MRI’s Effects Can Be Dizzying – Literally

It’s a good thing patients in MRI scanners are lying down, it turns out.

The authors of a study published online Thursday, in Current Biology, have sorted out the root of reported dizziness and vertigo reported by patients undergoing magnetic resonance imaging.

MRI systems affect the inner ears’ labyrinths - the tube-like structures controlling balance, a Johns Hopkins University team led by Dale C. Roberts found. The more powerful the magnetic field, the more likely the interference, they say.

The researchers evaluated 10 healthy volunteers as well as two volunteers lacking labyrinthine function. They looked for involuntary eye movements, called nystagmus, which serve as clues to whether the brain is sensing motion or not. Because visual cues can affect this eye movement, the MRIs were done in the dark, with eye movements detected using infrared cameras.

The cameras showed involuntary eye movement among all the healthy volunteers and among neither of the two who lacked labyrinthine function. The higher the researchers dialed up the MRI machine’s magnetic field strength, the more eye movement they saw among the healthy volunteers.

The findings may have implications for functional MRI (fMRI) studies, used to monitor the brain’s activity in real time as patients perform tasks, Roberts and colleagues said. The MRI scanner itself could be triggering brain activity - not just monitoring it.

“We've shown that even when you think there’s nothing happening in the brain while volunteers are in the scanner, there’s actually a lot happening because MRI itself is causing some effect,” Roberts said. “These effects must be taken into account in the way we interpret functional imaging.”

There may be some good news, though. The MRI effect could in future, be harnessed to stimulate the labyrinth in the diagnosis and treatment of inner-ear disorders, Roberts and colleagues said.