Evaluation of RF heating on humerus implant in phantoms during 1.5T MR imaging and comparisons with electromagnetic simulation.

PURPOSE: To evaluate the effect of radiofrequency (RF) heating on a metallic implant during magnetic resonance imaging (MRI), temperatures at several positions of an implant were measured, and results are compared with electromagnetic simulations using a finite element method. METHODS: A humerus nail implant made of stainless steel was embedded at various depths of tissue-equivalent gel-phantoms with loop (loop phantom) and partially cut loop (loop-cut phantom), and the phantoms were placed parallel to the static magnetic field of a 1.5T MRI device. Scans were conducted at maximum RF for 15 min, and temperatures were recorded with 2 RF-transparent fiberoptic sensors. Finally, electromagnetic-field analysis was performed. RESULTS: Temperatures increased at both ends of the implants at various depths, and temperature increase was suppressed with increasing depth. The maximum temperature rise was 12.3 degrees C at the tip of the implant and decreased for the loop-cut phantom. These tendencies resembled the results of electromagnetic simulations. CONCLUSION: RF heating was verified even in a nonmagnetizing metal implant in a case of excessive RF irradiation. Particularly, rapid temperature rise was observed at both ends of the implant having large curvatures. The difference in temperature increase by depth was found to reflect the skin-depth effect of RF intensity. Electromagnetic simulation was extremely useful for visualizing the eddy currents within the loop and loop-cut phantoms and for evaluating RF heating of a metallic implant for MRI safety.