Comparing position and orientation accuracy of different electromagnetic sensors for tracking during interventions

Purpose To compare the position and orientation accuracy between using one 6-degree of freedom (DOF) electromagnetic (EM) sensor, or the position information of three 5DOF sensors within the scope of tumor tracking. Methods The position accuracy of Northern Digital Inc Aurora 5DOF and 6DOF sensors was determined for a table-top field generator (TTFG) up to a distance of 52 cm. For each sensor 716 positions were measured for 10 s at 15 Hz. Orientation accuracy was determined for each of the orthogonal axis at the TTFG distances of 17, 27, 37 and 47 cm. For the 6DOF sensors, orientation was determined for sensors in-line with the orientation axis, and perpendicular. 5DOF orientation accuracy was determined for a theoretical 4 cm tumor. An optical tracking system was used as reference. Results Position RMSE and jitter were comparable between the sensors and increasing with distance. Jitter was within 0.1 cm SD within 45 cm distance to the TTFG. Position RMSE was approximately 0.1 cm up to 32 cm distance, increasing to 0.4 cm at 52 cm distance. Orientation accuracy of the 6DOF sensor was within 1 ∘ , except when the sensor was in-line with the rotation axis perpendicular to the TTFG plane (4 ∘ errors at 47 cm). Orientation accuracy using 5DOF positions was within 1 ∘ up to 37 cm and 2 ∘ at 47 cm. Conclusions The position and orientation accuracy of a 6DOF sensor was comparable with a sensor configuration consisting of three 5DOF sensors. To achieve tracking accuracy within 1 mm and 1 ∘ , the distance to the TTFG should be limited to approximately 30 cm.