Adaptive <scp>SAR</scp> mass‐averaging framework to improve predictions of local <scp>RF</scp> heating near a hip implant for parallel transmit at 7 <scp>T</scp>

Destruel, Aurélien; O’Brien, Kieran; Jin, Jin; F, Liu; Barth, Markus; Crozier, Stuart

doi:10.1002/mrm.27379

Cited by 16 publications

(31 citation statements)

References 40 publications

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“…The male model Duke, from the Virtual Family, was modified to include 2 CoCrMo hip prostheses, and screws were added on the acetabular components . The heads of the femurs were replaced with muscle tissue to simulate a bilateral total hip arthroplasty, and bone tissue was added in the pelvis to ensure a tight fit of the acetabular component (Figure A).…”

Section: Methodsmentioning

confidence: 99%

“…SAR 10g is used widely as a RF monitoring parameter in surface coils at 7 T, but was not designed to be used in volume coils and in tissues near metal implants . The reliability of SAR 10g near the hip implants was evaluated and compared with adSAR, calculated as m gram‐averaged SAR in a layer of tissues surrounding metal implants . The mass m depends on the local geometry of the implant, the dielectric and thermal properties of surrounding tissue, and can have different values near the different components of the implants (Figure ).…”

Section: Methodsmentioning

confidence: 99%

“…Although thermal simulations were not performed, they estimated that this would have caused temperature increases larger than 1°C. Limitations of this study are that SAR 10g was used to correlate with temperature increase, but the averaging mass of 10 g was shown to be unreliable in scenarios with metal implants . Therefore, the correlation between SAR 10g and temperature cannot be inferred.…”

Section: Introductionmentioning

confidence: 92%

“…Alternatively, electromagnetic simulations could complement current standards for pTx scenarios. A more advanced SAR‐based method was recently introduced to predict temperature increase near a hip prosthesis at 7 T in an 8‐channel pTx hip coil . The SAR averaging mass was adapted locally, using a concept called adaptive SAR (adSAR), to optimize agreement between SAR distributions and thermal behaviors.…”

Section: Introductionmentioning

confidence: 99%

“…However, the current methods such as the ASTM standards and wbSAR are not compatible with the use of RF shimming, and the purpose of this work is to investigate and propose an alternative that may be used in the case of a 2‐channel volume coil. Similarly to the combination of adSAR and SAR 10g that was used at 7 T for a surface coil, combinations of wbSAR, adSAR, and SAR 10g were evaluated in this study to complement current guidelines on volume coils. Simulations were performed on a realistic human model, and the adSAR optimization was performed with realistic thermal simulations.…”

Section: Introductionmentioning

confidence: 99%

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A numerical and experimental study of RF shimming in the presence of hip prostheses using adaptive SAR at 3 T

Destruel

Fuentes

Weber

et al. 2019

Magnetic Resonance in Med

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Purpose Parallel transmission techniques in MRI have the potential to improve the image quality near metal implants at 3 T. However, current testing of implants only evaluates the risk of radiofrequency (RF) heating in phantoms in circularly polarized mode. We investigate the influence of changing the transmission settings in a 2‐channel body coil on the peak temperature near 2 CoCrMo hip prostheses, using adaptive specific absorption rate (SAR) as an estimate of RF heating. Methods Adaptive SAR is a SAR averaging method that is optimized to correlate with thermal simulations and limit the temperature to 39°C near hip implants. The simulated peak temperature was compared when using whole‐body SAR, SAR10g, and adaptive SAR as a constraint for the maximum allowed input power. Adaptive SAR was used as a fast estimate of temperature to evaluate the trade‐off between good image quality and low heating near the hip implants. Electromagnetic simulations were validated by simulating and measuring B1 maps and electric fields in a phantom at 3 T. Results Simulations and measurements showed excellent agreement. Limiting whole‐body SAR to 2 W/kg and SAR10g to 10 W/kg resulted in temperatures up to 49.3°C and 40.7°C near the hip implants after 30 minutes of RF exposure, respectively. Predictions based on adaptive SAR limited the temperature to 39°C, and allowed to improve the B1 field distribution while preventing peak temperatures near the hip implants. Conclusion Significant RF heating can occur at 3 T near hip implants when parallel transmission is used. Adaptive SAR can be integrated in RF shimming algorithms to improve the uniformity and reduce heating.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A numerical and experimental study of RF shimming in the presence of hip prostheses using adaptive SAR at 3 T

Destruel

Fuentes

Weber

et al. 2019

Magnetic Resonance in Med

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Study of the radiofrequency‐induced heating inside the human head with dental implants at 7 T

Duan,

Wu,

Shi

et al. 2023

Bioelectromagnetics

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Conductive dental implants are commonly used in restorative therapy to replace missing teeth in patients. Ensuring the radiofrequency (RF) safety of these patients is crucial when performing 7 T magnetic resonance scans of their heads. This study aimed to investigate RF‐induced heating inside the human head with dental implants at 7 T. Dental implants and their attachments were fabricated and integrated into an anatomical head model, creating different measurement configurations (MCs). Numerical simulations were conducted using a 7 T transmit coil loaded with the anatomical head model, both with and without dental implants. The maximum temperatures inside the head for various MCs were computed using the maximum permissible input powers (MPIPs) obtained without dental implants and compared with published limits. Additionally, the MPIPs with dental implants were calculated for scenarios where the temperature limits were exceeded. The maximum temperatures observed inside the head ranged from 38.4°C to 39.6°C. The MPIPs in the presence of dental implants were 81.9%–97.3% of the MPIPs in the absence of dental implants for scenarios that exceeded the regulatory limit. RF‐induced heating effect of the dental implants was not significant. The safe scanning condition in terms of RF exposure was achievable for patients with dental implants. For patients with conductive dental implants of unknown configuration, it is recommended to reduce the input power by 18.1% of MPIP without dental implants to ensure RF safety.

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MRI‐Related Heating of Implants and Devices: A Review

Winter

Seifert

Zilberti

et al. 2020

Magnetic Resonance Imaging

128

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During an MRI scan, the radiofrequency field from the scanner's transmit coil, but also the switched gradient fields, induce currents in any conductive object in the bore. This makes any metallic medical implant an additional risk for an MRI patient, because those currents can heat up the surrounding tissues to dangerous levels. This is one of the reasons why implants are, until today, considered a contraindication for MRI; for example, by scanner manufacturers. Due to the increasing prevalence of medical implants in our aging societies, such general exclusion is no longer acceptable. Also, it should be no longer needed, because of a much‐improved safety‐assessment methodology, in particular in the field of numerical simulations. The present article reviews existing literature on implant‐related heating effects in MRI. Concepts for risk assessment and quantification are presented and also some first attempts towards an active safety management and risk mitigation. Level of Evidence 5 Technical Efficacy Stage 5

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Adaptive SAR mass‐averaging framework to improve predictions of local RF heating near a hip implant for parallel transmit at 7 T

Abstract: Adaptive SAR can accurately monitor RF heating and could be used for parallel transmit at 7 T to supplement current standards.

Cited by 16 publications

References 40 publications

A numerical and experimental study of RF shimming in the presence of hip prostheses using adaptive SAR at 3 T

A numerical and experimental study of RF shimming in the presence of hip prostheses using adaptive SAR at 3 T

Study of the radiofrequency‐induced heating inside the human head with dental implants at 7 T

MRI‐Related Heating of Implants and Devices: A Review

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