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11/10/2012

Evaluation of the RF Heating of a Generic Deep Brain Stimulator Exposed in 1.5 T Magnetic Resonance Scanners

Eugenia Cabot, Tom Lloyd, Andreas Christ, Wolfgang Kainz, Mark Douglas, Gregg Stenzel, Steve Wedan, and Niels Kuster, Bioelectromagnetics, Online ahead of print October 11, October 2012

Patients with active conductive implants are currently excluded from magnetic resonance scans because the radio frequency (RF) electromagnetic field of the B1 field couples to the implant that can result in significant tissue heatings close to the active electrodes. Since a growing portion of the population having active implants are in the need for the advanced diagnostic features only MR technology offers, the medical device industry is developing novel leads that are MR safe. 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 (TS 10974, ISO 2012). 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 conclude with a suggestion for a procedure that follows the same concept but is between Tier 3 and 4.

The scientific and technical impact of the study can be summarized as:

  • applying optimized tools results in reasonable uncertainties for the overall evaluation
  • each tier reduces the overestimation by several dB at the cost of more demanding evaluation steps
  • 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
  • Tier 3 is not sufficient for the helical implant
  • Tier 4 might be too demanding to be performed for complex implants.
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