Health Effects and Safety of Magnetic Resonance Imaging

Abstract

Dear Sir, With interest we took note of a review on health effects and safety of Magnetic Resonance Imaging by Drs Ng, Faust and Acharya U, published online on March 30 2010 in the Journal of Medical Systems [1]. As adequately described by the authors there are a wide number of advantages to the use of MRI as a medical imaging modality that have led to improved diagnostic outcomes without the drawbacks of for example the use of X-rays; hence the exponential growth in usage since its first introduction in the late 1970s [2]. Nonetheless, there are several serious drawbacks related to the strong static and time-varying magnetic fields and radiofrequency fields required for scanning which as discussed by the authors require specific safety recommendations.Unfortunately, set out as a review of current knowledge of adverse health effects and current safety issues related to MRI environments for both patients and staff members this review fails to achieve its aim. Surprisingly, the most recent non-self citation reference to peer-reviewed work is from 2007 despite ongoing research since then. As such, it is no surprise that the safety recommendations provided by the authors focus on prevention of accidents due to ferromagnetic objects and implants, (local) tissue heating and reduction of acoustic noise, which were the only notable risks associated with MRI identified at the end of the previous century [3].However, since the publications cited by the authors an additional body of work (of which the first peer-reviewed papers were in fact already published in the period supposedly covered in the review) into acute transient adverse effects related to exposure to the static and time-varying magnetic fields present in, but also surrounding MRI systems has emerged. Controlled human trials [4][5][6] have provided evidence that visual perception and visuo-motor performance are negatively affected during movement (of the head) in the heterogeneous static magnetic stray field surrounding MR systems. A more recent study has also shown that different cognitive domains can also be affected by time-varying magnetic fields [7]. In line with proposed biological mechanisms for these effects [8,9] no effects were observed within the homogeneous magnet bore, where patients are located during scanning [10] nor were effects on cognition measurable immediately after exposure had ended [11]. However, recent data from a controlled trial using transcranial magnetic stimulation (TMS) does suggest a transient alteration in cortical excitability after undergoing an MRI scan and exposure has ended [12]. Although a threshold level seems to exist for at least some of the acute effects [13], effects could already be measured well below the 2 T and 6 Ts −1 limits mentioned in this review (although appropriate limit values would instead have been the most recent ICNIRP guidelines [14]). Field surveys have further shown that MR engineers [15] and nurses [16] routinely working with MRI scanners regularly experience adverse transient effects including

Exposure to static magnetic fields and risk of accidents among a cohort of workers from a medical imaging device manufacturing facility

“…Acute symptoms and neurocognitive effects have been reported to be associated with exposure to MRI‐related SMF and time‐varying magnetic fields, mainly among workers in MRI‐production, and to a limited extent, among imaging workers in healthcare . Hardly any data are available on effects of long‐term occupational exposure to SMF , but considering the nature of reported acute effects on balance , visual perception and hand–eye coordination , the question was raised whether long‐term SMF exposure may lead to increased risk of work‐related accidents, commute‐related (near) accidents, and accidents in general.…”

Personal exposure to static and time-varying magnetic fields during MRI procedures in clinical practice in the UK

“…We performed measurements at the hip, which was done so that wearing the dosimeter would not interfere with participants' work, but as outlined above this may have underestimated exposure to the head, which is generally considered the target organ for the observed effects. 37 We opted not to measure nearer the head, for example, at the chest as was done in the Dutch study, 29 because it is fairly unlikely that if in the future routine monitoring of staff is introduced, it will be carried out using relatively inconvenient protocols. Nonetheless, as it is difficult to determine whether the location of the dosimeter at the hip systematically overestimates or underestimates exposure measured at the chest, future work will need to assess correlations of exposures measured at different places on the body during simultaneous measurements of different movement patterns.…”

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

“…Therefore, in high Tesla environments, high dB / dt levels could likely be produced at the vestibular system level. This explains why moving outside the bore generates stronger dB / dt values than the ones obtained within the bore (Fuentes et al, 2008; Kännälä et al, 2009; De Vocht et al, 2012). Fuentes et al (2008) have found peak dB / dt of 7.3 T/s obtained by normal body movements within a 1.5 MRI scanner environment.…”