MRI magnetic field stimulates rotational sensors of the brain

Weak magnetic vestibular stimulation decreases postural sway

BACKGROUND

Perceptible galvanic vestibular stimulation (GVS) causes nystagmus and postural sway deterioration. Conversely, imperceptible GVS improves postural stability, suggesting the presence of stochastic resonance.

RESEARCH QUESTION

Similar to GVS, strong magnetic vestibular stimulation of 7 T induces nystagmus and increases body sway. Thus, a relatively small magnetic stimulation may improve postural stability. In this study, we measured the effect of a relatively small magnetic field on postural sway.

METHODS

Posturography was performed in eight healthy participants using a stabilometer with foam rubber on board. The center of pressure (COP) trajectories were recorded in both the anterior-posterior and medial-lateral directions for 60 s with the eye closed. Neodymium magnets (0.4 T) or aluminum disks of similar size (0 T) were placed bilaterally over the mastoid processes.

RESULTS

Both the trajectory length and envelopment area of the COP movement with 0.4 T were significantly smaller than those with 0 T.

SIGNIFICANCE

The relatively smaller magnetic vestibular stimulation decreased postural sway. This method may be useful for improving the vestibular function and related reflexes.

Sustained bias of spatial attention in a 3 T MRI scanner

When lying inside a MRI scanner and even in the absence of any motion, the static magnetic field of MRI scanners induces a magneto-hydrodynamic stimulation of subjects' vestibular organ (MVS). MVS thereby not only causes a horizontal vestibular nystagmus but also induces a horizontal bias in spatial attention. In this study, we aimed to determine the time course of MVS-induced biases in both VOR and spatial attention inside a 3 T MRI-scanner as well as their respective aftereffects after participants left the scanner. Eye movements and overt spatial attention in a visual search task were assessed in healthy volunteers before, during, and after a one-hour MVS period. All participants exhibited a VOR inside the scanner, which declined over time but never vanished completely. Importantly, there was also an MVS-induced horizontal bias in spatial attention and exploration, which persisted throughout the entire hour within the scanner. Upon exiting the scanner, we observed aftereffects in the opposite direction manifested in both the VOR and in spatial attention, which were statistically no longer detectable after 7 min. Sustained MVS effects on spatial attention have important implications for the design and interpretation of fMRI-studies and for the development of therapeutic interventions counteracting spatial neglect.

Is activation of the vestibular system by electromagnetic induction a possibility in an MRI context?

In recent years, an increasing number of studies have discussed the mechanisms of vestibular activation in strong magnetic field settings such as occur in a magnetic resonance imaging scanner environment. Amid the different hypotheses, the Lorentz force explanation currently stands out as the most plausible mechanism, as evidenced by activation of the vestibulo-ocular reflex. Other hypotheses have largely been discarded. Nonetheless, both human data and computational modeling suggest that electromagnetic induction could be a valid mechanism which may coexist alongside the Lorentz force. To further investigate the induction hypothesis, we provide, herein, a first of its kind dosimetric analysis to estimate the induced electric fields at the vestibular system and compare them with what galvanic vestibular stimulation would generate. We found that electric fields strengths from induction match galvanic vestibular stimulation strengths generating vestibular responses. This review examines the evidence in support of electromagnetic induction of vestibular responses, and whether movement-induced time-varying magnetic fields should be further considered and investigated.

Decrease of 7T MR short-term effects with repeated exposure

PURPOSE

Although participants in 7 T magnetic resonance (MR) studies tolerate ultra-high field (UHF) well, subjectively experienced short-term effects, such as dizziness, inconsistent movement, nausea, or metallic taste, are reported. Evidence on subjectively experienced short-term effects in multiple exposures to UHF MR is scarce. The purpose of this study is to investigated experience of short-term effects, and occurrence of motion in healthy subjects exposed to seven weekly 7 T MR examinations.

METHODS

A questionnaire on short-term effects was completed by participants in an fMRI motor skill study. Seven UHF MR examinations were conducted over 7 weeks (exposure number: 1 to 7). Changes of experienced short-term effects were analyzed. Motion in fMRI images was quantified.

RESULTS

The questionnaire was completed 360 times by 67 participants after one to seven 7T MR examinations. Logistic mixed model analysis showed a significant association between dizziness, inconsistent movement, nausea, and headache and the examination numbers (p<0.03). Exposure to repeated examinations had no significant effect on peripheral nerve stimulation (PNS) or motion of the subjects. The overall experience of a 7T examination improved significantly (p<0.001) with increasing examination numbers.

CONCLUSION

During multiple 7T examinations, subjects adapt to the strong static field. The short-term effects dizziness, inconsistent movement, nausea, and headache decrease over time as the MR sessions continue and experienced comfort increases. There was no significant difference in motion during the multiple fMRI examinations.

Implementation of a 7T Epilepsy Task Force consensus imaging protocol for routine presurgical epilepsy work-up: effect on diagnostic yield and lesion delineation

OBJECTIVE

Recently, the 7 Tesla (7 T) Epilepsy Task Force published recommendations for 7 T magnetic resonance imaging (MRI) in patients with pharmaco-resistant focal epilepsy in pre-surgical evaluation. The objective of this study was to implement and evaluate this consensus protocol with respect to both its practicability and its diagnostic value/potential lesion delineation surplus effect over 3 T MRI in the pre-surgical work-up of patients with pharmaco-resistant focal onset epilepsy.

METHODS

The 7 T MRI protocol consisted of T1-weighted, T2-weighted, high-resolution-coronal T2-weighted, fluid-suppressed, fluid-and-white-matter-suppressed, and susceptibility-weighted imaging, with an overall duration of 50 min. Two neuroradiologists independently evaluated the ability of lesion identification, the detection confidence for these identified lesions, and the lesion border delineation at 7 T compared to 3 T MRI.

RESULTS

Of 41 recruited patients > 12 years of age, 38 were successfully measured and analyzed. Mean detection confidence scores were non-significantly higher at 7 T (1.95 ± 0.84 out of 3 versus 1.64 ± 1.19 out of 3 at 3 T, p = 0.050). In 50% of epilepsy patients measured at 7 T, additional findings compared to 3 T MRI were observed. Furthermore, we found improved border delineation at 7 T in 88% of patients with 3 T-visible lesions. In 19% of 3 T MR-negative cases a new potential epileptogenic lesion was detected at 7 T.

CONCLUSIONS

The diagnostic yield was beneficial, but with 19% new 7 T over 3 T findings, not major. Our evaluation revealed epilepsy outcomes worse than ILAE Class 1 in two out of the four operated cases with new 7 T findings.

Effects of ultra-high field MRI environment on cognitive performance in healthy participants

INTRODUCTION

Ultra-high field MRI (UHF MRI) is rapidly becoming an essential part of our toolbox within health care and research studies; therefore, we need to get a deeper understanding of the physiological effects of ultra-high field. This study aims to investigate the cognitive performance of healthy participants in a 7 T (T) MRI environment in connection with subjectively experienced effects.

METHODS

We measured cognitive performance before and after a 1-h 7T MRI scanning session using a Digit Symbol Substitution Test (DSST) in 42 subjects. Furthermore, a computer-based survey regarding the subjectively experienced effects in connection with the MRI examination was distributed. Similarly, two DSSTs were also performed by a control group of 40 participants.

RESULTS

Even though dizziness was the strongest sensory perception in connection to the MRI scanning, we did not find any correlation between dizziness and cognitive performance. Whilst the control group improved (p=<0.001) on their second DSST the MRI group showed no significant difference (p=0.741) in the DSST before and after MRI scanning.

CONCLUSION

Transient effect on cognition after undergoing MRI scanning can't be ruled out as the expected learning effect on the DSST was not observed.

IMPLICATIONS FOR PRACTICE

Increasing understanding of the possible adverse effects may guide operators in performing UHF MRI in a safe way and with person-centered care. Furthermore, it can guide researchers in setting up research protocols to minimize confounding factors in their fMRI studies due to the transient adverse effects of the UHF environment.

Human vestibular perceptual thresholds - A systematic review of passive motion perception

BACKGROUND

The vestibular system detects head accelerations within 6 degrees of freedom. How well this is accomplished is described by vestibular perceptual thresholds. They are a measure of perceptual performance based on the conscious evaluation of sensory information. This review provides an integrative synthesis of the vestibular perceptual thresholds reported in the literature. The focus lies on the estimation of thresholds in healthy participants, used devices and stimulus profiles. The dependence of these thresholds on the participants clinical status and age is also reviewed. Furthermore, thresholds from primate studies are discussed.

RESULTS

Thresholds have been measured for frequencies ranging from 0.05 to 5 Hz. They decrease with increasing frequency for five of the six main degrees of freedom (inter-aural, head-vertical, naso-occipital, yaw, pitch). No consistent pattern is evident for roll rotations. For a frequency range beyond 5 Hz, a U-shaped relationship is suggested by a qualitative comparison to primate data. Where enough data is available, increasing thresholds with age and higher thresholds in patients compared to healthy controls can be observed. No effects related to gender or handedness are reported.

SIGNIFICANCE

Vestibular thresholds are essential for next generation screening tools in the clinical domain, for the assessment of athletic performance, and workplace safety alike. Knowledge about vestibular perceptual thresholds contributes to basic and applied research in fields such as perception, cognition, learning, and healthy aging. This review provides normative values for vestibular thresholds. Gaps in current knowledge are highlighted and attention is drawn to specific issues for improving the inter-study comparability in the future.

Longer duration entry mitigates nystagmus and vertigo in 7-Tesla MRI

Introduction

Patients and technologists commonly describe vertigo, dizziness, and imbalance near high-field magnets, e.g., 7-Tesla (T) magnetic resonance imaging (MRI) scanners. We sought a simple way to alleviate vertigo and dizziness in high-field MRI scanners by applying the understanding of the mechanisms behind magnetic vestibular stimulation and the innate characteristics of vestibular adaptation.

Methods

We first created a three-dimensional (3D) control systems model of the direct and indirect vestibulo-ocular reflex (VOR) pathways, including adaptation mechanisms. The goal was to develop a paradigm for human participants undergoing a 7T MRI scan to optimize the speed and acceleration of entry into and exit from the MRI bore to minimize unwanted vertigo. We then applied this paradigm from the model by recording 3D binocular eye movements (horizontal, vertical, and torsion) and the subjective experience of eight normal individuals within a 7T MRI. The independent variables were the duration of entry into and exit from the MRI bore, the time inside the MRI bore, and the magnetic field strength; the dependent variables were nystagmus slow-phase eye velocity (SPV) and the sensation of vertigo.

Results

In the model, when the participant was exposed to a linearly increasing magnetic field strength, the per-peak (after entry into the MRI bore) and post-peak (after exiting the MRI bore) responses of nystagmus SPV were reduced with increasing duration of entry and exit, respectively. There was a greater effect on the per-peak response. The entry/exit duration and peak response were inversely related, and the nystagmus was decreased the most with the 5-min duration paradigm (the longest duration modeled). The experimental nystagmus pattern of the eight normal participants matched the model, with increasing entry duration having the strongest effect on the per-peak response of nystagmus SPV. Similarly, all participants described less vertigo with the longer duration entries.

Conclusion

Increasing the duration of entry into and exit out of a 7T MRI scanner reduced or eliminated vertigo symptoms and reduced nystagmus peak SPV. Model simulations suggest that central processes of vestibular adaptation account for these effects. Therefore, 2-min entry and 20-s exit durations are a practical solution to mitigate vertigo and other discomforting symptoms associated with undergoing 7T MRI scans. In principle, these findings also apply to different magnet strengths.

Keeping track of reality: embedding visual memory in natural behaviour

Since immersive virtual reality (IVR) emerged as a research method in the 1980s, the focus has been on the similarities between IVR and actual reality. In this vein, it has been suggested that IVR methodology might fill the gap between laboratory studies and real life. IVR allows for high internal validity (i.e., a high degree of experimental control and experimental replicability), as well as high external validity by letting participants engage with the environment in an almost natural manner. Despite internal validity being crucial to experimental designs, external validity also matters in terms of the generalizability of results. In this paper, we first highlight and summarise the similarities and differences between IVR, desktop situations (both non-immersive VR and computer experiments), and reality. In the second step, we propose that IVR is a promising tool for visual memory research in terms of investigating the representation of visual information embedded in natural behaviour. We encourage researchers to carry out experiments on both two-dimensional computer screens and in immersive virtual environments to investigate visual memory and validate and replicate the findings. IVR is valuable because of its potential to improve theoretical understanding and increase the psychological relevance of the findings.

Frequency-dependent tuning of the human vestibular "sixth sense" by transcranial oscillatory currents

OBJECTIVE

The vestibular cortex is a multisensory associative region that, in neuroimaging investigations, is activated by slow-frequency (1-2 Hz) galvanic stimulation of peripheral receptors. We aimed to directly activate the vestibular cortex with biophysically modeled transcranial oscillatory current stimulation (tACS) in the same frequency range.

METHODS

Thirty healthy subjects and one rare patient with chronic bilateral vestibular deafferentation underwent, in a randomized, double-blind, controlled trial, to tACS at slow (1 or 2 Hz) or higher (10 Hz) frequency and sham stimulations, over the Parieto-Insular Vestibular Cortex (PIVC), while standing on a stabilometric platform. Subjective symptoms of motion sickness were scored by Simulator Sickness Questionnaire and subjects' postural sways were monitored on the platform.

RESULTS

tACS at 1 and 2 Hz induced symptoms of motion sickness, oscillopsia and postural instability, that were supported by posturographic sway recordings. Both 10 Hz-tACS and sham stimulation on the vestibular cortex did not affect vestibular function. As these effects persisted in a rare patient with bilateral peripheral vestibular areflexia documented by the absence of the Vestibular-Ocular Reflex, the possibility of a current spread toward peripheral afferents is unlikely. Conversely, the 10 Hz-tACS significantly reduced his chronic vestibular symptoms in this patient.

CONCLUSIONS

Weak electrical oscillations in a frequency range corresponding to the physiological cortical activity of the vestibular system may generate motion sickness and postural sways, both in healthy subjects and in the case of bilateral vestibular deafferentation.

SIGNIFICANCE

This should be taken into account as a new side effect of tACS in future studies addressing cognitive functions. Higher frequencies of stimulation applied to the vestibular cortex may represent a new interventional option to reduce motion sickness in different scenarios.

Behavioral and neural responses to high-strength magnetic fields are reduced in otolith mutant mice

Static high magnetic fields (MFs) interact with the vestibular system of humans and rodents. In rats and mice, exposure to MFs causes perturbations such as head movements, circular locomotion, suppressed rearing, nystagmus, and conditioned taste aversion acquisition. To test the role of otoconia, two mutant mouse models were examined, head-tilt Nox3het (het) and tilted Otop1 (tlt), with mutations, respectively, in Nox3, encoding the NADPH oxidase 3 enzyme, and Otop1, encoding the otopetrin 1 proton channel, which are normally expressed in the otolith organs, and are critical for otoconia formation. Consequently, both mutants show a near complete loss of otoconia in the utricle and saccule, and are nonresponsive to linear acceleration. Mice were exposed to a 14.1 Tesla MF for 30 min. After exposure, locomotor activity, conditioned taste aversion and c-Fos (in het) were assessed. Wild-type mice exposed to the MF showed suppressed rearing, increased latency to rear, locomotor circling, and c-Fos in brainstem nuclei related to vestibular processing (prepositus, spinal vestibular, and supragenual nuclei). Mutant het mice showed no response to the magnet and were similar to sham animals in all assays. Unlike het, tlt mutants exposed to the MF showed significant locomotor circling and suppressed rearing compared with sham controls, although they failed to acquire a taste aversion. The residual responsiveness of tlt versus het mice might reflect a greater semicircular deficit in het mice. These results demonstrate the necessity of the otoconia for the full effect of exposure to high MFs, but also suggest a semicircular contribution.

Characteristics and Possible Mechanisms of Direction-Reversing Nystagmus During Positional Testing in Patients With Benign Paroxysmal Positional Vertigo

OBJECTIVES

The occurrence of direction-reversing nystagmus during positional testing in patients with benign paroxysmal positional vertigo (BPPV) is not uncommon. Further in-depth analysis of the characteristics and possible mechanisms of direction-reversing nystagmus will help us to diagnose and treat BPPV more precisely. The study aimed to analyze the incidence and characteristics of direction-reversing nystagmus during positional testing in BPPV patients, evaluate the outcomes of canalith repositioning procedure for these patients, and further explore the possible mechanism of reversal nystagmus in BPPV patients.

STUDY DESIGN

Retrospective study.

SETTING

Single-center study.

PATIENTS

A total of 575 patients with BPPV who visited the Vertigo Clinic of our hospital between April 2017 and June 2021 were enrolled.

MAIN OUTCOME MEASURES

Dix-Hallpike and supine roll tests were performed. The nystagmus was recorded using videonystagmography. The characteristics of direction-reversing nystagmus and the possible underlying mechanism were analyzed.

RESULTS

Patients with BPPV who showed reversal nystagmus accounted for 9.39% (54 of 575) of all BPPV patients visiting our hospital during the same period, of which 5.57% (32 of 575) had horizontal semicircular canal BPPV (HC-BPPV), and 3.83% (22 of 575) had posterior semicircular canal BPPV (PC-BPPV). The maximum slow-phase velocities (mSPVs) of the first-phase nystagmus were greater in HC-BPPV and PC-BPPV patients with reversal nystagmus than those without (p = 0.04 and p = 0.01, respectively). In all HC-BPPV and PC-BPPV patients with reversal nystagmus, the mSPV of the first-phase nystagmus was greater than that of the second-phase nystagmus (p < 0.01). The duration of the second-phase nystagmus was longer than 60 seconds in 93.75% (30 of 32) of the HC-BPPV patients and 77.27% (17 of 22) of the PC-BPPV patients (p = 0.107, Fisher exact test). HC-BPPV and PC-BPPV patients with reversal nystagmus both required more than one canalith repositioning procedure compared with those without (HC-BPPV: 75 versus 28.13%, p < 0.001; PC-BPPV: 59.09 versus 13.64%, p = 0.002).

CONCLUSIONS

The cause of second-phase nystagmus in BPPV patients with direction-reversing nystagmus may be related to the involvement of central adaptation mechanisms secondary to the overpowering mSPV of the first-phase nystagmus.

Novel ways to modulate the vestibular system: Magnetic vestibular stimulation, deep brain stimulation and transcranial magnetic stimulation / transcranial direct current stimulation

BACKGROUND

Advances in neurotechnologies are revolutionizing our understanding of complex neural circuits and enabling new treatments for disorders of the human brain. In the vestibular system, electromagnetic stimuli can now modulate vestibular reflexes and sensations of self-motion by artificially stimulating the labyrinth, cerebellum, cerebral cortex, and their connections.

OBJECTIVE

In this narrative review, we describe evolving neuromodulatory techniques including magnetic vestibular stimulation (MVS), deep brain stimulation (DBS), transcranial magnetic stimulation (TMS), and transcranial direct-current stimulation (tDCS) and discuss current and potential future application in the field of neuro-otology.

RESULTS

MVS triggers both vestibular nystagmic (persistent) and perceptual (lasting ∼1 min) responses that may serve as a model to study central adaptational mechanisms and pathomechanisms of hemispatial neglect. By systematically mapping DBS electrodes, targeted stimulation of central vestibular pathways allowed modulating eye movements, vestibular heading perception, spatial attention and graviception, resulting in reduced anti-saccade error rates and hypometria, improved heading discrimination, shifts in verticality perception and transiently decreased spatial attention. For TMS/tDCS treatment trials have demonstrated amelioration of vestibular symptoms in various neuro-otological conditions, including chronic vestibular insufficiency, Mal-de-Debarquement and cerebellar ataxia.

CONCLUSION

Neuromodulation has a bright future as a potential treatment of vestibular dysfunction. MVS, DBS and TMS may provide new and sophisticated, customizable, and specific treatment options of vestibular symptoms in humans. While promising treatment responses have been reported for TMS/tDCS, treatment trials for vestibular disorders using MVS or DBS have yet to be defined and performed.

Effect of Acoustic fMRI-Scanner Noise on the Human Resting State

Our knowledge about the human resting state is predominantly based on either electroencephalographic (EEG) or functional magnetic resonance imaging (fMRI) methods. While EEG recordings can be performed in seated posture in quiet conditions, the fMRI environment presents a substantial contrast with supine and restricted posture in a narrow tube that is filled with acoustic scanner noise (ASN) at a chainsaw-like volume level. However, the influence of these diverging conditions on resting-state brain activation is neither well studied nor broadly discussed. In order to promote data as a source of sharper hypotheses for future studies, we investigated alterations in EEG-frequency-band power (delta, theta, alpha, beta, gamma) and spatial power distribution as well as cortical vigilance measures in different postures and ASN surroundings over the course of time. Participants (N = 18) underwent three consecutive resting-state EEG recordings with a fixed posture and ASN setting sequence; seated, supine, and supine with ASN (supnoise) using an MRI simulator. The results showed that compared to seated, supnoise, the last instance within the posture sequence, was characterized by lower power and altered spatial power distribution in all assessed frequency bands. This might also have been an effect of time alone. In delta, theta, alpha, and beta, the power of supnoise was also reduced compared to supine, as well as the corresponding distribution maps. The vigilance analysis revealed that in supine and supnoise, the highest and lowest vigilance stages were more dominant compared to the seated and earliest posture condition within the sequence. Hence, our results demonstrate that the differences in recording settings and progress of time are related to changes in cortical arousal and vigilance regulation, findings that should be taken into account more profoundly for hypothesis generation as well as analytic strategies in future resting-state studies.

Eye tracking: empirical foundations for a minimal reporting guideline

In this paper, we present a review of how the various aspects of any study using an eye tracker (such as the instrument, methodology, environment, participant, etc.) affect the quality of the recorded eye-tracking data and the obtained eye-movement and gaze measures. We take this review to represent the empirical foundation for reporting guidelines of any study involving an eye tracker. We compare this empirical foundation to five existing reporting guidelines and to a database of 207 published eye-tracking studies. We find that reporting guidelines vary substantially and do not match with actual reporting practices. We end by deriving a minimal, flexible reporting guideline based on empirical research (Section "An empirically based minimal reporting guideline").

Radiographers' awareness level of MRI-induced vertigo and their perspectives on the post-examination care provided to patients in Saudi Arabia

INTRODUCTION

Vertigo has been reported by operators and patients during magnetic resonance imaging (MRI) examinations and found to increase in severity as the strength of the scanner magnet increases. This study examined a cohort of MRI radiographers' awareness of MRI-induced vertigo and their perspectives on post-MRI care.

METHODS

This cross-sectional study used a web-based survey distributed to 110 radiographers. The 18-item survey included questions to elicit demographic information, MRI radiographers' awareness of MRI-induced vertigo, and their perspectives on the post-MRI care that should be provided to patients. Responses were collected between June 2021 and January 2022. The collected data were analyzed using SPSS, version 27.

RESULTS

A total of 110 MRI radiographers completed the survey. Participants were predominantly male (64.5 %) and working in public practice (91.8 %). Almost all the radiographers were aware of MRI-induced vertigo. About two-thirds of participants knew patients needed assistance off the couch. Nearly all participants knew patients should be asked about their experience with MRI-induced vertigo after their procedures. There were statistically significant associations between the size of magnetic field strength used by the participants and their appreciation of the needed support for patients post-MRI examinations (p= 0.012).

CONCLUSION

This study provides the first insight into Saudi Arabian MRI radiographers' awareness and perceptions of MRI-induced vertigo. Radiographers were largely aware of MRI-induced vertigo and the supportive care they were supposed to provide their patients.

IMPLICATIONS FOR PRACTICE

The current study points to a need for training to expand awareness levels of MRI-induced vertigo among a few Saudi MRI radiographers.

Health effects related to exposure of static magnetic fields and acoustic noise-comparison between MR and CT radiographers

OBJECTIVES

We explored the prevalence of health complaints subjectively associated with static magnetic field (SMF) and acoustic noise exposure among MR radiographers in Sweden, using CT radiographers as a control group. Additionally, we explored radiographers' use of strategies to mitigate adverse health effects.

METHODS

A cross-sectional survey was sent to all hospitals with MR units in Sweden. MR and/or CT personnel reported prevalence and attribution of symptoms (vertigo/dizziness, nausea, metallic taste, illusion of movement, ringing sensations/tinnitus, headache, unusual drowsiness/tiredness, forgetfulness, difficulties concentrating, and difficulties sleeping) within the last year. We used logistic regression to test associations between sex, age, stress, SMF strength, working hours, and symptom prevalence. Data regarding hearing function, work-environmental noise, and strategies to mitigate adverse symptoms were also analysed.

RESULTS

In total, 529 out of 546 respondents from 86 hospitals were eligible for participation. A ≥ 20 working hours/week/modality cut-off rendered 342 participants grouped into CT (n = 75), MR (n = 121), or mixed personnel (n = 146). No significant differences in symptom prevalence were seen between groups. Working at ≥ 3T increased SMF-associated symptoms as compared with working at ≤ 1.5T (OR: 2.03, CI95: 1.05-3.93). Stress was a significant confounder. Work-related noise was rated as more troublesome by CT than MR personnel (p < 0.01). MR personnel tended to use more strategies to mitigate adverse symptoms.

CONCLUSION

No significant differences in symptom prevalence were seen between MR and CT radiographers. However, working at 3T increased the risk of SMF symptoms, and stress increased adverse health effects. Noise nuisance was considered more problematic by CT than MR personnel.

KEY POINTS

• No significant differences in symptom prevalence were seen between MR and CT radiographers. • Working at ≥ 3 T doubled the odds of experiencing SMF symptoms (vertigo/dizziness, nausea, metallic taste, and/or illusion of movement) as compared to working exclusively at ≤ 1.5 T. • Work-related acoustic noise was less well mitigated and was rated as more troublesome by CT personnel than by MR personnel.

Correlation between Histopathology and Signal Loss on Spin-Echo T2-Weighted MR Images of the Inner Ear: Distinguishing Artifacts from Anatomy

BACKGROUND AND PURPOSE

MR imaging of the inner ear on heavily T2-weighted sequences frequently has areas of signal loss in the vestibule. The aim of the present study was to correlate the anatomic structures of the vestibule with areas of low signal intensity.

MATERIALS AND METHODS

We reviewed T2-weighted spin-echo MR imaging studies of the internal auditory canal from 27 cases and cataloged signal intensity variations in the vestibulum of inner ears. Using a histologic preparation of a fully mounted human ear, we prepared 3D reconstructions showing the regions of sensory epithelia (semicircular canal cristae, utricular, and saccular maculae). Regions of low signal intensity were reconstructed in 3D, categorized by appearance, and compared with the 3D histologic preparation.

RESULTS

The region corresponding to the lateral semicircular canal crista showed signal loss in most studies (94%). In the utricle, a focus of signal loss occurred in the anterior-cranial portion of the utricle and corresponded to the location of the utricular macula and associated nerve on histopathologic specimens (63% of studies). Additional areas of low signal were observed in the vestibule, corresponding to the fluid-filled endolymphatic space and not to a solid anatomic structure.

CONCLUSIONS

Small foci of signal loss within the inner ear vestibule on T2-weighted spin-echo images correlate with anatomic structures, including the lateral semicircular canal crista and the utricular macula. More posterior intensity variations in the endolymphatic space are likely artifacts, potentially representing fluid flow within the endolymph caused by magneto-hydrodynamic Lorentz forces.

Strange nonchaotic dynamics in a discrete FitzHugh-Nagumo neuron model with sigmoidal recovery variable

We report the appearance of strange nonchaotic attractors in a discrete FitzHugh-Nagumo neuron model with discontinuous resetting. The well-known strange nonchaotic attractors appear in quasiperiodically forced continuous-time dynamical systems as well as in a discrete map with a small intensity of noise. Interestingly, we show that a discrete FitzHugh-Nagumo neuron model with a sigmoidal recovery variable and discontinuous resetting generates strange nonchaotic attractors without external force. These strange nonchaotic attractors occur as intermittency behavior (locally unstable behavior in laminar flow) in the periodic dynamics. We use various characterization techniques to validate the existence of strange nonchaotic attractors in the considered system.

Magnetic exposure using Samarium Cobalt (SmCO5) increased proliferation and stemness of human Umbilical Cord Mesenchymal Stem Cells (hUC-MSCs)

Despite the extensive reports on the potential hazard of magnetic field (MF) exposures on humans, there are also concurrently reported on the improved proliferative property of stem cells at optimum exposure. However, the effect on mesenchymal stem cells (MSCs) remains unknown. Therefore, we aimed to investigate the impact of induced static MF (SMF) on human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) using Samarium Cobalt (SmCO5). At passage 3, hUC-MSCs (1 × 10⁴) were exposed to 21.6 mT SMF by a direct exposure (DE) showed a significantly higher cell count (p < 0.05) in the growth kinetics assays with the shortest population doubling time relative to indirect exposure and negative control. The DE group was committed into the cell cycle with increased S phase (55.18 ± 1.38%) and G2/M phase (21.75 ± 1.38%) relative to the NC group [S-phase (13.54 ± 2.73%); G2/M phase (8.36 ± 0.28%)]. Although no significant changes were observed in the immunophenotype, the DE group showed an elevated expression of pluripotency-associated markers (OCT4, SOX2, NANOG, and REX1). These results suggest that the MFs could potentially induce proliferation of MSCs, a promising approach to promote stem cells propagation for clinical therapy and research without compromising the stemness of hUC-MSCs.

Static magnetic field stimulation over motor cortex modulates resting functional connectivity in humans

Focal application of transcranial static magnetic field stimulation (tSMS) over the human motor cortex induces local changes in cortical excitability. Whether tSMS can also induce distant network effects, and how these local and distant effects may vary over time, is currently unknown. In this study, we applied 10 min tSMS over the left motor cortex of healthy subjects using a real/sham parallel design. To measure tSMS effects at the sensori-motor network level, we used resting-state fMRI. Real tSMS, but not sham, reduced functional connectivity within the stimulated sensori-motor network. This effect of tSMS showed time-dependency, returning to sham levels after the first 5 min of fMRI scanning. With 10 min real tSMS over the motor cortex we did not observe effects in other functional networks examined (default mode and visual system networks). In conclusion, 10 min of tSMS over a location within the sensori-motor network reduces functional connectivity within the same functional network.

Persistent horizontal and vertical, MR-induced nystagmus in resting state Human Connectome Project data

OBJECTIVE

Strong magnetic fields from magnetic resonance (MR) scanners induce a Lorentz force that contributes to vertigo and persistent nystagmus. Prior studies have reported a predominantly horizontal direction for healthy subjects in a 7 Tesla (T) MR scanner, with slow phase velocity (SPV) dependent on head orientation. Less is known about vestibular signal behavior for subjects in a weaker, 3T magnetic field, the standard strength used in the Human Connectome Project (HCP). The purpose of this study is to characterize the form and magnitude of nystagmus induced at 3T.

METHODS

Forty-two subjects were studied after being introduced head-first, supine into a Siemens Prisma 3T scanner. Eye movements were recorded in four separate acquisitions over 20 minutes. A biometric eye model was fitted to the recordings to derive rotational eye position and then SPV. An anatomical template of the semi-circular canals was fitted to the T2 anatomical image from each subject, and used to derive the angle of the B₀ magnetic field with respect to the vestibular apparatus.

RESULTS

Recordings from 37 subjects yielded valid measures of eye movements. The population-mean SPV ± SD for the horizontal component was -1.38 ± 1.27 deg/sec, and vertical component was -0.93 ± 1.44 deg/sec, corresponding to drift movement in the rightward and downward direction. Although there was substantial inter-subject variability, persistent nystagmus was present in half of subjects with no significant adaptation over the 20 minute scanning period. The amplitude of vertical drift was correlated with the roll angle of the vestibular system, with a non-zero vertical SPV present at a 0 degree roll.

INTERPRETATION

Non-habituating vestibular signals of varying amplitude are present in resting state data collected at 3T.

Short- and long-term effects of 3.5-23.0 Tesla ultra-high magnetic fields on mice behaviour

OBJECTIVES

Higher static magnetic field (SMF) enables higher imaging capability in magnetic resonance imaging (MRI), which encourages the development of ultra-high field MRIs above 20 T with a prerequisite for safety issues. However, animal tests of ≥ 20 T SMF exposure are very limited. The objective of the current study is to evaluate mice behaviour consequences of 3.5-23.0 T SMF exposure.

METHODS

We systematically examined 112 mice for their short- and long-term behaviour responses to a 2-h exposure of 3.5-23.0 T SMFs. Locomotor activity and cognitive functions were measured by five behaviour tests, including balance beam, open field, elevated plus maze, three-chamber social recognition, and Morris water maze tests.

RESULTS

Besides the transient short-term impairment of the sense of balance and locomotor activity, the 3.5-23.0 T SMFs did not have long-term negative effects on mice locomotion, anxiety level, social behaviour, or memory. In contrast, we observed anxiolytic effects and positive effects on social and spatial memory of SMFs, which is likely correlated with the significantly increased CaMKII level in the hippocampus region of high SMF-treated mice.

CONCLUSIONS

Our study showed that the short exposures to high-field SMFs up to 23.0 T have negligible side effects on healthy mice and may even have beneficial outcomes in mice mood and memory, which is pertinent to the future medical application of ultra-high field SMFs in MRIs and beyond.

KEY POINTS

• Short-term exposure to magnetic fields up to 23.0 T is safe for mice. • High-field static magnetic field exposure transiently reduced mice locomotion. • High-field static magnetic field enhances memory while reduces the anxiety level.

Post-Concussive Vestibular Dysfunction Is Related to Injury to the Inferior Vestibular Nerve

Symptoms of vestibular dysfunction such as dizziness and vertigo are common after sports-related concussions (SRC) and associated with a worse outcome and a prolonged recovery. Vestibular dysfunction after SRC can be because of an impairment of the peripheral or central neural parts of the vestibular system. The aim of the present study was to establish the cause of vestibular impairment in athletes with SRC who have persisting post-concussive symptoms (PPCS). We recruited 42 participants-21 athletes with previous SRCs and PPCS ≥6 months and 21 healthy athletic age- and sex-matched controls-who underwent symptom rating, a detailed test battery of vestibular function and 7T magnetic resonance imaging with diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) of cerebellar white matter tracts, and T1-weighted imaging for cerebellar volumetrics. Vestibular dysfunction was observed in 13 SRC athletes and three controls (p = 0.001). Athletes with vestibular dysfunction reported more pronounced symptoms on the Dizziness Handicap Inventory (DHI; p < 0.001) and the Hospital Anxiety and Depression Scale (HADS; p < 0.001). No significant differences in DTI metrics were found, while in DKI two metrics were observed in the superior and/or inferior cerebellar tracts. Cerebellar gray and white matter volumes were similar in athletes with SRC and controls. Compared with controls, pathological video head impulse test results (vHIT; p < 0.001) and cervical vestibular evoked myogenic potentials (cVEMP; p = 0.002) were observed in athletes with SRC, indicating peripheral vestibular dysfunction and specifically suggesting injury to the inferior vestibular nerve. In athletes with persisting symptoms after SRC, vestibular dysfunction is associated with injury to the inferior vestibular nerve.

MR- safety: Evaluation of compliance with screening routines using a structured screening interview

Background

Magnetic resonance (MR) safety procedures are designed to allow patients, research subjects and personnel to enter the MR-scanner room under controlled conditions and without the risk to be harmed during the examination. Ferromagnetic objects in the MR-environment or inside the human body represent the main safety risks potentially leading to human injuries. Screening for MR-safety risks with dedicated procedures is therefore mandatory. As human errors during the screening procedure might align and lead to an incident compliance is essential.

Purpose

To evaluate compliance with a documented structured MR-safety screening process.

Method

Written and signed MR-safety screening documentation collected at a national 7T MR facility during a four-year period was evaluated for compliance of trained personnel with multi-step MR-safety routines. We analysed whether examinations were performed or why they were not performed. Data analysis further included descriptive statistics of the study population (age, gender and patient or healthy volunteer status), identification of missing documents and omitted or incorrect answers, and whether these compliance shortcomings concerned predominantly administrative or MR-safety related issues.

Results

Documentation of the screening process in 1819 subjects was incomplete in 19% of subjects. The most common documentation shortcoming was omitted fields. Out of 478 omitted answer-fields in 307 subjects, 36% were of administrative nature and 64% related directly to MR-safety issues.

Conclusion

Compliance with MR-safety screening procedures cannot be taken for granted and deficiencies to comply with screening routines were revealed. Documentation shortcomings concerned both administrative and MR-safety related issues.

Functional connectome of brainstem nuclei involved in autonomic, limbic, pain and sensory processing in living humans from 7 Tesla resting state fMRI

Despite remarkable advances in mapping the functional connectivity of the cortex, the functional connectivity of subcortical regions is understudied in living humans. This is the case for brainstem nuclei that control vital processes, such as autonomic, limbic, nociceptive and sensory functions. This is because of the lack of precise brainstem nuclei localization, of adequate sensitivity and resolution in the deepest brain regions, as well as of optimized processing for the brainstem. To close the gap between the cortex and the brainstem, on 20 healthy subjects, we computed a correlation-based functional connectome of 15 brainstem nuclei involved in autonomic, limbic, nociceptive, and sensory function (superior and inferior colliculi, ventral tegmental area-parabrachial pigmented nucleus complex, microcellular tegmental nucleus-prabigeminal nucleus complex, lateral and medial parabrachial nuclei, vestibular and superior olivary complex, superior and inferior medullary reticular formation, viscerosensory motor nucleus, raphe magnus, pallidus, and obscurus, and parvicellular reticular nucleus - alpha part) with the rest of the brain. Specifically, we exploited 1.1mm isotropic resolution 7 Tesla resting-state fMRI, ad-hoc coregistration and physiological noise correction strategies, and a recently developed probabilistic template of brainstem nuclei. Further, we used 2.5mm isotropic resolution resting-state fMRI data acquired on a 3 Tesla scanner to assess the translatability of our results to conventional datasets. We report highly consistent correlation coefficients across subjects, confirming available literature on autonomic, limbic, nociceptive and sensory pathways, as well as high interconnectivity within the central autonomic network and the vestibular network. Interestingly, our results showed evidence of vestibulo-autonomic interactions in line with previous work. Comparison of 7 Tesla and 3 Tesla findings showed high translatability of results to conventional settings for brainstem-cortical connectivity and good yet weaker translatability for brainstem-brainstem connectivity. The brainstem functional connectome might bring new insight in the understanding of autonomic, limbic, nociceptive and sensory function in health and disease.

Spiral waves in a hybrid discrete excitable media with electromagnetic flux coupling

Though there are many neuron models based on differential equations, the complexity in realizing them into digital circuits is still a challenge. Hence, many new discrete neuron models have been recently proposed, which can be easily implemented in digital circuits. We consider the well-known FitzHugh-Nagumo model and derive the discrete version of the model considering the sigmoid type of recovery variable and electromagnetic flux coupling. We show the various time series plots confirming the existence of periodic and chaotic bursting as in differential equation type neuron models. Also, we have used the bifurcation plots, Lyapunov exponents, and frequency bifurcations to investigate the dynamics of the proposed discrete neuron model. Different topologies of networks like single, two, and three layers are considered to analyze the wave propagation phenomenon in the network. We introduce the concept of using energy levels of nodes to study the spiral wave existence and compare them with the spatiotemporal snapshots. Interestingly, the energy plots clearly show that when the energy level of nodes is different and distributed, the occurrence of the spiral waves is identified in the network.

Lying in a 3T MRI scanner induces neglect-like spatial attention bias

The static magnetic field of MRI scanners can induce a magneto-hydrodynamic stimulation of the vestibular organ (MVS). In common fMRI settings, this MVS effect leads to a vestibular ocular reflex (VOR). We asked whether - beyond inducing a VOR - putting a healthy subject in a 3T MRI scanner would also alter goal-directed spatial behavior, as is known from other types of vestibular stimulation. We investigated 17 healthy volunteers, all of which exhibited a rightward VOR inside the MRI-scanner as compared to outside-MRI conditions. More importantly, when probing the distribution of overt spatial attention inside the MRI using a visual search task, subjects scanned a region of space that was significantly shifted toward the right. An additional estimate of subjective straight-ahead orientation likewise exhibited a rightward shift. Hence, putting subjects in a 3T MRI-scanner elicits MVS-induced horizontal biases of spatial orienting and exploration, which closely mimic that of stroke patients with spatial neglect.

Vestibular-Evoked Cerebral Potentials

The human vestibular cortex has mostly been approached using functional magnetic resonance imaging and positron emission tomography combined with artificial stimulation of the vestibular receptors or nerve. Few studies have used electroencephalography and benefited from its high temporal resolution to describe the spatiotemporal dynamics of vestibular information processing from the first milliseconds following vestibular stimulation. Evoked potentials (EPs) are largely used to describe neural processing of other sensory signals, but they remain poorly developed and standardized in vestibular neuroscience and neuro-otology. Yet, vestibular EPs of brainstem, cerebellar, and cortical origin have been reported as early as the 1960s. This review article summarizes and compares results from studies that have used a large range of vestibular stimulation, including natural vestibular stimulation on rotating chairs and motion platforms, as well as artificial vestibular stimulation (e.g., sounds, impulsive acceleration stimulation, galvanic stimulation). These studies identified vestibular EPs with short latency (<20 ms), middle latency (from 20 to 50 ms), and late latency (>50 ms). Analysis of the generators (source analysis) of these responses offers new insights into the neuroimaging of the vestibular system. Generators were consistently found in the parieto-insular and temporo-parietal junction-the core of the vestibular cortex-as well as in the prefrontal and frontal areas, superior parietal, and temporal areas. We discuss the relevance of vestibular EPs for basic research and clinical neuroscience and highlight their limitations.

Safety for Human MR Scanners at 7T

After introduction of the first human 7 tesla (7T) system in 1999, 7T MR systems have been employed as one of the most advanced platforms for human MR research for more than 20 years. Currently, two 7T MR models are approved for clinical use in the U.S.A. The approval facilitated introduction of the 7T system, summing up to around 100 worldwide. The approval in Japan is much awaited. As a clinical MR scanner, the 7T MR system is drawing attention in terms of safety.Several large-sized studies on bioeffects have been reported for vertigo, dizziness, motion disturbances, nausea, and others. Such effects might also be found in MR workers and researchers. Frequency and severity of reported bioeffects will be presented and discussed, including their variances. The high resonance frequency and shorter RF wavelength of 7T increase the concern about the safety. Homogeneous RF pulse excitation is difficult even for the brain, and a multi-channel parallel transmit (pTx) system is considered mandatory. However, pTx may create a hot spot, which makes the estimation of specific absorption rate (SAR) to be difficult. The stronger magnetic field of 7T causes a large force of displacement and heating on metallic implants or devices, and the scan of patients with them should not be conducted at 7T. However, there are some opinions that such patients might be scanned even at 7T, if certain criteria are met. This article provides a brief review on the effect of the static magnetic field on humans (MR subjects, workers, and researchers) and neurons, in addition to scan sound, SAR, and metal implants and devices. Understanding and avoiding adverse effects will contribute to the reduction in safety risks and the prevention of incidents.

New Frontiers in Managing the Dizzy Patient

Despite progress in vestibular research in the last 20 years, much remains poorly understood about vestibular pathophysiology and its management. A shared language is a critical first step in understanding vestibular disorders and is under development. Telehealth will continue for patients with dizziness, and ambulatory monitoring of nystagmus will become a diagnostic tool. In the next 2 decades, it is anticipated that vestibular perceptual threshold testing will become common in tertiary centers, imaging with improved spatial resolution will yield better understanding of vestibular pathophysiology, and that vestibular implants will become a part of clinical practice.

Evidence of Large Vestibulo-Ocular Reflex Reduction in Patients With Menière Attacks

OBJECTIVE

To examine the high frequency horizontal vestibular ocular-reflex (hVOR) during acute attacks of vertigo in Menière's disease (MD).

STUDY DESIGN

Retrospective case series and literature review.

SETTING

Tertiary academic medical center.

PATIENTS

Patients with clinical diagnosis of unilateral "definite MD."

INTERVENTION

Review of medical records.

MAIN OUTCOME MEASURES

Spontaneous nystagmus and the dynamic hVOR gain change at different stages of an acute episode of MD attack.

RESULTS

We studied 10 vertigo attacks during the unique stages of the episode. During the acme stage of the attack, lower hVOR gain was recorded on the affected side (mean 0.48 ± 0.23), which was associated with a paralytic nystagmus (beating away from the affected ear). Additionally, the mean hVOR gain remained significantly (p < 0.05) reduced during each of the other stages of the attack as compared with the unaffected side and a control group. After the attack, mean hVOR gains normalized in the affected ear. Mean hVOR gain of the unaffected ear remained normal during all stages.

CONCLUSION

Vestibular function during an attack of MD is a dynamic process associated with fluctuation of the dynamic (hVOR gain) and static (spontaneous nystagmus) processes, which exist in parallel with the perception of vertigo. Our data support vHIT monitoring during an episode to provide objective and accurate evidence of the ear with active disease. This would be particularly useful for those patients with MD presentations of unreliable hearing or assisting to identify the ear to be treated in the case of bilateral MD.

Long-term behavioral effects observed in mice chronically exposed to static ultra-high magnetic fields

PURPOSE

The primary goal of this study was to investigate whether chronic exposures to ultra-high B₀ fields can induce long-term cognitive, behavioral, or biological changes in C57BL/6 mice.

METHODS

C57BL/6 mice were chronically exposed to 10.5-T or 16.4-T magnetic fields (3-h exposures, two exposure sessions per week, 4 or 8 weeks of exposure). In vivo single-voxel ¹ H magnetic resonance spectroscopy was used to investigate possible neurochemical changes in the hippocampus. In addition, a battery of behavioral tests, including the Morris water-maze, balance-beam, rotarod, and fear-conditioning tests, were used to examine long-term changes induced by B₀ exposures.

RESULTS

Hippocampal neurochemical profile, cognitive, and basic motor functions were not impaired by chronic magnetic field exposures. However, the balance-beam-walking test and the Morris water-maze testing revealed B₀ -induced changes in motor coordination and balance. The tight-circling locomotor behavior during Morris water-maze tests was found as the most sensitive factor indexing B₀ -induced changes. Long-term behavioral changes were observed days or even weeks subsequent to the last B₀ exposure at 16.4 T but not at 10.5 T. Fast motion of mice in and out of the 16.4-T magnet was not sufficient to induce such changes.

CONCLUSION

Observed results suggest that the chronic exposure to a magnetic field as high as 16.4 T may result in long-term impairment of the vestibular system in mice. Although observation of mice may not directly translate to humans, nevertheless, they indicate that studies focused on human safety at very high magnetic fields are necessary.

Derealization and motion-perception related to repeated exposure to 3T Magnetic Resonance Image scanner in healthy adults

BACKGROUND:

Magnetic Resonance Imaging (MRI) scanning can induce psychological effects. No studies have investigated the role of magnetic vestibular stimulation (MVS) in 3TMRI scanner-induced psychological reactions.

OBJECTIVE:

To assess depersonalization/derealization (DD), state anxiety and motion-perception in a 3TMRI scanner, acutely and long-term.

PARTICIPANTS:

48 healthcare professionals and students were included, after preliminary rejection of claustrophobes and neuro-otology and psychiatry assessments.

PROCEDURES:

Participants completed questionnaires on personal habits, dissociation, anxiety/depression and motion sickness susceptibility. Validated DD and state anxiety questionnaires were administered before and after magnetic exposure twice, entering the bore head and feet first in random order, one week apart. During the following week, dizziness/disorientation was reported daily. One month later, 11 subjects repeated the procedure to assess reproducibility.

RESULTS:

Considerable individual susceptibility was observed, circa 40% of the subjects reported self-motion perception related to the exposure, with variable increase on DD symptoms. Multivariate analysis showed that DD scores after any exposure were influenced by entering the bore “feet first”, motion-perception, and the mean sleep hours/week (MANCOVA, R = 0.58, p = 0.00001). There was no clear effect of scanner exposure on state anxiety, which was related to trait anxiey but not to DD scores. During repeated exposures, about half of all subjects re-entering the scan reported motion-perception, but DD or anxiety symptoms were not consistent.

CONCLUSION:

Psychological effects during 3TMRI scanning result from multiple, interacting factors, including novelty of the procedure (first-exposure effect), motion-perception due to MVS, head/body orientation, sleeping habits and individual susceptibility. Forewarning subjects of these predisposing factors may increase tolerance to MRI scanning.

Qualitative and quantitative assessment of magnetic vestibular stimulation in humans

The sensation of phantom motion or exhibition of bodily sway is often reported in the proximity of an MR scanner. It is proposed that the magnetic field stimulates the vestibular system. There are a number of possible mechanisms responsible, and the relative contributions of susceptibility on the otolithic receptors and the Lorentz force on the cupulae have not yet been explored. This exploratory study aims to investigate the impact of being in the proximity of a 7.0 T MR scanner.The modified clinical test of sensory interaction on balance (mCTSIB) was used to qualitatively ascertain whether or not healthy control subjects who passed the mCTSIB in normal conditions 1) experienced subjective sensations of dizziness, vertigo or of leaning or shifting in gravity when in the magnetic field and 2) exhibited visibly increased bodily sway whilst in the magnetic field compared to outside the magnetic field. Condition IV of the mCTSIB was video recorded outside and inside the magnetic field, providing a semi-quantitative measure of sway.For condition IV of the mCTSIB (visual and proprioceptive cues compromised), all seven locations/orientations around the scanner yielded significantly more sway than at baseline (p < 0.01 FDR). A Student's t-test comparing the RMS velocity of a motion marker on the upper arm during mCTSIB condition IV showed a significant increase in the amount of motion exhibited in the field (T = 2.59; d.f. = 9; p = 0.029) compared to outside the field.This initial study using qualitative measures of sway demonstrates that there is evidence for MR-naïve individuals exhibiting greater sway while performing the mCTSIB in the magnetic field compared to outside the field. Directional polarity of sway was not significant. Future studies of vestibular stimulation by magnetic fields would benefit from the development of a sensitive, objective measure of balance function, which can be performed inside a magnetic field.

Modulatory effects of magnetic vestibular stimulation on resting-state networks can be explained by subject-specific orientation of inner-ear anatomy in the MR static magnetic field

Strong static magnetic fields, as used in magnetic resonance imaging (MRI), stimulate the vestibular inner ear leading to a state of imbalance within the vestibular system that causes nystagmus. This magnetic vestibular stimulation (MVS) also modulates fluctuations of resting-state functional MRI (RS-fMRI) networks. MVS can be explained by a Lorentz force model, indicating that MVS is the result of the interaction of the static magnetic field strength and direction (called "B0 magnetic field" in MRI) with the inner ear's continuous endolymphatic ionic current. However, the high variability between subjects receiving MVS (measured as nystagmus slow-phase velocity and RS-fMRI amplitude modulations) despite matching head position, remains to be explained. Furthermore, within the imaging community, an "easy-to-acquire-and-use" proxy accounting for modulatory MVS effects in RS-fMRI fluctuations is needed. The present study uses MRI data of 60 healthy volunteers to examine the relationship between RS-fMRI fluctuations and the individual orientation of inner-ear anatomy within the static magnetic field of the MRI. The individual inner-ear anatomy and orientation were assessed via high-resolution anatomical CISS images and related to fluctuations of RS-fMRI networks previously associated with MVS. More specifically, we used a subject-specific proxy for MVS (pMVS) that corresponds to the orientation of the individual inner-ear anatomy within the static magnetic field direction (also called "z-direction" in MR imaging). We found that pMVS explained a considerable fraction of the total variance in RS-fMRI fluctuations (for instance, from 11% in the right cerebellum up to 36% in the cerebellar vermis). In addition to pMVS, we examined the angle of Reid's plane, as determined from anatomical imaging as an alternative and found that this angle (with the same sinus transformation as for pMVS) explained considerably less variance, e.g., from 2 to 16%. In our opinion, an excess variability due to MVS should generally be addressed in fMRI research analogous to nuisance regression for movement, pulsation, and respiration effects. We suggest using the pMVS parameter to deal with modulations of RS-fMRI fluctuations due to MVS. MVS-induced variance can easily be accounted by using high-resolution anatomical imaging of the inner ear and including the proposed pMVS parameter in fMRI group-level analysis.

The Lorentz force on ions in membrane channels of neurons as a mechanism for transcranial static magnetic stimulation

Transcranial static magnetic stimulation is a novel noninvasive method of reduction of the cortical excitability in certain neurological diseases that makes use of static magnetic fields generated by permanent magnets. By contrast, ordinary transcranial magnetic stimulation makes use of pulsed magnetic fields generated by strong currents. Whereas the physical principle underlying ordinary transcranial magnetic stimulation is well known, that is, the Faraday´s law, the physical mechanism that explains the interaction between neurons and static magnetic fields in transcranial static magnetic stimulation remains unclear. In the present work, it is discussed the possibility that this mechanism might be the Lorentz force exerted on the ions flowing along the membrane channels of neurons. The overall effect of the static magnetic field would be to introduce an additional friction between the ions and the walls of the membrane channels, thus reducing its conductance. Calculations performed by using a Hodgkin-Huxley model demonstrate that even a slight reduction of the conductance of the membrane channels can lead to the suppression of the action potential, thus inhibiting neuronal activity.

Suppressive control of optokinetic and vestibular nystagmus by the primate frontal eye field

In this study, electrical stimulation in the frontal eye field (FEF) suppressed the quick and slow phases of optokinetic and vestibular nystagmus at an intensity subthreshold for eliciting saccades. Furthermore, the activity of fixation neurons in the FEF was related to the suppression of optokinetic and vestibular nystagmus by visual fixation. This suggests that a common neuronal assembly in the FEF may contribute to the suppressive control of different functional classes of eye movements.

10.5 T MRI static field effects on human cognitive, vestibular, and physiological function

PURPOSE

To perform a pilot study to quantitatively assess cognitive, vestibular, and physiological function during and after exposure to a magnetic resonance imaging (MRI) system with a static field strength of 10.5 Tesla at multiple time scales.

METHODS

A total of 29 subjects were exposed to a 10.5 T MRI field and underwent vestibular, cognitive, and physiological testing before, during, and after exposure; for 26 subjects, testing and exposure were repeated within 2-4 weeks of the first visit. Subjects also reported sensory perceptions after each exposure. Comparisons were made between short and long term time points in the study with respect to the parameters measured in the study; short term comparison included pre-vs-isocenter and pre-vs-post (1-24 h), while long term compared pre-exposures 2-4 weeks apart.

RESULTS

Of the 79 comparisons, 73 parameters were unchanged or had small improvements after magnet exposure. The exceptions to this included lower scores on short term (i.e. same day) executive function testing, greater isocenter spontaneous eye movement during visit 1 (relative to pre-exposure), increased number of abnormalities on videonystagmography visit 2 versus visit 1 and a mix of small increases (short term visit 2) and decreases (short term visit 1) in blood pressure. In addition, more subjects reported metallic taste at 10.5 T in comparison to similar data obtained in previous studies at 7 T and 9.4 T.

CONCLUSION

Initial results of 10.5 T static field exposure indicate that 1) cognitive performance is not compromised at isocenter, 2) subjects experience increased eye movement at isocenter, and 3) subjects experience small changes in vital signs but no field-induced increase in blood pressure. While small but significant differences were found in some comparisons, none were identified as compromising subject safety. A modified testing protocol informed by these results was devised with the goal of permitting increased enrollment while providing continued monitoring to evaluate field effects.

Cognisance of magnetic resonance imaging-induced vertigo and supported care: A study among a cohort of MRI radiographers in a country in West Africa

INTRODUCTION

Magnetic resonance imaging (MRI) can induce vertigo in patients undergoing such examinations. The severity of the vertigo is thought to increase with higher magnetic field strengths and could cause a patient to fall. The study assessed the awareness levels on MRI-induced vertigo among a cohort of MRI radiographers and their perspectives on the care that should be administered to patients post MRI examinations.

METHODS

The study utilized a quantitative cross-sectional research design and a questionnaire. Out of a total of 40 MRI-radiographers identified nationwide, 31 participated in the study. Statistical Package for Social Sciences v.21.0 was used to analyse the data.

RESULTS

Most participants (n = 21, 67.7%) were aware of MRI-induced vertigo. Many knew that patients (able and weaker) need to be assisted off the couch (n = 28, 90.3%) and escorted to the changing rooms post MRI examinations (n = 31,100%). There were statistically significant associations between the size of magnetic field strength used by the participants and their level of awareness about MRI-induced vertigo (r = 0.691, p = 0.003), appreciation of the needed support for patients post MRI examinations (r = 0.530, p = 0.041) and the frequency of occurrence of MRI-induced vertigo among their patients (r = 0.530, p = 0.001).

CONCLUSION

The radiographers were mostly cognisant of MRI-induced vertigo and the supported care they were supposed to administer to their patients. The size of magnetic field strength used by the participants correlated with their level of awareness about MRI-induced vertigo and their appreciation of the needed support for patients post MRI examinations.

IMPLICATION FOR PRACTICE

The study highlights the need for a refresher training to expand the knowledge-base of a few of the radiographers who were not very cognisant about MRI-induced vertigo.

Effects of Moderate Static Magnetic Field on Neural Systems Is a Non-invasive Mechanical Stimulation of the Brain Possible Theoretically?

Static magnetic fields have been shown to induce effects on the human brain. Different experiments seem to support the idea that moderate static magnetic field can exert some influence on the gating processes of the membrane channels. In this article we visit the order of magnitude of the energy magnetic terms associated with moderate applied field (between 10 and 200 milliteslas). It is shown that gradients of the Zeeman energy associated with the inhomogeneous applied fields can induce pressures of the order of 10^–2Pa. The surface tension generated by the magnetic pressure, on the surface delimiting the brain region subject to relevant field and gradients, is found to range between 10^–1 and 1 mN⋅m^–1. These pressures seem to be strong enough to interfere with the elastic and electrostatic energies involved in the channel activation-inactivation-deactivation mechanisms of biological membranes. It has been described that small mechanical force can activate voltage gated potassium channels. Moreover, stretch-activated ion channels are widely described in different biological tissues. Virtually, all these channels can modify their activity if stressed by a sufficient pressure delivered for enough time. We propose mechanical stimulation – possibly not exclusively – as a candidate mechanism how static magnetic field can produce effects in biological systems. It must be emphasized, that such field gradients were not previously proposed as a possible source of neural activity modification.

Magnetoreception: A Dynamo in the Inner Ear of Pigeons

A phylogenetically diverse set of animals are able to orient by the Earth's magnetic field, but how they do so is an open problem. A new study identifies ion channels in the avian inner ear that could detect magnetic fields via induced electric fields.

Falling post-MRI examinations: 2 case reports

Background

The phenomenon where ambulant patients suffer sudden falls during the process of getting off the couch and walking to the changing room post magnetic resonance imaging (MRI) examination is uncommon. However, it can be a very disturbing experience for such patients. Therefore, there is the need to effectively support patients to avoid falls when they are getting off the MRI couch when the examination is completed.

Methods

Two ambulant patients who had undergone MRI were observed to have lost their balance when they attempted to get off from the MRI couch after their procedures. Face-to-face interrogations were made about what they felt.

Results

The two patients complained of experiencing some form of dizziness/vertigo when they got off the MRI couch.

Conclusion

This paper reported two cases of falls that occurred in an MRI facility. The aim was to emphasize the need for extra care and support for all patients who undergo MRI examinations due to the potential risk of MRI induced vertigo or dizziness regardless of the patient's condition.

Review of Audiovestibular Symptoms Following Exposure to Acoustic and Electromagnetic Energy Outside Conventional Human Hearing

Objective: We aim to examine the existing literature on, and identify knowledge gaps in, the study of adverse animal and human audiovestibular effects from exposure to acoustic or electromagnetic waves that are outside of conventional human hearing. Design/Setting/Participants: A review was performed, which included searches of relevant MeSH terms using PubMed, Embase, and Scopus. Primary outcomes included documented auditory and/or vestibular signs or symptoms in animals or humans exposed to infrasound, ultrasound, radiofrequency, and magnetic resonance imaging. The references of these articles were then reviewed in order to identify primary sources and literature not captured by electronic search databases. Results: Infrasound and ultrasound acoustic waves have been described in the literature to result in audiovestibular symptomology following exposure. Technology emitting infrasound such as wind turbines and rocket engines have produced isolated reports of vestibular symptoms, including dizziness and nausea and auditory complaints, such as tinnitus following exposure. Occupational exposure to both low frequency and high frequency ultrasound has resulted in reports of wide-ranging audiovestibular symptoms, with less robust evidence of symptomology following modern-day exposure via new technology such as remote controls, automated door openers, and wireless phone chargers. Radiofrequency exposure has been linked to both auditory and vestibular dysfunction in animal models, with additional historical evidence of human audiovestibular disturbance following unquantifiable exposure. While several theories, such as the cavitation theory, have been postulated as a cause for symptomology, there is extremely limited knowledge of the pathophysiology behind the adverse effects that particular exposure frequencies, intensities, and durations have on animals and humans. This has created a knowledge gap in which much of our understanding is derived from retrospective examination of patients who develop symptoms after postulated exposures. Conclusion and Relevance: Evidence for adverse human audiovestibular symptomology following exposure to acoustic waves and electromagnetic energy outside the spectrum of human hearing is largely rooted in case series or small cohort studies. Further research on the pathogenesis of audiovestibular dysfunction following acoustic exposure to these frequencies is critical to understand reported symptoms.

Subjectively Reported Effects Experienced in an Actively Shielded 7T MRI: A Large-Scale Study

BACKGROUND

Ultrahigh-field (UHF) MRI advances towards clinical use. Patient compliance is generally high, but few large-scale studies have investigated the effects experienced in 7T MRI systems, especially considering peripheral nerve stimulation (PNS) and caregiving.

PURPOSE

To evaluate the quantity, the intensity, and subjective experiences from short-term effects, focusing on the levels of comfort and compliance of subjects.

STUDY TYPE

Prospective.

POPULATION

In all, 954 consecutive MRIs in 801 subjects for 3 years.

FIELD STRENGTH

7T.

ASSESSMENT

After the 7T examination, a questionnaire was used to collect data.

STATISTICAL TESTS

Descriptive statistics, Spearman's rank correlation, Mann-Whitney U-test, and t-test.

RESULTS

The majority (63%) of subjects agreed that the MRI experience was comfortable and 93% would be willing to undergo future 7T MRI as a patient (5% undecided) and 82% for research purposes (12% undecided). The most common short-term effects experienced were dizziness (81%), inconsistent movement (68%), PNS (63%), headache (40%), nausea (32%), metallic taste (12%), and light flashes (8%). Of the subjects who reported having PNS (n = 603), 44% experienced PNS as "not uncomfortable at all," 45% as "little or very little uncomfortable," and 11% as "moderate to very much uncomfortable." Scanner room temperature was experienced more comfortable before (78%) than during (58%) examinations, and the noise level was acceptable by 90% of subjects. Anxiety before the examination was reported by 43%. Patients differed from healthy volunteers regarding an experience of headache, metallic taste, dizziness, or anxiety. Room for improvement was pointed out after 117 examinations concerning given information (n = 73), communication and sound system (n = 35), or nursing care (n = 15).

DATA CONCLUSION

Subjectively reported effects occur in actively shielded 7T MRI and include physiological responses and individual psychological issues. Although leaving room for improvement, few subjects experienced these effects being so uncomfortable that they would lead to aversion to future UHF examinations.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 5 J. Magn. Reson. Imaging 2020;52:1265-1276.