title: In vitro and in silico assessment of RF-induced heating around intracranial aneurysm clips at 7 Tesla.
abstract: OBJECTIVE
  To examine radiofrequency-induced tissue heating around intracranial aneurysm clips during a 7 Tesla (T) head MR examination.
  
  
  METHODS
  Radiofrequency (RF), temperature simulations, and RF measurements were employed to investigate the effects of polarization and clip length on the electric field (E-field) and temperature. Heating in body models was studied using both a conservative approach and realistic exposure scenarios.
  
  
  RESULTS
  Worst-case orientation was found for clips aligned parallel to the E-field polarization. Absolute tissue temperature remained below International Electrotechnical Commission regulatory limits for 44 of 50 clinical scenarios. No significant effect on heating was determined for clip lengths below 18.8 mm, and worst-case heating was found for clip length 51.5 mm. The conservative approach led to a maximum permissible E-field of 72 V/m corresponding to B1+ of 1.2 µT, and an accepted power of 4.6 W for the considered RF head coil instead of 38.5 W without clip.
  
  
  CONCLUSIONS
  Safe scanning conditions with respect to RF-induced heating can be applied depending on the information about the clip gained during screening interviews. However, force and torque measurements in the MR system shall be conducted to give a final statement on the MR safety of aneurysm clips at 7T. Magn Reson Med 79:568-581, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.|MR:comp GmbH, MR Safety Testing Laboratory, Gelsenkirchen, Germany.
authors.forename: Yacine
authors.initials: Y
authors.lastname: Noureddine
authors.affiliation: Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kraff
authors.affiliation: Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.|Division of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Ladd
authors.affiliation: Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.|Department of Neurosurgery, University Hospital Essen, Essen, Germany.
authors.forename: Karsten H
authors.initials: KH
authors.lastname: Wrede
authors.affiliation: Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.|Department of Neurosurgery, University Hospital Essen, Essen, Germany.
authors.forename: Bixia
authors.initials: B
authors.lastname: Chen
authors.affiliation: Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.|High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
authors.forename: Harald H
authors.initials: HH
authors.lastname: Quick
authors.affiliation: MR:comp GmbH, MR Safety Testing Laboratory, Gelsenkirchen, Germany.|MRI-STaR-Magnetic Resonance Institute for Safety, Technology and Research GmbH, Gelsenkirchen, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Schaefers
authors.affiliation: Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.|Division of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Heidelberg, Germany.|Faculty of Electrical Engineering and Information Technology, FH Aachen-University of Applied Sciences, Aachen, NRW, Germany.
authors.forename: Andreas K
authors.initials: AK
authors.lastname: Bitz
mesh_terms: D003198:Computer Simulation; D006358:Hot Temperature; D006801:Humans; D006979:Hyperthermia, Induced; D007223:Infant; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging; D019047:Phantoms, Imaging; D011846:Radio Waves; D013314:Stress, Mechanical; D013525:Surgical Instruments; D019415:Torque
keywords: 7T; MR safety; MRI; UHF; aneurysm clips; implants; ultra-high field