Measurement of visual evoked potential during and after periods of pulsed magnetic field exposure

Purpose: To study the effect of switched magnetic fields used in MR scanners on the visual evoked potential (VEP) in human subjects. Materials and Methods: We have used an MRI gradient coil, remote, from an MRI magnet to produce a time-varying magnetic field (0.5 kHz, peak field similar to 8.7 T/second) in the human brain without the confounding effects of static field exposure, or accompanying acoustic noise. The VEP response to a 2-Hz reversal, 8 x 8 checkerboard, occupying 20 degrees of the visual field was recorded from occipital locations O1 and O2. VEP recordings were made every five minutes before, during, and after a 10-minute magnetic field exposure, period for seven subjects. Results: In contradiction to studies previously reported in the literature for fields of 50 Hz and 60 mT, no significant effects on the peak amplitude or latency of the VEP P100 O1 and O2 responses were found. Conclusion: Switched magnetic fields of a level and frequency comparable to those used in MRI do not have a significant effect on primary retinal or visual processing.