Characterization of Ultrasound Probe-Dependent Interference in Electromagnetic Tracking for Image-Guided Procedures

Ultrasound (US) imaging is widely used to guide minimally invasive procedures such as percutaneous nephrolithotomy (PCNL), while electromagnetic (EM) tracking can complement US guidance by providing line-of-sight-independent instrument localization. However, US probes may distort the EM tracking field in a probe-dependent manner. This study characterized probe-induced EM interference for a conventional 3D/4D phased-array probe and a handheld wireless probe. Three experiments were conducted using an EM tracking system: spatial mapping of interference along each probe body, assessment of probe-sensor separation for the handheld probe, and evaluation of probe-induced tracking deviations in a simulated EM-guided PCNL setup with tracked needle and catheter sensors. EM-US calibration was then performed using low-interference sensor positions. The phased-array probe produced minimal disturbance, maintaining submillimetric positional and subdegree orientational precision across tested modes. Compared with the evaluated phased-array probe, the evaluated handheld wireless probe generated stronger, spatially localized interference, requiring ≥75 mm positional and ≥50 mm orientational separation to recover baseline precision. In the PCNL simulation, the phased-array probe maintained tracking stability, whereas the handheld probe introduced localized deviations. Both probes produced RMS calibration residuals below 1 mm under controlled conditions. These results provide device-specific baseline measurements and a workflow for probe-dependent interference assessment and sensor-placement optimization in EM-US navigation.