Wellcome/EPSRC Center for Interventional and Surgical Sciences, University College London, London, UK.
Center for Medical Image Computing, University College London, London, UK.
Med Phys. 2018 Nov;45(11):5094-5104. doi: 10.1002/mp.13210. Epub 2018 Oct 19.
In 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.
We 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.
In 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.
The 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.
在影像引导腹腔镜手术中，通常使用光学跟踪，但电磁（EM）系统已在文献中提出。本文对用于影像引导腹腔镜手术的 EM 和光学跟踪系统进行了全面比较，并对 EM 跟踪腹腔镜和腹腔镜超声（LUS）图像引导系统的组合进行了可行性研究。
我们首先使用标准评估板评估带有两个光学跟踪器的腹腔镜的跟踪精度，这两个光学跟踪器分别使用安装在轴上的反射标记和嵌入在近端的 EM 传感器进行跟踪。然后，我们使用触笔测试跟踪器的位置测量精度和距离测量精度。最后，我们评估由 EM 跟踪腹腔镜和 EM 跟踪 LUS 探头组成的图像引导系统的准确性。
在使用标准评估板的实验中，两个光学跟踪器在位置和方向测量方面的抖动比 EM 跟踪器小。此外，光学跟踪器在测试体积内表现出更好的方向测量一致性。然而，它们测量相对位置的精度随着距离的增加而显著下降，而 EM 跟踪器的性能则保持稳定；在 50mm 距离处，两个光学跟踪器的 RMS 误差分别为 0.210mm 和 0.233mm，而 EM 跟踪器的 RMS 误差为 0.214mm；在 250mm 距离处，两个光学跟踪器的 RMS 误差分别变为 1.031mm 和 1.178mm，而 EM 跟踪器的 RMS 误差为 0.367mm。在使用触笔的实验中，两个光学跟踪器在定位触笔尖端时的 RMS 误差分别为 1.278mm 和 1.555mm，而 EM 跟踪器的 RMS 误差为 1.117mm。我们使用代表性的校准方法的组合式 EM 跟踪腹腔镜和 LUS 系统原型显示腹腔镜的 RMS 点定位误差为 3.0mm，LUS 探头的 RMS 点定位误差为 1.3mm，前者的较大误差主要是由于使用窄基线立体腹腔镜时的三角测量误差所致。
如果 EM 传感器放置在腹腔镜的近端，由于杠杆臂效应和深度方向跟踪精度的变化，光学跟踪器会产生误差，因此 EM 跟踪解决方案更为可取。
