Vibratory sample magnetometry of middle ear prostheses and manufacturing materials.
OBJECTIVE
To assess the magnetic properties of stapes prostheses and manufacturing materials using a vibratory sample magnetometer (VSM).


METHODS
VSM was performed on 16 samples, including ferromagnetic 420F stainless steel, with an LDJ Model 9600 VSM in accordance with American Society for Testing and Materials standard A894.


RESULTS
A VSM measures the magnetic dipole moment of a sample in a magnetic field. The magnetic field is swept over a range of magnetic fields, and the magnetic dipole moment is plotted as a function of field. The prostheses made of 316L stainless steel previously found to be ferromagnetic had the highest specific magnetic moments. The specific magnetic moments ranged from 0.023 electromagnetic units (emu)/g to 156 emu/g. The samples made with 316L stainless steel, which is used in otologic implants, were significantly less magnetic than was the 420F stainless steel.


CONCLUSIONS
VSM demonstrates that prostheses made with 316L stainless steel are relatively nonferromagnetic compared with 420F stainless steel. However, none of the implants are nonmagnetic. The torque and linear force on the prosthesis is a concern. The safety of performing MRI on patients with these implants needs to be further assessed.
Syms
M J
MJ
House Ear Clinic, Los Angeles, California 90057, USA.
Peterman
D W
DW
D004574:Electromagnetic Fields / Q000009:adverse effects*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000009:adverse effects*; D008670:Metals / Q000627:therapeutic use*; D009998:Ossicular Prosthesis; D011475:Prosthesis Failure; D013199:Stapes; D013701:Temporal Bone / Q000601:surgery; D019415:Torque; D014732:Vibration
D008670:Metals