High-resolution assessment of velocity fields and shear stresses distal toprosthetic heart valves using high-field magnetic resonance imaging

Background and aim of the study: Complications after replacement of disease d heart valves with mechanical prostheses have been shown to be related to the hemodynamics distal to the valve, For this reason, the velocity pattern s have been disclosed in vitro with. a variety of different techniques. Thi s study introduces a magnetic resonance imaging (MRI) -based technique, whi ch entails easy acquisition of fluid velocity field data with a high accura cy and spatial resolution. Methods: A high-field magnetic resonance scanner equipped with short echo t ime phase-contrast velocity measurement software was applied in a detailed mapping of the axial velocity profile across the entire vessel area at two positions downstream of a bileaflet valve prosthesis inserted in a pulsatil e flow system in vitro. The laminar shear forces were calculated from the f luid velocity field data. Results: The velocity profiles very close to the valve reflected the bileaf let design as also shown in previous studies, but the extent and velocities of the jet emanating from the slit between the leaflets were clearly bette r visualized. However, one diameter downstream of the valve the central jet was completely dispersed and the hemodynamic complexity was significantly reduced. Recirculation and refro-grade flow regions that might be relevant for understanding typical long-term complications after implantation were o bserved close to the value. Conclusions: In one scan experiment the presented method provides informati on on flow characteristics that previously required application of differen t types of experiment. Thus, the method seems promising as a new technique for detailed and extensive mapping of the velocities and laminar shear stre sses downstream of prosthetic heart valves in vitro.