Symptoms and Cognitive Effects of Exposure to Magnetic Stray Fields of MRI Scanners

Abstract

People working routinely with magnetic resonance imaging (MRI) systems report a number of symptoms related to their presence in the inhomogeneous static magnetic fields (the stray field) surrounding these scanners. Experienced symptoms and neurobehavioral performance among engineers manufacturing 0.5, 1.0 and 1.5 Tesla systems were assessed and compared to that of employees from a reference department at the same company. Average exposure to static magnetic fields (SMF) was estimated at 25.9 mT/8h for working with a 1.0 T system and at 40.4 mT/8h for a 1.5 T system. Vertigo, metal taste, and concentration problems were more often reported in the MRI-manufacturing department, and were dependent on intensity and duration of exposure to SMF. All symptoms, except for headaches, were more frequently reported by engineers who moved through the magnetic stray field more rapidly than others. Mercury levels in urine samples were determined, but did not correlate with exposure to SMF. Experiencing a metal taste is most likely caused by "random" excitation of nerve tissue in the mouth or due to electrolysis of metallic fillings, and not to release from mercury from amalgam fillings. In a series of experimental volunteer studies neurobehavioral performance during exposure to SMF from MRI scanners up to 7.0 Tesla was quantitatively assessed. Acute adverse effects were measured during exposure ranging from approximately 600 milliTesla up to 1600 mT, but no significant changes in performance were found after exposure had ended. The visual sensory domain and the cognitive-motor domain were affected by exposure to SMF, and performance at visual tracking and eye-hand coordination tasks depended on the intensity of exposure. Visual contrast sensitivity was slightly decreased, but an exposure-response relation was not found. These effects were most likely related to movement in the stray fields, and associated exposure to a time-varying magnetic field. Performances at tests assessing visuo-verbal interference, verbal attention, visuo-motor speed, dexterity and visual scanning were not affected. It remained inconclusive whether working memory was affected, but most likely effects are not significant enough to confound results from functional MRI studies. People regularly working in the vicinity of MRI scanners, such as engineers in MR manufacturing or members of operating teams involved in interventional procedures applying MRI, should be made consciously aware of these potential hazards and should limit their movement speed and presence in the stray fields of MRI scanners. It remains unknown what the measured neurobehavioral effects mean for functional capacity in the occupational setting, since it has not been studied in this thesis. In spite of rapid new developments in MRI systems and applications that most likely lead to an increase in the intensity and duration of exposure to SMF in the near future, existing gaps in knowledge about the effects of occupational exposure to magnetic stray fields of MRI systems are evident. Despite the fact that studies presented in this thesis point at transient neurobehavioral effects in the visual sensory and visuomotor domains, independent replicate studies are needed to confirm these findings.