ID Number		2260
Study Type		Engineering & Physics
Model		RF tissue heating near metallic implants.
Details		Authors's abstract: Kyriakou et al. 2011 (IEEE #5121): The objective of this study was to investigate if persons with implantable medical devices are intrinsically protected by the current electromagnetic safety guidelines. For inter-laboratory comparisons, the U.S. Food and Drug Administration has defined a generic implant as consisting of an insulated wire with noninsulated tips, simulating active implants composed of a metallic case, and insulated wires with electric contacts at the tip. In this study, we determined the amplitude of the uniform electric fields induced in body tissues that cause a local increase in the tissue temperature by 1 °C in the presence of this generic implant for a wide range of frequencies and wire lengths. The field amplitudes were compared to the basic restrictions of the current exposure guidelines for both occupational and uncontrolled exposure. Results showed that a 1 °C temperature increase in the tissues around the tips of the generic implant can be reached for field strengths much smaller than 1% of those in the basic restrictions. The simulated results were validated by experimental evaluations. The impact of perfusion was investigated and was found to lead to a reduction in the local temperature peak by only 1.6-3 times. Additional simulations inside an inhomogeneous anatomical model were performed to ascertain whether similar heating as in the generic model was observed. The significant temperature elevations due to the presence of a generic implant indicate that demonstrating compliance with the basic restrictions might not be sufficient for persons with implants. Special considerations may be required, especially in the case of novel, emerging technologies that feature strong near-fields at frequencies below 10 MHz (e.g., wireless power-transfer systems). AUTHORS' ABSTRACT: Cabot et al. 2013 (IEEE #5249): The radio frequency (RF) electromagnetic field of magnetic resonance (MR) scanners can result in significant tissue heating due to the RF coupling with the conducting parts of medical implants. The objective of this article is to evaluate the advantages and shortcomings of a new four-tier approach based on a combined numerical and experimental procedure, designed to demonstrate safety of implants during MR scans. To the authors' best knowledge, this is the first study analyzing this technique. The evaluation is performed for 1.5 T MR scanners using a generic model of a deep brain stimulator (DBS) with a straight lead and a helical lead. The results show that the approach is technically feasible and provides sound and conservative information about the potential heating of implants. We demonstrate that (1) applying optimized tools results in reasonable uncertainties for the overall evaluation; (2) each tier reduces the overestimation by several dB at the cost of more demanding evaluation steps; (3) the implant with the straight lead would cause local temperature increases larger than 18 °C at the RF exposure limit for the normal operating mode; (4) Tier 3 is not sufficient for the helical implant; and (5) Tier 4 might be too demanding to be performed for complex implants. We conclude with a suggestion for a procedure that follows the same concept but is between Tier 3 and 4. In addition, the evaluation of Tier 3 has shown consistency with current scan practice, namely, the resulting heat at the lead tip is less than 3.5 °C for the straight lead and 0.7 °C for the helix lead for scans at the current applied MR scan restrictions for deep brain stimulation at a head average SAR of 0.1 W/kg.
Findings		Effects
Status		Completed With Publication
Principal Investigator		ETH, IT'TS, Zurich, Switzerland - kuster@itis.ethz.ch
Funding Agency		?????
Country		SWITZERLAND
References		Kyriakou, A et al. Bioelectromagnetics., (2012) 33:366-374 Cabot, E et al. Bioelectromagnetics. , (2013) 34:14-113
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