MRI-based, wireless determination of the transfer function of a linear implant: Introduction of the transfer matrix
Tokaya, Janot P.; Raaijmakers, Alexander J.E.; Luijten, Peter R.; van den Berg, Cornelis A.T.
(2018) Magnetic Resonance in Medicine, volume 80, issue 6, pp. 2771 - 2784
(Article)
Abstract
Purpose: We introduce the transfer matrix (TM) that makes MR-based wireless determination of transfer functions (TFs) possible. TFs are implant specific measures for RF-safety assessment of linear implants. The TF relates an incident tangential electric field on an implant to a scattered electric field at its tip that generally governs
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local heating. The TM extends this concept and relates an incident tangential electric field to a current distribution in the implant therewith characterizing the RF response along the entire implant. The TM is exploited to measure TFs with MRI without hardware alterations. Theory and Methods: A model of rightward and leftward propagating attenuated waves undergoing multiple reflections is used to derive an analytical expression for the TM. This allows parameterization of the TM of generic implants, e.g., (partially) insulated single wires, in a homogeneous medium in a few unknowns that simultaneously describe the TF. These unknowns can be determined with MRI making it possible to measure the TM and, therefore, also the TF. Results: The TM is able to predict an induced current due to an incident electric field and can be accurately parameterized with a limited number of unknowns. Using this description the TF is determined accurately (with a Pearson correlation coefficient R≥0.9 between measurements and simulations) from MRI acquisitions. Conclusion: The TM enables measuring of TFs with MRI of the tested generic implant models. The MR-based method does not need hardware alterations and is wireless hence making TF determination in more realistic scenarios conceivable.
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Keywords: Active implantable medical device (AIMD), EM simulations, RF heating, Safety, SAR, Transfer function, transfer function, active implantable medical device (AIMD), safety, Temperature, Electromagnetic Fields, Humans, Radio Waves, Prostheses and Implants, Electrodes, Implanted, Equipment Design, Magnetic Resonance Imaging, Computer Simulation, Phantoms, Imaging, Radiology Nuclear Medicine and imaging, Journal Article
ISSN: 0740-3194
Publisher: John Wiley and Sons Inc.
Note: Publisher Copyright: © 2018 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine Copyright: Copyright 2020 Elsevier B.V., All rights reserved.
(Peer reviewed)