Study type: Medical/biological study (experimental study)

Simulated MR magnetic field induces steady-state changes in brain dynamics: Implications for interpretation of functional MR studies. med./bio.

Published in: Magn Reson Med 2010; 64 (2): 349-357

Aim of study (acc. to author)

To test the hypothesis that a magnetic field comparable to a field generated during a MR scan produced changes in human brain electrical activity that persisted until the field was removed (called a "presence effect" to distinguish it from evoked potentials).

Background/further details

Individual subjects (n=22, 9 males, 13 females) served as their own controls. As a positive control a binaural 424 Hz tone was presented.
Following an acclimation period, every subject underwent three blocks of trials: the magnetic field was applied in either the first or third block, as determined randomly from subject to subject. The data from the block where the field was not applied were analyzed as a negative control (sham exposure). The auditory stimulus was applied in the middle block (positive control).



Exposure Parameters
Exposure 1: 60 Hz
Exposure duration: 2 s on - 5 s off - for 560 s

Exposure 1

Main characteristics
Frequency 60 Hz
Exposure duration 2 s on - 5 s off - for 560 s
Exposure setup
Exposure source
Setup paired set of coils in an isolation chamber; subject's head positioned in the center of the coil system; field uniform (+/- 5 %) in the head region
Sham exposure A sham exposure was conducted.
Measurand Value Type Method Mass Remarks
magnetic flux density 100 µT minimum measured - -
magnetic flux density 200 µT maximum measured - -

Reference articles

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated material:
Investigated organ system:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

Using non-linear recurrence analysis, changes in brain activity lasting 1 sec (the longest interval considered) were found in 21 of 22 subjects. The "presence effect" was not detected using linear analysis and was reversible, as indicated by a return of brain activity to baseline levels in all subjects within 2 seconds of field offset.
The authors suggest that actual MRI magnetic fields produce nonlinear steady-state perturbations of brain dynamical activity. The effect may influence the picture of brain connectivity inferred in some functional MRI studies.

Study character:

Study funded by

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