[Magnetically Induced Displacement Force Test Method for Ultralight Implants Based on Counterweight Correction Method].

ASTM (American Society for Testing and Materials) F2052-21 (Chinese corresponding standard titled as YY/T 0987.2) introduces a test method to measure the magnetically induced displacement force on medical devices in the magnetic resonance environment. This method has been widely accepted and utilized globally, which is intended for implantable medical devices that can be suspended from a string. The angular deflection of the string from the vertical is measured and thereby measuring out the magnitude of the magnetically induced deflection force relative to gravity. When applying this method on ultralight implants, it is practically almost impossible to use a suspension string that weighs less than 1% of the mass of the implant. That study proposes a method for measuring the magnetically induced displacement force on ultralight implants based on counterweight correction by using a string and clamp that exceed 1% of the weight of the implant. And then to measure the deflection angle according to the standard requirement, following that to correct the deflection angle by using the proportion of the mass of the implant under test to the total mass of the tested object, to obtain the measurement result. That study also provides theoretical calculations and experimental verification to the counterweight correction method, the results prove that the proposed method can effectively measure the magnetically induced displacement force on ultralight implants.