Article

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

Institute for Risk Assessment Sciences, Utrecht University, PO Box 80178, Utrecht 3508 TD, The Netherlands
Occupational and environmental medicine (Impact Factor: 3.27). 08/2012; 69(10):759-66. DOI: 10.1136/oemed-2011-100468
Source: PubMed

ABSTRACT

This study characterises neurocognitive domains that are affected by movement-induced time-varying magnetic fields (TVMF) within a static magnetic stray field (SMF) of a 7 Tesla (T) MRI scanner.
Using a double-blind randomised crossover design, 31 healthy volunteers were tested in a sham (0 T), low (0.5 T) and high (1.0 T) SMF exposure condition. Standardised head movements were made before every neurocognitive task to induce TVMF.
Of the six tested neurocognitive domains, we demonstrated that attention and concentration were negatively affected when exposed to TVMF within an SMF (varying from 5.0% to 21.1% per Tesla exposure, p<0.05), particular in situations were high working memory performance was required. In addition, visuospatial orientation was affected after exposure (46.7% per Tesla exposure, p=0.05).
Neurocognitive functioning is modulated when exposed to movement-induced TVMF within an SMF of a 7 T MRI scanner. Domains that were affected include attention/concentration and visuospatial orientation. Further studies are needed to better understand the mechanisms and possible practical safety and health implications of these acute neurocognitive effects.

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    • "The pathophysiology of the magnetic-fieldrelated vertigo is under evaluation but it could result from both magnetic susceptibility differences between vestibular organs and surrounding fluid, and induced currents acting on the vestibular hair cells[16]. A reduced postural stability with increased exposure to static and variable magnetic fields in healthy volunteers has been objectively measured in the literature[17]. Since previous observations demonstrated that only moving subjects in a static magnetic field reported vestibularrelated symptoms[16]the discomfort could be limited by decreasing the movement within the magnet[18]or, as in our setting, by slowing down the bed speed in the magnet. A further unpleasant sensation during UHF MR examination is the noise. "
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    ABSTRACT: To study patient tolerability of brain imaging that employs an ultrahigh field (7 T) MR system METHODS: We examined 180 subjects that underwent brain MR examination at 7 T. A tolerability test consisting of two parts (during patient table motion and during the examination) was administered to all subjects in order to monitor their discomfort. The scores range from 0 to 5 for the first part, and from 0 to 10 for the second part, the total score of each subject therefore ranging from 0 (no side effects reported) to 15 (lowest tolerability) RESULTS: A total of 51 % of subjects reported at least one side effect but all were mild in intensity and did not require examination interruption. No serious adverse event was reported. The total score (mean ± standard deviation) was 1.1 ± 1.5 out of 15 (mean score 0.4 ± 0.7 out of 5 during patient table motion and 0.7 ± 1.1 out of 10 during MR). Patient discomfort was not related to gender or health status, but it was reduced with time after system installation with increasing operator experience in performing UHF MR examinations. Ultrahigh field MRI is well tolerated without excessive discomfort to subjects. • 7-T MRI is well tolerated with low incidence of side effects • The subjects' discomfort during 7-T MRI is reduced as the operators' experience increases • 7-T MRI is practicable in healthy subjects and patients with neurodegenerative diseases.
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    • "However, peripheral nerve stimulation induced during volunteer exposure to the switched gradient magnetic fields of magnetic resonance (MR) systems suggested that the threshold for perception may be as low as about 2 Vm j1 (Nyenhuis et al. 2001), based on calculations using a homogeneous human simulation model. A more accurate calculation of the electric fields induced in the tissues of a heterogeneous human model based on data from the above MR study has been carried out by So et al. (2004). These authors estimated the minimum threshold for peripheral nerve stimulation to lie between 3.8 and 5.8 Vm j1 , based on the assumption that stimulation takes place in the skin or subcutaneous fat. "

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    ABSTRACT: Klinisches/methodisches Problem Die räumliche, zeitliche oder spektrale Auflösung der MRT ist heute vielfach nicht ausreichend, um Submillimeterläsionen zu detektieren oder um die Dynamik des Herzschlags darzustellen. Radiologische Standardverfahren Zur Zeit sind MR-Tomographen bei 1,5 oder 3 T die Standardgeräte für klinische Untersuchungen. Methodische Innovationen Der Einsatz ultrahoher Magnetfelder von 7 T verspricht durch die Erhöhung des Signal-zu-Rausch-Verhältnisses eine deutliche Verbesserung der räumlichen und/oder zeitlichen Auflösung sowie die Generierung neuer Kontraste. Leistungsfähigkeit Mit der 7-T-MRT ist es gelungen, MR-Aufnahmen des Hirns routinemäßig mit 0,3 mm Auflösung zu akquirieren. Die theoretisch erwartete Verbesserung des Signal-zu-Rausch-Verhältnisses wird aber auf Grund von B1-Inhomogenitäten und Kontrastvariationen oft nicht erreicht. Bewertung Mit Hilfe der 7-T-MRT kann eine deutliche Erhöhung der räumlichen Auflösung erzielt werden. Techniken wie die Time-of-flight(TOF)-MR-Angiographie und suszeptibilitätsgewichtete Methoden (z. B. die neurofunktionelle MRT) profitieren in verstärktem Maße von den hohen Feldern. Sendefeldinhomogenitäten sind immer noch eine große Herausforderung für die Ultrahochfeld(UHF)-MRT und stellen auch ein nur teilweise gelöstes Sicherheitsproblem dar. Empfehlung für die Praxis Die UHF-MRT ist z. Z. auf spezielle Anwendungsgebiete beschränkt, und der erwartete Gewinn muss oft gegen technische Komplikationen bei der Datenaufnahme und Bildinterpretation abgewogen werden.
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