title: Short term effects of magnetic resonance imaging on excitability of the motor cortex at 1.5T and 7T.
abstract: OBJECTIVE
  The increasing spread of high-field and ultra-high-field magnetic resonance imaging (MRI) scanners has encouraged new discussion of the safety aspects of MRI. Few studies have been published on possible cognitive effects of MRI examinations. The aim of this study was to examine whether changes are measurable after MRI examinations at 1.5 and 7 T by means of transcranial magnetic stimulation (TMS).
  
  
  METHODS
  TMS was performed in 12 healthy, right-handed male volunteers. First the individual motor threshold was specified, and then the cortical silent period (SP) was measured. Subsequently, the volunteers were exposed to the 1.5-T MRI scanner for 63 minutes using standard sequences. The MRI examination was immediately followed by another TMS session. Fifteen minutes later, TMS was repeated. Four weeks later, the complete setting was repeated using a 7-T scanner. Control conditions included lying in the 1.5-T scanner for 63 minutes without scanning and lying in a separate room for 63 minutes. TMS was performed in the same way in each case. For statistical analysis, Wilcoxon's rank test was performed.
  
  
  RESULTS
  Immediately after MRI exposure, the SP was highly significantly prolonged in all 12 subjects at 1.5 and 7 T. The motor threshold was significantly increased. Fifteen minutes after the examination, the measured value tended toward normal again. Control conditions revealed no significant differences.
  
  
  CONCLUSIONS
  MRI examinations lead to a transient and highly significant alteration in cortical excitability. This effect does not seem to depend on the strength of the static magnetic field.
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Essen, Hufelandstrasse 55, 45122 Essen, Germany. marc.schlamann@uni-due.de
authors.forename: Marc
authors.initials: M
authors.lastname: Schlamann
authors.forename: Min-Suk
authors.initials: MS
authors.lastname: Yoon
authors.forename: Stefan
authors.initials: S
authors.lastname: Maderwald
authors.forename: Thomas
authors.initials: T
authors.lastname: Pietrzyk
authors.forename: Andreas K
authors.initials: AK
authors.lastname: Bitz
authors.forename: Marcus
authors.initials: M
authors.lastname: Gerwig
authors.forename: Michael
authors.initials: M
authors.lastname: Forsting
authors.forename: Susanne C
authors.initials: SC
authors.lastname: Ladd
authors.forename: Mark E
authors.initials: ME
authors.lastname: Ladd
authors.forename: Oliver
authors.initials: O
authors.lastname: Kastrup
mesh_terms: D000328:Adult; D004056:Differential Threshold / Q000502:physiology / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004574:Electromagnetic Fields; D019054:Evoked Potentials, Motor / Q000502:physiology* / Q000528:radiation effects*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology* / Q000528:radiation effects*; D011829:Radiation Dosage; D050781:Transcranial Magnetic Stimulation