Polhemus EM tracked Micro Sensor for CT-guided interventions.

Area of Science:

• Medical Imaging and Instrumentation
• Biomedical Engineering
• Surgical Navigation Technologies

Background:

• Electromagnetic (EM) tracking is vital for image-guided therapy, enabling precise localization of medical instruments.
• Polhemus Inc. introduced a novel EM Micro Sensor designed for instrument tracking, featuring compact Field Generators (FGs).
• Assessing EM tracker accuracy and robustness in clinical settings, including computed tomography (CT) environments, is essential.

Purpose of the Study:

• To conduct a standardized assessment of the Polhemus EM Micro Sensor's accuracy and robustness.
• To evaluate the sensor's performance in both laboratory and CT environments.
• To determine the impact of metallic objects and instrument tracking on EM sensor performance.

Main Methods:

• The EM Micro Sensor was evaluated using a standardized protocol with a Polhemus Liberty tracker and three FGs (TX1, TX2, TX4).
• Positional and rotational accuracy, precision, and distortion effects were measured in lab and CT settings.
• Tracking of a hypodermic needle and a flexible endoscope, along with metallic cylinder interference, was assessed.

Main Results:

• Jitter was consistently low (≤0.02 mm), though TX2 FG data was unavailable in CT.
• Lab distance errors were ≤0.6 mm; CT errors varied (TX1: ≤1.6 mm, TX4: ~5.4 mm).
• Mean orientation errors were low (lab: ≤0.9°, CT: ≤1.2°), with minimal impact from instrument tracking.

Conclusions:

• The EM Micro Sensor facilitates accurate medical instrument tracking with low jitter, position, and rotation errors.
• Performance is robust for smaller tracking volumes (up to 15 cm), ideal for close-proximity applications.
• Accuracy challenges arise in larger tracking volumes (up to 50 cm), consistent with other EM trackers.