Illumination position estimation for 3D soft-tissue reconstruction in robotic minimally invasive surgery

For robotic assisted minimally invasive surgery, recovering the 3D soft-tissue shape and morphology in vivo is important for providing image-guidance, motion compensation and applying dynamic active constraints. In this paper, we propose a practical method for calibrating the illumination source position in monocular and stereoscopic laparoscopes. The method relies on using the geometric constraints from specular reflections obtained during the laparoscope camera calibration process. By estimating the light source position, the method forgoes the common assumption of coincidence with the camera centre and can be used to obtain constraints on the normal of the surface geometry during surgery from specularities. We demonstrate the effectiveness of the proposed approach with numerical simulations and by qualitative analysis of real stereo-laparoscopic calibrations.