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68th Annual Meeting of the German Society of Neurosurgery (DGNC)
7th Joint Meeting with the British Neurosurgical Society (SBNS)

German Society of Neurosurgery (DGNC)

14 - 17 May 2017, Magdeburg

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Radiofrequency-induced heating around intracranial aneurysm clips: An implant safety study at 7 Tesla MRI

Meeting Abstract

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  • Bixia Chen - Klinik für Neurochirurgie, Universitätsklinikum Essen, Universität Duisburg-Essen, Erwin L. Hahn Institute for Magnetic Resonance Imaging, Universität Duisburg-Essen, Essen, Deutschland
  • Yacine Noureddine - Erwin L. Hahn Institute for Magnetic Resonance Imaging, Universität Duisburg-Essen, Essen, Deutschland
  • Oliver Kraff - Erwin L. Hahn Institute for Magnetic Resonance Imaging, Universität Duisburg-Essen, Essen, Deutschland
  • Andreas K. Bitz - Erwin L. Hahn Institute for Magnetic Resonance Imaging, Universität Duisburg-Essen, Medizinische Physik in der Radiologie, Deutsches Krebsforschungszentrum, Heidelberg, Deutschland
  • Mark E. Ladd - Erwin L. Hahn Institute for Magnetic Resonance Imaging, Universität Duisburg-Essen, Medizinische Physik in der Radiologie, Deutsches Krebsforschungszentrum, Heidelberg, Deutschland
  • Ulrich Sure - Klinik für Neurochirurgie, Universitätsklinikum Essen, Universität Duisburg-Essen, Essen, Deutschland
  • Karsten H. Wrede - Klinik für Neurochirurgie, Universitätsklinikum Essen, Universität Duisburg-Essen, Erwin L. Hahn Institute for Magnetic Resonance Imaging, Universität Duisburg-Essen, Essen, Deutschland

Deutsche Gesellschaft für Neurochirurgie. Society of British Neurological Surgeons. 68. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC), 7. Joint Meeting mit der Society of British Neurological Surgeons (SBNS). Magdeburg, 14.-17.05.2017. Düsseldorf: German Medical Science GMS Publishing House; 2017. DocMO.21.04

doi: 10.3205/17dgnc124, urn:nbn:de:0183-17dgnc1246

Published: June 9, 2017

© 2017 Chen et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.

Outline

Text

Objective: Ultrahigh-field (UHF) magnetic resonance imaging (MRI) at 7 Tesla (T) has been shown to excellently delineate cerebral aneurysms and other neurovascular pathologies. However, electrically conductive implants like aneurysm clips remain a contraindication for 7T MRI. The goal of this study was to examine radiofrequency (RF) induced tissue heating around intracranial aneurysm clips during a 7T head MR examination. Test methods including a conservative approach and realistic exposure scenarios in heterogeneous models are presented.

Methods: The study focused on three main topics: the first part investigated polarization effects on the specific absorption rate (SAR) using both computer simulations and in-vitro measurements; the second part investigated the effect of clip length on both electric field (E-field) and temperature; and, finally, heating in heterogeneous models using both a conservative approach in case information about the clip is missing as well as realistic exposure scenarios were studied.

Results: Worst-case orientation was found for the clip aligned parallel to the E-field polarization for both simulation and measurement. Absolute local temperature remained below the International Electrotechnical Commission (IEC) regulatory limit for 44/50 clinical scenarios presented in this study. No significant effect on heating was determined for a short clip (length = 18.8mm); worst-case heating was determined for a clip with length 51.5mm. The conservative approach led to a maximum E-field strength in the head of 72V/m corresponding to a maximum B1+ of 1.2µT, resulting in an accepted power for the considered RF head coil of 4.6W instead of 38.5W without clip. Most scenarios with a single aneurysm clip allow safe scanning when SAR levels are adapted. Scenarios with multiple aneurysm clips will remain challenging especially when clips are closely related but without electrical connection.

Conclusion: This study indicates that safe scanning conditions at 7 T MRI can be applied for most scenarios with single aneurysm clips regarding RF-heating. Nevertheless, further studies on force and torque as well as scenarios with multiple aneurysm clips are mandatory before in-vivo examinations can be declared completely safe.