Rationale and Objectives
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).
Materials and 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.
Conclusion
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.
Magnetic resonance imaging (MRI) has been used in medical imaging and diagnostics for >25 years. Over this period, >300 million MRI examinations have been performed . Only a few incidents and injuries have occurred, mostly in relation to the nonobservance of common precautions and the examination of patients with implants not suitable for MRI . Generally, MRI is considered to be a harmless and safe procedure in routine clinical practice that is not associated with any ionizing radiation exposure or any permanent influence on the human body.
Higher magnetic field strengths have advantages such as higher signal-to-noise ratios and thus the possibility to achieve higher spatial resolution . This is the main reason MRI scanners with higher field strengths (>3 T) are increasingly being installed as investigational devices. The discussion of the biologic effects and the possible impact of higher magnetic fields on the human body has thus regained momentum.
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Material and methods
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Results
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Discussion
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Conclusion
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