Adaptive SAR mass-averaging compared against thermal simulations in the presence of a titanium hip prosthesis in 7T pTx MRI

8:48 am 20 Dec 2017

Acknowledgements
Aurelien Destruel acknowledges Siemens Healthcare Pty Ltd for providing funding for a PhD scholarship and ZMT for providing the free academic license of the software Sim4Life. Markus Barth acknowledges funding from ARC Future Fellowship grant FT140100865. The authors acknowledge the facilities of the National Imaging Facility at the Centre for Advanced Imaging, University of Queensland.

Authors

Aurelien Destruel, Kieran O’Brien, Markus Barth, Jin Jin, Feng Liu, and Stuart Crozier

Purpose
There is an increasing interest in imaging close to large orthopaedic implants such as hip prostheses, as a growing proportion of patients possess one or more metal implants. Up to 3T, metal implants are tested for mechanical attraction and heating following the ASTM-2182 guideline. However, there is no guiding document to test implants for whole-body 7T MRI research systems.

The 10-gram-averaged specific absorption rate (SAR10g) is the parameter used to monitor the patients’ local radiofrequency (RF) exposure. SAR10g is calculated using electromagnetic simulations of human models, and it has been shown that metal implants can lead to values that go beyond what is recommended in the IEC guidelines. More accurate thermal simulations have been used to evaluate the predictions from SAR10g, and results showed a relationship that is not straightforward. A study is needed concerning their correlation in the presence of metal implants at 7T. A new adaptive SAR mass-averaging method around metal implants is introduced and compared with SAR10g and thermal simulations.

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