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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.

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Title: Adaptive SAR mass‐averaging framework to improve predictions of local RF heating near a hip implant for parallel transmit at 7 T.
Authors: Destruel, Aurelien1,2 a.destruel@uq.edu.au, O'Brien, Kieran2,3, Jin, Jin1,4,5, Liu, Feng1, Barth, Markus2, Crozier, Stuart1
Source: Magnetic Resonance in Medicine. Jan2019, Vol. 81 Issue 1, p615-627. 13p.
Abstract: Purpose: Magnetic resonance imaging is used increasingly to scan patients with hip prostheses. We evaluated the reliability of 10 g–averaged specific absorption rate (SAR10g) to predict radiofrequency (RF) heating in tissues surrounding a hip implant at 7 T in an 8‐channel pTx hip coil. A new adaptive SAR mass‐averaging method is proposed to improve the correlation between the distribution of mass‐averaged SAR and that of tissue temperature. Methods: Currently, RF safety standards for implants are based on temperature instead of SAR, as SAR has not been introduced with regard to exposure scenarios with implants. In this manuscript, however, adaptive SAR is proposed for fast and reliable exposure evaluation with implants, after its correlation with tissue temperature is verified. A framework to calculate adaptive SAR mass‐averaging was introduced, which uses a different averaging mass in tissues surrounding the implants and was designed to prevent the temperature from exceeding 39ºC. Predictions from SAR10g and adaptive SAR were compared with thermal simulations. Results: The SAR10g method failed to predict both the location and amplitude of heating in tissue near the metal implants. In some cases, the temperature far exceeded 39ºC even when SAR10g was only 70% of the maximum allowed 10 W/kg. The distributions of adaptive SAR and temperature matched in most of the configurations, and the temperature remained below 39ºC when adaptive SAR was constrained. Conclusion: Adaptive SAR can accurately monitor RF heating and could be used for parallel transmit at 7 T to supplement current standards. [ABSTRACT FROM AUTHOR]
Copyright of Magnetic Resonance in Medicine is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Adaptive SAR mass‐averaging framework to improve predictions of local RF heating near a hip implant for parallel transmit at 7 T.
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  Data: <searchLink fieldCode="AR" term="%22Destruel%2C+Aurelien%22">Destruel, Aurelien</searchLink><relatesTo>1,2</relatesTo><i> a.destruel@uq.edu.au</i><br /><searchLink fieldCode="AR" term="%22O'Brien%2C+Kieran%22">O'Brien, Kieran</searchLink><relatesTo>2,3</relatesTo><br /><searchLink fieldCode="AR" term="%22Jin%2C+Jin%22">Jin, Jin</searchLink><relatesTo>1,4,5</relatesTo><br /><searchLink fieldCode="AR" term="%22Liu%2C+Feng%22">Liu, Feng</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Barth%2C+Markus%22">Barth, Markus</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Crozier%2C+Stuart%22">Crozier, Stuart</searchLink><relatesTo>1</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Magnetic+Resonance+in+Medicine%22">Magnetic Resonance in Medicine</searchLink>. Jan2019, Vol. 81 Issue 1, p615-627. 13p.
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Purpose: Magnetic resonance imaging is used increasingly to scan patients with hip prostheses. We evaluated the reliability of 10 g–averaged specific absorption rate (SAR10g) to predict radiofrequency (RF) heating in tissues surrounding a hip implant at 7 T in an 8‐channel pTx hip coil. A new adaptive SAR mass‐averaging method is proposed to improve the correlation between the distribution of mass‐averaged SAR and that of tissue temperature. Methods: Currently, RF safety standards for implants are based on temperature instead of SAR, as SAR has not been introduced with regard to exposure scenarios with implants. In this manuscript, however, adaptive SAR is proposed for fast and reliable exposure evaluation with implants, after its correlation with tissue temperature is verified. A framework to calculate adaptive SAR mass‐averaging was introduced, which uses a different averaging mass in tissues surrounding the implants and was designed to prevent the temperature from exceeding 39ºC. Predictions from SAR10g and adaptive SAR were compared with thermal simulations. Results: The SAR10g method failed to predict both the location and amplitude of heating in tissue near the metal implants. In some cases, the temperature far exceeded 39ºC even when SAR10g was only 70% of the maximum allowed 10 W/kg. The distributions of adaptive SAR and temperature matched in most of the configurations, and the temperature remained below 39ºC when adaptive SAR was constrained. Conclusion: Adaptive SAR can accurately monitor RF heating and could be used for parallel transmit at 7 T to supplement current standards. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Magnetic Resonance in Medicine is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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              Text: Jan2019
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