Numerical prediction of temperature elevation induced around metallic hip prostheses by traditional, split, and uniplanar gradient coils

Zilberti, Luca; Bottauscio, O.; Chiampi, Mario; Hand, J.W.; Lopez, Hector Sanchez; Brühl, Rüdiger; Crozier, Stuart

doi:10.1002/mrm.25687

Cited by 21 publications

(29 citation statements)

References 19 publications

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“…Applying, for comparison, the product echo planar imaging sequence, we obtained 40%, with Graf's sequence and implant position 2.6% of this value. The resulting tissue temperatures can only be determined by simulations that take into account heat dissipation, such as by perfusion , whereas here an independent experimental test of such simulations is intended. An RF heating test performed for comparison (http://onlinelibrary.wiley.com/store/10.1002/mrm.26652/asset/supinfo/mrm26652-sup-0001-suppfigs.pdf?v=1&s=9755943faffb22e5b22e520009512daf37a90d6d) showed no detectable temperature effect.…”

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confidence: 99%

Gradient heating of bulk metallic implants can be a safety concern in MRI

Brühl

Ihlenfeld

Ittermann

2017

Magnetic Resonance in Med

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confidence: 99%

Gradient heating of bulk metallic implants can be a safety concern in MRI

Brühl

Ihlenfeld

Ittermann

2017

Magnetic Resonance in Med

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“…Body RF coil transmission induces RF power deposition in a large volume including body regions far away from the ROI. This is of clinical relevance for cardiac patients with hip replacement prosthesis (clinical prevalence in an older population of up to 5% [41]) and other abdominal or peripheral implants (for example vena cava filter, clinical prevalence in an older population of up to 4% [42]) which constitute an RF-heating related contraindication if body RF coil transmission is used [43]. Local transmit RF coils dedicated for CMR restrict power deposition primarily to the upper chest and hence permit inclusion of these patients into CMR examinations.…”

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confidence: 99%

Local Multi-Channel RF Surface Coil versus Body RF Coil Transmission for Cardiac Magnetic Resonance at 3 Tesla: Which Configuration Is Winning the Game?

et al. 2016

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IntroductionThe purpose of this study was to demonstrate the feasibility and efficiency of cardiac MR at 3 Tesla using local four-channel RF coil transmission and benchmark it against large volume body RF coil excitation.MethodsElectromagnetic field simulations are conducted to detail RF power deposition, transmission field uniformity and efficiency for local and body RF coil transmission. For both excitation regimes transmission field maps are acquired in a human torso phantom. For each transmission regime flip angle distributions and blood-myocardium contrast are examined in a volunteer study of 12 subjects. The feasibility of the local transceiver RF coil array for cardiac chamber quantification at 3 Tesla is demonstrated.ResultsOur simulations and experiments demonstrate that cardiac MR at 3 Tesla using four-channel surface RF coil transmission is competitive versus current clinical CMR practice of large volume body RF coil transmission. The efficiency advantage of the 4TX/4RX setup facilitates shorter repetition times governed by local SAR limits versus body RF coil transmission at whole-body SAR limit. No statistically significant difference was found for cardiac chamber quantification derived with body RF coil versus four-channel surface RF coil transmission. Our simulation also show that the body RF coil exceeds local SAR limits by a factor of ~2 when driven at maximum applicable input power to reach the whole-body SAR limit.ConclusionPursuing local surface RF coil arrays for transmission in cardiac MR is a conceptually appealing alternative to body RF coil transmission, especially for patients with implants.

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“…In a recent paper , we showed that the tissues surrounding a metallic hip prosthesis exposed to a gradient field (GF) may undergo a nonnegligible heating (up to some degree), as a result of the electromagnetic energy deposited in the implant. Since then, we have realized that in the MR community these results are generally received with some skepticism, probably because of the fact that most of the scientific papers dealing with thermal problems in MRI focus on RF fields .…”

Section: Total Joule Losses P (In Watt) Developed Within the Spherementioning

confidence: 99%

The underestimated role of gradient coils in MRI safety

Zilberti

Arduino

Bottauscio

et al. 2016

Magnetic Resonance in Med

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MRI scanning of patients carrying implants is becoming a reality in many hospitals, because of the wide increase of population with implants, particularly in the orthopedic ones (1). The responsibility for this practice falls on the subscribing physicians or radiologists, who rely on guidance establishing safety and compatibility of implants in the MR environment (eg, (2)), which basically address issues related to magnetically induced mechanical actions and radiofrequency (RF) induced heating of tissues. Even if large-scale MR safety studies on orthopedic implants have been published that show no evidence of specific risks for patients' health (eg, (3)), additional analyses of the interaction between MR fields and metallic implants can contribute to support the scan decision on a firm scientific rationale.In a recent paper (4), we showed that the tissues surrounding a metallic hip prosthesis exposed to a gradient field (GF) may undergo a nonnegligible heating (up to some degree), as a result of the electromagnetic energy deposited in the implant. Since then, we have realized that in the MR community these results are generally received with some skepticism, probably because of the fact that most of the scientific papers dealing with thermal problems in MRI focus on RF fields (5-16). Similarly, the attention of relevant standardization and regulatory bodies is focused solely on RF-induced heating (2,17). This tendency is absolutely well-grounded when studying native tissues, where GFs are not able to develop significant thermal effects. However, in the presence of metallic foreign bodies the situation is different.Many papers show that a significant heating can be associated with the exposure of such bodies to RF fields, especially with wire-like structures, which may act as antennas (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). In this case, RF typically deposits a relatively low power inside the metallic parts, but their presence may cause the enhancement of the specific absorption rate directly developed in the tissues anyway. What we would like to highlight here is that, in presence of bulky metallic prostheses, GFs can produce a nonnegligible heating too, because of the thermal power generated inside the metal (Joule effect), which involves the tissues indirectly, by diffusion ("indirect effect" (31)). The GF thermal effect, which becomes sizable only for prostheses far from the coils' isocenter, has been considered up until now by a few articles (4,32-34). To sustain these findings, we exploit an analytical solution (35) that is not affected by possible artifacts of numerical results. The solution provides the current density J (in complex notation) induced within a nonmagnetic metallic sphere, with radius R, conductivity s and permeability m 0 , immersed in a nonconductive background. When the sphere is radiated by a homogeneous, timeharmonic, magnetic flux density B (peak value) at frequency f, the current density in an internal point iswhere r is the distance from the sphere center, u is the cola...

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Numerical prediction of temperature elevation induced around metallic hip prostheses by traditional, split, and uniplanar gradient coils

Cited by 21 publications

References 19 publications

Gradient heating of bulk metallic implants can be a safety concern in MRI

Gradient heating of bulk metallic implants can be a safety concern in MRI

Local Multi-Channel RF Surface Coil versus Body RF Coil Transmission for Cardiac Magnetic Resonance at 3 Tesla: Which Configuration Is Winning the Game?

The underestimated role of gradient coils in MRI safety

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