MRI Safety Considerations for Permanent Magnet Implants in Muscle

Area of Science:

• Biomedical Engineering
• Materials Science
• Radiology

Background:

• Permanent magnet implants are utilized in various medical devices, including cochlear implants and prosthetic controls.
• Their use necessitates caution due to potential interactions with Magnetic Resonance Imaging (MRI).
• Previous research assessed magnet stability and image artifacts, but intramuscular magnets for prosthetics require further MRI conditionality evaluation.

Purpose of the Study:

• To evaluate the position and magnetization stability of 3-mm-diameter spherical permanent magnets implanted in muscle.
• To assess image artifacts generated by these implants under MRI conditions.

Main Methods:

• A prospective longitudinal study was conducted using porcine models with magnets implanted in eight muscles.
• Histological examination assessed implant migration and fibrotic response, complemented by CT imaging for secondary analysis.
• Benchtop studies quantified worst-case demagnetization and MRI image artifact sizes.

Main Results:

• Histological analysis revealed intact fibrotic capsules around both magnet and control sites, indicating no significant migration.
• MRI exposure at 0.55-T and 1.5-T did not affect implant migration (p > 0.96).
• Maximum demagnetization was 13.5% at 1.5-T, and image artifacts extended up to 71 mm.

Conclusions:

• The studied permanent magnet implants demonstrated resistance to migration and substantial demagnetization under 0.55-T and 1.5-T MRI.
• Negligible image artifacts were observed, suggesting these implants do not contraindicate MRI up to 1.5T.
• Patients with these intramuscular permanent magnet implants can likely undergo MR imaging safely.