Assessment of magnetic field (4.7 T) induced forces on prosthetic heart valves and annuloplasty rings.
OBJECTIVE
To assess the magnetic field interactions on 11 heart valve prostheses and 12 annuloplasty rings subjected to a 4.7 T MR system.


METHODS
Ex vivo testing was performed to evaluate translational and rotational forces using previously described techniques.


RESULTS
Seventeen out of 23 prostheses showed zero interaction with the magnetic field. Translational forces with deflection angles of 2-20 degrees were demonstrated in six prostheses. Only two heart valves and two annuloplasty rings demonstrated rotational forces. The Carpentier Edwards (CE) Physio Ring, which contains Elgiloy, demonstrated deflection angles three times greater than those previously measured at 1.5 T. Furthermore, there was a direct relationship between increasing prosthesis size and increasing translational force. All heart valve prostheses attracted to the magnetic field were slightly paramagnetic/weakly ferromagnetic.


CONCLUSIONS
Twenty-three heart valve prostheses evaluated for MRI are considered safe in static fields up to 4.7 T based on current safety criteria. However, the CE Physio Ring appeared to develop an increasing magnetism upon re-entry into the MR system. We conclude that prostheses made from Elgiloy may not be acceptable for patients in an MR environment of > or =4.7 T. Further investigations are required to confirm the safety of Elgiloy.
Edwards
Maria-Benedicta
MB
United Kingdom Heart Valve Registry, Department of Cardiothoracic Surgery, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom. m.b.edwards@ic.ac.uk
Ordidge
Roger J
RJ
Hand
Jeffrey W
JW
Taylor
Kenneth M
KM
Young
Ian R
IR
D001705:Bioprosthesis; D019245:Compressive Strength; D004574:Electromagnetic Fields; D006350:Heart Valve Prosthesis; D006351:Heart Valves / Q000033:anatomy & histology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008422:Materials Testing / Q000379:methods*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012680:Sensitivity and Specificity; D013718:Tensile Strength