[Effects of MRI on the electrophysiology of the motor cortex: a TMS study]
M Schlamann1, M-S Yoon, S Maderwald
1Institut für Diagnostische und Interventionelle Radiologie und Neuroradiologie, Universitätsklinikum Essen, Essen, Germany. marc.schlamann@uni-due.de
Purpose:
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.
Materials And 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.
Conclusion:
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.
Insights
Magnetic Resonance Imaging (MRI) examinations transiently affect motor cortical excitability, indicated by a lengthened silent period and increased motor thresholds. These changes normalize within 10 minutes and are not linked to static magnetic fields.
Area of Science:
- Neuroscience
- Medical Imaging
Context:
- The proliferation of high-field MRI scanners necessitates a re-evaluation of examination safety.
- Previous research on MRI's effects on auditory evoked potentials yielded conflicting results.
Purpose:
- To investigate the impact of 1.5 T MRI examinations on motor cortical excitability using transcranial magnetic stimulation (TMS).
Summary:
- Twelve healthy male volunteers underwent a 63-minute 1.5 T MRI scan.
- Transcranial magnetic stimulation (TMS) assessed motor cortical excitability before, immediately after, and 10 minutes post-MRI.
- MRI examination led to a significant, transient lengthening of the post-excitatory silent period and an increase in motor thresholds.
Impact:
- MRI examinations induce temporary alterations in motor cortical excitability.
- These transient effects suggest a need for further research into the neurophysiological impacts of MRI.
- Findings indicate that the observed effects are not attributable to the static magnetic field alone.
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