High-resolution assessment of velocity fields and shear stresses distal to prosthetic heart valves using high-field magnetic resonance imaging.
OBJECTIVE
Complications after replacement of diseased heart valves with mechanical prostheses have been shown to be related to the hemodynamics distal to the valve. For this reason, the velocity patterns have been disclosed in vitro with a variety of different techniques. This study introduces a magnetic resonance imaging (MRI) -based technique, which entails easy acquisition of fluid velocity field data with a high accuracy and spatial resolution.


METHODS
A high-field magnetic resonance scanner equipped with short echo time 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 pulsatile flow system in vitro. The laminar shear forces were calculated from the fluid velocity field data.


RESULTS
The velocity profiles very close to the valve reflected the bileaflet design as also shown in previous studies, but the extent and velocities of the jet emanating from the slit between the leaflets were clearly better visualized. However, one diameter downstream of the valve the central jet was completely dispersed and the hemodynamic complexity was significantly reduced. Recirculation and retrograde flow regions that might be relevant for understanding typical long-term complications after implantation were observed close to the valve.


CONCLUSIONS
In one scan experiment the presented method provides information on flow characteristics that previously required application of different types of experiment. Thus, the method seems promising as a new technique for detailed and extensive mapping of the velocities and laminar shear stresses downstream of prosthetic heart valves in vitro.
Ringgaard
S
S
MR Research Center and Department of Cardiothoracic and Vascular Surgery, Institute of Experimental Clinical Research, Aarhus University Hospital, Denmark.
Botnar
R M
RM
Djurhuus
C
C
Stodkilde-Jorgensen
H
H
Hasenkam
J M
JM
Boesiger
P
P
Pedersen
E M
EM
D001783:Blood Flow Velocity; D006350:Heart Valve Prosthesis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging