A novel method for measuring the torque on implantable cardiovascular devices in MR static fields

Purpose To propose a novel quantitative method for measuring the torque acting on mechanical heart valve prostheses subjected to a high static magnetic field in a MR scanner. Materials and Methods Torque measurements were performed with a torsion balance, implemented with a copper wire. The reaction torque exerted by the static magnetic field on the device was measured optically from the deflection angle of a laser beam spot on a graduate scale. Three different types of mechanical valves (two bileaflet and one monoleaflet) were tested at different locations of a small bore 4.7 tesla system. Results The method proved to be particularly sensitive (detectability limit lower than 10 −6 N · m), reliable and yielded quantitative reproducible results. The equivalent force of the torque measured for the three valves was at least 10 3 ‐fold lower than the force exerted by the beating heart. Conclusion The proposed method provides a quantitative evaluation of the torque induced on prosthetic device by a MR scanner operating at high magnetic field. J. Magn. Reson. Imaging 2007;26:1368–1374. © 2007 Wiley‐Liss, Inc.