Incorporation of a laser range scanner into an image-guided surgical system

Laser range scanners provide rapid and accurate non-contact methods for acquiring three-dimensional surface data, offering many advantages over other techniques currently available during surgery. The range scanner was incorporated into our image-guided surgery system to augment registration and deformation compensation. A rigid body, embedded with infrared diodes, was attached to the scanner for tracking in physical space with an optical localization system. The relationship between the scanner’s coordinate system and the tracked rigid body was determined using a calibration phantom. Tracking of the scanner using the calibration phantom resulted in an error of 1.4 ± 0.8 mm (n=234). Once tracked, data acquired intraoperatively from the range scanner data is registered with preoperative tomographic volumes using the Iterative Closest Point (ICP) algorithm. Sensitivity studies were performed to ensure that this algorithm effectively reached a global minimum. In cases where tissue deformation is significant, rigid registrations can lead to inaccuracy during surgical navigation. Methods of non-rigid compensation may be necessary, and an initial study using a linearly elastic finite element model is presented. Differences between intraoperative and preoperative surfaces after rigid registration are used to formulate boundary conditions, and the resulting displacement field deforms the preoperative image volume. To test this protocol, a phantom was built, consisting of fiducial points and a silicone liver model. Range scan and CT data were captured both before and after deforming the organ. The pre-deformed images, after registration and modeling, were compared to post-deformation CT images to evaluate this technique. The rigid registration accounts for most of the error from deformation, although there is a noticeable improvement by implementing the finite element model. To improve accuracy, more elaborate surface registration and deformation compensation strategies will be investigated. The range scanner is an innovative, uncumbersome, and relatively inexpensive method of collecting intraoperative data. It has been integrated into our image-guided surgical system and software with virtually no overhead.