Human exposure to 4.0-Tesla magnetic fields in a whole-body scanner

Abstract

Details are given for the design, construction, properties, and performance of a large, highly homogeneous magnet designed to permit whole-body magnetic resonance imaging and spectroscopy at 4 T. The magnet has an inductance of 1289 H and a stored energy of 33.4 MJ at rated field. The health of a group of 11 volunteers who had varying degrees of exposure to this field was followed over a 12-month period and no change that could be associated with this exposure was detected. A mild level of sensory experiences, apparently associated with motion within the field of the magnet, was reported by some of the volunteers during some of their exposures. A questionnaire regarding sensory effects associated with magnetic resonance scanners and possibly caused by the static magnetic field of these instruments, was given to nine respondents who had experience within both 1.5-T scanners and this 4-T scanner and to another group of 24 respondents who had experience only within 1.5-T scanners. For the sensations of vertigo, nausea, and metallic taste there was statistically significant (p less than 0.05) evidence for a field-dependent effect that was greater at 4 T. In addition, there was evidence for motion-induced magnetophosphenes caused by motion of the eyes within the static field. These results indicate the practicality of experimental whole-body body scanners operating at 4 T and the possibility of mild sensory effects in humans associated with motion within a static magnetic field. The results also indicate the likelihood of a wide margin of safety for the exposure of noncompromised patients to the static fields of conventional magnetic resonance scanners operated at 1.5 to 2 T and below.

Cognitive effects of head‐movements in stray fields generated by a 7 Tesla whole‐body MRI magnet

“…Patient and staff safety is maintained by eliminating magnetic objects from the vicinity of the magnet, screening patients for pace-makers and aneurysm clips before they undergo a scan, limiting the strength of the rapidly switching gradient fields to avoid peripheral nerve stimulation, minimizing RF-induced heating and taking steps to avoid RF burns [Shellock, 2001]. Besides these potential acute risks, no adverse health effects have been associated with MRI [Schenck et al, 1992;Kangarlu et al, 1999;Shellock, 2001;Chakeres et al, 2003b]. However, with the introduction of interventional MR procedures [Schneider et al, 2001;Razavi et al, 2003;Nour et al, 2004;Quick et al, 2005] that involve medical staff working in the vicinity of the scanner for extended periods, any potential effects of short and/or long-term exposure would be inevitably increased [Chakeres and de Vocht, 2005].…”

Pooled analyses of effects on visual and visuomotor performance from exposure to magnetic stray fields from MRI scanners: Application of the Bayesian framework

“…This area has been largely overlooked, especially in the field of occupational health, mainly because several early studies, focusing on patient safety, did not find an association between exposure to electromagnetic fields (EMFs) from MRI systems and biological or neuropsychological effects (3,4). Although symptoms including vertigo, nausea, dizziness, headaches, a metal taste, and fatigue have been reported anecdotally since the introduction of MRI (5,6), the attention shifted to effects of more "potent" time-varying EMFs (7,8), such as peripheral nerve stimulation (9). Nonetheless, several recent studies have addressed patient safety issues during clinical imaging at ultrahigh (8 T) field strength (10,11).…”

Ultra-High Field NMR and MRI—The Role of Magnet Technology to Increase Sensitivity and Specificity

“…Susceptibility based contrast in (functional) MRI benefits particularly from higher field strength, thus methods increasing specificity like spin-echo based fMRI vs. gradient-echo based fMRI may be more viable. On the other hand, we must not risk any short or long term hazard to the patient and personnel (for more details see also above), or increase discomfort due to (reversible) physiological sensations and, thus, damage the reputation and non-invasive status of the MR methods altogether [70,74,76,78,81]. In addition, a recent paper describes that one third of the patient scanned at 3 T and 7 T noticed stronger vertigo and nausea at the higher field strength [79].…”