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DOI: 10.1148/radiol.2352041850
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(Radiology 2005;235:709.)

Letters to the Editor

Can Intrauterine Devices Actually Be Considered Safe at 3-T MR Imaging?

Matthias R. Mühler, MD

Charité Campus Mitte, Universitätsmedizin Berlin, Med. Fakultät der Humboldt Universität zu Berlin, 10098 Berlin, Germany. e-mail: matthias.muehler@charite.de

Editor:

In their article in the September 2004 issue of Radiology, Drs Shellock and Crues state that the Essure device (Conceptus, San Carlos, Calif) "was found to be safe for patients undergoing MR [magnetic resonance] procedures" at a field strength of 3 T (1). This is, from my point of view, incorrect.

The publication refers to an examination of the interaction of biomedical implants with a 3-T static magnetic field, yielding no harmful deflection or torque for the Essure device (2). Nevertheless, determination of whether a device is MR safe goes beyond the interaction with the static magnetic field, as published: "MR safety testing of an implant or object involves assessment of magnetic field interaction, heating, and induced electric currents" (3). This means that we have to demand reliable data about heating after radiofrequency load to assess MR safety. These data are not available for the Essure device, as they are not for metal-containing intrauterine devices. For the sake of completeness, there are also no data available, to my knowledge, about the interaction of intrauterine devices—ones containing metal in particular—with a 3-T static magnetic field.

While radiofrequency load is the determining factor of heating, these data are of special concern, since radiofrequency energy can increase by a factor of 4 when switching from 1.5 to 3 T (4,5). Additionally, the authors state that the results of the examination are highly dependent on the imaging system (short- vs long-bore MR systems) (2).

With regard to the safety of intrauterine implants (such as the Essure device) in the 1.5-T MR imager, there are no safety concerns. The Essure device and other intrauterine devices can be considered MR safe rather than MR compatible on the basis of data available in the peer-reviewed literature (5–9).

The intrauterine system IUS (Mirena, Schering, Germany) and metal-free intrauterine devices can be considered exceptions. Because the material they are made of is known (polypropylene, barium sulfate, silicone), there are no safety concerns when using the IUS and metal-free intrauterine devices in imagers up to 3 T (R. Schneidereit, written communication, 2004) (10).

REFERENCES

  1. Shellock FG, Crues JV. MR procedures: biologic effects, safety, and patient care. Radiology 2004; 232:635-652.[Abstract/Free Full Text]
  2. Shellock FG. Biomedical implants and devices: assessment of magnetic field interactions with a 3.0-Tesla MR system. J Magn Reson Imaging 2002; 16:721-732.[CrossRef][Medline]
  3. Shellock FG, Crues JV, 3rd. MR Safety and the American College of Radiology White Paper. AJR Am J Roentgenol 2002; 178:1349-1352.[Free Full Text]
  4. Engels JML. A-372 biophysical effects and MR safety Vienna, Austria: ECR, 2004.
  5. Shellock FG. Radiofrequency energy-induced heating during MR procedures: a review. J Magn Reson Imaging 2000; 12:30-36.[CrossRef][Medline]
  6. Hess T, Stepanow B, Knopp MV. Safety of intrauterine contraceptive devices during MR imaging. Eur Radiol 1996; 6:66-68.[CrossRef][Medline]
  7. Mark AS, Hricak H. Intrauterine contraceptive devices: MR imaging. Radiology 1987; 162:311-314.[Abstract/Free Full Text]
  8. Pasquale SA, Russer TJ, Foldesy R, Mezrich RS. Lack of interaction between magnetic resonance imaging and the copper-T380A IUD. Contraception 1997; 55:169-173.[CrossRef][Medline]
  9. Shellock FG. New metallic implant used for permanent contraception in women: evaluation of MR safety. AJR Am J Roentgenol 2002; 178:1513-1516.[Abstract/Free Full Text]
  10. Shellock FG. Intrauterine devices (IUDs). Available at: www.mrisafety.com. Accessed February 20 2004.



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This Article
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