title: [Effects of MRI on the electrophysiology of the motor cortex: a TMS study].
abstract: OBJECTIVE
  The increasing spread of high-field and ultra-high-field MRI scanners encouraged a new discussion on safety aspects of MRI examinations. Earlier studies report altered acoustically evoked potentials. This finding was not able to be confirmed in later studies. In the present study transcranial magnetic stimulation (TMS) was used to evaluate whether motor cortical excitability may be altered following MRI examination even at field strength of 1.5 T.
  
  
  METHODS
  In 12 right-handed male volunteers individual thresholds for motor responses and then the length of the post-excitatory inhibition (silent period) were determined. Subsequently the volunteers were examined in the MRI scanner (Siemens Avanto, 1.5 T) for 63 minutes using gradient and spin echo sequences. MRI examination was immediately followed by another TMS session and a third 10 minutes later. As a control condition, the 12 subjects spent one hour in the scanner without examination and one hour on a couch without the presence of a scanner.
  
  
  RESULTS
  After MRI examination, the silent period was significantly lengthened in all 12 subjects and then tended to the initial value after 10 min. Motor thresholds were significantly elevated and then normalized after 10 minutes. No significant effects were found in the control conditions.
  
  
  CONCLUSIONS
  MRI examination leads to a transient effect on motor cortical excitability indicated by elongation of the post-excitatory inhibition and to an increase in motor thresholds in some subjects. These effects do not seem to be associated with a static magnetic field.
authors.affiliation: Institut für Diagnostische und Interventionelle Radiologie und Neuroradiologie, Universitätsklinikum Essen, Essen, Germany. marc.schlamann@uni-due.de
authors.forename: M
authors.initials: M
authors.lastname: Schlamann
authors.forename: M-S
authors.initials: MS
authors.lastname: Yoon
authors.forename: S
authors.initials: S
authors.lastname: Maderwald
authors.forename: T
authors.initials: T
authors.lastname: Pietrzyk
authors.forename: A
authors.initials: A
authors.lastname: Bitz
authors.forename: M
authors.initials: M
authors.lastname: Gerwig
authors.forename: M
authors.initials: M
authors.lastname: Forsting
authors.forename: S C
authors.initials: SC
authors.lastname: Ladd
authors.forename: M E
authors.initials: ME
authors.lastname: Ladd
authors.forename: O
authors.initials: O
authors.lastname: Kastrup
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D012016:Reference Values; D012684:Sensory Thresholds / Q000502:physiology; D050781:Transcranial Magnetic Stimulation