An electro-magnetically tracked laparoscopic ultrasound for multi-modality minimally invasive surgery

An experimental workstation and surgical tools are presented utilizing electro-magnetic tracking to register real-time laparoscopic ultrasound (LUS) images with static, pre-acquired CT volumes. The registration and image fusion were used to guide tracked needles to target locations in an abdominal phantom. A custom-made sleeve equipped with magnetic sensor coils and attached to the steerable tip of a commercial LUS probe allowed precise localization of the imaging array without line-of-sight restrictions. For registration with CT image space, landmarks in physical space were identified using three different methods: (1) by pointing with a separate, electro-magnetically tracked pointer, (2) by pointing with the tip of the laparoscope, or (3) by imaging and subsequent manual identification of the landmark with LUS. The root-mean square (RMS) registration error using the three methods was 1.5 mm, 1.4 mm, and 1.1 mm, respectively. Overlays of real-time LUS with pre-acquired CT demonstrated the registration quality. Based on these registrations, tracked needles were guided into user-defined target locations. The RMS placement accuracy was 1.8 mm, 1.3 mm, and 1.9 mm, respectively. Accuracy is sufficient for planned clinical trials. (c) 2005 CARS & Elsevier B.V. All rights reserved.