Intraoperative tumor localization in laparoscopic liver surgery

Minimally invasive laparoscopic liver intervention has the advantages of reduced patient's trauma and consequently faster healing. However, limitations such as reduced depth perception and loss of tactile feedback can hinder the surgeon's capabilities to precisely localize the tumor. Computer-assisted tumor localization can help guiding the surgeon to the target tumor in laparoscopic procedures. Using an electromagnetic tracking system and by attaching a position sensor to a 2D laparoscopic ultrasound probe, a 3D intraoperative US volume containing the tumor can be reconstructed. By segmenting tumors in the reconstructed volumes and visualizing them intraoperatively within their surrounding tissue, we can enable the surgeon to localize tumors intraoperatively and navigate to them. We used a level set approach to accomplish the segmentation task. The preprocessing and segmentation process is required only once, and for each newly acquired volume, the expected tumor position is used as a prior knowledge. However, we still need to compensate for possible movements or deformations of the liver. First, the previously segmented tumor is rigidly registered to the new ultrasound volume using mutual information. Second, tumor contour is updated to match the new boundaries. The position of the tumor was recovered in 1 second and tumor contour was updated to match the deformed one in 3 seconds. The strengths of this technique are that it can be performed intraoperatively, and it is repeatable throughout the opera-tion. Additionally, localizing and displaying tumors in their 3D surrounding context gives the possibility to navigate tracked instruments to the target tumor.