COMPARISON OF MAGNETIC-RESONANCE-IMAGING AND LASER-DOPPLER ANEMOMETRYVELOCITY-MEASUREMENTS DOWNSTREAM OF REPLACEMENT HEART-VALVES - IMPLICATIONS FOR IN-VIVO ASSESSMENT OF PROSTHETIC VALVE FUNCTION

Background and aim of the study: The non-invasive, in-vivo assessment of prosthetic valve function is compromised by the lack of accurate me asurements of the trasvalvular flow fields or hemodynamics by current techniques. Short echo time magnetic resonance imaging (MRI) may provi de a method for the non-invasive, in vivo assessment of prosthetic val ve 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 pote ntial for using MRI as a tool to measure the complex flow fields dista l to replacement heart valves, and to assess the accuracy of MRI veloc ity 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 Row rate of 22.8 l/min, simulating peak systolic flow. The va lves were tested under normal and stenotic conditions to assess the MR I capabilities under a wide range of local flow conditions, velocities and turbulence levels. A new short echo time MRI technique (FAcE), wh ich allowed velocity measurements in stenotic jets with high turbulenc e, was tested. Results: Good overall agreement was obtained between th e MRI velocity measurements and the LDA data. The MRI velocity measure ments 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 pot ential to be used as a diagnostic tool to assess prosthetic valve func tion.