Step 1 – Preoperative Imaging
Preoperatively a bi- or tri-phasic CT scan of the patient is acquired and processed using the Virtual resection planning tool (MeVis Medical Solutions, Bremen, Germany). The processing includes segmentation of relevant anatomical or pathological structures of the liver (intrahepatic vessels, tumors, segments and the liver surface). The modelling enables calculation of patient-individual vascular territories for each vessel system and identification of vascular branches affected by resection.
Step 2 – Virtual Surgery Planning
The patient-individual 3D models provide support in analysing the remaining functional liver volume and associated risks with different resection strategies towards an optimized individual operative strategy. The 3D model itself is then loaded into the navigation device. Within the navigation system, the model can be zoomed, rotated and its different sub-models can be displayes according to the surgeons needs.
Step 3 – Intraoperative Setup
Prior to the surgical procedure, all components of the system are set up close to the OR table. Necessary sterile draping of the instrumentation is conducted. The computer displays a 3D model of the present anatomical situation, a plan of the surgical strategy and a view of the available ultrasound images.
Step 4 – Planning
After surgical preparation of the liver, a complete examination of the liver can be performed by palpation and intra-operative ultrasound. For preparation of the navigated procedure, a set of anatomical landmarks is selected by visual inspection and the dissecting device is placed on each of this landmarks. The navigation system stores each of the positions and uses them for registration.
Step 5 – Registration
The registration procedure requires a few seconds and can be repeated whenever necessary. The surgical situation on the display is then enhanced by displaying a virtual surgical instrument on the navigation device within the 3D model of the liver. The 3D model can be adjusted by the surgeon and displays the correct amount of information, necessary for optimal understanding.
Step 6 – Resection/Ablation
The computer system displays a 3D model of the liver anatomy, the resection/ablation plan, and a view of the available ultrasound images on a monitor near the operative field. This provided continuous real-time feedback and enables for the guidance of the surgical instruments towards the planned treatment locations (resection planes or ablation targets).