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  • EXPOSURE  (3)
  • 1
    Keywords: EXPOSURE ; STRENGTH ; ARRAY ; human brain ; POWER ; high-field MRI ; SCANNER ; COGNITIVE FUNCTION ; 8 TESLA ; CROSSOVER
    Abstract: Objectives: The aims of this study were to investigate the subjective discomfort and sensory side effects during ultrahigh field (UHF) magnetic resonance imaging (MRI) examinations in a large-scale study and to evaluate differences between magnetic resonance (MR) sites. Materials and Methods: Four MR sites with a 7-T MR system and 2 MR sites with a 9.4-T MR system participated in this multicenter study with a total number of 3457 completed questionnaires on causes of discomfort and sensations during the examination. For a pooled retrospective analysis of the results from the partially different questionnaires, all data were adapted to an answer option with a 4-point scale (0 = no discomfort/side effect, 3 = very unpleasant/very strong sensation). To differentiate effects evoked by the low-frequency time-varying magnetic fields due to movement through the static magnetic field, most questionnaires separated the manifestation of sensory side effects during movement on the patient table from manifestation while lying still in the isocenter. Results: In general, a high acceptance of UHF examinations was found, where in 82% of the completed questionnaires, the subjects stated the examination to be at least tolerable. Although in 7.6% of the questionnaires, subjects felt discomfort during the examination, only 0.9% of the image acquisitions had to be terminated prematurely. No adverse events occurred in any of the examinations. Only 1% of the subjects were unwilling to undergo further UHF MRI examinations. Examination duration was the most complained cause of discomfort, followed by acoustic noise and lying still. All magnetic-field-related sensations were more pronounced when moving the patient table versus the isocenter position (19%/2% of the subjects felt unpleasant vertigo during the moving/stationary state). In general, vertigo was the most often stated sensory side effect and was more pronounced at 9.4 T compared with 7 T. However, the results varied substantially among the different sites. Conclusions: The high levels of subjective acceptance found in this study lead to the conclusion that UHF MRI would be tolerated as a diagnostic tool in clinical practice. For more consistent data ascertainment, we propose a standardized questionnaire for subjective perception monitoring.
    Type of Publication: Journal article published
    PubMed ID: 24637589
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  • 2
    Keywords: EXPOSURE ; FUTURE ; OCCUPATIONAL-EXPOSURE ; COGNITIVE FUNCTION ; EU directive ; Exposure limits ; GRADIENT MAGNETIC-FIELDS ; Hall sensor ; Magnetic flux ; RESONANCE-IMAGING SYSTEMS ; Sensory effects ; Static magnetic field probe ; Time-varying fields ; Ultra high field MRI ; VITAL SIGNS
    Abstract: OBJECT: The EU directive on safety requirements (2004/40/EC) limits the exposure to time varying magnetic fields to dB /dt = 200 mT/s. This action value is not clearly defined as it considers only the temporal change of the magnitude of [Formula: see text] . Thus, only the translational motion in the magnet's fringe field is considered and rotations are neglected. MATERIALS AND METHODS: A magnetic field probe was constructed to simultaneously record the magnetic flux density [Formula: see text] (x, y, z) with a 3-axis Hall sensor and the induced voltage due to movements with a set of three orthogonal coils. Voltages were converted into time-varying magnetic flux d phi(x, y, z)/dt serving as an exposition parameter for both translations and rotations. To separate the two types of motion, d B/dt was additionally calculated on the basis of the Hall sensor's data. The calibrated probe was attached to the forehead of 8 healthcare workers and 17 MR physicists, and [Formula: see text] and dphi/dt were recorded during standard operating procedures at three different MR systems up to 7 T. RESULTS: The maximum percentage of the translational motion referring the data including both translations and rotations amounts to 32%. During volunteer measurements, maximum exposure values of dphi/dt = 21 mWb/s, dB/dt = 1.40 T/s and [Formula: see text] Twere found. CONCLUSION: The findings in this work indicate that both translations and rotations in the vicinity of an MR system should be taken into account, and that a single regulatory action level might not be sufficient.
    Type of Publication: Journal article published
    PubMed ID: 21755466
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  • 3
    Keywords: SYSTEM ; EXPOSURE ; Cognition ; 8 TESLA ; CASE-CROSSOVER
    Abstract: Increasing field strengths in MRI necessitate the examination of potential side effects. Previously reported results have been contradictory, possibly caused by imbalanced samples. We aimed to examine whether special groups of people are more prone to develop side effects that might have led to contradictory results in previous studies. We examined the occurrence of sensory side effects in static magnetic fields of MRI scanners of 1.5, 3, and 7 T and a mock scanner in 41 healthy participants. The contribution of field strength, sex, age, and attention to bodily processes, and stress hormone levels to the sensation of dizziness was examined in separate univariate analyses and in a joint analysis that included all variables. Field strength and sex were significant factors in the joint analysis (P=0.001), with women being more strongly affected than men by dizziness in higher static magnetic fields. This effect was not mediated by the other variables such as attention to bodily symptoms or stress hormones. Further research needs to elucidate the underlying factors of increased dizziness in women in static magnetic fields in MRI. We hypothesize that imbalanced samples of earlier studies might be one reason for previous contradictory results on the side effects of static magnetic fields.
    Type of Publication: Journal article published
    PubMed ID: 25089803
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