Numerical Investigations of MRI RF-Induced Heating for External Fixation Device in TEM and Birdcage Body Coils at 3 T

This paper investigates the radio frequency (RF)-induced heating in American Society for Testing and Materials phantom with a generic external fixation device for both birdcage (BC) coil and transverse electromagnetic (TEM) coil. Two typical orientations, i.e., fixture bar perpendicular to and parallel to the coil axis, have been considered. To compare the specific absorption rate and temperature rise in the two different RF coils at 3 T, both electromagnetic and thermal simulations were performed. It is found that tibia external fixation device with orientation parallel to the coil axis will induce severe heating effect in both coils. However, pelvic external fixation device induces larger heating level in TEM coil than BC coil. Furthermore, increasing the pin length or pin spacing of the pelvic external fixation device will cause a larger heating level in TEM coil, while such changes have no substantial effects on BC coil. We show that the transversely distributed electric field in TEM coil forms the underlying reason why pelvic external fixation device induces a higher heating level in TEM coil than BC coil. This finding also indicates that metallic external fixation devices with large dimensions along transverse direction, while might be safe in BC coil, can experience significant heating issue in TEM coil.