Organ surface deformation measurement and analysis in open hepatic surgery: method and preliminary results from 12 clinical cases.

The incidence of soft tissue deformation has been well documented in neurosurgical procedures and is known to compromise the spatial accuracy of image-guided surgery systems.Within the context of image-guided liver surgery (IGLS), no detailed method to study and analyze the observed organ shape change between preoperative imaging and the intra-operative presentation has been developed. Contrary to the studies of deformation in neurosurgical procedures, the majority of deformation in IGLS is imposed prior to resection and due to laparotomy and mobilization. As such, methods of analyzing the organ shape change must be developed to use the intra-operative data (e.g. laser range scan (LRS) surfaces) acquired with the organ in its fully deformed shape. To achieve this end we use a signed closest point distance deformation metric computed after rigid alignment of the intra-operative LRS data with organ surfaces generated from the preoperative tomograms. The rigid alignment between the intra-operative LRS surfaces and pre-operative image data was computed with a feature weighted surface registration algorithm. In order to compare the deformation metrics across patients, an inter-patient non-rigid registration of the pre-operative CT images was performed. Given the inter-patient liver registrations, an analysis was performed to determine the potential similarities in the distribution of measured deformation between patients for which similar procedures had been performed. The results of the deformation measurement and analysis indicates the potential for soft tissue deformation to compromise surgical guidance information and suggests a similarity in imposed deformation among similar procedure types.