Design and implementation of an electromagnetic ultrasound-based navigation technique for laparoscopic ablation of liver tumors

Efficient laparoscopic ablation of liver tumors relies on precise tumor visualization and accurate positioning of ablation probes. This study evaluates positional accuracy and procedural efficiency of a dynamic navigation technique based on electromagnetic-tracked laparoscopic ultrasound (ELUS) for laparoscopic ablation of liver tumors. The proposed navigation approach combines intraoperative 2D ELUS-based planning for navigated positioning of ablation probes, with immediate 3D ELUS-based validation of intrahepatic probe position. The environmental influence on electromagnetic-tracking stability was evaluated in the operation room. Accuracy of navigated ablation probe positioning assessed as the target-positioning error (TPE), and procedural efficiency defined as time efforts for target definition/navigated targeting and number of probe repositionings, were evaluated in a laparoscopic model and compared with conventional laparoscopic ultrasound (LUS) guidance. The operation-room environment showed interferences < 1 mm on the EM-tracking system. A total of 60 targeting attempts were conducted by three surgeons, with ten targeting attempts using ELUS and ten using conventional LUS each. Median TPE and time for targeting using ELUS and LUS were 4.2 mm (IQR 2.9-5.3 mm) versus 6 mm (IQR 4.7-7.5 mm), and 39 s (IQR 24-47 s) versus 76 s (IQR 47-121 s), respectively (p < 0.01 each). With ELUS, median time for target definition was 48.5 s, with 0 ablation probe repositionings compared to 17 when using LUS. The navigation technique was rated with a mean score of 85.5 on a Standard Usability Scale. The proposed ELUS-based navigation approach allows for accurate and efficient targeting of liver tumors in a laparoscopic model. Focusing on a dynamic and tumor-targeted navigation technique relying on intraoperative imaging, this avoids potential inaccuracies due to organ deformation and yields a user-friendly technique for efficient laparoscopic ablation of liver tumors.