Development of an Apparatus for Digital Measurement of Magnetically Induced Torque on Medical Implants to Facilitate the Application of the ASTM F2213 Standard.

OBJECTIVE

The ASTM F2213 standard describes the measurement of the magnetically induced torques by means of a torsional spring method. As this method is highly complex, it has rarely ever been employed. The purpose was to develop an easy-to-handle measuring setup for the reproducible, fast, and precise measurement of magnetically induced torques, following ASTM F2213, at a static magnetic field (B) of 1.5 and 3 T.

METHODS

An magnetic resonance (MR)-save measuring platform was developed according to the ASTM F2213 standard and combined with a precision balance. The evaluation was performed with ten test objects, e.g., a steel screw (length 60 mm) and a neurostimulator, at 1.5 and 3 T. The torque was measured at 10° increments as the test object was rotated relative to B.

RESULTS

The measurement setup allows fast and reproducible measurements. The maximum magnetically induced torque measured was 397 ± 2 N·mm for the steel screw and 63 ± 1 N·mm for the neurostimulator. The maximum torque on a test object is insensitive to B if the magnetization of the object has reached saturation.

CONCLUSION

Ferromagnetic implants may exhibit strong magnetically induced torques during MRI examination. For analyzing these magnetically induced torques, we developed a digital measuring device that allows simplified and accelerated application of the ASTM F2213 standard test method.

SIGNIFICANCE

In a B, ferromagnetic implants may exert considerable torques on the surrounding tissue. These forces may affect the functionality of the implant and inflict severe injuries on a patient.