Design and application of an assessment protocol for electromagnetic tracking systems

Area of Science:

• Medical instrumentation
• Metrology
• Biomedical engineering

Background:

• Electromagnetic tracking systems are crucial for precise spatial measurements in various scientific and medical applications.
• Evaluating the performance and limitations of these systems, such as the NDI Aurora (A) and Ascension microBIRD (B), is essential for reliable data acquisition.
• Existing evaluation methods may lack consistency, comparability, or the ability to assess performance under realistic conditions.

Purpose of the Study:

• To develop and validate a standardized protocol and a novel phantom design for the competitive and quantified evaluation of electromagnetic tracking systems.
• To assess the reproducibility and comparability of different electromagnetic tracking systems within a controlled environment.
• To investigate the impact of metallic objects on the accuracy of these tracking systems.

Main Methods:

• Designed and manufactured a base plate with a precise grid for positional and rotational measurements.
• Developed a sensor mount fitting into the base plate's grid holes for consistent sensor placement.
• Introduced metallic rods (steel, aluminum, bronze) into the tracking volume to assess interference effects.
• Calculated fiducial registration error and fiducial location error using stylus calibration for both systems.

Main Results:

• Positional jitter was measured at 0.14 mm for system (A) and 0.08 mm for system (B).
• Relative positional errors at 50 mm distance were 0.96 mm ± 0.68 mm (A) and 1.14 mm ± 0.78 mm (B).
• Relative rotation errors were 0.51 degrees (A) and 0.04 degrees (B), with system (A) showing lower orientation accuracy.
• System (B) exhibited higher sensitivity to metallic objects, particularly SST 416, causing significant errors (>100 mm at 20 mm proximity), while system (A) showed a maximum error of 4.2 mm.
• System (B) demonstrated a systematic error in distance calculations.

Conclusions:

• The developed protocol and phantom enable reproducible and comparable evaluations of electromagnetic tracking systems.
• NDI Aurora (A) is less accurate in orientation measurements, while Ascension microBIRD (B) is more susceptible to metallic interference and shows systematic distance errors.
• The choice of tracking system depends on the specific application requirements regarding accuracy, orientation, and the presence of metallic objects.