Absence of radiofrequency heating from auditory implants during magnetic resonance imaging

The possibility of tissue heating due to an auditory brainstem implant (ABI) or a modified cochlear implant (CI) during magnetic resonance imaging (MRI) of the head was tested on a full-sized human phantom using a realistic phantom head consisting of simulated skull, brain, and muscle. Dielectric properties of the brain, muscle, and bone materials were similar to those of human tissues at 64 MHz. The body consisted of homogeneous phantom muscle enclosed in a human-shaped fiberglass shell. Thermographic and fiber-optic temperature measurements were conducted to reveal any heating. Thermograms of sagittal, frontal, and horizontal planes of the head with the ABI and CI electrodes were taken immediately before and after a 26 min MRI scan. The MRI sequence was set at 94 excitations and 25 ms echo time to induce maximum radiofrequency heating, as suggested by the General Electric Company. The difference of these two thermograms gives the heating results. In two uncut phantom heads. Teflon tubes were placed along the implanted ABI and CI, and temperature data were recorded via fiber-optic probes before, during, and after the MRI. Results showed no observable heating associated with the ABI and the modified CI during worst-case MRI of the head.