MRI Magnetic Field Stimulates Rotational Sensors of the Brain

Abstract

SUMMARY Vertigo in and around MRI machines has been noted for years [1, 2]. Several mechanisms have been suggested to explain these sensations [3, 4], yet without direct, objective measures, the cause is unknown. We found that all healthy human subjects lying in the static magnetic field of an MRI machine develop a robust nystagmus. Patients lacking labyrinthine function do not. Here we use the pattern of eye movements as a measure of vestibular stimulation to show that the stimulation is static (continuous, proportional to static magnetic field strength, requiring neither head movement nor dynamic change in magnetic field strength) and directional (sensitive to magnetic field polarity and head orientation). Our calculations and geometric model suggest that magnetic vestibular stimulation derives from a Lorentz force due to interaction between the magnetic field and naturally-occurring ionic currents in the labyrinthine endolymph fluid. This force pushes on the semicircular canal cupula, leading to nystagmus. We emphasize that the unique, dual role of endolymph in the delivery of both ionic current and fluid pressure, coupled with the cupula’s function as a pressure sensor, makes magnetic field induced nystagmus and vertigo possible. Such effects could confound fMRI studies of brain behavior, including resting-state brain activity.

ICNIRP Statement on Diagnostic Devices Using Non-Ionizing Radiation

“…Also, a study by Heinrich et al (2014), which reported dizziness among volunteers exposed to homogeneous SMF inside bores of MRI-scanners with different magnet strengths, was not discussed. This work has been supported by experimental studies that examined the effect of a strong SMF on vestibular responses in human subjects and found an effect on involuntary eye movements and vertigo, both of which were associated with the direction of the SMF in relation to the vestibular organ (Roberts et al, 2011;Mian et al, 2013;Ward et al, 2014). ICNIRP did report that "A meta-analysis of 5 studies published during 1992-2007 found the only neuropsychological effect relating to static magnetic field exposure to be visual impairment.…”

Magnetic Field-Induced Vertigo in the MRI Environment

“…Roberts et al [10] demonstrated that horizontal slow-phase eye nystagmus velocity (H-SPV) produced by exposure to a strong magnetic field is directly proportional to the magnetic field strength, with a response which has an adaption component and a linear response to field. This linear response measurement provided a new and vital piece of objective evidence.…”

“…Antunes et al [11]refined the calculation by Roberts et al by modelling the canals, currents and forces and confirmed that this mechanism is plausible and gives a realistic prediction of both the magnitude and direction of perception. As the Lorentz force is dependent on magnitude and directions of both magnetic field and orientation of the cupula then the SPV response is highly directional with both peaks and nulls in the response dependent upon head orientation [10,12]. The dynamics of the response may be modelled in terms of a low pass and high pass (partial) adaption model.…”

“…The following three references should receive an asterisk and associated textual commentary: [10] This work marks a breakthrough in the understanding of the vestibular response to high magnetic fields. Not only did it provide new measurements but it also hypothesised the Lorentz force mechanism for the first time to explain the response.…”

“…In the light of the physics of magnetic field interactions, it is now possible to discuss four likely candidates for the sensation of MFIV which have their origins in the vestibular system: forces due to the susceptibility of vestibular structures; current flow due to a net rate of change of magnetic flux; MHD due to head movement [8,9] and fluid pressure due to Lorentz forces [10].…”