Comprehensive Analysis of Lenz Effect on the Artificial Heart Valves During Magnetic Resonance Imaging

Abstract

Abstract-This work presents results of a comprehensive analysis of the Lenz effect due to motion of artificial heart valves during magnetic resonance imaging. The interaction of rotating metallic heart valves with magnetic fields is studied by performing a time-domain analysis of the corresponding electromagnetic problem. We applied the finite element method (FEM) to solve the T − Ω formulation of Maxwell equations in two cases: first, for metallic disks located in the high intensity homogenous field of the magnet iso-center, and second, disks located in the non-uniform fringe field of the bore entrance. We showed that for valves with full solid disks (such as Starr-Edwards 6500) located in the magnet iso-center, the magnitude of adverse forces can be comparable to the forces applied by the beating heart. However, for rings which consist of multiply connected conductive regions, skin effect and proximity effect counteract, which leads to a diminished magnetic force. Results of this study show that mechanical heart valves with strengthening rings may be considered safe even under ultra-high imaging conditions with field intensities as high as 10 T. However, heart valves with full conducting disks should be considered as a contraindication to MR imaging.

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

“…As previously mentioned, Condon and Hadley and Robertson et al theorized, the resistive field created by a prosthetic heart valve as it moves through the B 0 field could be sufficient to retard the opening and closing function of the valve, leading to breathlessness, chest pain, pulmonary oedema, cardiac failure, and possibly even death in extreme cases. In a recent study that supported Condon and Hadley and Robertson et al's theory, Golestanirad et al reported, valves containing metal wire in the occluder demonstrated some degree of resistance due to Lenz forces and noted the magnitude of these forces were less than the mechanical forces of the beating heart (ie, ≤7.2 N). The authors therefore concluded any impedance of the valve's occluder/leaflet(s) due to the Lenz Effect would be negligible compared with the rate of change of the magnetic field even at high field strengths (ie, ≤10 T).…”

Application of Surgical Lead Management and Reconfigurable Coil Technology to Reduce RF Heating of DBS Implants during MRI at 3T Under Variant Body Compositions

“…In the past few years, numerical simulations have been increasingly used to assess safety of medical devices and imaging instruments [36], [54]- [58]. An important aspect of such practice is to validate simulations against measurements whenever possible, in order to provide confidence in future predictions of such models.…”

The physics of MRI safety

“…Further, because the magnitude of the induced current is proportional to conductivity, significant current densities may also be generated in metals used in implants. For example, currents induced in metallic heart valves have been studied over such concerns …”

“…For example, currents induced in metallic heart valves have been studied over such concerns. 41,42 The RF Field…”