In vitro assessment of the lenz effect on heart valve prostheses at 1.5 T

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.

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“…The interaction between both mechanical and biological valve prostheses and magnetically induced electric currents has been demonstrated [34]. …”

Section: Discussionmentioning

confidence: 99%

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

Richau

Dieringer

Traber

et al. 2016

Journal of Cardiovascular Magnetic Resonance

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“…Golestanirad et al [14] concluded that the effect of induced vibration through gradient switching can be neglected because of the small amplitudes of the gradient fields. Edwards et al [15] built a flow rate setup to investigate potential flow rate irregularities of heart valves. These experiments revealed flow irregularities when valves were moved in the fringe field.…”

Section: Introductionmentioning

confidence: 99%

Gradient-Induced Mechanical Vibration of Neural Interfaces During MRI

Fuhrer

Jouda

Klein

et al. 2020

IEEE Trans. Biomed. Eng.

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Resonant vibrations of implanted structures during an MRI procedure pose a risk to the patient in the form of soft tissue irritation and degradation of the implant. In this study, the mechanical behavior of implant structures in air, water, and viscoelastic materials was explored. Methods: The static and dynamic transfer functions of various test samples in air, and immersed in both water, and hydrogels, were analyzed. The laser-based acquisition method facilitates high angular resolution (10 µDeg) and high dynamic range (0 to 6 kHz) measurements. Additional MRI experiments were conducted to investigate the dependence of vibration strength on MR sequence parameters in combination with the obtained transfer functions. Results: The largest forces were found to be in the µN to mN range, which is comparable to forces applied during implantation. Of additional concern was the damping introduced by viscoelastic tissue, which was less than expected, leading to an underdamped system. In contrast to current wisdom, the imaging experiments demonstrated drastically different vibration amplitudes for identical gradient slope but different timing parameters TR, mainly due to resonant amplification. Conclusion: The results showed that a safe, force-free MR procedure depends not only on the gradient slope, but also and more drastically on the choice of secure timing parameters. Significance: These findings delineate design improvements to achieve longevity of implants, and will lead to increased patient safety during MRI. A prudent choice of mechanical characteristics of implanted structures is sufficient to avoid resonant excitation due to mismatched MR sequence parameters.

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Gradient‐induced vibrations and motion‐induced Lenz effects on conductive nonmagnetic orthopedic implants in MRI

Zilberti,

Curreli,

Arduino

et al. 2024

Magnetic Resonance in Med

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PurposeTo quantify the extent of gradient‐induced vibrations, and the magnitude of motion‐induced displacement forces (“Lenz effect”), in conductive nonmagnetic orthopedic prostheses.MethodsThe investigation is carried out through numerical simulations, for a 3 T scanner. For gradient‐induced torques and vibrations, a knee and a shoulder implant are considered, at dB/dt equal to 42 T/s (rms). For motion‐induced forces associated with the Lenz effect, a knee and a hip implant are studied, considering a patient who translates on the examination couch, or walks next to it.ResultsGradient‐induced torques may be within the same order of magnitude as the worst case gravitational torque defined in the ASTM standards. However, for all investigated cases, they result to be lower. In vacuum, the extent of the corresponding vibration reduces with frequency. At the lowest investigated frequency (270 Hz), it keeps below 25 μm. For an implant partially embedded in bone, the extent of the vibration increases with frequency. Nevertheless, the displacement is far lower than the worst case observed in vacuum (negligible in contact with the bone; ˜1 μm or less where the implant emerges from the bone). The Lenz effect induced by the motion of the patient through the stationary magnetic field produces forces on the order of a few millinewtons (i.e., at least two orders of magnitude lower than the implant weight).ConclusionComparing the results with mechanical loads caused by ordinary activities of daily living, and with the levels of tolerable micromotions, a good safety margin is confirmed.

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In vitro assessment of the lenz effect on heart valve prostheses at 1.5 T

Cited by 6 publications

References 28 publications

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

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

Gradient-Induced Mechanical Vibration of Neural Interfaces During MRI

Gradient‐induced vibrations and motion‐induced Lenz effects on conductive nonmagnetic orthopedic implants in MRI

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