Dizziness/VertigoWhat causes some patients to experience dizziness and/or vertigo in an MR scanner?
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Dizziness and/or vertigo are experienced by up to 25% of patients scanned at 7 T, especially when being moved in or out of the scanner. These symptoms may be accompanied by nausea or simply an "uneasy feeling". The phenomenon may be also experienced at 1.5T and 3T, but with a much lower incidence (< 3%) and severity.
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True Vertigo: a feeling of movement (of either yourself or your surroundings) when no motion actually exists |
Although the details may vary, when most supine patients are pushed slowly head first into a 7T scanner, horizontal nystagmus first occurs, followed by the subjective feeling of continuous rotation in the horizontal plane. (These phenomena begin at entry to the scanner bore, the site of most dramatic change in magnetic field (ΔB) and hence maximum dB/dt during table motion). Once patients reach the homogeneous magnet isocenter (ΔB = 0), vertiginous sensations decrease but persist for about a minute. Nystagmus declines but never completely disappears. Upon being withdrawn from the scanner, patients experience a sensation of body rotation and nystagmus, this time in the opposite direction to that experienced on scanner entry.
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Balance, acceleration, and head position are sensed by the vestibular apparatus (VA) of the inner ear. The VA contains of three orthogonal semicircular canals filled with a potassium-rich fluid known as endolymph. During head motion, movement of endolymph displaces the plate-like ampullary crista, which through its connection with hair cells, generates a signal in the vestibular nerves. In addition to motion-induced fluidic pressure waves, an ionic current is always present accompanying the secretion and re-absorption of K+ ions in different parts of the VA.
The vestibular apparatus showing the three semicircular canals with their bulbous ampullae. The interaction of ionic current (green arrow) and B0 (orange arrow) creates a fluidic Lorentz force perpendicular to both (red arrow)
(Modified from Ward under CC BY) |
A worthwhile 2-minute review of the anatomy and function of the vestibular system.
Schema of the vestibular apparatus showing a single semicircular canal and its ampulla, where motion of the crista stimulates hair cells and generates action potentials in the vestibular nerve.
(From Pender under CC BY)
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Several theories have been proposed to explain how magnetic fields generate nystagmus and vertigo (described in the references below). The current favored explanation (Roberts) uses the concept of the Lorentz force (described in a prior Q&A) which is produced when an electric current crosses the lines of a magnetic field. Here the electric current derives from the normal potassium-based ionic current within the endolymph. The magnetic field is the main field of the scanner (Bo). A Lorentz force is thus created perpendicular to both. In the supine head position, this force is transmitted to the ampula, displacing the crista and hair cells of the horizontal canal, stimulating them to generate impulses within the vestibular nerve resulting in (predominantly) horizontal nystagmus and vertigo.
Although uncomfortable, dizziness/vertigo can be reduced by moving the patient table very slowly in and out of the scanner. Also, pretreatment with low-dose diphenhydramine (Benadryl®) has also shown to be effective.
References
Friebe B, Wollrab A, Thormann M, et al. Sensory perceptions of individuals exposed to the static field of a 7T MRI: a controlled blinded study. J Magn Reson Imaging 2015; 41:1675-1681. [DOI link]
Glover PM, Cavin I, Qian W, et al. Magnetic-field-induced vertigo: a theoretical and experimental investigation. Bioelectromagnetics 2007; 28:349-361. [DOI link]
Grant A, Metzger GJ, van de Moortele P-F, et al. 10.5 T MRI static field effects on human cognitive, vestibular, and physiological function. Magn Reson Imaging 2020; 73:163-176. [DOI LINK]
Mian OS, Li Y, Antunes A, et al. On the vertigo due to static magnetic fields. PLoS ONE 2013; 8(10): e78748. [DOI link]
Pender DJ. A model analysis of static stress in the vestibular membranes. Theor Biol Med Model 2009; 6:19 [DOI link]
Rauschenberg J, Nagel AM, Ladd S, et al. Multicenter study of subjective acceptance during magnetic resonance imaging at 7 and 9.4 T. Invest Radiol 2014; 49:249-259. [DOI link]
Roberts DC, Marcelli V, Gillen JS, et al. MRI magnetic field stimulates rotational sensors of the brain. Curr Biol 2011; 21:1635-1640. [DOI link]
Straumann D, Bockisch CJ. Neurophysiology: vertigo in MRI machines. Curr Biol 2011; 21:R806-7. (Editorial and discussion about Roberts article). [DOI link]
Thormann M, Arnthauer H, Adolf D, et al. Efficacy of diphenhydramine in the prevention of vertigo and nausea at 7 T MRI. Eur J Radiol 2013; 82:768-772. [DOI link]
Ward BK, Otero-Millan J, Jareonsettasin P, et al. Magnetic Vestibular Stimulation (MVS) as a technique for understanding the normal and diseased labyrinth. Front Neurol 2017; 8:122 [DOI link]
Friebe B, Wollrab A, Thormann M, et al. Sensory perceptions of individuals exposed to the static field of a 7T MRI: a controlled blinded study. J Magn Reson Imaging 2015; 41:1675-1681. [DOI link]
Glover PM, Cavin I, Qian W, et al. Magnetic-field-induced vertigo: a theoretical and experimental investigation. Bioelectromagnetics 2007; 28:349-361. [DOI link]
Grant A, Metzger GJ, van de Moortele P-F, et al. 10.5 T MRI static field effects on human cognitive, vestibular, and physiological function. Magn Reson Imaging 2020; 73:163-176. [DOI LINK]
Mian OS, Li Y, Antunes A, et al. On the vertigo due to static magnetic fields. PLoS ONE 2013; 8(10): e78748. [DOI link]
Pender DJ. A model analysis of static stress in the vestibular membranes. Theor Biol Med Model 2009; 6:19 [DOI link]
Rauschenberg J, Nagel AM, Ladd S, et al. Multicenter study of subjective acceptance during magnetic resonance imaging at 7 and 9.4 T. Invest Radiol 2014; 49:249-259. [DOI link]
Roberts DC, Marcelli V, Gillen JS, et al. MRI magnetic field stimulates rotational sensors of the brain. Curr Biol 2011; 21:1635-1640. [DOI link]
Straumann D, Bockisch CJ. Neurophysiology: vertigo in MRI machines. Curr Biol 2011; 21:R806-7. (Editorial and discussion about Roberts article). [DOI link]
Thormann M, Arnthauer H, Adolf D, et al. Efficacy of diphenhydramine in the prevention of vertigo and nausea at 7 T MRI. Eur J Radiol 2013; 82:768-772. [DOI link]
Ward BK, Otero-Millan J, Jareonsettasin P, et al. Magnetic Vestibular Stimulation (MVS) as a technique for understanding the normal and diseased labyrinth. Front Neurol 2017; 8:122 [DOI link]
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