Quantitative determination of magnetic force on a coronary stent in MRI.

ABSTRACT

PURPOSE: To introduce an analytical method for a quantitative determination of magnetic force on a coronary stent in the magnetic resonance imaging (MRI) magnet that is generally applicable to metallic implants. Magnetic forces on metallic implants in the MRI magnets are traditionally determined empirically by measuring deflection from the vertical plane at the central axis of the magnet and at the point of the largest force along the longitudinal axis of the magnet. MATERIALS AND METHODS: Magnetic and chemical characterization of the stents was performed by a commercial magnetometer and energy-dispersive X-ray spectroscopy. Magnetic force on the stents fabricated of paramagnetic alloys (surgical stainless steel and cobalt-chromium) was determined by measuring the stent's magnetic dipole moment and employing the on-axis magnetic field profile of an MRI magnet. RESULTS: The maximum force on the stainless steel stent was found to be F(S,max) = 0.18 mN, whereas on the cobalt-chromium stent it was F(C,max) = 0.06 mN. CONCLUSION: The magnetic force on the investigated paramagnetic stents is even smaller than the gravitational force acting on the stents in the Earth's gravity field, so that it has no physiological impact on the stented vessels.