Numerical Investigations of MRI RF-induced Heating for Passive Implants in Birdcage and TEM Body Coils at 3 Tesla

This paper compares the radiofrequency (RF) -induced heating for passive implants between the birdcage (BC) coil and the transverse electromagnetic (TEM) coil at 3 Tesla (T). Two common passive implants, orthopedic plate and spinal fixation device were considered. To assess the RF-induced heating in the two different coils, electromagnetic simulations were performed to calculate the local specific absorption rate (SAR) in the standard phantom. It is determined that the device length leading to the worst-case heating is around 10 cm in both BC coil and TEM coil. This worst-case length corresponds to the half wavelength of the RF field at 3 T. It is also shown that for both orthopedic plates and spinal fixations, the BC coil generates larger RF-induced heatings than those from the TEM coil. This result indicates that in the presence of passive implants, patients undergoing TEM coil can have a larger safety margin. It would be more conservative to use BC coil, rather than TEM coil, to evaluate the RF-induced heating of medical implants.