by
Brendon Nafziger, DOTmed News Associate Editor | September 23, 2011
Researchers at Johns Hopkins University's medical center think they know why some patients experience vertigo during MRI scans.
In an article published online Sept. 22 in Current Biology, they say powerful MRI magnets interact with ionic currents present in the fluid which circulates in the inner ear. This creates a force which in turn pushes the fluid against cells lining the inner ear, and which control our sense of balance.
In the study, the researchers showed that every healthy human volunteer they exposed to the static magnetic field of an MRI unit experienced involuntary eye movement, or nystagmus, in relation to the strength of the magnetic field and the orientation of the person in the scanner.
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The researchers, led by Dale C. Roberts, senior research systems engineer in the neurology department at Johns Hopkins, said MRI dizziness had long been reported by patients, and there was even evidence from animal studies. In experiments, animals would sometimes show abnormal postures when exposed to strong magnetic fields. Tellingly, this did not happen if they lacked labyrinthine function -- that is, their inner ear balance organ was destroyed.
To find out what was going on, they exposed 10 healthy human volunteers to a (static) magnetic field from a 3-Tesla or 7-Tesla MRI. They then exposed two volunteers who had no labyrinthine function. By tracking the patients' eye movements using infrared cameras (the subjects were tested in darkness as visual cues can suppress nystagmus), they found none of the labyrinthine-impaired subjects showed nystagmus, while all of the healthy volunteers did.
Based on their research, the scientists say the magnetic fields act on endolymph, the fluid in the inner which contains large numbers of potassium ions. According to models worked out by the researchers, vertigo is caused by a phenomenon known to physicists as the Lorentz force: and it does not require subject movement or changes in the magnetic field to trigger an effect.
In addition to possibly getting to the bottom of the mystery, the researchers said the results also suggest potential caveats for brain scientists.
"Such effects could confound functional MRI studies of brain behavior, including resting-state brain activity," they write in the article.
