Effects of heart valve prostheses on phase contrast flow measurements in Cardiovascular Magnetic Resonance – a phantom study

Abstract

BackgroundCardiovascular Magnetic Resonance is often used to evaluate patients after heart valve replacement. This study systematically analyses the influence of heart valve prostheses on phase contrast measurements in a phantom trial.MethodsTwo biological and one mechanical aortic valve prostheses were integrated in a flow phantom. B0 maps and phase contrast measurements were acquired at a 1.5 T MR scanner using conventional gradient-echo sequences in predefined distances to the prostheses. Results were compared to measurements with a synthetic metal-free aortic valve.ResultsThe flow results at the level of the prosthesis differed significantly from the reference flow acquired before the level of the prosthesis. The maximum flow miscalculation was 154 ml/s for one of the biological prostheses and 140 ml/s for the mechanical prosthesis. Measurements with the synthetic aortic valve did not show significant deviations. Flow values measured approximately 20 mm distal to the level of the prosthesis agreed with the reference flow for all tested all prostheses.ConclusionsThe tested heart valve prostheses lead to a significant deviation of the measured flow rates compared to a reference. A distance of 20 mm was effective in our setting to avoid this influence.

Standardized image interpretation and post-processing in cardiovascular magnetic resonance - 2020 update

“…iii) In general, the area that exceeds the VENC in the ROI is in the center of the vessel and not at the edges; if it is at the edges, it is usually (but not always) outside the vessel. iv) If imaging in the presence of devices, signal loss may be present as artifact and interpretation must proceed with caution [80]. v) When measuring peak velocity, some software packages will determine the peak velocity in one pixel in the ROI whereas others may take the peak velocity of the average of a few adjacent pixels in the ROI.…”

CMR quantitation of change in mitral regurgitation following transcatheter aortic valve replacement (TAVR): impact on left ventricular reverse remodeling and outcome

“…MR fraction in the context of severe AS may be overestimated using CMR phase contrast imaging due to underestimation of aortic forward flow when sampling high velocities. When performing phase contrast-based flow measurements in patients with heart valve replacement, there is also a potential for flow and volume miscalculation due to prosthesis-related distortions of the magnetic field [ 29 ]. Confounders such as primary or ischemic etiology, change in medications and development of bundle branch block or aortic regurgitation could additionally impact on cardiac reverse remodeling following TAVR.…”

4D Flow MRI quantification of blood flow patterns, turbulence and pressure drop in normal and stenotic prosthetic heart valves

“…and kv is the amount of flow sensitivity, which is related to the velocity encoding parameter (VENC) as kv = π/VENC. When turbulent flow occurs in the region of interest, the intravoxel velocity variance (IVVV) of the turbulent flow along the i-direction, 2 , can be estimated by the magnitude ratio between the reference signal without velocity encoding S(0) and the signal with velocity encoding along the i-direction Si(kv) as follows [22,23]:…”

“…The replacement of diseased heart valves with prosthetic heart valves (PHVs) has saved numerous lives since the first implant in the early 1960s. Approximately 90,000 patients receive a PHV each year in the United States and 280,000 worldwide [1,2]. The continuous improvement in surgical and interventional procedures will lead to an increasing number of patients living with a PHV in the future.…”

“…However, TTE can be observer-dependent and mean or peak velocity of the flow provides only limited information about the valvular blood flow, and is occasionally misleading as to the severity of the stenosis [5][6][7][8]. Therefore, assessment of the hemodynamics using cardiovascular magnetic resonance (CMR) has been proposed as a complement to the conventional TTE evaluation as it is independent of the anatomy of the patient and less observer-dependent [2,9]. Time-resolved, three-directional and three-dimensional phase-contrast magnetic resonance imaging (which is widely known as 4D PC-MRI or 4D Flow MRI) has been demonstrated to provide non-invasive and multi-dimensional hemodynamic analysis [10][11][12].…”