Cause of Vertigo from MRI Scanning Identified

A team of researchers reported that it has discovered why so many people undergoing magnetic resonance imaging (MRI), particularly in newer high-strength scanners, get vertigo, or the dizzy sensation of free falling, while inside or when coming out of the tunnel-like machine.

In a new study published online September 22, 2011, in the journal Current Biology, a team led by Johns Hopkins University’s (JHU; Baltimore, MD, USA) scientists suggests that MRI scanner’s strong magnet pushes on fluid that circulates in the inner ear’s balance center, leading to a feeling of unexpected or unsteady movement. The finding could also call into question results of so-called functional MRI studies designed to detect what the brain and mind are doing under various circumstances.

To determine the mechanism behind MRI-induced vertigo, Dale C. Roberts, MS, senior research systems engineer in the laboratory of David Zee, MD, within the department of neurology at the Johns Hopkins University School of Medicine, and his colleagues placed 10 volunteers with healthy labyrinths and 2 volunteers who lacked labyrinthine function into MRI scanners. They tracked vertigo not only by the volunteers’ reports, but also by looking for nystagmus. Because visual clues can help suppress nystagmus, the researchers conducted their experiments in the dark.

Footage from night vision cameras revealed that all the healthy volunteers had nystagmus in the MRI, but those without labyrinthine function did not a definite sign that the labyrinth plays a key role in MRI-related vertigo. To determine how MRI’s magnetic field acts on the labyrinth, the researchers tested the healthy volunteers in MRI scanners of different strengths for various periods of time. They also tracked the study participants’ nystagmus as they were moved in and out of the scanners’ tunnels, called bores, both from the usual entryway and from behind research designed to assess the impact of motion or direction of magnetic field on the volunteers’ balance centers.

Mr. Roberts’ team discovered that higher magnetic field strengths caused considerably faster nystagmus. These eye movements persisted throughout the time volunteers spent in the machine, no matter how long the experiments lasted. Moreover, the direction of the eye movements changed depending on which way the volunteers entered the bores, suggesting that the effect on the labyrinth was directionally sensitive.

Combining their findings with what is known about the inner ear, the researchers deduced that MRI-related vertigo most likely relates to interplay between electrical currents flowing through the salty fluid in the canals of the labyrinth and MRI’s magnetic field. Through an effect well known to physicists called the Lorentz force, the magnetic field apparently pushes on the current of charged particles in the inner ear’s fluid. This exerts a force on cells that use the fluid’s flow as a way to perceive motion.

Mr. Roberts noted that the finding not only answers a decades-long scientific question, but also has implications for research that uses MRI. In one technique, known as functional MRI (fMRI), researchers measure brain activity by tracking blood flow in the brain as participants perform tasks. The new findings suggest that the scanner itself could be causing previously unnoticed brain activity related to movement and balance, potentially affecting results.

“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,” Mr. Roberts said. “These effects must be taken into account in the way we interpret functional imaging.”

The researchers added that physicians already use methods that stimulate the labyrinth to diagnose and treat inner ear and balance disorders, but these methods can be uncomfortable. They note that MRI scanners strong magnetic field could eventually be used for the same purpose, providing an innovative approach that is more comfortable and noninvasive.

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