Assessment Of Magnetically Induced Displacement Force And Torque On Metal Alloys Used In Medical Devices

Millions of patients receive magnetic resonance imaging (MRI) scans each year, and thousands of healthcare professionals and other individuals also routinely enter the magnetic resonance (MR) environment. The electric and magnetic fields used by the MR system to create MR images produce hazards that must be considered to determine whether a medical device or other object may safely be used in or near an MR system. Magnetically induced deflection force and torque are two of the hazards that must be addressed to determine the MRI safety of any device or object that will be used in or near an MR system. This article presents magnetically induced force and torque test results for a variety of common medical implant alloys. For seven of the eleven tested alloys, magnetically induced force is less than the device weight in any current clinical 1.5, 3.0, and 7.0-T MR system. For the other alloys, the magnetically induced force is greater than the device weight in some MR systems. The torque test results for the tested alloys demonstrate that for static magnetic fields of 3.0 T or less, the magnetically induced torque will always be less than the worst case torque produced by gravity. These results may be leveraged in MRI safety assessments for medical devices and other objects composed of those alloys and conforming to the same ASTM specifications and may be used as part of the information needed to generate MR Conditional labeling for the devices.