Potential MR hazard to patients with metallic heart valves: The Lenz effect

The Lenz effect on the motion of metal containing moving parts of artificia l heart valves has not been considered to date. In this paper the basic the ory is outlined and a simple model applied to estimate worst-case forces on such valves. The results indicate a potential for forces over 100 times gr eater than for the more widely recognized ferromagnetic interation. Resisti ve pressure effects comparable to cardiac pressure differences may occur fo r such valves in the mitral position even at fields as low as 1.5 T. The ef fect will increase linearly with field strength. Additional monitoring and perhaps even exclusion of such patients may be prudent, even at 1.5 T. (C) 2000 Wiley-Liss, Inc.