Surface Registration for Use in Interactive, Image—Guided Liver Surgery

Abstract

Objective: Liver surgery is diflicult because of limited external landmarks, significant vascularity, and inexact definition of intra-hepatic anatomy. htra-operative ultrasound (IOUS) has been widely used in an attempt to overcome these difficulties, but is limited by its two-dimensional nature, inter-user variability, and image obliteration with ablative or resectional techniques. Because the anatomy of the liver and intra-operative removal of hepatic ligaments make inuinsic or extrinsic point-based registration impractical, we have implemented a surface registration technique to map physical space into CT image space, and have tested the accuracy of this method on an anatomical liver phantom with embedded tumor targets.Materials and Methods: Liver phantoms were created from anatomically correct molds with “tumors” embedded within the substance of the liver. Helical CT scans were performed with 3-mm slices. Using an optically active position sensor, the surface of the liver was digitized according to anatomical segments. A surface registration was performed and RMS errors of the locations of internal tumors are presented as verification. An initial point-based marker registration was performed and considered the “gold standard” for error measurement.Results: Errors for surface registration were 2.9 mm for the entire surface and 2.8 mm for embedded targets.Conclusion: This is an initial study considering the use of surface registration for the purpose of physical-to-image registration in the area of liver surgery.