title: Flow-sensitive 4D MRI of the thoracic aorta: comparison of image quality, quantitative flow, and wall parameters at 1.5 T and 3 T.
abstract: OBJECTIVE
  To evaluate the effect of field strength on flow-sensitive 4D magnetic resonance imaging (MRI) of the thoracic aorta. A volunteer study at 1.5 T and 3 T was conducted to compare phase-contrast MR angiography (MRA) and 3D flow visualization quality as well as quantification of aortic hemodynamics.
  
  
  METHODS
  Ten healthy volunteers were examined by flow-sensitive 4D MRI at both 1.5 T and 3 T MRI with identical imaging parameters (TE/TR = 6/5.1 msec, spatial/temporal resolution ≈2 mm/40.8 msec). Analysis included assessment of image quality of derived aortic 3D phase contrast (PC) angiography and 3D flow visualization (semiquantitative grading on a 0-2 scale, two blinded observers) and quantification of blood flow velocities, net flow per cardiac cycle, wall shear stress (WSS), and velocity noise.
  
  
  RESULTS
  Quality of 3D blood flow visualization (average grading = 1.8 ± 0.4 at 3 T vs. 1.1 ± 0.7 at 1.5 T) and the depiction of aortic lumen geometry by 3D PC-MRA (1.7 ± 0.5 vs. 1.2 ± 0.6) were significantly (P < 0.01) improved at 3 T while velocity noise was significantly higher (P < 0.01) at 1.5 T. Velocity quantification resulted in minimally altered (0.05 m/s, 3 mL/cycle and 0.01 N/m(2)) but not statistically different (P = 0.40, P = 0.39, and P = 0.82) systolic peak velocities, net flow, and WSS for 1.5 T compared to 3 T.
  
  
  CONCLUSIONS
  Flow-sensitive 4D MRI at 3 T provided improved image quality without additional artifacts related to higher fields. Imaging at 1.5 T MRI, which is more widely available, was also feasible and provided information on aortic 3D hemodynamics of moderate quality with identical performance regarding quantitative analysis.
authors: Department of Neurology, University Hospital Freiburg, Freiburg, Germany. christoph.strecker@uniklinik-freiburg.de
authors: Christoph
authors: C
authors: Strecker
authors: Andreas
authors: A
authors: Harloff
authors: Wolf
authors: W
authors: Wallis
authors: Michael
authors: M
authors: Markl
mesh_terms: D000328:Adult; D001013:Aorta, Thoracic / Q000033:anatomy & histology / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D055424:Cardiac-Gated Imaging Techniques / Q000379:methods*; D002318:Cardiovascular Diseases / Q000175:diagnosis*; 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*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity