manual vessel wall segmentation of the ascending aorta (MATLAB, The Mathworks, Natick, MA), a 3D surface was created using spline interpolation. Spatial WSS variation based on surface division in 12 segments and temporal variation were evaluated in AscAD and normal aortas. Visual analysis of flow patterns was performed based on streamlines and particle traces using EnSight (v9.0, CEI, Apex, NC).
  
  
  RESULTS
  AscAD was associated with significantly increased diastolic WSS, decreased systolic to diastolic WSS ratio, and delayed onset of peak WSS (all P < 0.001). Temporally averaged WSS was increased and peak systolic WSS was decreased. The maximum WSS in AscAD was on the anterior wall of the ascending aorta. Vortical flow with highest velocities along the anterior wall and increased helical flow during diastole were observed in AscAD compared with controls.
  
  
  CONCLUSIONS
  Changes in WSS in the ascending aorta of AscAD correspond to observed alterations in flow patterns compared to controls.
authors.affiliation: Department of Radiology, University of Wisconsin-Madison, Wisconsin 53792-3252, USA.
authors.forename: Erik T
authors.initials: ET
authors.lastname: Bieging
authors.forename: Alex
authors.initials: A
authors.lastname: Frydrychowicz
authors.forename: Andrew
authors.initials: A
authors.lastname: Wentland
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Landgraf
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Johnson
authors.forename: Oliver
authors.initials: O
authors.lastname: Wieben
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: François
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001011:Aorta / Q000473:pathology*; D001018:Aortic Diseases / Q000473:pathology*; D002648:Child; D004108:Dilatation, Pathologic / Q000175:diagnosis* / Q000473:pathology; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008858:Microscopy, Phase-Contrast / Q000379:methods; D008875:Middle Aged; D033081:Shear Strength; D013314:Stress, Mechanical; D013997:Time Factors