Electromyography in MRI--first recordings of peripheral nerve activation caused by fast magnetic field gradients.
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.
Hoffmann
A
A
Institute of Diagnostic Radiology, Klinikum Grosshadern, University of Munich, Germany. alexander.hoffmann@ikra.med.uni-muenchen.de
Faber
S C
SC
Werhahn
K J
KJ
Jäger
L
L
Reiser
M
M
D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004574:Electromagnetic Fields; D004576:Electromyography / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D010525:Peripheral Nerves / Q000502:physiology*; D012016:Reference Values; D012680:Sensitivity and Specificity; D012684:Sensory Thresholds / Q000502:physiology