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Accelerating implant RF safety assessment using a low-rank inverse update method.

  • Stijnman, Peter R S1, 2
  • Tokaya, Janot P1
  • van Gemert, Jeroen3, 4
  • Luijten, Peter R5
  • Pluim, Josien P W2
  • Brink, Wyger M4
  • Remis, Rob F3
  • van den Berg, Cornelis A T1
  • Raaijmakers, Alexander J E1, 2
  • 1 Computational Imaging Group for MRI diagnostics and therapy, Centre for Image Sciences UMC Utrecht, Utrecht, The Netherlands. , (Netherlands)
  • 2 Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands. , (Netherlands)
  • 3 Circuit & Systems Group of the Electrical Engineering, Delft University of Technology, Delft, The Netherlands. , (Netherlands)
  • 4 C. J. Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, The Netherlands. , (Netherlands)
  • 5 Department of Radiology, UMC Utrecht, Utrecht, The Netherlands. , (Netherlands)
Published Article
Magnetic Resonance in Medicine
Wiley (John Wiley & Sons)
Publication Date
Sep 30, 2019
DOI: 10.1002/mrm.28023
PMID: 31566265


Patients who have medical metallic implants, e.g. orthopaedic implants and pacemakers, often cannot undergo an MRI exam. One of the largest risks is tissue heating due to the radio frequency (RF) fields. The RF safety assessment of implants is computationally demanding. This is due to the large dimensions of the transmit coil compared to the very detailed geometry of an implant. In this work, we explore a faster computational method for the RF safety assessment of implants that exploits the small geometry. The method requires the RF field without an implant as a basis and calculates the perturbation that the implant induces. The inputs for this method are the incident fields and a library matrix that contains the RF field response of every edge an implant can occupy. Through a low-rank inverse update, using the Sherman-Woodbury-Morrison matrix identity, the EM response of arbitrary implants can be computed within seconds. We compare the solution from full-wave simulations with the results from the presented method, for two implant geometries. From the comparison, we found that the resulting electric and magnetic fields are numerically equivalent (maximum error of 1.35%). However, the computation was between 171 to 2478 times faster than the corresponding GPU accelerated full-wave simulation. The presented method enables for rapid and efficient evaluation of the RF fields near implants and might enable situation-specific scanning conditions. © 2019 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

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