Hoffmann A, Faber S C, Werhahn K J, Jäger L, Reiser M
Institute of Diagnostic Radiology, Klinikum Grosshadern, University of Munich, Germany.
Magn Reson Med. 2000 Apr;43(4):534-9. doi: 10.1002/(sici)1522-2594(200004)43:4<534::aid-mrm7>3.0.co;2-j.
Prior studies on the evaluation of stimulation by MRI were based on the subjective feeling of the volunteers. A wide variety of stimulation thresholds between the subjects was observed. In order to exclude subjective perception levels as a cause of this variation, we developed a method to investigate the activation of peripheral nerves after gradient switching by electromyography (EMG) within the MR-imager. Five healthy volunteers were positioned in the MR-scanner with the bridge of the nose at isocenter. The amplitude of sinusoidal pulse trains of the anterior-posterior gradient (rise-times: 200 or 300 micros, various numbers of oscillations) was increased stepwise. Four surface electrodes were placed on the region where a muscle-twitch was reported. Electric activity of the muscle during stimulation experiments was recorded with an MR-compatible electro-physiologic amplifier. Stimulation thresholds were defined by the appearance of an EMG-signal. Thresholds were sharp and consistent with the report of the subjects.
