title: Comparison of magnetic resonance imaging and Laser Doppler Anemometry velocity measurements downstream of replacement heart valves: implications for in vivo assessment of prosthetic valve function.
abstract: OBJECTIVE
  The non-invasive, in-vivo assessment of prosthetic valve function is compromised by the lack of accurate measurements of the transvalvular flow fields or hemodynamics by current techniques. Short echo time magnetic resonance imaging (MRI) may provide a method for the non-invasive, in vivo assessment of prosthetic valve function by accurately measuring changes in the transvalvular flow fields associated with normal and dysfunctional prosthetic valves. The objectives of these in vitro experiments were to investigate the potential for using MRI as a tool to measure the complex flow fields distal to replacement heart valves, and to assess the accuracy of MRI velocity measurements by comparison with Laser Doppler Anemometry (LDA), a gold standard.
  
  
  METHODS
  The velocity fields downstream of tilting disc, bileaflet, ball and cage, and pericardial tissue valves were measured using both three-component LDA and MRI phase velocity encoding under a steady flow rate of 22.8 l/min, simulating peak systolic flow. The valves were tested under normal and stenotic conditions to assess the MRI capabilities under a wide range of local flow conditions, velocities and turbulence levels. A new short echo time MRI technique (FAcE), which allowed velocity measurements in stenotic jets with high turbulence, was tested.
  
  
  RESULTS
  Good overall agreement was obtained between the MRI velocity measurements and the LDA data. The MRI velocity measurements adequately reproduced the spatial structure of the flow fields. In most cases peak velocities were accurately measured to within 15%.
  
  
  CONCLUSIONS
  The results indicate that the FAcE MRI method has the potential to be used as a diagnostic tool to assess prosthetic valve function.
authors.affiliation: Cardiovascular Fluid Mechanics Laboratory, Georgia Institute of Technology, Altanta, GA, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Fontaine
authors.forename: R S
authors.initials: RS
authors.lastname: Heinrich
authors.forename: P G
authors.initials: PG
authors.lastname: Walker
authors.forename: E M
authors.initials: EM
authors.lastname: Pedersen
authors.forename: M B
authors.initials: MB
authors.lastname: Scheidegger
authors.forename: P
authors.initials: P
authors.lastname: Boesiger
authors.forename: S P
authors.initials: SP
authors.lastname: Walton
authors.forename: A P
authors.initials: AP
authors.lastname: Yoganathan
mesh_terms: D001021:Aortic Valve / Q000503:physiopathology / Q000601:surgery*; D001705:Bioprosthesis; D001783:Blood Flow Velocity / Q000502:physiology*; D004867:Equipment Design; D004868:Equipment Failure; D006350:Heart Valve Prosthesis; D006801:Humans; D017078:Laser-Doppler Flowmetry; D019028:Magnetic Resonance Imaging, Cine; D008955:Models, Cardiovascular; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity