title: Evaluation of 3D blood flow patterns and wall shear stress in the normal and dilated thoracic aorta using flow-sensitive 4D CMR.
abstract: BACKGROUND
  The purpose of this study was to investigate 3D flow patterns and vessel wall parameters in patients with dilated ascending aorta, age-matched subjects, and healthy volunteers.
  
  
  METHODS
  Thoracic time-resolved 3D phase contrast CMR with 3-directional velocity encoding was applied to 33 patients with dilated ascending aorta (diameter≥40 mm, age=60±16 years), 15 age-matched normal controls (diameter≤37 mm, age=68±7.5 years) and 15 young healthy volunteers (diameter≤30 mm, age=23±2 years). 3D blood flow was visualized and flow patterns were graded regarding presence of supra-physiologic-helix and vortex flow using a semi-quantitative 3-point grading scale. Blood flow velocities, regional wall shear stress (WSS), and oscillatory shear index (OSI) were quantified.
  
  
  RESULTS
  Incidence and strength of supra-physiologic-helix and vortex flow in the ascending aorta (AAo) was significantly higher in patients with dilated AAo (16/33 and 31/33, grade 0.9±1.0 and 1.5±0.6) than in controls (2/15 and 7/15, grade 0.2±0.6 and 0.6±0.7, P<.05) or healthy volunteers (1/15 and 0/15, grade 0.1±0.3 P<.05). Greater strength of the ascending aortic helix and vortex flow were associated with significant differences in AAo diameters (P<.05). Peak systolic WSS in the ascending aorta and aortic arch was significantly lower in patients with dilated AAo (P<.0157-.0488). AAo diameter positively correlated to time to peak systolic velocities (r=0.30-0.53, P<.04), OSI (r=0.33-0.49, P<0.02) and inversely correlated to peak systolic WSS (r=0.32-0.40, P<.03). Peak systolic WSS was significantly lower in AAo aneurysms at the right and outer curvature within the AAo and proximal arch (P<.01-.05).
  
  
  CONCLUSIONS
  Increase in AAo diameter is significantly correlated with the presence and strength of supra-physiologic-helix and vortex formation in the AAo, as well with decrease in systolic WSS and increase in OSI.
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, University Hospital, Freiburg, Germany. jonas.buerk@uniklinik-freiburg.de
authors.forename: Jonas
authors.initials: J
authors.lastname: Bürk
authors.forename: Philipp
authors.initials: P
authors.lastname: Blanke
authors.forename: Zoran
authors.initials: Z
authors.lastname: Stankovic
authors.forename: Alex
authors.initials: A
authors.lastname: Barker
authors.forename: Maximilian
authors.initials: M
authors.lastname: Russe
authors.forename: Julia
authors.initials: J
authors.lastname: Geiger
authors.forename: Alex
authors.initials: A
authors.lastname: Frydrychowicz
authors.forename: Mathias
authors.initials: M
authors.lastname: Langer
authors.forename: Michael
authors.initials: M
authors.lastname: Markl
mesh_terms: D000328:Adult; D000368:Aged; D001013:Aorta, Thoracic / Q000473:pathology / Q000503:physiopathology*; D017545:Aortic Aneurysm, Thoracic / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology; D001783:Blood Flow Velocity; D004108:Dilatation, Pathologic; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012039:Regional Blood Flow; D012189:Retrospective Studies; D013314:Stress, Mechanical; D013997:Time Factors