Measuring organ shift and deformation for port placement in robot-assisted minimally invasive surgery

Objective: Port placement is a crucial pre-operative task in robot-assisted minimally invasive surgery. Due to the insufflation process, the abdominal shape is deformed while the internal organs are shifted in position. These changes need to be considered when determining the optimal port locations for the robotic manipulators. However, intra-operative medical image acquisition systems are not always available. In this study, we aim to estimate the shift extent of the abdominal organs in humans by measuring the changed volume and position of the abdominal organs before and after insufflation in three pigs. Methods: A 3D model of the abdomen and abdominal organs was reconstructed from 3D images of the pigs taken by an MRI scanner before and after insufflation. Position shift and shape changes of the abdominal organs after insufflation were determined. The corresponding shift in port location for the robotic manipulators was determined based on the abdominal model. Results: Organ movements as a result of insufflation ranged from 6.37 ± 0.10 cm for the spleen, to 1.64 ± 0.22 cm for the liver. Even a slight planar motion of the target organ (e.g., 1.33 ± 0.06 cm, 2.38 ± 0.21 cm in X-Y plane for the left kidney) can shift the access port for the robot manipulator by about 1.6 cm on the abdominal surface. Conclusions: The target organs’ motion due to insufflation is a critical factor in determining port locations in robot-assisted minimally invasive surgery.