Purely phase-encoded MRI of turbulent flow through a dysfunctional bileaflet mechanical heart valve.
OBJECTIVE
We have used a purely phase-encoded magnetic resonance imaging (MRI) technique, single-point ramped imaging with T1 enhancement (SPRITE), to investigate the steady, turbulent flow dynamics through a bileaflet mechanical heart valve (BMHV).


METHODS
We have measured in vitro the turbulent diffusivity and velocity downstream of the valve in two configurations (fully opened and partially opened), which mimic normal and dysfunctional operation. Our constant-time implementation of the MRI measurement is unusually robust to fast turbulent flows, and to artefacts caused by the pyrolytic carbon construction of the valve.


RESULTS
Turbulent diffusivity downstream of the normally functioning valve peaks at 1.05 × 10(-6)m(2)/s, while the turbulent diffusivity is higher downstream of the dysfunctional valve (peaking at 3.15 × 10(-6) m(2)/s) and is accompanied by a high-velocity fluid jet and re-circulating flow. The fluid jet is not along the centreline of the valve, as might be anticipated in conventional Doppler echocardiography measurements.


CONCLUSIONS
The nature of motion-sensitized SPRITE makes it unusually capable in turbulent flows and near to boundaries between different magnetic susceptibilities. These qualities have allowed us to compare the three-dimensional flow fields through normal and dysfunctional BMHVs.
Department of Physics, University of New Brunswick, 8, Bailey Dr., Fredericton, NB, E3B 5A3, Canada.
Olusegun
O
Adegbite
Lyes
L
Kadem
Benedict
B
Newling
D001783:Blood Flow Velocity / Q000502:physiology*; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000295:instrumentation / Q000379:methods; D006351:Heart Valves / Q000502:physiology* / Q000601:surgery; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000295:instrumentation / Q000379:methods*; D017711:Nonlinear Dynamics; D019047:Phantoms, Imaging; D011474:Prosthesis Design; D011475:Prosthesis Failure; D015203:Reproducibility of Results; D012212:Rheology / Q000295:instrumentation / Q000379:methods*; D012680:Sensitivity and Specificity