Abstract
PurposeIn image‐guided laparoscopy, optical tracking is commonly employed, but electromagnetic (EM) systems have been proposed in the literature. In this paper, we provide a thorough comparison of EM and optical tracking systems for use in image‐guided laparoscopic surgery and a feasibility study of a combined, EM‐tracked laparoscope and laparoscopic ultrasound (LUS) image guidance system.MethodsWe first assess the tracking accuracy of a laparoscope with two optical trackers tracking retroreflective markers mounted on the shaft and an EM tracker with the sensor embedded at the proximal end, using a standard evaluation plate. We then use a stylus to test the precision of position measurement and accuracy of distance measurement of the trackers. Finally, we assess the accuracy of an image guidance system comprised of an EM‐tracked laparoscope and an EM‐tracked LUS probe.ResultsIn the experiment using a standard evaluation plate, the two optical trackers show less jitter in position and orientation measurement than the EM tracker. Also, the optical trackers demonstrate better consistency of orientation measurement within the test volume. However, their accuracy of measuring relative positions decreases significantly with longer distances whereas the EM tracker's performance is stable; at 50 mm distance, the RMS errors for the two optical trackers are 0.210 and 0.233 mm, respectively, and it is 0.214 mm for the EM tracker; at 250 mm distance, the RMS errors for the two optical trackers become 1.031 and 1.178 mm, respectively, while it is 0.367 mm for the EM tracker. In the experiment using the stylus, the two optical trackers have RMS errors of 1.278 and 1.555 mm in localizing the stylus tip, and it is 1.117 mm for the EM tracker. Our prototype of a combined, EM‐tracked laparoscope and LUS system using representative calibration methods showed a RMS point localization error of 3.0 mm for the laparoscope and 1.3 mm for the LUS probe, the lager error of the former being predominantly due to the triangulation error when using a narrow‐baseline stereo laparoscope.ConclusionsThe errors incurred by optical trackers, due to the lever‐arm effect and variation in tracking accuracy in the depth direction, would make EM‐tracked solutions preferable if the EM sensor is placed at the proximal end of the laparoscope.
Highlights
Laparoscopic surgery has significant advantages over open surgery due to less patient trauma and faster recovery times, yet it can be difficult to perform due to the restricted field of view and lack of haptic feedback
For the NDI Tabletop Field Generator (TTFG) used in our study which has a large flat surface to enable securing on top the plywood platform supporting the Hummel Plate, we found that the variance of the z coordinates measured for each level is under 0.14 mm;[2] the z axis of the coordinate system could be considered orthogonal to the Hummel Plate and used as the axis of rotation
We have found that, for optical trackers, the accuracy of measuring relative positions drops significantly with longer distances, due to decrease in tracking accuracy with increasing depth which is intrinsic to optical trackers, as well as possible systematic errors, whereas EM tracking is more consistent in this respect
Summary
Laparoscopic surgery has significant advantages over open surgery due to less patient trauma and faster recovery times, yet it can be difficult to perform due to the restricted field of view and lack of haptic feedback. Augmented reality, has been proposed as a way to alleviate this problem and reduce the risk of complication.[1] Most guidance systems use optical tracking.[2,3,4,5] When using optical tracking, to ensure a free line-of-sight, markers must be placed on the distal end of the laparoscope, far from the optical center of its camera, thereby creating a lever-arm effect, reducing system accuracy. We carried out a feasibility study of a combined, EM-tracked laparoscope and laparoscopic ultrasound (LUS) image guidance system
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