Investigation of the factors responsible for burns during MRI

Dempsey, Mary F.; Condon, Barrie; Hadley, Donald M.

doi:10.1002/jmri.1088

Cited by 204 publications

(158 citation statements)

References 17 publications

(21 reference statements)

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“…Dempsey and Condon supposed that RF heating may take place in MR procedures by electromagnetic induction, formation of resonance circuit, and antenna effect. 23,24 In the present situations, in which the implant is present in the ‰ow of the eddy current, these mechanisms are thought to be related to RF heating.…”

Section: Rf-heating Mechanismmentioning

confidence: 95%

Evaluation of RF Heating due to Various Implants during MR Procedures

et al. 2011

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We evaluated radiofrequency (RF) heating of various implants embedded in a gel phantom during magnetic resonance (MR) procedures. We examined the dependence of RF heating on variation in speciˆc absorption rate (SAR) and angle between the implant and the static magneticˆeld (B 0 ) and on the displacement of the phantom in the irradiation coil using a 1.5-tesla MR system, and we compared the in‰uence of RF heating on the same implant using a 3.0T MR system.Our results support the occurrence of RF heating of implants made of non-magnetizing metal. We observed greater RF heating when the implant was set parallel to B 0 , embedded at a shallower depth, and placed at the center of the RF irradiation coil. We also conˆrmed that the rise in temperature was proportionate to the increase in SAR. We considered the diŠerence in temperature elevation on depth of embedding to re‰ect the skin-depth eŠect of RF intensity for both the 1.5-and 3.0-T MR systems.

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Section: Rf-heating Mechanismmentioning

confidence: 95%

Evaluation of RF Heating due to Various Implants during MR Procedures

et al. 2011

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“…A fundamental line of development for fMRI has been the pursuit of higher magnetic field strengths, which leads to super-linear gains in functional sensitivity (van der Zwaag et al, 2009), that can be traded for increased spatial resolution (Da Costa et al, 2011;Yacoub et al, 2008). Unfortunately, however, simultaneous EEG-fMRI acquisitions at ultra-high field suffer from various undesirable interactions that can degrade data quality and potentially compromise subject safety (Dempsey et al, 2001;Neuner et al, 2014). Safety concerns have been effectively moderated (Lemieux et al, 1997;Noth et al, 2012), and although EEG components can reduce the signal-to-noise ratio (SNR) of MR images, numerous studies have found that losses in temporal SNR remain acceptable for fMRI, even at ultra-high field strengths with fairly high electrode densities (Jorge et al, 2015;Luo and Glover, 2012;Mullinger et al, 2008b).…”

Section: Introductionmentioning

confidence: 99%

Towards high-quality simultaneous EEG-fMRI at 7 T: Detection and reduction of EEG artifacts due to head motion

et al. 2015

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a b s t r a c t a r t i c l e i n f oThe enhanced functional sensitivity offered by ultra-high field imaging may significantly benefit simultaneous EEG-fMRI studies, but the concurrent increases in artifact contamination can strongly compromise EEG data quality. In the present study, we focus on EEG artifacts created by head motion in the static B 0 field. A novel approach for motion artifact detection is proposed, based on a simple modification of a commercial EEG cap, in which four electrodes are non-permanently adapted to record only magnetic induction effects. Simultaneous EEG-fMRI data were acquired with this setup, at 7 T, from healthy volunteers undergoing a reversingcheckerboard visual stimulation paradigm. Data analysis assisted by the motion sensors revealed that, after gradient artifact correction, EEG signal variance was largely dominated by pulse artifacts (81-93%), but contributions from spontaneous motion (4-13%) were still comparable to or even larger than those of actual neuronal activity (3-9%). Multiple approaches were tested to determine the most effective procedure for denoising EEG data incorporating motion sensor information. Optimal results were obtained by applying an initial pulse artifact correction step (AAS-based), followed by motion artifact correction (based on the motion sensors) and ICA denoising. On average, motion artifact correction (after AAS) yielded a 61% reduction in signal power and a 62% increase in VEP trial-by-trial consistency. Combined with ICA, these improvements rose to a 74% power reduction and an 86% increase in trial consistency. Overall, the improvements achieved were well appreciable at single-subject and single-trial levels, and set an encouraging quality mark for simultaneous EEG-fMRI at ultra-high field.

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“…4 According to the IEC recommendation, the upper limit in the Japanese Industrial Standards (JIS) was also reviewed in 1999 5 and provided for an upper limit of 2.0 W/kg for 6 min average as the usual operation mode and 4.0 W/kg for 15 min average as theˆrst-level operation mode, which is the same as the IEC standard. However, risk of burn accidents remains during MR imaging following these standards, [6][7][8][9] most resulting from contact between the skin of the human body and the cable of the electrocardiography monitor, oxygen color saturation monitor, or RF receiving coil. 10 Knopp's group has also reported cases where burning occurred during MR imaging procedures without such environmental conditions.…”

Section: Introductionmentioning

confidence: 99%

Dependence of RF Heating on SAR and Implant Position in a 1.5T MR System

Muranaka

Horiguchi

Usui

et al. 2007

MRMS

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Purpose: We evaluated radiofrequency (RF) heating of a humerus implant embedded in a gel phantom during magnetic resonance (MR) imaging for the speciˆc absorption rate (SAR), angle between the implant and static magneticˆeld (B 0 ), and position of the implant in the irradiation coil.Methods: We embedded a stainless steel humerus implant 2 cm deep in tissue-equivalent loop and mass phantoms, placed it parallel to the static magneticˆeld of a 1.5T MR scanner, and recorded the temperatures of the implant surface with RF-transparentˆberoptic sensors. We measured rises in temperature at the tips of the implant by varying the SAR from 0.2 to 4.0 W/kg and evaluated RF heating of the implant for its angle to B 0 and its displacement along B 0 from the center of the RF irradiation coil.Results: RF heating was similar for the loop and mass phantoms because the eddy current ‰ows through the periphery of both. As the SAR increased, the temperature at the implant tip increased, and there was a linear relationship between the SAR and temperature rise. The values were 6.49 C at 2.0 W/kg and 12.79 C at 4.0 W/kg. Rise in temperature decreased steeply as the angle between the implant and B 0 surpassed 459 . In addition, as the implant was displaced from the center of the RF coil to both ends, the rise in temperature decreased.Conclusion: The rise in temperature in deep tissue was estimated to be higher than 1.09 C for SAR above 0.4 W/kg. RF heating was greatest when the implant was set parallel to B 0 . In MR imaging of patients with implants, there is a risk of RF heating when the loop of the eddy current is formed inside the body.

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Investigation of the factors responsible for burns during MRI

Cited by 204 publications

References 17 publications

Evaluation of RF Heating due to Various Implants during MR Procedures

Evaluation of RF Heating due to Various Implants during MR Procedures

Towards high-quality simultaneous EEG-fMRI at 7 T: Detection and reduction of EEG artifacts due to head motion

Dependence of RF Heating on SAR and Implant Position in a 1.5T MR System

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