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Related Experiment Videos

Systematic distortions in magnetic position digitizers

W Birkfellner1, F Watzinger, F Wanschitz

  • 1Department of Biomedical Engineering and Physics, University of Vienna General Hospital, Austria. wbirk@bmtp.akh-wien.ac.at

Medical Physics
|November 26, 1998
PubMed
Summary

Electromagnetic trackers used in medical devices are susceptible to distortions from metals and surgical tools. AC trackers are less affected by non-ferromagnetic materials, while DC trackers are more sensitive to ferromagnetic interference.

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Area of Science:

  • Medical device technology
  • Surgical navigation systems
  • Electromagnetic tracking

Background:

  • Position sensors are crucial for medical devices in image-guided surgery and augmented reality.
  • Real-time 3D position data acquisition is a key enabling technology in this field.

Purpose of the Study:

  • To assess systematic distortions in commercial electromagnetic tracking systems.
  • To quantify performance in the presence of metals, surgical tools, and ultrasound probes.
  • To compare alternating current (AC) and direct current (DC) based tracking systems.

Main Methods:

  • Developed a nonmetallic six degree-of-freedom measurement rack for quantitative comparison.
  • Conducted phantom studies on an acrylic skull model in an operating room (OR).

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  • Evaluated AC and DC electromagnetic trackers under various conditions.

    • Main Results:

    • AC trackers showed average distortions of 0.7 mm and 0.5 degrees from metallic objects >120 mm away.
    • In the OR, AC systems had mean errors of 3.2 mm and 2.9 degrees.
    • DC trackers were more sensitive to ferromagnetic materials (1.6 mm, 0.5 degrees error >120 mm) and less accurate in the OR (6.4 mm, 4.9 degrees error).
    • Errors increased significantly at distances <100 mm.
    • Ultrasound probe influence depends on shielding material.

    Conclusions:

    • Non-conductive surgical instruments are recommended for AC trackers.
    • Non-ferromagnetic instruments are recommended for DC trackers.
    • Calibration is necessary to compensate for OR-induced distortions.