Modification of pulse sequences reduces occupational exposure from MRI switched gradient fields: Preliminary results

Wilén, Jonna; Hauksson, Jón; Mild, Kjell Hansson

doi:10.1002/bem.20544

Cited by 13 publications

(23 citation statements)

References 2 publications

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“…In particular, the “whisper” gradient mode improves patient safety, reducing SR p to 75.3 T m ‐1 s ‐1 . More generally, all experimental findings highlight, in accordance with previous studies [Wilén et al, ; Trevisan et al, ; Frankel et al, ], that not only different types of sequences, but also scan settings can affect SR p values. In particular, regardless of the type of sequence, the “fast” gradient mode is always associated with increased slew rate.…”

Section: Resultssupporting

confidence: 92%

Magnetic Resonance Examinations of Patients With Implanted Active Devices. A Low‐Cost Approach in Slew Rate Evaluation

Trevisan¹,

Nichelatti²,

Maieron

et al. 2019

Bioelectromagnetics

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Time‐varying magnetic field gradients involved in magnetic resonance examinations can damage implanted electronic systems. The quantity related to this side effect is the gradient slew rate, which is usually not directly available on magnetic resonance console. The present study proposes a low‐cost approach in slew rate assessment, which is useful in risks versus benefits evaluation as well as in sequences optimization. The experimental method is based on an analog circuit, which senses the output voltage of the scanner waveform generator. This allows taking easy and reliable slew rate measurements, even during clinical examinations on patients. Whereas previous studies required managing a considerable amount of data, the present work addresses only the maximal slew rate of any clinical sequence. Experimental results show that the smooth gradient mode, selectable on the two scanners examined, is very effective in patient safety improvement. In particular, it reduces slew rate values in the range from 52.4 up to 132.4 T m‐1 s‐1, i.e. far below the interval 216–346 T m‐1 s‐1, indicated as slew rate tolerance limit of modern implanted electronic devices. Bioelectromagnetics. 2019;40:512–521. © 2019 Bioelectromagnetics Society

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Section: Resultssupporting

confidence: 92%

Magnetic Resonance Examinations of Patients With Implanted Active Devices. A Low‐Cost Approach in Slew Rate Evaluation

Trevisan¹,

Nichelatti²,

Maieron

et al. 2019

Bioelectromagnetics

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“…Sensitive patients may require more advanced adjustments to a sequence, such as SAR‐reducing adjustments to the RF field, to prevent heating of certain kinds of implants or fever in patients who have a reduced ability to regulate body heat. For patients with sensitive hearing, a sequence can be run in noise‐reducing mode, which, in addition to reducing the noise level, also reduces the time derivative of the gradient magnetic field [Wilén et al, ].…”

Section: Discussionmentioning

confidence: 99%

EMF exposure variation among MRI sequences from pediatric examination protocols

Frankel

Mild

Olsrud

et al. 2018

Bioelectromagnetics

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The magnetic resonance imaging (MRI) exposure environment is unique due to the mixture and intensity of magnetic fields involved. Current safety regulations are based on well‐known acute effects of heating and neuroexcitation while the scientific grounds for possible long‐term effects from MRI exposure are lacking. Epidemiological research requires careful exposure characterization, and as a first step toward improved exposure assessment we set out to characterize the MRI‐patient exposure environment. Seven MRI sequences were run on a 3‐Tesla scanner while the radiofrequency and gradient magnetic fields were measured inside the scanner bore. The sequences were compared in terms of 14 different exposure parameters. To study within–sequence variability, we varied sequence settings such as flip angle and slice thickness one at a time, to determine if they had any impact on exposure endpoints. There were significant differences between two or more sequences for all fourteen exposure parameters. Within–sequence differences were up to 60% of the corresponding between‐sequence differences, and a 5–8 fold exposure increase was caused by variations in flip angle, slice spacing, and field of view. MRI exposure is therefore not only sequence‐specific but also patient‐ and examination occurrence‐specific, a complexity that requires careful consideration for an MRI exposure assessment in epidemiological studies to be meaningful. Bioelectromagnetics. 40:3–15, 2019. © 2018 The Authors. Bioelectromagnetics Published by Wiley Periodicals, Inc.

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“…Early measurements involving a single search coil established that significant gradient fringe fields exist beyond the bore of the scanner [76]. These results have been extended using three-axis calibrated meters [6,70,74,[77][78][79][80]. Table 6 summarises all the known results for exposure measurements at the entrance of the bore in terms of peak B, dB/dt or percentage of the ICNIRP and NRPB (old ICNIRP) RLs.…”

Section: Time-varying Gradient Fieldsmentioning

confidence: 99%

Occupational exposure in MRI

McRobbie¹

2012

BJR

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This article reviews occupational exposure in clinical MRI; it specifically considers units of exposure, basic physical interactions, health effects, guideline limits, dosimetry, results of exposure surveys, calculation of induced fields and the status of the European Physical Agents Directive. Electromagnetic field exposure in MRI from the static field B(0), imaging gradients and radiofrequency transmission fields induces electric fields and currents in tissue, which are responsible for various acute sensory effects. The underlying theory and its application to the formulation of incident and induced field limits are presented. The recent International Commission on Non-Ionizing Radiation Protection (ICNIRP) Bundesministerium für Arbeit und Soziales and Institute of Electrical and Electronics Engineers limits for incident field exposure are interpreted in a manner applicable to MRI. Field measurements show that exposure from movement within the B(0) fringe field can exceed ICNIRP reference levels within 0.5 m of the bore entrance. Rate of change of field dB/dt from the imaging gradients is unlikely to exceed the new limits, although incident field limits can be exceeded for radiofrequency (RF) exposure within 0.2-0.5 m of the bore entrance. Dosimetric surveys of routine clinical practice show that staff are exposed to peak values of 42 ± 24% of B(0), with time-averaged exposures of 5.2 ± 2.8 mT for magnets in the range 0.6-4 T. Exposure to time-varying fields arising from movement within the B(0) fringe resulted in peak dB/dt of approximately 2 T s(-1). Modelling of induced electric fields from the imaging gradients shows that ICNIRP-induced field limits are unlikely to be exceeded in most situations; however, movement through the static field may still present a problem. The likely application of the limits is discussed with respect to the reformulation of the European Union (EU) directive and its possible implications for MRI.

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Modification of pulse sequences reduces occupational exposure from MRI switched gradient fields: Preliminary results

Cited by 13 publications

References 2 publications

Magnetic Resonance Examinations of Patients With Implanted Active Devices. A Low‐Cost Approach in Slew Rate Evaluation

Magnetic Resonance Examinations of Patients With Implanted Active Devices. A Low‐Cost Approach in Slew Rate Evaluation

EMF exposure variation among MRI sequences from pediatric examination protocols

Occupational exposure in MRI

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