Magnetic fields: Memory effects

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  • Published: Sep 1, 2012
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Magnetic fields: Memory effects

MRI and health

Effects of magnetic stray fields from a 7 Tesla MRI scanner on neurocognition: a double-blind randomised crossover study 

Concerns about the effects on healthcare professional, maintenance and engineering staff and evening cleaners have been raised with regards to exposure to the strong magnetic fields generated by MRI instruments.

A small-scale study published in the journal Occupational and Environmental Medicine, published by the British Medical Journal group, looked at the effects on 31 healthy volunteers of exposure to a 7 Tesla MRI magnetic field. The researchers allowed the volunteers to make standard head movements while they exposed them to one of three electromagnetic field strengths from what is described as a heavy-duty MRI scanner. For such a machine the magnetic field is present even when the instrument is not in use.

The team of Hans Kromhout at the Institute for Risk Assessment Sciences, at Utrecht University in The Netherlands, and colleagues carried out exposure at levels of zero (sham), 0.5 (medium), and 1 (high) Tesla, in a random order, one week apart for the volunteers. The experiment was of a double-blind randomised crossover design. The volunteers apparently experienced temporarily lower concentration and spatial-visual awareness during the experiments as evaluated by tests carried out after each exposure level. The researchers set the volunteers twelve timed cognitive tasks, which were designed to assess the ability of the volunteers to carry out tasks associated with the sorts of skills needed by a surgeon or other healthcare professional working in the vicinity of an MRI scanner. The tests included visual tracking and movement, as well as more general functions, such as attention, concentration and working memory. The tests were neutral in that they didn't test intelligence nor were they dependents on practice for success.

Of the 31 volunteers, 30 completed all three sessions. When compared to the control group, with zero filed, the researchers observed that more general functions, such as attention and concentration and visuospatial awareness were significantly affected in those exposed to the magnetic fields while carrying out standard head movements. For complex mental tasks, reaction and disengagement times were longer, the team says, varying from 5 to 21% at the higher the level of Tesla exposure. The researchers suggest that complex tasks rely on the brain's working memory and that this is affected detrimentally during exposure to the strong magnetic field.

The team reports that non-verbal memory does not seem to be affected by exposure to the high magnetic field but there was temporary decline in verbal memory, although only at a borderline level of significance. The team reports that for those volunteers exposed to the strongest magnetic field several physical symptoms were also reported, such as a metallic taste in the mouth (12 people), dizziness (6), headache (5), and nausea (1).

Cause or effect?

The study looked at only a very small number of people and does not demonstrate direct cause and effect, there might be many other confounding factors that give rise to the observations. "The exact implications and mechanisms of these subtle acute effects in [practice] remain unclear," the researchers report. However, increasingly powerful MRI magnets are being used in hospitals, which may have implications for healthcare workers and other members of staff working in close to such equipment. "Further studies are needed to better understand the mechanisms and possible practical safety and health implications of these acute neurocognitive effects," the team concludes.

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Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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