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Heart motion-adapted MR velocity mapping of blood velocity distribution downstream of aortic valve prostheses: initial experience.

PURPOSE
To investigate blood flow velocities and shear rates at two distances downstream of an artificial aortic valve in patients.


MATERIALS AND METHODS
Blood velocity was quantified downstream of the valve prosthesis (for replacement after aortic valve stenosis or combined stenosis and regurgitation) in 10 patients by using a magnetic resonance (MR) cine velocity mapping method in which the imaging section position is adapted according to the excursion of the valvular plane of the heart. Two acquisitions were performed to display the blood velocity distributions one-fourth valve diameter and one valve diameter downstream of the valve and to quantify blood volumes and shear rates.


RESULTS
The velocity profiles measured during flow acceleration one-fourth valve diameter downstream were characterized by a distinct pattern of two lateral jets and one central jet of antegrade flow. High shear rates were found along the leaflet tips. The profiles obtained one valve diameter downstream were skewed, with varying velocity patterns among patients. Peak shear rates were found close to the vessel wall. With correction for through-plane motion of the valve, the mean apparent regurgitant fraction (+/- SD) was 14% +/- 6; the mean regurgitant fraction without correction was 9% +/- 5.


CONCLUSION
The described noninvasive procedure for velocity mapping enables measurements close to the valve and thus evaluation of blood flow patterns with respect to valve design in humans.