Technical note: Nonrigid registration for laparoscopic liver surgery using sparse intraoperative data

Soft tissue deformation can be a major source of error for image-guided interventions. Deformations associated with laparoscopic liver surgery can be substantially different from those concomitant with open approaches due to intraoperative practices such as abdominal insufflation and variable degrees of mobilization from the supporting ligaments of the liver. This technical note outlines recent contributions towards nonrigid registration for laparoscopic liver surgery published in the Journal of Medical Imaging special issue on image-guided procedures, robotic interventions, and modeling [10]. In particular, we review (1) a characterization of intraoperative liver deformation from clinically-acquired sparse digitizations of the organ surface through a series of laparoscopic-to-open conversions, and (2) a novel deformation correction strategy that leverages a set of control points placed across anatomical regions of mechanical support provided to the organ. Perturbations of these control points on a finite element model were used to iteratively reconstruct the intraoperative deformed organ shape from sparse measurements of the liver surface. These characterization and correction methods for laparoscopic deformation were applied to a retrospective clinical series of 25 laparoscopic-to-open conversions performed under image guidance and a phantom validation framework.