Cognitive effects of head‐movements in stray fields generated by a 7 Tesla whole‐body MRI magnet

Abstract

The study investigates the impact of exposure to the stray magnetic field of a whole-body 7 T MRI scanner on neurobehavioral performance and cognition. Twenty seven volunteers completed four sessions, which exposed them to approximately 1600 mT (twice), 800 mT and negligible static field exposure. The order of exposure was assigned at random and was masked by placing volunteers in a tent to hide their position relative to the magnet bore. Volunteers completed a test battery assessing auditory working memory, eye-hand co-ordination, and visual perception. During three sessions the volunteers were instructed to complete a series of standardized head movements to generate additional time-varying fields ( approximately 300 and approximately 150 mT.s(-1) r.m.s.). In one session, volunteers were instructed to keep their heads as stable as possible. Performance on a visual tracking task was negatively influenced (P<.01) by 1.3% per 100 mT exposure. Furthermore, there was a trend for performance on two cognitive-motor tests to be decreased (P<.10). No effects were observed on working memory. Taken together with results of earlier studies, these results suggest that there are effects on visual perception and hand-eye co-ordination, but these are weak and variable between studies. The magnitude of these effects may depend on the magnitude of time-varying fields and not so much on the static field. While this study did not include exposure above 1.6 T, it suggests that use of strong magnetic fields is not a significant confounder in fMRI studies of cognitive function. Future work should further assess whether ultra-high field may impair performance of employees working in the vicinity of these magnets.

Pooled analyses of effects on visual and visuomotor performance from exposure to magnetic stray fields from MRI scanners: Application of the Bayesian framework

“…However, the estimate of average effect was smaller (-0.7%/100 mT) than the estimates from individual studies (-3%/100 mT and -1.3%/100 mT, respectively, (13,14)), which can be attributed to the fact that the posterior summarization is based on the measurement data and the assumed prior distribution.…”

“…It should be noted, however, that these exposure-response analysis, assuming a linear association, implies that at an exposure of 1600 mT, which can be achieved in close proximity to a 7-T cylindrical magnet (14), performance will be reduced with ϳ16%. Furthermore, the use of interventional procedures guided by MRI is increasing dramatically and involves delicate procedures.…”

“…Details of the three experimental case-crossover studies have been described in detail in de Vocht et al (12)(13)(14). In summary, in each study a neurobehavioral test battery was administered repeatedly (three to four times) to a group of human volunteers (N ϭ 17, 20, and 27), who were seated in stray magnetic fields surrounding MRI systems (1.5, 3.0, and 7.0 T).…”

“…In addition, performance at a visual tracking test that also assessed the visual system and that showed a negative associations (P Ͻ 0.0001) with increased exposure in both studies (13,14) was also reanalyzed to quantify the pooled effect of exposure to stray fields. In the pooled analyses, a Bayesian approach was used to assess parameter intervals and densities without the problems associated with specifications of the variance and correlations in hierarchical mixed effects modeling.…”

Human MRI above the FDA 8T guideline: Can we conclude that it is safe?

“…This will allow the scientific community to assess whether these data indeed point to an absence of cognitive effects after exposure to static magnetic fields (SMF), or whether this is primarily a problem with statistical power. Although conducted at lower field strengths, results from similar studies among 17-40 human volunteers (3)(4)(5)(6) suggested that most likely 25 subjects was insufficient to detect any effects (after adjustment for learning effects) still present several minutes after exposure. However, information on the distributions and results from power calculations are needed to be able to properly assess this aspect.…”