On the RF safety of titanium mesh head implants in 7 T MRI systems: an investigation

Abstract

Purpose

Patients undergoing craniofacial surgery for skull reconstruction may have titanium mesh implants. The safety risks related to 7 T MRI with these patients are not well understood. This study investigates the RF heating of titanium mesh head implants at 7 T.

Methods

A simulation model for a 7 T birdcage head coil was developed and validated against $\left(B_1^{+}\right)$, 1 g-averaged specific absorption rate (SAR), and temperature measurements in the presence of a titanium mesh. Various mesh sizes and shapes at different angular positions were simulated to determine the worst-case scenario in a spherical phantom in addition to the effect of rounding the mesh edges. Full-wave electromagnetic and bioheat thermal simulations were conducted on anatomical human models.

Results

Preliminary results indicate an increase in the local SAR near the meshes depending on the shape, size, and location. The maximum absolute temperatures in the head were, on average, around 38.2°C after 15 min of RF power exposure, corresponding to 3.2 W/kg whole-head SAR without a titanium mesh implant. The maximum absolute temperatures did not significantly change after introducing the titanium mesh implants, and the highest temperature was 38.4°C, observed near the cerebellum and the facial muscles. The maximum local increase in temperature was observed at the vicinity of the mesh as 2.8°C. Finally, it was shown that large mesh implants can negatively impact $\left(B_1^{+}\right)$ field.

Conclusions

Small rounded titanium mesh head implants can be generally safe for 7 T MRI scans under the standard guidelines. Avoiding sharp corners and edges may reduce the chances of RF safety risks.