Safe electrical stimulation of the cochlear nerve at the promontory duringfunctional magnetic resonance imaging

The purpose of this study was to evaluate possibilities and technical risks for combining intended electrical stimulation of the cochlear nerve and fu nctional magnetic resonance imaging (fMRI). Theoretical considerations and experiments indicate that fMRI can be performed safely during electrical st imulation, A nerve stimulator was developed with minimized length of electr ical conductors, current limiting resistance, high inner impedance of a cur rent source, radio frequency (RF)-shielding, and avoidance of ferromagnetic materials. This nerve stimulator transfers the optically encoded stimulati ng current signal via a fiber optic cable located near the area of stimulat ion. There, the optical signal drives an MRI-compatible current source. Thi s set-up was tested with transtympanic electrical stimulation of the cochle ar nerve at the promontory during an fMRI examination, No hazardous effects could be detected. The stimulation resulted in activation of the Heschl's gyrus. Compared to the conventional promontory testing this method may allo w a more objective examination of cochlear implant candidates. Magn Reson M ed 42:371-378, 1999. (C) 1999 Wiley-Liss, Inc.